A Cytochrome P450 AaCP1 Is Required for Conidiation and Pathogenicity in the Tangerine Pathotype of Alternaria alternata

Citrus <i>Alternaria</i> brown spot caused by the necrotrophic fungal pathogen of the tangerine pathotype of <i>Alternaria alternata</i> causes yield losses in global tangerine production. In this study, we focus on a cytochrome P450 monooxygenase encoding gene, <i>Aacp1</i>, for its role in the sporulation, toxin production, and virulence of the tangerine pathotype of <i>Alternaria alternata</i>. <i>Aacp1</i>-deficient mutants (<i>∆Aacp1</i>) produced significantly fewer conidia than the wild-type strain. Chemical assays demonstrated that <i>Aacp1</i> plays a negative role in resistance to oxidant stress and biosynthesis of ACT toxin. Virulence assays revealed that <i>ΔAacp1</i> fails to induce necrotic lesions on detached Hongjv leaves. Transcriptomic analyses of WT and <i>ΔAacp1</i> revealed that many metabolic process genes were regulated. Furthermore, our results revealed a previously unrecognized <i>Aacp1</i> affected the expression of the gene encoding a naphthalene dioxygenase (<i>AaNdo1</i>) for sporulation and full virulence. Overall, this study revealed the diverse functions of cytochrome P450 monooxygenase in the phytopathogenic fungus.