Involvement of a putative response regulator FgRrg‐1 in osmotic stress response, fungicide resistance and virulence in <i>Fusarium graminearum</i>

<jats:title>SUMMARY</jats:title><jats:p>Response regulator (RR) proteins are core elements of the high‐osmolarity glycerol (HOG) pathway, which plays an important role in the adaptation of fungi to a variety of environmental stresses. In this study, we constructed deletion mutants of two putative RR genes, <jats:italic>FgRRG‐1</jats:italic> and <jats:italic>FgRRG‐2</jats:italic>, which are orthologues of <jats:italic>Neurospora crassa RRG‐1</jats:italic> and <jats:italic>RRG‐2</jats:italic>, respectively. The <jats:italic>FgRRG‐1</jats:italic> deletion mutant (ΔFgRrg1‐6) showed increased sensitivity to osmotic stress mediated by NaCl, KCl, sorbitol or glucose, and to metal cations Li<jats:sup>+</jats:sup>, Ca<jats:sup>2+</jats:sup> and Mg<jats:sup>2+</jats:sup>. The mutant, however, was more resistant than the parent isolate to dicarboximide and phenylpyrrole fungicides. Inoculation tests showed that the mutant exhibited decreased virulence on wheat heads. Quantitative real‐time polymerase chain reaction assays indicated that the expression of <jats:italic>FgOS‐2</jats:italic>, the putative downstream gene of <jats:italic>FgRRG‐1</jats:italic>, was decreased significantly in ΔFgRrg1‐6. All of the defects were restored by genetic complementation of ΔFgRrg1‐6 with the wild‐type <jats:italic>FgRRG‐1</jats:italic> gene. Different from the <jats:italic>FgRRG‐1</jats:italic> deletion mutant, <jats:italic>FgRRG‐2</jats:italic> deletion mutants were morphologically indistinguishable from the wild‐type progenitor in virulence and in sensitivity to the dicarboximide fungicide iprodione and osmotic stresses. These results indicate that the RR FgRrg‐1 of <jats:italic>F. graminearum</jats:italic> is involved in the osmotic stress response, pathogenicity and sensitivity to dicarboximide and phenylpyrrole fungicides and metal cations.</jats:p>