CCR4-Not Complex Subunit Not2 Plays Critical Roles in Vegetative Growth, Conidiation and Virulence in Watermelon Fusarium Wilt Pathogen Fusarium oxysporum f. sp. niveum

Abstract

CCR4-Not complex is a multifunctional regulator that plays important roles in multiple cellular processes in eukaryotes. In the present study, the biological function of FonNot2, a core subunit of the CCR4-Not complex, was explored in <i>Fusarium oxysporum</i> f. sp. <i>niveum</i> (<i>Fon</i>), the causal agent of watermelon wilt disease. <i>FonNot2</i> was expressed at higher levels in conidia and germinating conidia and during infection in <i>Fon</i>-inoculated watermelon roots than in mycelia. Targeted disruption of <i>FonNot2</i> resulted in retarded vegetative growth, reduced conidia production, abnormal conidial morphology, and reduced virulence on watermelon. Scanning electron microscopy observation of infection behaviors and qRT-PCR analysis of <i>in planta</i> fungal growth revealed that the Δ<i>FonNot2</i> mutant was defective in the ability to penetrate watermelon roots and showed reduced fungal biomass in root and stem of the inoculated plants. Phenotypic and biochemical analyses indicated that the Δ<i>FonNot2</i> mutant displayed hypersensitivity to cell wall perturbing agents (e.g., Congo Red and Calcofluor White) and oxidative stress (e.g., H₂O₂ and paraquat), decreased fusaric acid content, and reduced reactive oxygen species (ROS) production during spore germination. Our data demonstrate that <i>FonNot2</i> plays critical roles in regulating vegetable growth, conidiogenesis and conidia morphology, and virulence on watermelon via modulating cell wall integrity, oxidative stress response, ROS production and FA biosynthesis through the regulation of transcription of genes involved in multiple pathways.