Host Alternative NADH:Ubiquinone Oxidoreductase Serves as a Susceptibility Factor to Promote Pathogenesis of <i>Rhizoctonia solani</i> in Plants

Abstract

Phytopathogens have evolved mechanisms to utilize host genes (commonly known as susceptibility factors) to promote their pathogenesis. <i>Rhizoctonia solani</i> is a highly destructive fungal pathogen of various plants, including rice. We previously reported rice genes that were differentially regulated during <i>R. solani</i> pathogenesis. In this study, we analyzed the role of tomato homologs of two rice genes, isoflavone reductase (<i>IFR</i>) and alternative NADH:ubiquinone oxidoreductase (<i>NUOR</i>), as potential susceptibility factors for <i>R. solani</i>. Virus-induced gene silencing of <i>NUOR</i> in tomato resulted in compromised susceptibility against <i>R. solani</i>, whereas <i>IFR</i>-silenced plants demonstrated susceptibility similar to that of control plants. <i>NUOR</i> silencing in tomato led to homogenous accumulation of reactive oxygen species (optimum range) upon <i>R. solani</i> infection. In addition, the expression and enzyme activity of some host defense and antioxidant genes was enhanced, whereas H₂O₂ content, lipid peroxidation, and electrolyte leakage were reduced in <i>NUOR</i>-silenced plants. Similarly, transient silencing of <i>OsNUOR</i> provided tolerance against <i>R. solani</i> infection in rice. Overall, the data presented in this study suggest that <i>NUOR</i> serves as a host susceptibility factor to promote <i>R. solani</i> pathogenesis.