Identification of new regulatory genes involved in the pathogenic functions of the rice-pathogenic bacterium Burkholderia glumae

Abstract

Burkholderia glumae is an emerging plant-pathogenic bacterium that causes disease in rice in several of the major rice-producing areas throughout the world. In the southern United States, B. glumae is the major causal agent of bacterial panicle blight of rice and has caused severe yield losses in recent decades. Despite its importance, few management options are available for diseases caused by B. glumae, and knowledge of how this pathogen causes disease is limited. In an effort to identify novel factors that contribute to the pathogenicity of B. glumae, random mutagenesis using the miniTn5gus transposon was performed on two strains of B. glumae. Resultant mutants were screened in the laboratory for altered phenotypes in various known or putative virulence factors, including toxoflavin, lipase and extracellular polysaccharides. Mutants that exhibited altered phenotypes compared to their parent strain were selected and subsequently characterized using a PCR-based method to identify the approximate location of the transposon insertion. Altogether, approximately 20 000 random mutants were screened and 51 different genes were identified as having potential involvement in the production of toxoflavin, lipase and/or extracellular polysaccharide. Especially, two regulatory genes, ntpR and tepR, encoding a LysR-type transcriptional regulator and a σ54-dependent response regulator, respectively, were discovered in this study as new negative regulatory factors for the production of toxoflavin, the major phytotoxin synthesized by B. glumae and involved in bacterial pathogenesis.

tepR encoding a bacterial enhancer‐binding protein orchestrates the virulence and interspecies competition of Burkholderia glumae through qsmR and a type VI secretion system

“…The transcriptomic analysis suggested that the toxoflavin biosynthesis and transport genes and the extracellular protease gene prtA were negatively and positively regulated by tepR and the tofI/tofR QS system, respectively. This is in line with the drastic increase and decrease of toxoflavin production and extracellular protease activity in ΔtepR and ΔtofI-tofR, respectively, compared with the wild type, B. glumae 336gr-1 (Chen et al, 2012;Melanson et al, 2017;Lelis et al, 2019). signal C 8 -HSL and its cognate receptor TofR form a complex to activate the expression of toxJ, a LuxR family transcriptional regulator gene, which further induces the toxoflavin biosynthesis/transport genes via ToxR (Kim et al, 2004(Kim et al, , 2009.…”

“…tepR, encoding a bEBP, was recently identified as a negative regulator of toxoflavin, the most important virulence factor of B. glumae (Melanson et al, 2017). Toxoflavin and other known virulence factors of B. glumae are under the tight regulation of the tofI/tofR QS system (Kim et al, 2004(Kim et al, , 2007Devescovi et al, 2007;Lelis et al, 2019).…”

“…Each entry is labelled with the GenBank ID followed by the strain name. The scale bar represents 0.5 substitutions per amino acid position was abolished in ΔtofI-tofR (Chen et al, 2012;Melanson et al, 2017). Table).…”

“…In a previous study, we identified tepR, encoding a group I bacterial enhancer-binding protein (bEBP), as a novel negative regulator of toxoflavin from a forward genetic screening experiment (Melanson et al, 2017). Though not previously investigated in B. glumae, group I bEBPs contain an N-terminal response regulator domain for signal perception, a σ 54 -binding domain for nucleotide binding, ATP hydrolysis, and interaction with σ 54 , and a DNA-binding domain that allows recognition of a specific cis-acting regulatory sequence (Wigneshweraraj et al, 2005;Bush and Dixon, 2012).…”

ScmR, a global regulator of gene expression, quorum sensing, pH homeostasis, and virulence inBurkholderia thailandensis

“…While the pathogenicity of B. multivorans ATCC 17616 in the Galleria mellonella larvae model of infection is apparently not regulated by the ScmR homologue LdhR (37), the loss of ScmR in both B. thailandensis E264 and B. pseudomallei Bp82 resulted in hypervirulence toward the model host C. elegans (26, 34). In addition, Melanson et al (38) demonstrated that the rice pathogen B. glumae 336gr-1 ScmR homologue, called NtpR, is a negative regulator of toxoflavin production, which is considered the primary virulence factor of B. glumae , suggesting that similarly to the B. thailandensis E264 and B. pseudomallei Bp82 ScmR homologues, NtpR influences virulence. In B. thailandensis and B. pseudomallei , ScmR was proposed to modulate the infection process by repressing the biosynthesis of malleilactone (26, 34).…”