The information in this preliminary prospectus supplement is not complete and may be changed. This preliminary prospectus supplement and the accompanying prospectus are not an offer to sell the securities and are not soliciting an offer to buy the securities in any jurisdiction where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED JULY 22,SEPTEMBER 19, 2022

PROSPECTUS

$50,000,000

7,760,000 Shares of

Common Stock Underlying Outstanding

Preferred Stock

Warrants

Subscription Rights

Units

Debt Securities

This prospectus relates to the issuance by Calyxt, Inc. (“Calyxt” or the “Company”) of upmay offer and sell from time to 7,760,000time in one or more offerings shares of its common stock, $0.0001 par value $0.0001 per share issuable upon the exercise(“common stock”), shares of outstandingpreferred stock, warrants, withsubscription rights, units or debt securities for an exerciseaggregate offering price of $1.41$50,000,000. Any of these securities may be offered separately or in combination at prices and on other terms to be determined at the time of the offering.

As of September 16, 2022, the aggregate market value of the Company’s outstanding common equity held by non-affiliates, or public float, was $5.9 million, based on 22,593,988 shares of the Company’s common stock held by non-affiliates and a per share (the “Warrants”). The Warrants were initially issued by Calyxtprice of $0.26, which equaled the closing price of the Company’s common stock on February 23, 2022 pursuantthe Nasdaq Global Market on such date. Pursuant to a prospectus dated September 16, 2019 and a related prospectus supplement dated February 17, 2022, in each case under Calyxt’s Registration Statement onGeneral Instruction I.B.6 of Form S-3, (Registrationin no event will the Company sell securities in a primary offering with a value exceeding more than No. 333-233231).one-third The Warrantsof its public float in any 12-month period so long as its public float remains below $75,000,000. If subsequent to the date of this prospectus the Company’s public float equals or exceeds $75,000,000, such one-third limitation on sales shall not apply to sales subsequently made pursuant to this prospectus. During the 12 calendar months prior to and including the date of this prospectus supplement, we have offered and sold $388.00 worth of our securities pursuant to General Instruction I.B.6 of Form S-3.

Each time the Company offers any securities pursuant to this prospectus, it will provide a prospectus supplement that will provide the specific terms of the securities to the extent those terms are exercisable beginning on August 23, 2022 and will expire on August 23, 2027.

Calyxt will receive the proceedsnot described in this prospectus or are different from the exerciseterms described in this prospectus. The prospectus supplements may also add to, update or change information contained in this prospectus. In addition, the Company may supplement, update or change any of the Warrants but not frominformation contained in this prospectus by incorporating information by reference into this prospectus. You should read this prospectus, any applicable prospectus supplements and any documents incorporated by reference carefully before you invest.

The Company may offer these securities directly to investors, through agents, underwriters or dealers, or through a combination of these methods. Each applicable prospectus supplement will provide the terms of the plan of distribution relating to the specific offering. If any agents, dealers or underwriters are involved in the sale of any securities, the underlying shares of common stock.applicable prospectus supplement will set forth their names and any applicable commissions or discounts.

Calyxt’sThe Company’s common stock is listed on the Nasdaq Global Market (“Nasdaq”) under the symbol “CLXT.” On July 21,September 16, 2022, the last reportedclosing sale price of Calyxt’sthe common stock on the Nasdaq Global Market was $0.25$0.26 per share.

Investing in Calyxt’s securities involves a high degree of risk. Before making an investment decision, please read the information in the section titledrisks. See “Risk Factors” beginning on page S-3 of thisS-4 and any risk factors included in any accompanying prospectus supplement and in the documents incorporated by reference intoin this prospectus.prospectus for a discussion of the factors you should carefully consider before investing in Calyxt’s securities.

Neither the U.S. Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the adequacy or accuracy of this prospectus. Any representation to the contrary is a criminal offense.

The date of this prospectus is                 , 2022.

Throughout this prospectus, unless the context otherwise requires, the terms “Calyxt,” the “Company” and “it” refer to Calyxt, Inc. The term “Cellectis” refers to Cellectis S.A., Calyxt’s majority stockholder as of the date of this prospectus.

Calyxt owns the names PlantSpring and BioFactory. Calyxt also owns the trademarks Calyxt^® and Calyno^® and owns or licenses other trademarks, trade names, and service marks appearing in this this prospectus and any prospectus supplement or any free writing prospectus. The names and trademarks Cellectis^® and TALEN^®, along with any other trademarks, trade names, and service marks of Cellectis appearing in this this prospectus and any prospectus supplement or any free writing prospectus are the property of Cellectis. This prospectus, any prospectus supplement and any free writing prospectus may also contain additional trade names, trademarks and service marks belonging to other companies. Calyxt does not intend its use or display of other parties’ trademarks, trade names, or service marks to imply, and such use or display should not be construed to imply a relationship with, or endorsement or sponsorship of these other parties.

S-iiiii

THE OFFERING

The number of shares of common stock to be outstanding after the exercise of all outstanding Warrants is based on 42,741,763 shares outstanding as of March 31, 2022, and as of that date:

Unless otherwise stated, information in this prospectus assumes no further exercise of outstanding options or Warrants and no future issuances by Calyxt of shares of its common stock.

RISK FACTORS

You should consider carefully the risks described below, which update and supplement the risk factors discussed under the section titled “Risk Factors” in Calyxt’s Annual Report on Form 10-K for the year ended December 31, 2021, as may be updated by the Company’s subsequent filings under the Securities Exchange Act of 1934 (the “Exchange Act”), that are incorporated by reference in this prospectus, together with other information in this prospectus, the documents incorporated by reference in this prospectus , and any free writing prospectus that Calyxt may authorize for use in connection with this offering before you make a decision to invest in Calyxt’s securities. If any of these risks actually occur, Calyxt’s business, operating results, prospects or financial condition could be harmed. This could cause the trading price of Calyxt’s common stock to decline and you may lose all or part of your investment. The risks below and incorporated by reference in this prospectus are not the only ones Calyxt faces. Additional risks not currently known to Calyxt or that Calyxt currently deems immaterial may also affect Calyxt’s business operations. Please also read carefully the section below titled “Cautionary Note Regarding Forward-Looking Statements.”

Risks Relating to the Offering

If you exercise Warrants, you will experience substantial and immediate dilution.

The exercise price of the Warrants is substantially higher than the net tangible book value per share of Calyxt’s common stock as of March 31, 2022. Assuming that all 7,760,000 shares of common stock are issued in connection with the exercise of Warrants and giving effect to the issuance of 3,880,000 shares of common stock in connection with the full exercise on May 4, 2022 of all outstanding Pre-Funded Warrants, you will incur immediate and substantial dilution of approximately $0.93 per share. For a further description of the dilution that you will experience immediately after the exercise of the Warrants, see the section in this prospectus entitled “Dilution” beginning on page S-18.

You may experience future dilution as a result of future equity offerings.

In order to raise additional capital, Calyxt may in the future offer additional shares of Calyxt’s common stock or other securities convertible into or exchangeable for Calyxt’s common stock. Investors purchasing shares or other securities in the future could have rights superior to holders of Calyxt’s existing securities.

Furthermore, you could experience further dilution if outstanding options are exercised or if Calyxt issues additional shares of common stock. As of March 31, 2022, approximately 11,555,883 shares of common stock that are either subject to outstanding options, issuable upon vesting of outstanding restricted stock units, issuable upon vesting of outstanding performance stock units, or reserved for future issuance under Calyxt’s equity incentive plans are eligible for sale in the public market to the extent permitted by the provisions of various vesting schedules.

Calyxt’s management will have broad discretion over the use of the proceeds Calyxt receives from the exercise of the Warrants and might not apply the proceeds in ways that increase the value of your investment.

