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Genetic analysis of the contribution of bacterial phenyl acetic acid production to virulence of Rhizoctonia solani AG2-2IIIB


<div><em>Rhizoctonia solani</em> is species complex of genetically distinct subgroups described as anastomosis groups (AGs), and strains of fungus infect many economically important crops, resulting in significant yield losses. We have demonstrated that an endosymbiont bacterium in a strain of AG 2-2IIIB contributes to pathogenicity on creeping bentgrass. Loss of the bacterium, <em>Enterobacter</em> sp. EnCren, was shown to affect the production of phenylacetic acid (PAA), which is considered a virulence factor of the fungus. PAA production was significantly reduced in the bacteria-free fungus. The correlation between PAA biosynthesis by the bacterium and virulence of the host fungus in sugarbeet was examined. An indole-3-pyruvate decarboxylase (IpdC) bacteria mutant (EnCren<em><sup>-IpdC</sup></em>), which in the free-living state showed reduced PAA levels, was reintroduced into a bacteria-free strain of the fungus to generate Restored<em><sup>-IpdC</sup></em>-RsCren. An IpdC-complemented strain of EnCren<em><sup>-IpdC</sup></em>,<sup> </sup>designated as EnCren<em><sup>+IpdC</sup></em>, was also reintroduced into the bacteria-free fungus to generate Restored<em><sup>+IpdC</sup></em>-RsCren. Disease assays of Restored<em><sup>-IpdC</sup></em>-RsCren and Restored<em><sup>+IpdC</sup></em>-RsCren on sugarbeet seedlings under growth-chamber conditions indicate reduced virulence in the Restored<em><sup>-IpdC</sup></em>-RsCren strain. Findings from this study could lead to better understanding of the underlying mechanism(s) of bacterial-endosymbiont-mediated pathogenicity in <em>R. solani</em> AG 2-2IIIB and the development of novel disease management strategies.</div>