Characterizing membrane anchoring of leaf-form ferredoxin-NADP+
oxidoreductase in rice
Abstract
Leaf-form ferredoxin-NADP+ oxidoreductases (LFNRs) function in the last
step of the photosynthetic electron transport chain, exist as soluble
proteins in the chloroplast stroma, and are weakly associated with
thylakoids or tightly anchored to chloroplast membranes. Arabidopsis
thaliana has two LFNRs, and the chloroplast proteins AtTROL (THYLAKOID
RHODANESE-LIKE PROTEIN) and AtTIC62 (62-kDa SUBUNIT OF TRANSLOCON OF
INNER CHLOROPLAST MEMBRANE) participate in anchoring AtLFNRs to the
thylakoid membrane. By contrast, the membrane anchoring mechanism of
rice (Oryza sativa) LFNRs has not been elucidated. Here, we investigated
the membrane-anchoring mechanism of LFNRs and its physiological roles in
rice. We characterized the rice protein OsTROL1 based on its homology to
AtTROL and showed that OsTROL1 is also a thylakoid membrane anchor and
its loss led to a compensatory increase in OsTIC62. Moreover, OsLFNR1
attachment through a membrane anchor depends on OsLFNR2, unlike their
Arabidopsis counterparts. In addition, OsTIC62 was more highly expressed
in rice under dark than under light conditions, consistent with the
increased membrane binding of OsLFNR in the dark. Moreover, we observed
reciprocal stabilization between OsLFNRs and their membrane anchors.
Therefore, our study sheds light on the mechanisms anchoring LFNRs to
membranes in rice and highlights differences with Arabidopsis