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. Although senescence-associated genes are critical for 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) through the ABA signaling component ABA INSENSITIVE 4 (ABI4). SEN1 interacts with TRXm1, and this interaction modulates the sulfotransferase activity of SEN1. Disruption of these genes in the sen1 and trxm1 mutants reduces the level of reactive oxygen species, alters the balance between oxidized and reduced glutathione, increases susceptibility to pathogens, and delays senescence. Hydrogen sulfide (H2S), a product of SEN1-mediated sulfur transfer, amplifies this module by inducing ABI4 expression. Notably, H2S enhances the transcriptional activity of ABI4 via persulfuration at Cys250, establishing a self-reinforcing loop. We propose a regulatory triad in which the ABI4-SEN1-TRXm1 module integrates ABA and H2S signaling to dynamically balance redox homeostasis, acting as a molecular switch that fine-tunes plant responses to biotic stress.