Rice ONAC016 promotes leaf senescence through abscisic acid signaling pathway involving OsNAP

Senescence-induced NAC(senNAC)TFs play a crucial role in senescence during the final stage of leaf development.In this study,we identified a rice senNAC,ONAC016,which functions as a positive regulator of leaf senescence.The expression of ONAC016 increased rapidly in rice leaves during the progression of dark-induced and natural senescence.The onac016-1 knockout mutant showed a delayed leaf yellowing phenotype,whereas the overexpression of ONAC016 accelerated leaf senescence.Notably,ONAC016 expression was upregulated by abscisic acid(ABA),and thus detached leaves of the onac016-1 mutant remained green much longer under ABA treatment.Quantitative RT-PCR analysis showed that ONAC016 upregulates the genes associated with chlorophyll degradation,senescence,and ABA signaling.Yeast one-hybrid and dual-luciferase assays revealed that ONAC016 binds directly to the promoter regions of OsNAP,a key gene involved in chlorophyll degradation and ABA-induced senescence.Taken together,these results suggest that ONAC016 plays an important role in promoting leaf senescence through the ABA signaling pathway involving OsNAP.

The OsAGO2–OsNAC300–OsNAP module regulates leaf senescence in rice

Leaves play a crucial role in the growth and development of rice(Oryza sativa) as sites for the production of photosynthesis.Early leaf senescence leads to substantial drops in rice yields.Whether and how DNA methylation regulates gene expression and affects leaf senescence remains elusive.Here,we demonstrate that mutations in rice ARGONAUTE 2(OsAGO2)lead to premature leaf senescence,with chloroplasts in Osago2 having lower chlorophyll content and an abnormal thylakoid structure compared with those from wild-type plants.We show that OsAGO2 associates with a 24-nt micro RNA and binds to the promoter region of Os NAC300,which causes DNA methylation and suppressed expression of Os NAC300.Overexpressing Os NAC300 causes the similar premature leaf senescence as Osago2 mutants and knocking out Os NAC300 in the Osago2mutant background suppresses the early senescence of Osago2 mutants.Based on yeast one-hybrid,dual-luciferase,and electrophoresis mobility shift assays,we propose that Os NAC300 directly regulates transcription of the key rice aging gene NAC-like,activated by APETALA3/PISTILLATA(Os NAP)to control leaf senescence.Our results unravel a previously unknown epigenetic regulatory mechanism underlying leaf senescence in which OsAGO2–Os NAC300–Os NAP acts as a key regulatory module of leaf senescence to maintain leaf function.