The Kelch Repeat Protein VdKeR1 Is Essential for Development, Ergosterol Metabolism, and Virulence in Verticillium dahliae

<i>Verticillium dahliae</i> is a soil-borne fungal pathogen that can cause severe vascular wilt in many plant species. Kelch repeat proteins are essential for fungal growth, resistance, and virulence. However, the function of the Kelch repeat protein family in <i>V. dahliae</i> is unclear. In this study, a Kelch repeat domain-containing protein DK185_4252 (VdLs.17 VDAG_08647) included in the conserved <i>VdPKS9</i> gene cluster was identified and named VdKeR1. Phylogenetic analysis demonstrated a high degree of evolutionary conservation of VdKeR1 and its homologs among fungi. The experimental results showed that the absence of <i>VdKeR1</i> impaired vegetative growth, microsclerotia development, and pathogenicity of <i>V. dahliae</i>. Osmotic and cell wall stress analyses suggested that <i>VdKeR1</i>-deleted mutants were more tolerant to NaCl, sorbitol, CR, and CFW, while more sensitive to H₂O₂ and SDS. In addition, analyses of the relative expression level of <i>sqe</i> and the content of squalene and ergosterol showed that <i>VdKeR1</i> mediates the synthesis of squalene and ergosterol by positively regulating the activity of squalene epoxidase. In conclusion, these results indicated that <i>VdKeR1</i> was involved in the growth, stress resistance, pathogenicity, and ergosterol metabolism of <i>V. dahliae</i>. Investigating <i>VdKeR1</i> provided theoretical and experimental foundations for subsequent control of <i>Verticillium</i> wilt.