1-Hydroxyphenazine Targets PLP-Dependent Transferase to Control Corynespora Target Spot

Corynespora leaf spot, caused by Corynespora cassiicola, is an emerging disease in crops that significantly impacts both yield and quality. Currently, the use of fungicides to control Corynespora leaf spot has led to the development of varying degrees of resistance in the pathogen. Therefore, it is crucial to screen for highly effective fungicides with novel modes of action. This study evaluated the antifungal activity of 1-hydroxyphenazine (1OH-PHZ) against multiple phytopathogenic fungi, with a half-maximal effective concentration (EC 50 ) of 19.23 μg/ml against C. cassiicola hyphae. In vivo assay demonstrated antifungal activity of 67.22 and 45.03% on detached tomato leaves and fruits, respectively, at a dose of 500.0 μg/ml. Microscopic and ultrastructural observations revealed hyphal collapse, surface wrinkling, and indistinct organelle boundaries following treatment. Integrated transcriptomic and metabolomic analyses showed differentially expressed genes and differentially abundant metabolites, primarily affecting amino acid metabolism and biosynthesis pathways. Molecular docking, dynamic simulations, and microscale thermophoresis assays demonstrated that 1OH-PHZ binds to PLP-dependent transferase (PLPDT), exhibiting a binding free energy of −7.2 kcal/mol and a dissociation constant (Kd) value of 1.16 μM. Collectively, these findings suggest that 1OH-PHZ potentially binds to PLPDT, thereby disrupting amino acid metabolism and biosynthesis, which subsequently affects the synthesis and morphological development of the fungal cell wall and cell membrane. Through the combination and screening of highly active fungicidal substances, this study offers mechanistic insights that support the potential development of 1OH-PHZ as a novel agricultural fungicide for managing C. cassiicola infections.