Calyxt’s management will have broad discretion to use the net proceeds from the exercise of the Warrants, and you will be relying on the judgment of Calyxt’s management regarding the application of these proceeds. You will not have the opportunity to influence Calyxt’s decisions on how to use the proceeds, and the Company may not apply the net proceeds from the exercise of the Warrants in ways that increase the value of your investment. Because of the number and variability of factors that will determine Calyxt’s use of the net proceeds from this offering, their ultimate use may vary substantially from their currently intended use. The failure by Calyxt’s management to apply these funds effectively could harm Calyxt’s business. Pending their use, the Company intends to invest the net proceeds from this offering in marketable securities that may include investment-grade interest-bearing securities, money market accounts, certificates of deposit, commercial paper and guaranteed obligations of the U.S. government in accordance with Calyxt’s investment policy. These investments may not yield a favorable return to Calyxt’s stockholders. If Calyxt does not invest or apply the net

proceeds from this offering in ways that enhance stockholder value, the Company may fail to achieve expected financial results, which could cause its stock price to decline.

Future sales of Calyxt’s common stock by Cellectis or others, or the perception that such sales may occur, could depress the market price of Calyxt’s common stock.

As of March 31, 2022, Cellectis owned 56.1 percent of Calyxt’s outstanding shares of common stock. Future sales of Calyxt’s common stock in the public market will be subject to the volume and other restrictions of Rule 144 under the Securities Act of 1933 (the “Securities Act”) for so long as Cellectis is deemed to be Calyxt’s affiliate, unless the shares to be sold are registered with the SEC. Cellectis is entitled to various rights with respect to the registration of its shares under the Securities Act pursuant to the Stockholders Agreement. Registration of these shares under the Securities Act would result in these shares becoming freely tradable without restriction under the Securities Act immediately upon the effectiveness of the registration statement. In addition, the issuance of the shares of Calyxt common stock issuable upon exercise of the outstanding Warrants has been registered under the Securities Act and such upon issuance, such shares of Calyxt common stock will be freely tradable without restriction under the Securities Act. Calyxt is unable to predict whether or when Cellectis will sell a substantial number of shares of Calyxt’s common stock. The sale by Cellectis of a substantial number of shares, or a perception that such sales could occur, could significantly reduce the market price of Calyxt’s common stock.

The market price of Calyxt’s common stock has been and could remain volatile, which could adversely affect the market price of Calyxt’s common stock.

The market price of Calyxt’s common stock has experienced, and may continue to experience, volatility in response to various factors. Between January 1, 2022, and July 21, 2022, the closing price of Calyxt’s common stock on the Nasdaq Global Market fluctuated from a high of $2.46 per share to a low of $0.21 per share. Some factors that may cause the market price of Calyxt’s common stock to fluctuate include Calyxt’s quarterly operating results, Calyxt’s perceived prospects or the perceptions of the market of Calyxt’s pipeline, new products or technologies, changes in securities analysts’ recommendations or earnings estimates and Calyxt’s ability to meet such estimates, changes in general conditions in the economy or the financial markets, capital raising activity and other developments affecting Calyxt, its competitors or Cellectis.

These and other market and industry factors may cause the market price and demand for Calyxt’s common stock to fluctuate substantially, regardless of Calyxt’s actual operating performance, which may limit or prevent investors from readily selling their common stock at a favorable price or at all and may otherwise negatively affect the liquidity of Calyxt’s common stock.

Calyxt has in the past failed to satisfy certain continued listing requirements of the Nasdaq Global Market and could fail to satisfy those requirements again in the future which could affect the market price of Calyxt’s common stock and liquidity and reduce its ability to raise capital.

Currently, Calyxt’s common stock trades on the Nasdaq Global Market. In May 2022, Calyxt received a notification from Nasdaq informing it that the closing bid price for Calyxt’s common stock had been below $1.00 for 30 consecutive business days and that the Company, therefore, was not in compliance with the bid price requirements for continued listing on the Nasdaq Global Market. At Calyxt’s 2022 annual meeting, Calxyt’s stockholders approved a reverse stock split that, if effected, could cure this deficiency. However, there can be no assurance that Calyxt will be able to implement the reverse stock split and cure this deficiency, or if Calyxt does cure this deficiency, that it will not fall out of compliance again in the future. If Calyxt fails to maintain compliance with any Nasdaq listing requirements, Calyxt could be delisted and its stock would be considered a penny stock under regulations of the SEC, and would therefore be subject to rules that impose additional sales practice requirements on broker-dealers who sell Calyxt’s securities. The additional burdens imposed upon broker-dealers by these requirements could discourage broker-dealers from effecting transactions in Calyxt’s common stock, which could severely limit the market liquidity of Calyxt’s common stock and your ability to sell its securities in the secondary market.

The Delaware General Corporation Law (the “DGCL”) provides that the holders of preferred stock will have the right to vote separately as a class (or, in some cases, as a series) on an amendment to Calyxt’s Certificate of Incorporation if the amendment would change the par value, the number of authorized shares of the class or the powers, preferences or special rights of the class or series so as to adversely affect the class or series, as the case may be. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

Calyxt’s Board of Directors may authorize the issuance of preferred stock with voting or conversion rights that could adversely affect the voting power or other rights of the holders of Calyxt’s common stock. The issuance of preferred stock, while providing flexibility in connection with possible acquisitions and other corporate purposes, could, among other things, have the effect of delaying, deferring or preventing a change in control of Calyxt and may adversely affect the market price of the common stock and the voting and other rights of the holders of common stock. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of Calyxt’s common stock.

Delaware Anti-Takeover Law and Provisions of Calyxt’s Charter and Bylaws

The following provisions may make a change in control of Calyxt’s business more difficult and could delay, defer or prevent a tender offer or other takeover attempt that a stockholder might consider to be in its best interest, including takeover attempts that might result in the payment of a premium to stockholders over the market price for their shares. These provisions also may promote the continuity of Calyxt’s management by making it more difficult for a person to remove or change the incumbent members of Calyxt’s Board of Directors.

Authorized but Unissued Shares; Undesignated Preferred Stock. The authorized but unissued shares of Calyxt’s common stock will be available for future issuance without stockholder approval. These additional shares may be used for a variety of corporate purposes, including future public offerings to raise additional capital, acquisitions and employee benefit plans. In addition, Calyxt’s Board of Directors may authorize, without stockholder approval, the issuance of undesignated preferred stock with voting rights or other rights or preferences designated from time to time by Calyxt’s Board of Directors. The existence of authorized but unissued shares of common stock or preferred stock may enable Calyxt’s Board of Directors to render more difficult or to discourage an attempt to obtain control of Calyxt by means of a merger, tender offer, proxy contest or otherwise.

Election and Removal of Directors. Calyxt’s Board of Directors consists of not less than five nor more than eleven directors, excluding any directors elected by holders of preferred stock pursuant to provisions of any applicable series of preferred stock entitling the holders thereof to separately elect directors. The exact number of directors will be fixed from time to time by resolution of Calyxt’s Board of Directors. As of the date of this prospectus, Calyxt’s Board of Directors has eight members.

Pursuant to the Stockholders Agreement, Cellectis has the right to nominate the greater of three directors or a majority of directors to Calyxt’s Board of Directors so long as it continues to own at least 15% of the then-outstanding shares of Calyxt’s common stock.

