Fis is a global regulator critical for modulation of virulence factor production and pathogenicity of Dickeya zeae

Abstract

Dickeya zeae is the causal agent of rice foot rot disease, which has recently become a great threat to rice planting countries and regions. The pathogen produces a family of phytotoxins named zeamines that is critical for bacterial virulence, but little is known about the signaling pathways and regulatory mechanisms that govern zeamine production. In this study, we showed that a conserved transcriptional regulator Fis is involved in the regulation of zeamine production in D. zeae strain EC1. Deletion mutants were markedly attenuated in the virulence against rice seed germination. Transcriptome and phenotype analyses showed that Fis is a potent global transcriptional regulator modulating various virulence traits, including production of extracellular enzymes and exopolysaccharides, swimming and swarming motility, biofilm formation and cell aggregation. DNA gel retardation analysis showed that Fis directly regulates the transcription of key virulence genes and the genes encoding Vfm quorum sensing system through DNA/protein interaction. Our findings unveil a key regulator associated with the virulence of D. zeae EC1, and present useful clues for further elucidation of the regulatory complex and signaling pathways which govern the virulence of this important pathogen.

A two‐component regulatory system VfmIH modulates multiple virulence traits in Dickeya zeae

“…In fact, this study has verified that the VfmE but not the VfmH regulated the transcription of slyA (Fig. B), and our previous transcriptome analysis of ΔslyA has showed that the expression of vfm genes especially vfmA , vfmD , vfmE , vfmF , vfmU , vfmR and vfmQ was significantly reduced in this mutant, and qRT‐PCR data showed that the expression of vfmE in ΔslyA is only 0.186 ± 0.013‐folds of strain EC1 (Zhou et al , ), additionally, Fis protein directly binds to the promoter of vfmE (Lv et al , ), and SlyA significantly regulates the expression of fis in EC1 (Zhou et al , ), we proposed that zeamine production is regulated in such pathway: SlyA to Fis to zeamines or SlyA to Fis to VfmE to zeamines (Fig. ).…”

“…The unlabelled vfmE DNA promoter fragments of 100 and 200‐fold as the competitor, were used in competition with the labelled DNA promoter fragments in the binding assay with the VfmH‐GST fusion protein and its derivatives. The positions of free DNA (F) and of protein‐DNA complexes (C) were shown and the GST∙tag protein is unable to bind to the promoter DNAs (Lv et al, ). B.…”

“…Bacterial cell motility of D. zeae EC1 was modulated by at least two different pathways, one is by AHL signal through SlyA transcriptional regulator (Zhou et al, ), the other is by Vfm signal. Zeamine production is regulated by SlyA protein through Fis and VfmE transcriptional regulators (Lv et al, ). CWDE production is negatively regulated by SlyA protein and positively regulated by Fis and VfmE regulators.…”

“…After 24 h, inhibition zone radius surrounding the wells was measured. The zeamine concentration was determined using the formula: Zeamines (unit) = 0.5485e 0.886x , with a correlation coefficient ( R 2 ) of 0.9957, X is the radius in millimetres of the zone of growth inhibition surrounding each well (Liao et al , ; Lv et al , ).…”

Flp, a Fis‐like protein, contributes to the regulation of type III secretion and virulence processes in the phytopathogen Xanthomonas campestris pv. campestris

“…Here, the deletion of Flp in Xcc caused a series of changes in virulence and HRassociated phenotypes. Although virulence factor regulation by Fis has been seen in other bacterial plant pathogens such as Dickeya dadantii (Ouafa et al, 2012) and Dickeya zeae (Lv et al, 2018), no role has been attributed to its regulation of HR, suggesting a differentiate role in Xcc.…”