Alternative sigma factor RpoN2 is required for flagellar motility and full virulence of Xanthomonas oryzae pv. oryzae

Abstract

Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen of rice, harbors a single polar flagellum for motility. How the flagellar system is regulated and how it is related to bacterial pathogenesis are not well understood. The genomic sequence of Xoo strain PXO99(A) revealed a flagellar regulon containing over 60 contiguous genes. A gene encoding alternative sigma factor 54 (σ(54)), named as rpoN2, is located in the central region of the regulon. RT-PCR analysis demonstrated rpoN2 was transcribed in an operon with flgRR, and fleQ. Single gene deletion mutants of the rpoN2 operon were generated. The rpoN2 and fleQ mutant lost swimming motility, whereas the flgRR mutant remained motile. Quantitative RT-PCR analysis further demonstrated that expression of regulatory genes fliA and flgM, and structural genes flgG, flhB, and fliC were significantly down-regulated in the rpoN2 and fleQ mutants. These results indicated that RpoN2 and FleQ synergistically controlled flagellar motility by regulating gene expression. Interestingly, the rpoN2 mutant, but not the fleQ mutant was impaired in its virulence on rice. In addition, we showed that the flagellin gene fliC mutant, which was non-motile, was not defective in virulence. Thus, we concluded that flagellar motility might not be essential for Xoo virulence in rice, and RpoN2 probably regulated bacterial virulence through a manner independent of its role in controlling flagellar gene expression.

RpoN (σ 54 ) Is Required for Floc Formation but Not for Extracellular Polysaccharide Biosynthesis in a Floc-Forming Aquincola tertiaricarbonis Strain

“…It has also been revealed that some bacteria, including Xanthomonas oryzae pv. oryzae, Bradyrhizobium japonicum, Rhizobium etli, Burkholderia fungorum, and Ralstonia solanacearum, carry two copies of rpoN (31)(32)(33)(34), and four copies of rpoN are encoded in the genome of Rhodobacter sphaeroides (35). The four paralogues were designated rpoN1, rpoN2, rpoN3, and rpoN4, and their GϩC contents were 68.29%, 68.48%, 69.57%, and 56.13%, respectively.…”

Quantitative, image-based phenotyping methods provide insight into spatial and temporal dimensions of plant disease

“…Combined estimated means and SE are presented, as well as the difference between the means and the P values for each pairwise statistical contrast. (Lee et al, 2003;Tian et al, 2015). Using a Raspberry Pi-controlled camera, images of the plates were taken for several days, and the area of bacterial spread was quantified (Supplemental Fig.…”

PXO_00987, a putative acetyltransferase, is required for flagellin glycosylation, and regulates flagellar motility, exopolysaccharide production, and biofilm formation in Xanthomonas oryzae pv. oryzae

“…Like many other Xanthomonads, Xoo harbors a single-polar flagellum, which is required for its swimming motility [20]. The flagellin protein is encoded by a fliC gene, which is located in the middle of a large flagellar regulon consisting of approximately 60 genes [20].…”

“…The flagellin protein is encoded by a fliC gene, which is located in the middle of a large flagellar regulon consisting of approximately 60 genes [20]. Although the motility driven by flagella has been shown to be an important virulence factor in several bacterial species, we have recently demonstrated that the flagellar motility of Xoo does not contribute to its virulence directly [20].…”

“…The flagellin protein is encoded by a fliC gene, which is located in the middle of a large flagellar regulon consisting of approximately 60 genes [20]. Although the motility driven by flagella has been shown to be an important virulence factor in several bacterial species, we have recently demonstrated that the flagellar motility of Xoo does not contribute to its virulence directly [20]. However, comparative analysis between the rice transcriptional responses to wild-type and the flagellin-deficient mutant treatment revealed that over 1,500 rice genes displayed differential expression, suggesting that the Xoo flagellin has an impact on the host immune system [21].…”