At any time after Cellectis beneficially owns less than 50% of Calyxt’s then outstanding common stock, Calyxt’s Certificate of Incorporation provides that directors may be removed only for cause and only by the affirmative vote of holders of a majority of Calyxt’s then outstanding stock. Prior to such time, directors may be removed with or without cause.

of Calyxt’s then outstanding common stock. The number of directors will be fixed from time to time by a majority of the total number of directors that Calyxt would have at the time such number is fixed if there were no vacancies. The directors will be divided into three classes, designated class I, class II and class III. Each class will consist, as nearly as may be possible, of one-third of the total number of directors constituting the entire Board of Directors. At each annual meeting of stockholders, successors to the class of directors whose term expires at that annual meeting will be elected for a three-year term and until their successors are duly elected and qualified. In addition, if the number of directors is changed, any increase or decrease will be apportioned by Calyxt’s Board of Directors among the classes so as to maintain the number of directors in each class as nearly equal as possible, and any additional director of any class elected to fill a vacancy resulting from an increase in such class or from the removal from office, death, disability, resignation or disqualification of a director or other cause will hold office for a term that will coincide with the remaining term of that class, but in no case will a decrease in the number of directors have the effect of removing or shortening the term of any incumbent director.

Director Vacancies. Calyxt’s Certificate of Incorporation authorizes only its Board of Directors to fill vacant directorships.

No Cumulative Voting. Calyxt’s Certificate of Incorporation provides that stockholders do not have the right to cumulate votes in the election of directors.

Special Meetings of Stockholders. At any time after Cellectis beneficially owns less than 50% of Calyxt’s then outstanding common stock, Calyxt’s By-laws and Certificate of Incorporation provide that special meetings of its stockholders may only be called by the Board of Directors. Prior to such time, a special meeting may also be called by the secretary of the Company at the request of stockholders holding a majority of the outstanding shares entitled to vote.

Advance Notice Procedures for Director Nominations. Calyxt’s By-laws establish advance notice procedures for stockholders seeking to nominate candidates for election as directors at an annual or special meeting of stockholders. Although Calyxt’s By-laws do not give the Board of Directors the power to approve or disapprove stockholder nominations of candidates to be elected at an annual meeting, the By-laws may have the effect of precluding the conduct of certain business at a meeting if the proper procedures are not followed or may discourage or deter a potential acquirer from conducting a solicitation of proxies to elect its own slate of directors or otherwise attempting to obtain control of the Company.

Action by Written Consent. At any time after Cellectis beneficially owns less than 50% of Calyxt’s then outstanding common stock, Calyxt’s By-laws and Certificate of Incorporation provide that any action required or permitted to be taken by the stockholders must be effected at a duly called annual or special meeting of stockholders and may not be effected by any consent in writing in lieu of a meeting of such stockholders, subject to the rights of the holders of any series of preferred stock. Prior to such time, such actions may be taken without a meeting by written consent.

Amending Calyxt’s Certificate of Incorporation and Bylaws. At any time after Cellectis beneficially owns less than 50% of Calyxt’s then outstanding common stock, Calyxt’s Certificate of Incorporation and By-laws may be amended by the affirmative vote of the holders of at least two-thirds of Calyxt’s common stock. Prior to such time, Calyxt’s Certificate of Incorporation and By-laws may be amended by the affirmative vote of the holders of a majority of the voting power of Calyxt’s common stock.

Exclusive Jurisdiction. Calyxt’s Certificate of Incorporation provides that, unless it consents to the selection of an alternative forum, the Court of Chancery of the State of Delaware shall be the sole and exclusive forum for any derivative action or proceeding brought on Calyxt’s behalf, any action asserting a claim of breach of

federal jurisdiction over all suits brought to enforce duties or liabilities created by the Exchange Act or the rules and regulations thereunder, the exclusive forum provision does not apply to any action arising under the Exchange Act. Although the exclusive forum provision applies, to the extent permitted by law, to Securities Act claims, the Securities Act creates concurrent federal and state jurisdiction over suits brought to enforce duties or liabilities created by the Securities Act or the rules and regulations thereunder. Accordingly, there is uncertainty as to whether a court would enforce this exclusive forum provision with respect to a Securities Act claim. Neither Calyxt nor its stockholders may waive compliance with the federal securities laws or the rules and regulations thereunder.

Business Combinations with Interested Stockholders. Subject to certain exceptions, Section 203 of the DGCL prohibits a public Delaware corporation from engaging in a business combination (as defined in such section) with an “interested stockholder” (defined generally as any person who beneficially owns 15% or more of the outstanding voting stock of such corporation or any person affiliated with such person) for a period of three years following the time that such stockholder became an interested stockholder, unless (i) prior to such time the Board of Directors of such corporation approved either the business combination or the transaction that resulted in the stockholder becoming an interested stockholder; (ii) upon consummation of the transaction that resulted in the stockholder becoming an interested stockholder, the interested stockholder owned at least 85% of the voting stock of such corporation at the time the transaction commenced (excluding for purposes of determining the voting stock of such corporation outstanding (but not the outstanding voting stock owned by the interested stockholder) those shares owned (A) by persons who are directors and also officers of such corporation and (B) by employee stock plans in which employee participants do not have the right to determine confidentially whether shares held subject to the plan will be tendered in a tender or exchange offer); or (iii) at or subsequent to such time the business combination is approved by the Board of Directors of such corporation and authorized at a meeting of stockholders (and not by written consent) by the affirmative vote of at least 66 2/3% of the outstanding voting stock of such corporation not owned by the interested stockholder.

A Delaware corporation may “opt out” of these provisions with an express provision in its original certificate of incorporation or an express provision in its certificate of incorporation or bylaws resulting from a stockholders’ amendment approved by at least a majority of the outstanding voting shares. Calyxt has expressly elected not to be governed by the “business combination” provisions of Section 203 of the DGCL until after such time as Cellectis no longer beneficially owns at least 50% of Calyxt’s common stock. At that time, such election shall be automatically withdrawn and Calyxt will thereafter be governed by the “business combination” provisions of Section 203 of the DGCL.

Conflicts of Interest

Delaware law permits corporations to adopt provisions renouncing any interest or expectancy in certain opportunities that are presented to the corporation or its officers, directors or stockholders. Calyxt’s Certificate of Incorporation renounces, to the maximum extent permitted from time to time by Delaware law, any interest or expectancy that Calyxt has in, or right to be offered an opportunity to participate in, specified business opportunities that are from time to time presented to Calyxt’s officers, directors or stockholders or their respective affiliates, other than those officers, directors, stockholders or affiliates who are Calyxt’s or its subsidiaries’ employees. Calyxt’s Certificate of Incorporation provides that, to the fullest extent permitted by law, none of Cellectis or any of its affiliates or any director who is not employed by Calyxt, or his or her affiliates has any duty to refrain from (i) engaging in a corporate opportunity in the same or similar lines of business in which Calyxt or its subsidiaries now engage or propose to engage or (ii) otherwise competing with Calyxt or its subsidiaries. In addition, to the fullest extent permitted by law, in the event that Cellectis or any non-employee director acquires knowledge of a potential transaction or other business opportunity which may be a corporate opportunity for itself or himself or its or his affiliates or for Calyxt or its affiliates, such person has no

non-employee director solely in his or her capacity as a director of Calyxt. To the fullest extent permitted by law, no business opportunity will be deemed to be a potential corporate opportunity for Calyxt unless Calyxt would be permitted to undertake the opportunity under its Certificate of Incorporation, Calyxt has sufficient financial resources to undertake the opportunity and the opportunity would be in line with Calyxt’s business.

Registration Rights

The Stockholders Agreement provides Cellectis with certain registration rights, as follows:

Demand Registration—Cellectis may request that Calyxt register for resale all or a portion of their shares. Any such request must cover a quantity of shares with an anticipated aggregate offering price of at least $25.0 million. To the extent Calyxt is a well-known seasoned issuer, Cellectis may also request that Calyxt file an automatic shelf registration statement on Form S-3 that covers the registrable securities requested to be registered. Depending on certain conditions, Calyxt may defer a demand registration for up to 90 days in any twelve month period. Cellectis will agree pursuant to a contractual lock-up not to exercise any of its rights under the registration rights agreement during a 90-day restricted period.

