Ethylene accelerates maize leaf senescence in response to nitrogen deficiency by regulating chlorophyll metabolism and autophagy

Leaf senescence is an orderly and highly coordinated process, and finely regulated by ethylene and nitrogen (N), ultimately affecting grain yield and nitrogen-use efficiency (NUE). However, the underlying regulatory mechanisms on the crosstalk between ethylene- and N-regulated leaf senescence remain a mystery in maize. In this study, ethylene biosynthesis gene ZmACS7 overexpressing (OE-ZmACS7) plants were used to study the role of ethylene regulating leaf senescence in response to N deficiency, and they exhibited the premature leaf senescence accompanied by increased ethylene release, decreased chlorophyll content and Fv/Fm ratio, and accelerated chloroplast degradation. Then, we investigated the dynamics changes of transcriptome reprogramming underlying ethylene-accelerated leaf senescence in response to N deficiency. The differentially expressed genes (DEGs) involved in chlorophyll biosynthesis were significantly down-regulated, while DEGs involved in chlorophyll degradation and autophagy processes were significantly up-regulated, especially in OE-ZmACS7 plants in response to N deficiency. A gene regulatory network (GRN) was predicted during ethylene-accelerated leaf senescence in response to N deficiency. Three transcription factors (TFs) ZmHSF4, ZmbHLH106, and ZmEREB147 were identified as the key regulatory genes, which targeted chlorophyll biosynthesis gene ZmLES22, chlorophyll degradation gene ZmNYC1, and autophagy-related gene ZmATG5, respectively. Furthermore, ethylene signaling key genes might be located upstream of these TFs, generating the signaling cascade networks during ethylene-accelerated leaf senescence in response to N deficiency. Collectively, these findings improve our molecular knowledge of ethylene-accelerated maize leaf senescence in response to N deficiency, which is promising to improve NUE by manipulating the progress of leaf senescence in maize.