The pathogenicity-associated regulators participating in the regulatory cascade for RaxSTAB and RaxX in Xanthomonas oryzae pv. oryzae.

The RaxX sulfopeptide, secreted via a type Ι secretion system, is crucial for activating XA21-mediated innate immunity in resistant rice lines bearing the XA21 receptor kinase. Certain pathogenicity-associated regulators that control the expression of the raxSTAB-raxX gene cluster have been functionally characterized, but the comprehensive regulatory cascade of RaxSTAB and RaxX in Xanthomonas oryzae pv. oryzae (Xoo) remains incompletely understood. Our investigation revealed that pathogenicity-associated regulators, including HrpG, HrpX, VemR, PhoR, and Clp, form a regulatory cascade governing the expression of the raxSTAB-raxX gene cluster. HrpG regulates the raxSTAB-raxX gene cluster transcription through the key regulator HrpX. VemR also participates in the transcription of the raxSTAB-raxX. The histidine kinase PhoR positively modulates raxSTAB-raxX expression, while the global regulator Clp directly binds the raxX promoter region to promote its transcription. These findings shed light on the intricate regulatory cascade of rax-related genes in Xoo, emphasizing the complex roles of pathogenicity-associated regulators within the pathogenic regulatory system.