Piggyback Registration Rights—In the event that Calyxt proposes to register any of its securities under the Securities Act of 1933, either for its own account or for the account of its other security holders, Cellectis is entitled to certain piggyback registration rights allowing it to include its shares in the registration, subject to certain marketing and other limitations. As a result, whenever Calyxt proposes to file a registration statement under the Securities Act, Cellectis is entitled to notice of the registration.

Expenses; Indemnification—The registration rights provides that Calyxt must pay all registration expenses (other than the underwriting discounts and commissions) in connection with effecting any demand registration or shelf registration. The registration rights contain customary indemnification and contribution provisions.

Term—The registration rights will remain in effect with respect to any shares covered by the Stockholders Agreement until (i) all of Cellectis’ shares have been sold pursuant to an effective registration statement under the Securities Act; (ii) all of Cellectis’ shares have been sold to the public pursuant to Rule 144 under the Securities Act; or (iii) Cellectis owns less than 10% of the then outstanding shares of Calyxt’s common stock.

Indemnification and Limitations on Directors’ Liability

Section 145 of the DGCL grants each Delaware corporation the power to indemnify any person who is or was a director, officer, employee or agent of a corporation, against expenses, including attorneys’ fees, judgments, fines and amounts paid in settlement actually and reasonably incurred by him or her in connection with any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative, other than an action by or in the right of the corporation, by reason of serving or having served in any such capacity, if he or she acted in good faith in a manner reasonably believed to be in, or not opposed to, the best interests of the corporation, and, with respect to any criminal action or proceeding, had no reasonable cause to believe his or her conduct was unlawful. A Delaware corporation may similarly indemnify any such person in actions by or in the right of the corporation if he or she acted in good faith in a manner reasonably believed to be in, or not opposed to, the best interests of the corporation, except that no indemnification may be made in respect of any claim, issue or matter as to which the person shall have been adjudged to be liable to the corporation unless and only to the extent that the Delaware Court of Chancery or the court in which the action was brought determines that, despite adjudication of liability, but in view of all of the circumstances of the case, the person is fairly and reasonably entitled to indemnity for expenses which the Delaware Court of Chancery or other court shall deem proper.

damages for violations of the director’s fiduciary duty as a director, except (i) for any breach of the director’s duty of loyalty to the corporation or its stockholders, (ii) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (iii) pursuant to Section 174 of the DGCL (providing for director liability with respect to unlawful payment of dividends or unlawful stock purchases or redemptions) or (iv) for any transaction from which a director derived an improper personal benefit.

Calyxt’s Certificate of Incorporation indemnifies its directors and principal officers to the fullest extent permitted by Delaware law and Calyxt’s Certificate of Incorporation also allows Calyxt’s Board of Directors to indemnify other employees. This indemnification extends to the payment of judgments in actions against officers and directors and to reimbursement of amounts paid in settlement of such claims or actions and may apply to judgments in favor of the corporation or amounts paid in settlement to the corporation. This indemnification also extends to the payment of attorneys’ fees and expenses of principal officers and directors in suits against them where the officer or director acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, Calyxt’s best interests, and, with respect to any criminal action or proceeding, he or she had no reasonable cause to believe his or her conduct was unlawful. This right of indemnification is not exclusive of any right to which the officer or director may be entitled as a matter of law.

Calyxt’s directors and officers are insured pursuant to a “directors and officers” insurance policy, which provides protection against un-indemnified losses arising from certain wrongful acts in their capacities as directors and officers and reimburses us for losses incurred by Calyxt in response to securities claims involving directors and officers. The policy contains various customary exclusions for policies of this type.

In addition, Calyxt’s Board of Directors has adopted a policy to enter into an indemnification agreement with each of its directors and officers, which provide for certain advancement and indemnification rights. Each indemnification agreement provides, subject to certain exceptions, to indemnify and hold harmless the director or officer to the fullest extent permitted by Delaware law.

With respect to any indemnification available to directors affiliated with Cellectis, Calyxt has agreed (i) that it is the indemnitor of first resort with respect to any amounts incurred or sustained in connection with such person’s role as a director of Calyxt, (ii) that it will be responsible for, and required to advance, the full amount of such amounts without regard to any rights such person may have, or be pursuing, against Cellectis, and (iii) to irrevocably waive, relinquishe and release Cellectis from any and all claims for contribution, subrogation or any other recovery in respect of such amounts.

Calyxt believes that the limitation of liability and indemnification provisions in its Certificate of Incorporation, By-laws, indemnification agreements and insurance policies are necessary to attract and retain qualified directors and officers. However, these provisions may discourage derivative litigation against directors and officers, even though an action, if successful, might benefit Calyxt and its stockholders. Furthermore, a stockholder’s investment may be adversely affected to the extent Calyxt pays the costs of settlement and damage awards against directors and officers as required or allowed by these limitations of liability and indemnification provisions.

At present, there is no pending litigation or proceeding involving any of Calyxt’s directors, officers, employees or agents as to which indemnification is sought from Calyxt, nor is the Company aware of any threatened litigation or proceeding that may result in an indemnification claim.

Rights Upon Distribution of Assets; Purchase Rights

If Calyxt distributes assets, including cash dividends, any securities (other than a stock dividend of Calyxt Common Stock, described under “—Certain Adjustments”) or other property, to Calyxt’s stockholders, the warrant holders shall be entitled to participate in such distribution to the same extent that such holder would have participated had the holder held the number of shares of common stock acquirable upon complete exercise of its warrant. If such distribution would cause such holder to exceed the Beneficial Ownership Limitation, the holder will not be entitled to participate in the distribution to such extent that Beneficial Ownership Limitation would be exceeded and the distribution will be held in abeyance for the holder’s benefit until such time or times, if ever, as would not result in the holder exceeding the Beneficial Ownership Limitation.

If Calyxt grants, issues or sells pro rata to its stockholders, any options, convertible securities or rights to purchase stock, warrants, securities or other property, the Warrant holders will be entitled to acquire such purchase rights to the same extent such holder would have acquired had the holder held the number of shares of common stock acquirable upon complete exercise of its warrant. If such right to participate in any such purchase rights would cause such holder to exceed Beneficial Ownership Limitation, then the holder will not be entitled to participate in such purchase right to such extent that the Beneficial Ownership Limitation would be exceeded such purchase right, to the extent necessary to prevent such occurrence, will be held in abeyance for the holder’s benefit until such time or times, if ever, as would not result in the holder exceeding the Beneficial Ownership Limitation.

Transferability

Subject to applicable laws and restrictions, a holder may transfer a Warrant upon surrender of the Warrant to Calyxt with a duly executed assignment in the form attached to the Warrant. The transferring holder will be responsible for any tax that liability that may arise as a result of the transfer.

No Listing

There is no established public trading market for the Warrants and Calxyt does not expect a market to develop. In addition, Calxyt does not intend to apply for listing of the Warrants on any securities exchange or trading system. Without an active market, the liquidity of the Warrants will be limited.

Rights as Stockholder

Except as otherwise provided or by virtue of such holder’s ownership of shares of Calyxt’s common stock, the holder of a Warrant, solely in such holder’s capacity as a holder of a Warrant, will not be entitled to vote, to receive dividends, or to any of the other rights of Calyxt’s stockholders.

Fundamental Transactions

In the event Calyxt (or Calyxt and all of its subsidiaries, taken as a whole) effects certain mergers, consolidations, sales of substantially all of its assets, tender or exchange offers, reclassifications or share exchanges in which its common stock is effectively converted into or exchanged for other securities cash or property, Calyxt consummates a business combination in which another person acquires 50% of the outstanding shares of its common stock, or any person or group becomes the beneficial owner of 50% of the aggregate ordinary voting power represented by Calyxt’s issued and outstanding common stock, then, upon any subsequent exercise of the Warrants,that the holders of the Warrantsseries of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless otherwise provided in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts Calyxt’s ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of its assets as an entirety or substantially as an entirety. However, any successor to or acquirer of such assets (other than a subsidiary of Calyxt’s) must assume all of Calyxt’s obligations under the indenture or the debt securities, as appropriate.

Events of Default under the Indenture

Unless otherwise provided in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that Calyxt may issue:

DILUTION

If you purchase shares of Calyxt’s common stock upon the exercise of your Warrant, you will experience immediate and substantial dilution to the extent of the difference between the exercise price per share and the adjusted net tangible book value per share of Calyxt’s common stock as of March 31, 2022, as adjusted to give effect to the exercise of all outstanding Warrants.

Calyxt’s net tangible book value as of March 31, 2022, was $14.9 million, or $0.35 per share of common stock. Net tangible book value per share is determined by dividing Calyxt’s total tangible assets, less total liabilities, by the number of shares of Calyxt’s common stock outstanding as of March 31, 2022. Dilution with respect to net tangible book value per share represents the difference between the Warrant exercise price per share paid by purchasers exercising Warrants and the net tangible book value per share of Calyxt’s common stock immediately after giving effect to the exercise of all outstanding Warrants.

After giving effect to the exercise of all outstanding Warrants and the issuance of 3,880,000 shares of common stock in connectionfollowing changes only with the full exercise on May 4, 2022consent of alleach holder of any outstanding Pre-Funded Warrants, Calyxt’s as adjusted net tangible book value as of March 31, 2022 would have been approximately $25.9 million, or $0.48 per share of common stock. This represents an immediate increase in net tangible book value of $0.13 per share to existing stockholders and immediate dilution of $0.93 per share to new investors exercising Warrants. The following table illustrates this dilution on a per share basis:

The number of shares of common stock to be outstanding after this offering is based on 42,741,763 shares outstanding as of March 31, 2022, and as of that date:debt securities affected:

Discharge

The indenture provides that Calyxt can elect to be discharged from its obligations with respect to one or more series of debt securities that shall become due and settlementpayable within one year or are to be called for redemption within one year, including obligations to:

CERTAIN UNITED STATES FEDERAL INCOME TAX CONSIDERATIONS

Subject toaccompanying prospectus supplement. To comply with applicable state securities laws, the limitations, assumptions and qualifications described herein, the following is a summary of certain U.S. federal income tax considerations of the purchase, ownership and disposition of shares of Calyxt’s common stock issuedsecurities offered by this prospectus will be sold, if necessary, in such jurisdictions only through registered or licensed brokers or dealers. In addition, securities may not be sold in some states absent registration or pursuant to this offering (the “Shares”), the purchase, exercise, disposition and lapse of Warrants to purchase shares of Calyxt’s common stock issued pursuant to this offering, and the purchase, ownership and disposition of shares of Calyxt’s common stock issuable upon exercise of the Warrants (the “Warrant Shares”). The Shares, the Warrants and the Warrant Shares are collectively referred to herein as the “Offered Securities.” All prospective holders of the Offered Securities should consult their tax advisors with respect to the U.S. federal, state, local and non-U.S. tax consequences of the purchase, ownership and disposition of the Offered Securities.

This discussion is based on current provisions of the U.S. Internal Revenue Code of 1986, as amended (the “Code”), existing U.S. Treasury regulations promulgated thereunder, published administrative pronouncements and rulings of the U.S. Internal Revenue Service (the “IRS”), and judicial decisions, all as in effect as of the date of this prospectus. These authorities are subject to change and to differing interpretation, possibly with retroactive effect. Any change or differing interpretation could alter the tax consequences to holders described in this discussion. There can be no assurance that a court or the IRS will not challenge one or more of the tax consequences described herein, and Calyxt has not obtained, nor does it intend to obtain, a ruling with respect to the U.S. federal income tax consequences to a holder of the purchase, ownership or disposition of the Offered Securities.

This discussion addresses only Offered Securities that are held as capital assets within the meaning of Section 1221 of the Code (generally, property held for investment). This discussion does not address all the U.S. federal income tax consequences that may be relevant to particular holders in light of their individual circumstances, nor does it address any alternative minimum, Medicare contribution, estate or gift tax consequences, or any aspects of U.S. state, local or non-U.S. taxes). It does not address holders that are subject to special rules, such as:

If a holder is a partnership or other pass-through entity (including an entity or arrangement treated as a partnership or other type of pass-through entity for U.S. federal income tax purposes), the U.S. federal income tax treatment of a partner or beneficial owner will generally depend on the status of such partner or beneficial owner and the entity’s activities. Partnerships, partners and beneficial owners in partnerships or other pass-through entities that own the Offered Securities should consult their tax advisors as to the particular U.S. federal income tax considerations applicable to the acquisition, ownership and disposition of the Offered Securities.

For purposes of this discussion, a “U.S. Holder” is a beneficial owner of the Offered Securities, that, for U.S. federal income tax purposes, is:

As used herein, the term “Non-U.S. Holder” means a beneficial owner, other than an entity treated as a partnership for U.S. federal income tax purposes, of the Offered Securities that is for U.S. federal income tax purposes not a U.S. Holder.

PROSPECTIVE INVESTORS ARE URGED TO CONSULT THEIR TAX ADVISORS REGARDING THE PARTICULAR FEDERAL, STATE, LOCAL AND NON-U.S. TAX CONSEQUENCES TO THEM OF THE PURCHASE, OWNERSHIP AND DISPOSITION OF THE OFFERED SECURITIES.

Allocation of Purchase Price

Each Share and Warrant is expected to be treated for U.S. federal income tax purposes as an investment unit consisting of one Share and one Warrant. In determining the tax basis of each Share and Warrant constituting a unit, holders should allocate their purchase price for the unit between the Share and Warrant on the basis of their relative fair market values at the time of issuance. Calyxt does not intend to advise holders of the Offered Securities with respect to this determination. A holder’s allocation of the purchase price between the Shares Warrants is not binding on the IRS or the courts, and no assurance can be given that the IRS or the courts will agree with a holder’s allocation. All holders are advised to consult their tax and financial advisors with respect to the relative fair market values of the Shares and Warrants for U.S. federal income tax purposes.

Tax Considerations Applicable to U.S. Holders

Distributions on Shares and Warrant Shares

Calyxt does not anticipate declaring or paying any cash dividends to holders of Calyxt’s common stock in the foreseeable future. If Calyxt makes distributions of cash or other property on the Shares or Warrant Shares (other than certain distributions of stock), such distributions will constitute dividends to the extent paid out of Calyxt’s current or accumulated earnings and profits, as determined for U.S. federal income tax purposes. Dividends received by a corporate U.S. Holder may be eligible for a dividends received deduction, subject to applicable limitations. Dividends received by certain non-corporate U.S. Holders, including individuals, are generally taxed at the lower applicable capital gains rate provided certain holding period and other requirements are satisfied. Distributions in excess of Calyxt’s current and accumulated earnings and profits will constitute a

return of capital and first be applied against and reduce a U.S. Holder’s adjusted tax basis in its Shares or Warrant Shares, as applicable, but not below zero. Any excess will be treated as capital gain and will be treated as described below under “—Sale or Other Taxable Disposition of the Shares and Warrant Shares.”

Sale or Other Taxable Disposition of the Shares and Warrant Shares

Upon the sale, exchange or other taxable disposition of the Shares or Warrant Shares, a U.S. Holder will generally recognize capital gain or loss equal to the difference between the amount of cash and the fair market value of any property received upon the sale, exchange or other taxable disposition and such U.S. Holder’s adjusted tax basis in the Shares or Warrant Shares. This capital gain or loss will be long term capital gain or loss if the U.S. Holder’s holding period in such Shares or Warrant Shares is more than one year at the time of the sale, exchange or other taxable disposition. Long-term capital gains recognized by certain non-corporate U.S. Holders, including individuals, generally will be subject to reduced rates of U.S. federal income tax. The deductibility of capital losses is subject to certain limitations.

Sale or Other Disposition or Exercise of Warrants

Upon the sale, exchange or other disposition of a Warrant (other than by exercise), a U.S. Holder will generally recognize capital gain or loss equal to the difference between the amount realized on the sale, exchange or other disposition and the U.S. Holder’s tax basis in the Warrant. This capital gain or loss will be long-term capital gain or loss if the U.S. Holder’s holding period in such Warrant is more than one year at the time of the sale, exchange or other disposition. The deductibility of capital losses is subject to certain limitations.

In general, a U.S. Holder will not be required to recognize income, gain or loss upon exercise of a Warrant for its exercise price. A U.S. Holder’s tax basis in Warrant Shares received upon exercise of Warrants will be equal to the sum of (i) the U.S. Holder’s tax basis in the Warrants exchanged therefor and (ii) the exercise price of such Warrants. A U.S. Holder’s holding period in the Warrant Shares received upon exercise will commence on the day after such U.S. Holder exercises the Warrants. Although there is no direct legal authority as to the U.S. federal income tax treatment of an exercise of a warrant on a cashless basis, Calyxt intends to take the position that such exercise will not be taxable, either because the exercise is not a gain realization event or because it qualifies as a tax-free recapitalization. In the former case, the holding period of Warrant Shares received upon exercise of Warrants should commence on the day after the Warrants are exercised. In the latter case, the holding period of the Warrant Shares received upon exercise of Warrants would include the holding period of the exercised Warrants. However, Calyxt’s position is not binding on the IRS and the IRS may treat a cashless exercise of a warrant as a taxable exchange. U.S. Holders are urged to consult their tax advisors as to the consequences of an exercise of a Warrant on a cashless basis, including with respect to their holding period and tax basis in the Warrant Shares received.

Lapse of Warrants

If a Warrant expires without being exercised, a U.S. Holder will recognize a capital loss in an amount equal to such U.S. Holder’s tax basis in the warrant. Such loss will be long-term capital loss if, at the time of the expiration, the U.S. Holder’s holding period in such warrant is more than one year. The deductibility of capital losses is subject to certain limitations.

Certain Adjustments to and Distributions on Warrants

Under Section 305 of the Code, an adjustment to the number of Warrant Shares that will be issued on the exercise of the Warrants, or an adjustment to the exercise price of the Warrants (or in certain circumstances, there is a failure to make adjustments), may be treated as a constructive distribution to a U.S. Holder of the Warrants if, and to the extent that, such adjustment has the effect of increasing such U.S. Holder’s proportionate interest in Calyxt’s earnings and profits as determined under U.S. federal income tax principles or Calyxt’s assets,

depending on the circumstances of such adjustment (for example, if such adjustment is to compensate for a distribution of cash or other property to Calyxt’s shareholders). Such distributions will constitute dividends to the extent deemed paid out of Calyxt’s current or accumulated earnings and profits, as discussed above under “Distributions on Shares and Warrant Shares.” U.S. Holders should consult their tax advisors regarding the proper treatment of any adjustments to the number of Warrant Shares that will be issued on the exercise of the Warrants or the exercise price of the Warrants.

In addition, if Calyxt were to make a distribution in cash or other property with respect to its common stock after the issuance of the Warrants, then Calyxt may, in certain circumstances, make a corresponding distribution to holders of Warrants. The taxation of a distribution received with respect to a Warrant is unclear. It is possible such a distribution would be treated as a distribution (or constructive distribution), although other treatments are possible. U.S. Holders should consult their tax advisors regarding the proper treatment of distributions received with respect to Warrants.

Backup Withholding and Information Reporting

In general, backup withholding and information reporting requirements may apply to payments on the Offered Securities and to the receipt of proceeds on the sale, exchange or other taxable disposition of the Offered Securities. Backup withholding (currently at a rate of 24 percent) may apply if a U.S. Holder fails to furnish its taxpayer identification number, a U.S. Holder fails to certify under penalties of perjury that such taxpayer identification number is correct and that such U.S. Holder is not subject to backup withholding (generally on a properly completed and duly executed IRS Form W-9), the applicable withholding agent is notified by the IRS that the holder previously failed to properly report payments of interest or dividends, or such U.S. Holder otherwise fails to comply with the applicable requirements of the backup withholding rules.

Certain U.S. Holders generally are not subject to backup withholding and information reporting requirements, provided that their exemptions from backup withholding and information reporting are properly established. Backup withholding is not an additional tax. Any amounts withheld from a payment to a U.S. Holder under the backup withholding rules generally will be allowed as a credit against such U.S. Holder’s U.S. federal income tax liability and may entitle such U.S. Holder to a refund, provided the required information is furnished to the IRS in a timely manner. U.S. Holders should consult their tax advisors regarding the application of backup withholding, the availability of an exemption from backup withholding, and the procedure for obtaining such an exemption, if available.

Tax Considerations Applicable to Non-U.S. Holders

Distributions on Shares and Warrant Shares

As mentioned above, Calyxt does not anticipate declaring or paying any cash dividends to holders of Calyxt’s common stock in the foreseeable future. However, distributions of cash or other property (other than certain distributions of stock) on the Shares or Warrant Shares will constitute dividends to the extent paid out of Calyxt’s current or accumulated earnings and profits, as determined for U.S. federal income tax purposes. Distributions in excess of Calyxt’s current and accumulated earnings and profits will constitute a return of capital and first be applied against and reduce a Non-U.S. Holder’s adjusted tax basis in its common stock, but not below zero. Any excess will be subject to the treatment as described below under “— Gain on Sale or Other Taxable Disposition of the Offered Securities”.

Dividends paid to a Non-U.S. Holder that are not effectively connected with the Non-U.S. Holder’s conduct of a trade or business in the United States generally will be subject to withholding tax at a 30-percent rate or a reduced rate specified by an applicable income tax treaty. In order to obtain a reduced rate of withholding, the Non-U.S. Holder will be required to provide Calyxt or Calyxt’s paying agent with a properly executed applicable IRS Form W-8BEN orIRS Form W-8BEN-E (or appropriate successor form), as applicable, certifying under

penalties of perjury that the Non-U.S. Holder is not a United States person and is eligible for the benefits under the applicable tax treaty. These forms may need to be periodically updated. If a Non-U.S. Holder holds the Offered Securities through a financial institution or other intermediary, the Non-U.S. Holder generally will be required to provide the appropriate documentation to the financial institution or other intermediary. A Non-U.S. Holder eligible for a reduced rate of U.S. withholding tax pursuant to an income tax treaty who fails to timely provide an IRS Form W-8BEN or W-8BEN-E, as applicable, may obtain a refund of any excess amounts withheld by timely filing an appropriate claim with the IRS.

If dividends paid to a Non-U.S. Holder are effectively connected with the Non-U.S. Holder’s conduct of a trade or business in the United States (and, if required by an applicable income tax treaty, are attributable to a permanent establishment or fixed base maintained by the Non-U.S. Holder in the United States), the Non-U.S. Holder will generally be taxed on the dividends in the same manner as a U.S. Holder. In this case, the Non-U.S. Holder will be exempt from the withholding tax discussed in the preceding paragraph, although the Non-U.S. Holder will be required to provide a properly executed IRS Form W-8ECI (or appropriate successor form) in order to claim an exemption from withholding. Such effectively connected dividends, although not subject to U.S. federal withholding tax, are subject to U.S. federal income tax on a net income basis at the regular graduated U.S. federal income tax rates generally applicable to Non-U.S. Holders. Dividends received by a corporate Non-U.S. Holder that are effectively connected with such Non-U.S. Holder’s conduct of a trade or business in the United States (and, if required by an applicable income tax treaty, attributable to a permanent establishment or fixed base maintained by the Non-U.S. Holder in the United States) may be subject to an additional branch profits tax at a 30-percent rate (or such lower rate as may be specified by an applicable income tax treaty). Non-U.S. Holders should consult their tax advisors with respect to other U.S. tax consequences of the acquisition, ownership and disposition of the Offered Securities, including the possible imposition of the branch profits tax.

Exercise of Warrants

A Non-U.S. Holder generally will not recognize gain or loss on the exercise of a Warrant and the related receipt of Warrant Shares. However, if a cashless exercise of Warrants results in a taxable exchange, as described above under “—Tax Considerations Applicable to U.S. Holders— Sale or Other Disposition or Exercise of Warrants,” the rules described below under “Gain on Sale or Other Taxable Disposition of the Offered Securities” would apply.

Gain on Sale or Other Taxable Disposition of the Offered Securities

Subject to the discussions below under “—Information Reporting and Backup Withholding” and “—FATCA,” a Non-U.S. Holder generally will not be subject to U.S. federal income or withholding tax on gain realized on a sale, exchange or other taxable disposition of the Offered Securities unless:

Calyxt believes that it is not, and does not anticipate becoming, a United States real property holding corporation. Even if Calyxt is or has been a United States real property holding corporation during the specified testing period, as long as Calyxt’s common stock is regularly traded on an establishedstate securities market (such as

the Nasdaq Global Market) at any time during the calendar year in which the disposition occurs, a Non-U.S. Holder will not be subject to U.S. federal income tax on the disposition of Shares or Warrant Shares if the Non-U.S. Holder does not own or has not owned (actually or constructively) more than 5 percent of Calyxt’s common stock at any time during the shorter of the two periods mentioned above. Special rules may apply to the determination of the 5-percent threshold in the case of a Non-U.S. Holder of Warrants. Non-U.S. Holders are urged to consult their tax advisors regarding the effect of holding Warrants on the calculation of such 5-percent threshold. Non-U.S. Holders should consult their tax advisors regarding the application of this regularly traded exception.

In addition, although a 15% withholding tax generally applies to gross proceeds from the sale or other taxable disposition of the stock of or certain other interests in a United States real property holding company, such 15% withholding tax generally will not apply to the disposition of Shares or Warrant Shares so long as Calyxt’s common stock is regularly traded on an established securities market. However, the exception described in the previous sentence may not apply to certain dispositions of Warrants if the Non-U.S. Holder exceeds the 5-percent threshold mentioned above.

If a Non-U.S. Holder recognizes gain on a sale, exchange or other disposition of the Offered Securities that is effectively connected with the Non-U.S. Holder’s conduct of a trade or business in the United States (and if required by an applicable income tax treaty, is attributable to a permanent establishment or fixed base maintained by the Non-U.S. Holder in the United States), the Non-U.S. Holder will generally be subject to U.S. federal income tax at the regular graduated U.S. federal income tax rates generally applicable to a United States person. If the Non-U.S. Holder is a corporation, the Non-U.S. Holder may also be subject to the branch profits tax at a 30-percent rate or such lower rate as may be specified by an applicable income tax treaty. Non-U.S. Holders should consult their tax advisors with respect to other U.S. tax consequences of the acquisition, ownership and disposition of the Offered Securities, including the possible imposition of the branch profits tax.

Certain Adjustments to and Distributions on Warrants

As discussed above under “—Tax Considerations Applicable to U.S. Holders—Certain Adjustments to and Distributions on Warrants,” certain adjustments to the number of Warrant Shares on the exercise of the Warrants, or an adjustment to the exercise price of the Warrants (or certain failures to make adjustments), may be deemed to be the payment of a distribution with respect to the Warrants. Such a deemed distribution could be deemed to be the payment of a dividend to a Non-U.S. Holder to the extent of Calyxt’s earnings and profits, notwithstanding the fact that such Holder will not receive a cash payment. In the event of such a deemed dividend, Calyxt may be required to withhold tax from subsequent distributions of cash or property to Non-U.S. Holders. Non-U.S. Holders should consult their tax advisors regarding the proper treatment of any adjustments to the Warrants.

In addition, as discussed above under “—Tax Considerations Applicable to U.S. Holders— Certain Adjustments to and Distributions on Warrants,” the taxation of a distribution received with respect to a Warrant is unclear. It is possible such a distribution would be treated as a distribution (or constructive distribution), although other treatments are possible. Non-U.S. Holders should consult their tax advisors regarding the U.S. withholding tax and other U.S. tax consequences of distributions received with respect to Warrants.

Information Reporting and Backup Withholding

Information returns will be filed with the IRS in connection with payments of dividends on the Offered Securities. Copies of the information returns reporting those dividends and withholding may also be made available to the tax authorities in the country in which a Non-U.S. Holder is a resident under the provisions of an applicable income tax treaty or agreement. Unless a Non-U.S. Holder complies with certification procedures to establish that the Non-U.S. Holder is not a United States person, information returns may also be filed with the IRS in connection with the proceeds from a sale, exchange or other disposition of the Offered Securities to or through the U.S. office (and, in certain cases, the foreign office) of a broker.

A Non-U.S. Holder may be subject to backup withholding (currently at a rate of 24 percent) on payments on the Offered Securities or on the proceeds from a sale, exchange or other disposition of the Offered Securities unless the Non-U.S. Holder complies with certification procedures to establish that the Non-U.S. Holder is not a United States person or otherwise establishes an exemption. Compliance with the certification procedures required to claim a reduced rate of withholding under a treaty (including properly certifying non-U.S. status on an IRS Form W-8BEN, IRSForm W-8BEN-E or other appropriate version of IRS Form W-8 (or appropriate successor form)) generally will satisfy the certification requirements necessary to avoid backup withholding as well. Notwithstanding the foregoing, U.S. federal backup withholding may apply if the payor has actual knowledge, or reason to know, that a holder is a United States person.

Backup withholding is not an additional tax. Any amounts withheld from a payment to a Non-U.S. Holder under the backup withholding rules generally will be allowed as a credit against such Non-U.S. Holder’s U.S. federal income tax liability and may entitle such Non-U.S. Holder to a refund, provided the required information is furnished to the IRS in a timely manner. Non-U.S. Holders are urged to consult their tax advisors regarding the application of backup withholding and the availability of and procedure for obtaining an exemption from backup withholding in their particular circumstances.

FATCA

Provisions of the Code commonly referred to as “FATCA” require withholding of 30 percent on payments of dividends on the Offered Securities, as well as payments of gross proceeds of dispositions of the Offered Securities, to a “foreign financial institution” (which is broadly defined for this purpose and in general includes investment vehicles) and certain other non-U.S. entities unless various U.S. information reporting and due diligence requirements (generally relating to ownership by United States persons of interests in or accounts with those entities) have been satisfied or an exemption applies. However, the IRS has issued proposed Treasury regulations that eliminate FATCA withholding on payments of gross proceeds (but not on payments of dividends). Pursuant to the preamble to the proposed Treasury regulations, any applicable withholding agent may (but is not required to) rely on this proposed change to FATCA withholding until final Treasury regulations are issued or the proposed Treasury regulations are withdrawn. An intergovernmental agreement between the United States and an applicable foreign country may modify these requirements. If FATCA withholding is imposed, a beneficial owner that is not a foreign financial institution generally may obtain a refund of any amounts withheld by filing a U.S. federal income tax return (which may entail significant administrative burden). Non-U.S. Holders should consult their tax advisors regarding the effects of FATCA on their investments in the Offered Securities.

Calyxt will not pay any additional amounts to Non-U.S. Holders with respect to any amounts withheld, including pursuant to FATCA.

THE PRECEDING DISCUSSION OF U.S. FEDERAL TAX CONSIDERATIONS IS FOR GENERAL INFORMATION ONLY. IT IS NOT TAX ADVICE. PROSPECTIVE INVESTORS SHOULD CONSULT THEIR TAX ADVISORS REGARDING THE PARTICULAR U.S. FEDERAL, STATE AND LOCAL AND NON-U.S. TAX CONSEQUENCES OF PURCHASING, HOLDING AND DISPOSING OF THE OFFERED SECURITIES, INCLUDING THE CONSEQUENCES OF ANY PROPOSED CHANGE IN APPLICABLE LAWS.laws.

7,760,000 Shares of Common Stock

PROSPECTUS

            , 2022

PART II. INFORMATION NOT REQUIRED IN PROSPECTUS

The following table sets forth the expenses payable by Calyxt, Inc., a Delaware corporation (the “Registrant), in connection with the offering of securities described in this registration statement, other than underwriting discounts and commissions. All amounts shown are estimates, except for the Securities and Exchange Commission (the “SEC”) registration fee. The Registrant will bear all expenses shown below.

Section 145 of the DGCL grants each Delaware corporation the power to indemnify any person who is or was a director, officer, employee or agent of a corporation, against expenses, including attorneys’ fees, judgments, fines and amounts paid in settlement actually and reasonably incurred by him or her in connection with any threatened, pending or completed action, suit or proceeding, whether civil, criminal, administrative or investigative, other than an action by or in the right of the corporation, by reason of serving or having served in any such capacity, if he or she acted in good faith in a manner reasonably believed to be in, or not opposed to, the best interests of the corporation, and, with respect to any criminal action or proceeding, had no reasonable cause to believe his or her conduct was unlawful. A Delaware corporation may similarly indemnify any such person in actions by or in the right of the corporation if he or she acted in good faith in a manner reasonably believed to be in, or not opposed to, the best interests of the corporation, except that no indemnification may be made in respect of any claim, issue or matter as to which the person shall have been adjudged to be liable to the corporation unless and only to the extent that the Delaware Court of Chancery or the court in which the action was brought determines that, despite adjudication of liability, but in view of all of the circumstances of the case, the person is fairly and reasonably entitled to indemnity for expenses which the Delaware Court of Chancery or other court shall deem proper.

Section 102(b)(7) of the DGCL enables a corporation in its certificate of incorporation, or an amendment thereto, to eliminate or limit the personal liability of a director to the corporation or its stockholders for monetary damages for violations of the director’s fiduciary duty as a director, except (i) for any breach of the director’s duty of loyalty to the corporation or its stockholders, (ii) for acts or omissions not in good faith or which involve intentional misconduct or a knowing violation of law, (iii) pursuant to Section 174 of the DGCL (providing for director liability with respect to unlawful payment of dividends or unlawful stock purchases or redemptions) or (iv) for any transaction from which a director derived an improper personal benefit.

The Registrant’s Certificate of Incorporation indemnifies its directors and principal officers to the fullest extent permitted by Delaware law and its Certificate of Incorporation also allows its Board of Directors to indemnify other employees. This indemnification extends to the payment of judgments in actions against officers and directors and to reimbursement of amounts paid in settlement of such claims or actions and may apply to

II-1

officer or director acted in good faith and in a manner he or she reasonably believed to be in, or not opposed to, the Registrant’s best interests, and, with respect to any criminal action or proceeding, he or she had no reasonable cause to believe his or her conduct was unlawful. This right of indemnification is not exclusive of any right to which the officer or director may be entitled as a matter of law.

The Registrant’s directors and officers are insured pursuant to a “directors and officers” insurance policy, which provides protection against unindemnified losses arising from certain wrongful acts in their capacities as directors and officers and reimburses us for losses incurred by it in response to securities claims involving directors and officers. The policy contains various customary exclusions for policies of this type.

In addition, the Registrant’s board of directors has adopted a policy to enter into an indemnification agreement with each of its directors and officers, which provide for certain advancement and indemnification rights. Each indemnification agreement, provides, subject to certain exceptions, to indemnify and hold harmless the director or officer to the fullest extent permitted by Delaware law.

With respect to any indemnification available to directors affiliated with Cellectis, the Registrant has agreed (i) that it is the indemnitor of first resort with respect to any amounts incurred or sustained in connection with such person’s role as a director of the Registrant, (ii) that it will be responsible for, and required to advance, the full amount of such amounts without regard to any rights such person may have, or be pursuing, against Cellectis, and (iii) to irrevocably waive, relinquish and release Cellectis from any and all claims for contribution, subrogation or any other recovery in respect of such amounts.

The indemnification rights set forth above are not exclusive of any other right which an indemnified person may have or hereafter acquire under any statute, provision of the Registrant’s Certificate of Incorporation, By-laws, agreement, vote of stockholders or disinterested directors or otherwise.

The exhibit index immediately preceding the signature page hereto is incorporated herein by reference.

(a) The undersigned Registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act;

(ii) To reflect in the prospectus any facts or events arising after the effective date of this registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the SEC pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20 percent change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in this registration statement or any material change to such information in this registration statement;

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to the SEC by the Registrant pursuant to Section 13 or Section 15(d) of the Securities Exchange Act of 1934, as amended (the “Exchange Act”) (15 U.S.C. 78m or 78o(d)), that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for the purpose of determining liability under the Securities Act to any purchaser:

(i) Each prospectus filed by the Registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by section 10(a) of the Securities Act shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which the prospectus forms a part, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of this registration statement or made in a document incorporated or deemed incorporated by reference into this registration statement or prospectus that is a part of this registration statement will, as to a purchaser with a time of contract sale prior to such effective date, supersede or modify any statement that was made in this registration statement or prospectus that was a part of this registration statement or made in any such document immediately prior to such effective date.

(5) That, for the purpose of determining liability of the Registrant under the Securities Act to any purchaser in the initial distribution of the securities, in a primary offering of securities of the undersigned Registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned Registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

(i) any preliminary prospectus or prospectus of the undersigned Registrant relating to the offering required to be filed pursuant to Rule 424;

(ii) any free writing prospectus relating to the offering prepared by or on behalf of the undersigned Registrant or used or referred to by the undersigned Registrant;

(iii) the portion of any other free writing prospectus relating to the offering containing material information about the undersigned Registrant or its securities provided by or on behalf of the undersigned Registrant; and

(iv) any other communication that is an offer in the offering made by the undersigned Registrant to the purchaser.

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Act (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to Section 15(d) of the Exchange Act) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(c) Insofar as indemnification for liabilities arising under the Securities Act may be permitted to directors, officers and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted against the Registrant by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question of whether such indemnification by it is against public policy as expressed in the Securities Act and will be governed by the final adjudication of such issue.

(d) The undersigned Registrant hereby undertakes to file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of section 310 of the Trust Indenture Act of 1939 (the “Act”) in accordance with the rules and regulations prescribed by the SEC under section 305(b)(2) of the Act.

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