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

Monilinia spp. is a pathogen that causes brown rot in stone fruit. In general, fungi have the ability to synthesise melanin through several pathways, producing different kinds of pigments. Monilinia spp. uses the melanin secondary metabolism for the development, survival, and longevity of the fungus.In this study we have identified, for the first time, and through BLAST analysis the presence of the L-DOPA pathway in Monilinia spp. ( M. laxa , M. fructicola and M. fructigena ) as well as derived pigments through UHPLC MS/MS analysis. The use of this pathway was analysed in control conditions, when the DHN-melanin pathway was inhibited by tricyclazole and also with the presence of kojic acid, demonstrating that L-DOPA pathway was active in all conditions under darkness. The addition of tricyclazole induced changes in the colony phenotype and also a transcriptional regulation in Monilinia spp., while the inhibitor kojic acid, at the tested conditions, did not act as a blocker of L-DOPA pathway in Monilinia spp. Finally, several developmental parameters were evaluated in Monilinia spp. under control conditions and when DHN pathway was blocked by the presence of tricyclazole. The results showed that L-DOPA derived pigments could be enough to ensure the correct development of the three species.These results prove, for the first time, the capability of Monilinia spp. to use more than one melanin biosynthetic pathway as a strategy to survive and develop properly. