Photosystem I-independent oxygenic photosynthesis in cyanobacteria

Photosystem I-independent oxygenic photosynthesis in cyanobacteria | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Photosystem I-independent oxygenic photosynthesis in cyanobacteria Dario Leister, Marta Ludwiczak, Marcel Dann, Theo Figueroa-Gonzalez, and 12 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8366641/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract Oxygenic photosynthesis in cyanobacteria, algae, and plants fixes carbon dioxide and releases oxygen. This process depends on ATP and NADPH generated by light-driven reactions involving multi-protein complexes and mobile electron carriers. Central to these reactions are Photosystem II (PSII) and Photosystem I (PSI), which enable linear electron flow (LEF) from water to NADP + molecules 1 . LEF both drives proton gradient formation for ATP synthesis and supports NADP + reduction via ferredoxin-mediated electron transfer from PSI 2 – 4 . According to prevailing models, LEF cannot occur without PSI, as its absence would block NADP⁺ reduction. Here we show that oxygenic photosynthesis can take place independently of PSI in the cyanobacterium Synechocystis PCC 6803. Through adaptive laboratory evolution, we obtained PSI-deficient lineages capable of photoautotrophic growth, inorganic carbon fixation, and light-dependent oxygen evolution. PSI-independent photoautotrophy emerged following co-mutations in at least two proteins, including the translation elongation factor G (FusA), and was abolished when the NDH-1 complex was disrupted. These results suggest that NDH-1 can substitute for PSI by operating in reverse to transfer electrons from plastoquinone to ferredoxin. Our findings reveal an unanticipated plasticity in the thylakoid electron transport network of cyanobacteria and compel a revision of existing models of oxygenic photosynthesis. Biological sciences/Plant sciences/Photosynthesis/Photosystem I Biological sciences/Evolution/Molecular evolution Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8366641","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":586468253,"identity":"e8e0dec9-ef9d-4d8e-8e4a-1c3a49407afa","order_by":0,"name":"Dario 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This process depends on ATP and NADPH generated by light-driven reactions involving multi-protein complexes and mobile electron carriers. Central to these reactions are Photosystem II (PSII) and Photosystem I (PSI), which enable linear electron flow (LEF) from water to NADP\u003csup\u003e+\u003c/sup\u003e molecules\u003csup\u003e1\u003c/sup\u003e. LEF both drives proton gradient formation for ATP synthesis and supports NADP\u003csup\u003e+\u003c/sup\u003e reduction via ferredoxin-mediated electron transfer from PSI\u003csup\u003e\u003cspan additionalcitationids=\"CR3\" citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e. According to prevailing models, LEF cannot occur without PSI, as its absence would block NADP⁺ reduction. Here we show that oxygenic photosynthesis can take place independently of PSI in the cyanobacterium \u003cem\u003eSynechocystis\u003c/em\u003e PCC 6803. Through adaptive laboratory evolution, we obtained PSI-deficient lineages capable of photoautotrophic growth, inorganic carbon fixation, and light-dependent oxygen evolution. PSI-independent photoautotrophy emerged following co-mutations in at least two proteins, including the translation elongation factor G (FusA), and was abolished when the NDH-1 complex was disrupted. These results suggest that NDH-1 can substitute for PSI by operating in reverse to transfer electrons from plastoquinone to ferredoxin. 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