摘要：SummaryIn natural habitats, plants have developed sophisticated regulatory mechanisms to optimize the photosynthetic electron transfer rate at the maximum efficiency and cope with the changing environments. Maintaining proper P700 oxidation at photosystem I (PSI) is the common denominator for most regulatory processes of photosynthetic electron transfers. However, the molecular complexes and cofactors involved in these processes and their function(s) have not been fully clarified. Here, we identified a redox-active chloroplast protein, the triplet-cysteine repeat protein (TCR). TCR shared similar expression profiles with known photosynthetic regulators and contained two triplet-cysteine motifs (CxxxCxxxC). Biochemical analysis indicated that TCR localizes in chloroplasts and has a [3Fe-4S] cluster. Loss of TCR limited the electron sink downstream of PSI during dark-to-light transition.Arabidopsis pgr5-tcrdouble mutant reduced growth significantly and showed unusual oxidation and reduction of plastoquinone pool. These results indicated that TCR is involved in electron flow(s) downstream of PSI, contributing to P700 oxidation.Graphical AbstractDisplay OmittedHighlights•P700 oxidation at photosystem I is important for regulation of photosynthesis•TCR is a redox active chloroplast protein harboring a 3Fe-4S iron-sulfur cluster•TCR controls electron flow around photosystem I, contributing to P700 oxidationBiological sciences; plant biology; plant genetics; plant physiology
