Leaf senescence is a highly coordinated, complicated process involving the integration of numerous internal and environmental signals. Salicylic acid (SA) and reactive oxygen species (ROS) are two well-defined inducers of leaf senescence whose contents progressively and inter-dependently increase during leaf senescence via an unknown mechanism. Here, we characterized the transcription factor WRKY75 as a positive regulator of leaf senescence in Arabidopsis thaliana. Knock-down or knock-out of WRKY75 delayed age-dependent leaf senescence, while over-expression of WRKY75 accelerated this process. WRKY75 transcription is induced by age, SA, H2O2, and multiple plant hormones. Meanwhile, WRKY75 promotes SA production by inducing the transcription of SA INDUCTION-DEFICIENT2 (SID2) and suppresses H2O2 scavenging (清除), partly by repressing the transcription of CATALASE2 (CAT2). Genetic analysis revealed that the mutation of SID2 or an increase in catalase activity (过氧化氢酶活性) rescued the precocious (较早显出的) leaf senescence phenotype evoked (诱发) by WRKY75 over-expression. Based on these results, we propose a tripartite amplification loop model (三重放大回路模型) in which WRKY75, SA, and ROS undergo a gradual (渐进的) but self-sustained (自持的) rise driven by three interlinking (连结) positive feedback loops. This tripartite amplification loop provides a molecular framework connecting upstream signals, such as age and plant hormones, to the downstream regulatory network executed by SA- and H2O2-responsive transcription factors during leaf senescence.

First Published data: October 23, 2017.