Multiple virulence factors regulated by AlgU contribute to the pathogenicity of Pseudomonas savastanoi pv. glycinea in soybean

Viet Tru Nguyen; Nanami Sakata; Giyu Usuki; Takako Ishiga; Yoshiteru Hashimoto; Yasuhiro Ishiga

doi:10.7717/peerj.12405

Multiple virulence factors regulated by AlgU contribute to the pathogenicity of Pseudomonas savastanoi pv. glycinea in soybean

PeerJ. 2021 Oct 29:9:e12405. doi: 10.7717/peerj.12405. eCollection 2021.

Authors

Viet Tru Nguyen^#^{1

2}, Nanami Sakata^#², Giyu Usuki², Takako Ishiga², Yoshiteru Hashimoto^{2

3}, Yasuhiro Ishiga²

Affiliations

¹ Western Highlands Agriculture and Forestry Science Institute, Buon Ma Thuot, Daklak, Vietnam.
² Faculty of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.
³ Microbiology Research Center for Sustainability (MiCS), University of Tsukuba, Tsukuba, Ibaraki, Japan.

^# Contributed equally.

Abstract

Pseudomonas savastanoi pv. glycinea (Psg) causes bacterial blight of soybean. To identify candidate virulence factors, transposon-mediated mutational analysis of Psg was carried out. We syringe-inoculated soybean leaves with Psg transposon mutants and identified 28 mutants which showed reduced virulence from 1,000 mutants screened. Next, we spray-inoculated soybean leaves with these mutants and demonstrated that the algU mutant showed significantly reduced virulence together with reduced bacterial populations in planta. Expression profiles comparison between the Psg wild-type (WT) and algU mutant in HSC broth revealed that expression of coronatine (COR)-related genes (including cmaA and corR) were down-regulated in the algU mutant compared with Psg WT. Moreover, we also showed that COR production were reduced in the algU mutant compared with WT. We also demonstrated that algD, which is related to alginate biosynthesis, showed reduced expression and biofilm formation was significantly suppressed in the algU mutant. Furthermore, hrpL also showed less expression in the algU mutant. These results indicate that AlgU plays a critical role in promoting Psg pathogenesis by regulating multiple virulence factors.

Keywords: AlgU; Coronatine; Extracellular polysaccharide; Pathogenicity; Pseudomonas savastanoi pv. glycinea; Soybean.

Grants and funding

This work was supported by JSPS KAKENHI (No. 19K06045) and by JST ERATO (No. JPMJER1502). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.