The copB Is a Key Copper Resistance Gene in Xanthomonas citri pv. mangiferaeindicae GXBS06

Background/Objectives: Mango bacterial angular leaf spot, caused by Xanthomonas citri pv. mangiferaeindicae (Xcm), is one of the most destructive bacterial diseases of mango, resulting in significant economic losses to the mango industry. Copper-based bactericides have been widely used for decades to control this disease, leading to increased copper resistance in the pathogen and heightened environmental risks. However, the copper resistance mechanisms of Xcm remain incompletely understood. Methods: In this study, we used Xcm GXBS06 isolated from major mango cultivars in Guangxi, China. We analyzed the homologs of known copper resistance-related genes in Xcm and found that these genes are relatively conserved across different strains. The functions of six important known copper resistance gene homologs in Xcm were investigated. Among them, five were functionally characterized by gene deletion, while the remaining one was characterized by overexpression because deletion was unsuccessful. Results: The result showed that copB is a critical copper resistance-related gene in Xcm. However, its deletion neither affects H₂O₂ tolerance nor virulence determinants such as extracellular polysaccharide production, biofilm formation, or cell motility. Additionally, it did not impact pathogenicity or bacterial growth within the host. The expression of copB was significantly induced at copper sulfate concentrations of 0.2 mM and 0.6 mM. Conclusions: These findings contribute to a better understanding of the copper resistance mechanisms in Xcm and provide a foundation for further studies on the biological control of this pathogen.