The virulence and motility of Pseudomonas syringae pv. Actinidiae mediated by a temperature sensor HktS-HktR

Kiwifruit bacterial canker (KBC), caused by Pseudomonas syringae pv. actinidiae (Psa) is one of the most devastating diseases of kiwifruit and can damage almost all kiwifruit varieties. The severity of the disease occurrence is closely related to the temperature. Our previous research indicated that Psa showed stronger pathogenicity and expansion ability at relatively cool temperatures, but how Psa senses environmental temperature and regulates its virulence mechanism remains unclear. In this study, 69 Histidine kinases (HK) in Psa were predicted through bioinformatics analysis, and 9 differentially expressed HK genes were identified at varying temperatures through pathogenicity detection and quantitative reverse transcription PCR (qRT-PCR). Among them, HktS as a temperature signal receiver was identified, and its response regulator (RR) HktR was determined through structure analysis and cotranscription assay. The results showed that HktR can bind to transcription factor RpoD, and RpoD bind to hrpRS promoter region, thus initiating the expression level of the type III secretion system (T3SS), which plays an important role in the pathogenesis of Psa. In addition, the motility of Psa was also regulated by HktS-HktR in a temperature-dependent manner. These findings reveal the molecular mechanism by which HktS-HktR acts as a temperature sensor to regulate bacterial virulence and motility of Psa, providing a new potential target for KBC control.