subsp. type III effector PthA4 directs the dynamical expression of a putative citrus carbohydrate-binding protein gene for canker formation.

subsp. (), the causal agent of citrus canker, elicits canker symptoms in citrus plants because of the transcriptional activator-like (TAL) effector PthA4, which activates the expression of the citrus susceptibility gene . This study reports the regulation of the putative carbohydrate-binding protein gene by PthA4-mediated induction of CsLOB1 during infection. We found that the transcription of was induced by infection with in a PthA4-dependent manner. Even though it specifically bound to a putative TAL effector-binding element in the promoter, PthA4 exerted a suppressive effect on the promoter activity. In contrast, CsLOB1 bound to the promoter to activate its expression. The silencing of significantly reduced the level of expression of , which demonstrated that was directly regulated by CsLOB1. Intriguingly, PhtA4 interacted with CsLOB1 and exerted feedback control that suppressed the induction of expression of by CsLOB1. Transient overexpression and gene silencing revealed that was required for the optimal development of canker symptoms. These results support the hypothesis that the expression of is dynamically directed by PthA4 for canker formation through the PthA4-mediated induction of CsLOB1.