Rice RuBisCO activase promotes the dark-induced leaf senescence by enhancing the degradation of filamentation temperature-sensitive H.

Leaf senescence is a complex process that is triggered by many developmental and environmental factors. However, the mechanisms regulating leaf senescence remain unclear. Here, we revealed that rice ribulose-1,5-bisphosphate carboxylase/oxygenase activase (RCA) promotes the onset of basal dark-induced senescence. RCA was mainly expressed in the leaves, and its expression level quickly declined under dark conditions. Furthermore, rca mutant plants presented a prolonged leaf longevity phenotype in the dark, whereas overexpression of the large isoform of RCA (RCA _L ), not small isoform (RCA _S ), in rice and Arabidopsis accelerated leaf senescence. Filamentation temperature-sensitive H (OsFtsH1), a zinc metalloprotease, interacts with RCA _L and RCA _S and presents a higher binding efficiency to RCA _L than RCA _S in darkness. Furthermore, we found that RCA _L promotes 26S proteasome-mediated degradation of OsFtsH1 protein, which can be inhibited by protease inhibitor MG132. Consequently, OsFtsH1 loss-of-function mutants exhibit accelerated leaf senescence, whereas OsFtsH1-overexpressing plants display delayed senescence. Collectively, our findings highlight the significant role of RCA _L isoform in regulating leaf senescence under dark conditions, particularly through enhancing the degradation of OsFtsH1.
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