The ABI4–SEN1–TRXm1 Module Integrates ABA and H2S Signaling to Coordinate Redox Homeostasis, Senescence and Plant Immunity

Plants undergo metabolic reprogramming, including senescence, in response to pathogen attack. While senescence-associated genes (SAGs) are critical to this process, the genes that integrate plant defense and senescence processes remain largely unknown. Here, we identified and characterized SENESCENCE ASSOCIATED GENE 1 (SEN1) as a central regulator that coordinates these processes in Arabidopsis. SEN1 is transcriptionally activated by abscisic acid (ABA) via its key component, ABA INSENSITIVE 4 (ABI4). SEN1 interacts with TRXm1, and the interaction modulates sulfotransferase activity of SEN1. Disruption of sen1 and trxm1 mutants reduces reactive oxygen species (ROS), alters the glutathione redox balance (GSH/GSSG), increases susceptibility to pathogens, and delays senescence. Hydrogen sulfide (H2S), a product of SEN1-mediated sulfur transfer, amplifies the module by inducing ABI4 expression. Notably, H2S enhances ABI4 transcriptional activity via persulfuration at Cys250, establishing a self-reinforcing loop. Overall, we propose a regulatory triad in which the ABI4-SEN1-TRXm1 module integrates ABA and H2S signaling to dynamically balance redox homeostasis. This study reveals a molecular switch that fine-tunes plant responses to biotic stress.