OxyR contributes to virulence of Acidovorax citrulli by regulating anti-oxidative stress and expression of flagellin FliC and type IV pili PilA

Jianan Wang; Jun Liu; Yuqiang Zhao; Minghui Sun; Guixu Yu; Jiaqin Fan; Yanli Tian; Baishi Hu

doi:10.3389/fmicb.2022.977281

OxyR contributes to virulence of Acidovorax citrulli by regulating anti-oxidative stress and expression of flagellin FliC and type IV pili PilA

Front Microbiol. 2022 Sep 20:13:977281. doi: 10.3389/fmicb.2022.977281. eCollection 2022.

Authors

Jianan Wang¹, Jun Liu^{1

2}, Yuqiang Zhao³, Minghui Sun¹, Guixu Yu¹, Jiaqin Fan⁴, Yanli Tian¹, Baishi Hu¹

Affiliations

¹ College of Plant Protection and Key Laboratory of Integrated Management of Crop Diseases and Pests, Nanjing Agricultural University, Nanjing, China.
² Institute of Plant Protection and Soil Fertilizer, Hubei Academy of Agricultural Sciences, Wuhan, China.
³ Institute of Botany, Jiangsu Province and Chinese Academy of Sciences (Nanjing Botanical Garden Mem. Sun Yat-Sen), Nanjing, China.
⁴ Laboratory of Bacteriology, Department of Plant Pathology, Nanjing Agricultural University, Nanjing, China.

Abstract

In many bacteria, OxyR acts as a transcriptional regulator that facilitates infection via degrading hydrogen peroxide (H₂O₂) generated by the host defense response. Previous studies showed that OxyR also plays an important role in regulating biofilm formation, cell motility, pili relate-genes expression, and surface polysaccharide production. However, the role of OxyR has not been determined in Acidovorax citrulli strain xjl12. In the current study, the qRT-PCR and western blot assays revealed that the expression level of oxyR was significantly induced by H₂O₂. The oxyR deletion mutant of A. citrulli was significantly impaired bacterial tolerance to oxidative stress and reduced catalase (CAT) activity. In addition, oxyR mutant resulted in reduced swimming motility, twitching motility, biofilm formation, virulence, and bacterial growth in planta by significantly affecting flagellin and type IV pili-related gene (fliC and pilA) expression. The qRT-PCR assays and western blot revealed that OxyR positively regulated the expression of fliC and pilA. Furthermore, bacterial one-hybrid assay demonstrated that OxyR directly affected pilA and fliC promoter. Through bacterial two-hybrid assay, it was found that OxyR can directly interact with PilA and FliC. These results suggest that OxyR plays a major role in the regulating of a variety of virulence traits, and provide a foundation for future research on the global effects of OxyR in A. citrulli.

Keywords: Acidovorax citrulli; OxyR; oxidative stress; virulence; virulence traits.