Vt35 antitoxin plays a central regulatory role in virulence of Pseudomonas savastanoi pv. glycinea on soybean.

Pseudomonas savastanoi pv. glycinea (Psg) causes bacterial blight on soybeans. Among Psg mutants that we previously generated by transposon mutagenesis to identify potential virulence factors, mutant VTP20 had reduced virulence. Genetic analysis of VTP20 revealed a mutation in operon PsgB076_26935-PsgB076_26940 (vt35-vt40). The vt35-vt40 operon is a toxin–antitoxin (TA) system, in which vt35 is functionally considered an antitoxin component. However, the function of this antitoxin in the vt35-vt40 TA system in Psg is unclear. Thus, here we used an overexpression approach to analyze the effects of vt35 on Psg virulence and found that Psg-vt35-OE caused less severe disease than Psg WT did in spray-inoculated and in syringe-infiltrated soybean leaves. Vt35 also regulated gene expression for multiple extracytoplasmic function (ECF) sigma factors during infection. These results suggest that Vt35 plays a central regulatory role in Psg virulence by regulating virulence factors and controlling alternate sigma factors. [ABSTRACT FROM AUTHOR]