Histidine Kinase RavS Governs Motility and Virulence in <i>Xanthomonas albilineans</i> Causing Sugarcane Leaf Scald

Sugarcane leaf scald, caused by Xanthomonas albilineans, is a destructive bacterial disease that threatens sugarcane production. Successful disease development depends on the pathogen's ability to move, colonize host tissues, and spread within plants, yet the regulatory mechanisms underlying these processes remain poorly understood. In this study, we investigated the role of the histidine kinase RavS in the pathogenicity of X. albilineans. A ravS deletion mutant (ΔravS) exhibited significantly reduced swimming and swarming motility, impaired growth, and markedly decreased virulence on sugarcane compared with the wild-type strain. Genetic complementation restored all phenotypes to wild-type levels. Comparative transcriptome analysis revealed that deletion of ravS resulted in coordinated repression of genes involved in flagellar assembly and chemotaxis, processes that are essential for bacterial movement and host colonization. In contrast, tolerances to oxidative stress (H₂O₂), ionic stress (CaCl₂ and MgSO₄), and pH stress were unaffected. Together, these results demonstrate that RavS promotes the development of sugarcane leaf scald by regulating motility-associated pathways that enable X. albilineans to colonize and cause disease in sugarcane effectively.