Tat system is required for the virulence of Dickeya zeae on rice plants

Abstract

The Gram-negative pathogenic bacterium Dickeya zeae causes soft rot in rice, corn and many other plants. The molecular mechanisms underlying D. zeae virulence are not clearly understood. In this study, we characterized the twin-arginine translocation (Tat) system of this pathogen. The mutants of tatA, tatB, tatC and tatE of D. zeae EC1 were generated through the use of the suicide vector pKNG101 and their phenotypic characters were determined. Our results showed that mutations in D. zeae Tat system have no effect on the bacterial growth. △tatA, △tatB and △tatE mutants reduced the motility distinctly, and could not form biofilm, while the △tatC mutant did not show a distinctive decrease on the motility and biofilm formation. Less production of proteases, pectate lyases and cellulases were shown in △tatA, △tatB, △tatC and △tatE mutants as compared with the wild type EC1, whereas the toxin in Tat mutants was reduced, as compared with the wild type. The Tat mutants △tatA, △tatB, △tatC and △tatE could cause soft rot in potato and Chinese cabbage and hypersensitive reactions (HR) in tobacco, that were not different significantly from those of the wild type EC1. However, △tatA, △tatB and △tatE were not significantly effective in the inhibition of rice seed germination compared to the wild type. Furthermore, the disease incidence of the Tat mutants decreased significantly when they were inoculated in rice plants. This reveals that the Tat system has a different role in the virulence of D. zeae in rice, potato and cabbage and it is required for the virulence of D. zeae in rice plants.