Exogenous hydrogen sulfide enhances the resistance of cabbage seedlings to black rot by improving phenolic synthesis and reducing reactive oxygen species.

Black rot, caused by Xanthomonas campestris pv. campestris (Xcc), is a devastating disease in cabbage. As a gaseous signaling molecule, hydrogen sulfide (H2S) is widely involved in plant disease resistance. However, the mechanism by which H2S enhances resistance to Xcc remains unclear. In our study, we demonstrate that exogenous H2S significantly enhances cabbage resistance to black rot by enhancing the phenylpropanoid pathway and antioxidant system. Physiological and biochemical analyses revealed that H2S pretreatment boosted endogenous H2S and nitric oxide (NO) levels by over 18.8% and 107.7%, respectively, and increased the contents of lignin and tannin by more than 16%. Concurrently, H2S reduced hydrogen peroxide (H2O2) accumulation by 10.9% and the superoxide anion (O2−) production rate by 42.2%, while enhancing the scavenging rates of superoxide and hydroxyl radicals. Physiological and biochemical results indicated that H2S application markedly promoted the accumulation of key phenolic acids, including protocatechuic acid (108.2%), chlorogenic acid (40.8%), and ferulic acid (68.9%), by upregulating the activities and related gene (PAL, C4H, COMT) expression level of pivotal enzymes. Integrated transcriptomic and metabolomic analyses further confirmed that H2S activated the phenylpropanoid biosynthesis pathway. Our findings providing new insights into the molecular mechanism of H2S-mediated disease resistance and a potential strategy for controlling black rot.