PNNL

Abstract

In cyanobacteria, photosynthesis simultaneously sustains growth through carbon fixation and generates reactive oxygen species (ROS) that damage biological molecules when energy intake does not match cellular demands. Maintaining redox balance, therefore, requires continuous coordination between photosynthetic electron flow and gene expression. This review traces how the flow of electrons through the photosynthetic electron transport chain transduces signals that regulate gene expression via membrane-localized sensors, cytoplasmic redox sensors downstream of photosystem I, and ROS produced when electron sinks are saturated. Membrane-bound histidine kinases relay the redox state of quinone acceptors and the plastoquinone pool to control photosystem remodeling, pigment biosynthesis, and circadian timing, while cytoplasmic one-component regulators sense redox signals through thiol-disulfide switches, iron-sulfur clusters, and metal-catalyzed oxidation, coordinating expression of photosystem cofactors, electron carriers, and transition metals. Post-transcriptional and translational mechanisms further shape redox-dependent gene expression programs by controlling transcript stability, ribosome assembly, and translation initiation. Finally, we discuss the implications of redox regulation for understanding photosynthetic physiology and the rational engineering of cyanobacteria.