AUTHOR=Ray Suvendra K. , Kumar Rahul , Peeters Nemo , Boucher Christian , Genin Stephane 

TITLE=rpoN1, but not rpoN2, is required for twitching motility, natural competence, growth on nitrate, and virulence of Ralstonia solanacearum

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00229

DOI=10.3389/fmicb.2015.00229

ISSN=1664-302X

ABSTRACT=<p>The plant pathogen <italic>Ralstonia solanacearum</italic> has two genes encoding for the sigma factor σ<sup>54</sup>: <italic>rpoN1</italic>, located in the chromosome and <italic>rpoN2</italic>, located in a distinct “megaplasmid” replicon. In this study, individual mutants as well as a double mutant of <italic>rpoN</italic> were created in <italic>R. solanacearum</italic> strain GMI1000 in order to determine the extent of functional overlap between these two genes. By virulence assay we observed that <italic>rpoN1</italic> is required for virulence whereas <italic>rpoN2</italic> is not. In addition <italic>rpoN1</italic> controls other important functions such twitching motility, natural transformation and growth on nitrate, unlike <italic>rpoN2</italic>. The <italic>rpoN1</italic> and <italic>rpoN2</italic> genes have different expression pattern, the expression of <italic>rpoN1</italic> being constitutive whereas <italic>rpoN2</italic> expression is induced in minimal medium and in the presence of plant cells. Moreover, the expression of <italic>rpoN2</italic> is dependent upon <italic>rpoN1</italic>. Our work therefore reveals that the two <italic>rpoN</italic> genes are not functionally redundant in <italic>R. solanacearum</italic>. A list of potential σ<sup>54</sup> targets was identified in the <italic>R. solanacearum</italic> genome and suggests that multiple traits are under the control of these regulators. Based on these findings, we provide a model describing the functional connection between RpoN1 and the PehR pathogenicity regulator and their dual role in the control of several <italic>R. solanacearum</italic> virulence determinants.</p>