The OmpR-like Transcription Factor as a Negative Regulator of in pv. .

Bacterial canker of kiwifruit is a devastating disease caused by pv. (). The type III secretion system (T3SS), which translocates effectors into plant cells to subvert plant immunity and promote extracellular bacterial growth, is required for virulence. Despite that the "HrpR/S-HrpL" cascade that sophisticatedly regulates the expression of T3SS and effectors has been well documented, the transcriptional regulators of remain to be determined. In this study, the OmpR-like transcription factor, previously identified by DNA pull-down assay, was found to be involved in the regulation of genes, and its regulatory mechanisms and other functions in were explored through techniques including gene knockout and overexpression, ChIP-seq, and RNA-seq. The OmpR-like transcription factor had binding sites in the promoter region of the , and the transcriptional level of the increased after the deletion of and decreased upon its overexpression in an deletion background. Additionally, overexpression reduced the strain's capacity to form biofilms and lipopolysaccharides, led to its slow growth in King's B medium, and reduced its swimming ability, although there was no significant effect on its pathogenicity against kiwifruit hosts. Our results indicated that OmpR-like directly and negatively regulates the transcription of and may be involved in the regulation of multiple biological processes in . Our results provide a basis for further understanding the transcriptional regulation mechanism of in .