biostudies-literatureDumas LAgence Nationale de la RechercheInstitut National des Sciences de l&apos;Ingénierie et des SystèmesInitiative d&apos;Excellence12063-12068https://www.ebi.ac.uk/biostudies/studies/S-EPMC5692589biostudies-literatureUnknown114(45)The cytochrome (cyt) <i>b</i>₆<i>f</i> complex and Stt7 kinase regulate the antenna sizes of photosystems I and II through state transitions, which are mediated by a reversible phosphorylation of light harvesting complexes II, depending on the redox state of the plastoquinone pool. When the pool is reduced, the cyt <i>b</i>₆<i>f</i> activates the Stt7 kinase through a mechanism that is still poorly understood. After random mutagenesis of the chloroplast <i>petD</i> gene, coding for subunit IV of the cyt <i>b</i>₆<i>f</i> complex, and complementation of a Δ<i>petD</i> host strain by chloroplast transformation, we screened for impaired state transitions in vivo by chlorophyll fluorescence imaging. We show that residues Asn122, Tyr124, and Arg125 in the stromaProceedings of the National Academy of Sciences of the United States of AmericaA stromal region of cytochrome <i>b</i>₆<i>f</i> subunit IV is involved in the activation of the Stt7 kinase in <i>Chlamydomonas</i>.PMC5692589ANR-11-LABEX-0011-01ANR-14-CE05-0041-01PhotoModes 72749Zito FPeltier GAlric JDumas LAuroy PBlangy SJohnson XfalseA stromal region of cytochrome <i>b</i>₆<i>f</i> subunit IV is involved in the activation of the Stt7 kinase in <i>Chlamydomonas</i>.The cytochrome (cyt) <i>b</i>₆<i>f</i> complex and Stt7 kinase regulate the antenna sizes of photosystems I and II through state transitions, which are mediated by a reversible phosphorylation of light harvesting complexes II, depending on the redox state of the plastoquinone pool. When the pool is reduced, the cyt <i>b</i>₆<i>f</i> activates the Stt7 kinase through a mechanism that is still poorly understood. After random mutagenesis of the chloroplast <i>petD</i> gene, coding for subunit IV of the cyt <i>b</i>₆<i>f</i> complex, and complementation of a Δ<i>petD</i> host strain by chloroplast transformation, we screened for impaired state transitions in vivo by chlorophyll fluorescence imaging. We show that residues Asn122, Tyr124, and Arg125 in the stroma2017-01-01T00:00:00Z2017 Nov2026-05-02T02:29:03.42Z2019-03-26T23:35:56ZS-EPMC56925892907838810.1073/pnas.1713343114