Regulatory Roles of Phytochrome-Interacting Factor-Like1 (OsPIL1) in Chlorophyll Synthesis and Leaf Senescence in Rice (Oryza sativa)

Abstract

Phytochrome-Interacting Factor (PIF) is an important transcription factor associated with several development processes, including photomorphogenesis, flowering and senescence in Arabidopsis thaliana. It has been reported that a rice PIF orthologue gene Phytochrome-Interacting Factor-Like 1 (OsPIL1) increases plant height through elongating cell size, but other functions of OsPIL1 have not been reported yet. In this study, we identified new functions of OsPIL1 in chlorophyll synthesis and leaf senescence. ospil1 T-DNA knockdown mutant displayed pale-green leaf color during development and of several chlorophyll synthesis enzyme genes are up-regulated in ospil1 mutant compared with WT. Yeast one-hybrid assay showed that OsPIL1 activates the expressions of some chlorophyll synthesis enzyme genes including OsPORA, OsPORB, and OsCAO by direct binding to their promoters. On the other hand, attached and detached leaves of ospil1 showed early senescence phenotype in dark-induced senescence condition with rapid degradation of Chls and photosynthetic capacity, indicating OsPIL1 acts as a senescence inhibiting TF. Furthermore, microarray and qRT-PCR analysis showed that not only several senescence-associated genes (SAGs) such as OsSGR, OsNYC1, and OsNAP but also phytohormone-related gene such as OsABF1 were up-regulated and another phytohormone-related gene OsYUC6 was down-regulated in ospil1 mutants. Our data strongly suggest that OsPIL1 is involved in the inhibition of leaf senescence through phytohormone synthesis or signaling including ABA and auxin.