Figure 9.

A Proposed Model Illustrating the Tripartite Amplification Loop Involving WRKY75, SA, and ROS That Accelerates Leaf Senescence.

WRKY75 is a senescence-associated gene that is induced by SA and ROS, two well-documented leaf senescence inducers. Meanwhile, WRKY75 promotes SA biosynthesis by activating SID2 transcription and enhances the H₂O₂ accumulation by repressing CAT2 transcription. Given that SA and ROS also mutually promote each other’s accumulation, WRKY75, SA, and ROS form a tripartite amplification loop to accelerate leaf senescence. As a result, the levels of WRKY75, SA, and ROS undergo a gradual but irreversible rise driven by the interlinking positive feedback loops during leaf aging.