Investigation of the role of the L-DOPA pathway in the production of melanin in Monilinia spp. and its relationship with fungal development

Abstract Monilinia spp., the causal agent of brown rot in stone fruits, relies on melanin biosynthesis for development, survival, and longevity. In this study, we identified for the first time the presence of the L-3,4-dihydroxyphenylalanine (L-DOPA) pathway in Monilinia spp. ( M. laxa , M. fructicola , and M. fructigena ) through BLAST analysis, and detected L-DOPA-derived pigments using UHPLC-MS/MS. The pathway was evaluated under control conditions, upon inhibition of the dihydroxynaphthalene (DHN)-melanin pathway by tricyclazole, and in the presence of kojic acid. Our results indicate that the L-DOPA pathway may remain active under all tested conditions in darkness. Tricyclazole induced phenotypic and transcriptional changes, whereas kojic acid did not inhibit the L-DOPA pathway. Moreover, developmental analyses showed that L-DOPA-derived pigments were sufficient to sustain normal fungal development (i.e., conidiation and viability) when the DHN pathway was blocked. However, in M. laxa , the absence of DHN affected the germination capacity. Although these differences were small, the results indicate that L-DOPA–derived pigments may contribute to proper development across the three species, without providing conclusive evidence of a causal role. Importantly, these findings provide the first evidence that Monilinia spp. can utilize more than one melanin biosynthetic pathway to support survival and development, underscoring the need for further investigation into the environmental factors that modulate their activation.