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

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.