Roles of rice PHYTOCHROME-INTERACTING FACTOR-LIKE1 (OsPIL1) in leaf senescence.

Rice (Oryza sativa) Phytochrome-Interacting Factor-Like1 (OsPIL1), a basic helix-loop-helix transcription factor, plays an important role in the elongation of internode cells. Recently, we found that OsPIL1 participates in chlorophyll biosynthesis by directly upregulating several genes encoding components of the photosystem apparatus. Here, we show that OsPIL1 negatively regulates leaf senescence in rice. During dark-induced senescence (DIS), ospil1 mutants senesced earlier than wild type; this is opposite to mutants of Arabidopsis PIF4 and PIF5, the closest homologs of OsPIL1. Microarray analysis revealed that during DIS, several senescence-associated genes were upregulated and OsGLKs, negative regulators of leaf senescence, were strongly repressed in ospil1 mutants. Transgenic Arabidopsis plants overexpressing OsPIL1 showed an early senescing phenotype during DIS. In addition, OsPIL1 expressed in Arabidopsis upregulates the transcription of ORESARA1, a major senescence-inducing NAC transcription factor and one of the downstream genes of Arabidopsis PIF4, by directly binding the promoter region. These results indicate that OsPIL1 and Arabidopsis PIF4 have similar functions, but their downstream regulatory cascades have opposite effects.