Function and transcription of stoS gene of Xanthomonas campestris pathovar campestris

StoS is a hybrid histidine kinase that, to date, has been investigated only in Xanthomonas oryzae pathovar oryzae. In this study, we elucidated the function and transcriptional regulation of the stoS gene in X. campestris pathovar campestris (Xcc). An stoS deletion mutant and its complemented strain were constructed to assess phenotypic characteristics. Inactivation of StoS markedly decreased tolerance to heat, sodium dodecyl sulfate, and hydrogen peroxide, impaired membrane integrity, and reduced stationary-phase survival, whereas complementation restored these phenotypes. Transcriptional mapping identified a guanine residue 22 nucleotides upstream of the start codon as the transcription start site. Promoter activity assays further revealed that stoS expression is regulated by nutrient availability and environmental stress. Together, these results demonstrate that stoS plays a crucial role in maintaining membrane stability and stress resilience in Xcc. By providing the first functional characterization of stoS in Xcc, this study extends its investigation beyond X. oryzae pathovar oryzae and advances current understanding of stress-adaptive regulation in Xanthomonas.