Oxygenic photosynthesis without photosystem I in a cyanobacterium

ABSTRACT: Cyanobacteria, algae and plants use oxygenic photosynthesis to fix CO2 and release O2. This process depends on ATP and NADPH, which are produced by the photosynthetic light reactions involving several multi-protein complexes and mobile electron carriers. These complexes include the two photosystems, PSII and PSI, which support linear electron flow (LEF) from water to NADP⁺ molecules1. LEF establishes a proton gradient for ATP formation and enables NADP⁺ reduction, a step which requires electron donation from PSI via ferredoxin2-4. According to this model, LEF is impossible without PSI, as its absence would prevent NADP⁺ reduction. However, we present evidence here that oxygenic photosynthesis can occur independently of PSI in the cyanobacterium Synechocystis PCC 6803. Through adaptive laboratory evolution, we generated PSI-deficient strain variants that can sustain growth under photoautotrophic conditions. Achieving PSI-independent photoautotrophy required the co-mutation of two or more proteins, including the translation elongation factor G (FusA). PSI-independent photoautotrophy was lost when the NDH-1 complex was inactivated, suggesting that the NDH-1 complex can replace PSI when operating in reverse by transferring electrons from plastoquinone to ferredoxin. These findings reveal an unexpected plasticity in cyanobacterial thylakoid electron transport, necessitating a revision of existing models of oxygenic photosynthesis.

INSTRUMENT(S):

ORGANISM(S): Synechocystis Sp. Pcc 6803 Substr. Gt-i

TISSUE(S): Photosynthetic Cell

SUBMITTER: Serena Schwenkert  

LAB HEAD: Serena Schwenkert

PROVIDER: PXD071953 | Pride | 2026-06-12

REPOSITORIES: Pride