Characterizing Membrane Anchoring of Leaf-Form Ferredoxin-Nadp+ Oxidoreductase in Rice

Leaf-form ferredoxin-NADP+ oxidoreductases (LFNRs) function in the laststep of the photosynthetic electron transport chain, exist as solubleproteins in the chloroplast stroma, and are weakly associated withthylakoids or tightly anchored to chloroplast membranes. Arabidopsisthaliana has two LFNRs, and the chloroplast proteins AtTROL (THYLAKOIDRHODANESE-LIKE PROTEIN) and AtTIC62 (62-kDa SUBUNIT OF TRANSLOCON OFINNER CHLOROPLAST MEMBRANE) participate in anchoring AtLFNRs to thethylakoid membrane. By contrast, the membrane anchoring mechanism ofrice (Oryza sativa) LFNRs has not been elucidated. Here, we investigatedthe membrane-anchoring mechanism of LFNRs and its physiological roles inrice. We characterized the rice protein OsTROL1 based on its homology toAtTROL and showed that OsTROL1 is also a thylakoid membrane anchor andits loss led to a compensatory increase in OsTIC62. Moreover, OsLFNR1attachment through a membrane anchor depends on OsLFNR2, unlike theirArabidopsis counterparts. In addition, OsTIC62 was more highly expressedin rice under dark than under light conditions, consistent with theincreased membrane binding of OsLFNR in the dark. Moreover, we observedreciprocal stabilization between OsLFNRs and their membrane anchors.Therefore, our study sheds light on the mechanisms anchoring LFNRs tomembranes in rice and highlights differences with Arabidopsis