RpoE Orchestrates Oxidative Stress Adaptation, Virulence, and Dual Plant Immune Modulation in Xanthomonas axonopodis pv. glycines

Abstract

In Xanthomonas axonopodis pv. glycines (Xag), rpoE (encoding σ^E) resided within the conserved rseA-mucD operon but was dually repressed by DSF signaling and the global regulator Clp. Although H₂O₂ induced rpoE transcription, its expression was paradoxically downregulated by H₂O₂-detoxification genes (oxyR, ahpC, ahpF, catB), suggesting a potential feedback loop. Notably, the rpoE mutant exhibited attenuated soybean virulence characterized by (1) reduced cell wall-degrading enzymes (CWDEs) production, leading to diminished activation of soybean innate immunity (ROS burst, callose deposition, programmed cell death, and jasmonic acid accumulation); (2) increased H₂O₂ sensitivity with impaired siderophore-mediated iron acquisition; (3) failure to elicit hypersensitive response (HR) in nonhosts. Significantly, rpoE complementation fully restored virulence traits. Collectively, RpoE emerges as a central regulator orchestrating oxidative stress adaptation, stealth pathogenesis via CWDEs-mediated immune suppression, and host-specific virulence/HR elicitation in Xag through its unique network, redefining sigma factor functionality in xanthomonads and providing targets for disrupting pathogen-host interactions.

Keywords: RpoE sigma factor; Xanthomonas axonopodis pv. glycines; expression regulation; oxidative stress adaptation; virulence mechanisms.