Regulatory Roles of DNA-binding One Zinc Finger 24 (OsDof24) in Leaf Senescence in Rice (Oryza sativa)

Abstract

Leaf senescence is a final stage of leaf development, which largely affects agronomic traits in cereal production. Although many genetic factors have been reported, it is still necessary to determine the key regulators that delay leaf senescence during grain filling in staple food crops including rice. Here we show that OsDOF24, one of DOF (DNA-binding One zinc Finger) transcription factor family, acts as a repressor of leaf senescence in rice. The T-DNA insertion-mediated enhancer-tagged overexpression of OsDOF24 (osdof24-D) in rice exhibits a stay-green phenotype during both age-dependent natural and dark-incubated senescence. The stay-green phenotype was further confirmed with the detached leaves of transgenic rice overexpressing OsDOF24 by 35S CaMV promoter. To elucidate the molecular mechanism of leaf senescence in osdof24-D mutants, we performed RT-qPCR analysis, revealing that senescence-associated genes (SAGs), Osl85 and Osl57, and chlorophyll degradation genes (CDGs), OsNYC1, OsNYC3, and OsSGR, are downregulated in osdof24-D mutants during dark incubation. In addition, the detached leaves of osdof24-D mutants were less sensitive to MeJA (methyl-jasmonate)-induced senescence. Consistent with this stay-green phenotype, expression levels of MeJA-responsive genes, OsJAmyb and OsCOI1a, decreased in osdof24-D mutants. Taken together, our results demonstrate that OsDOF24 suppresses the induction of leaf senescence during vegetative growth by downregulating MeJA-responsive signaling.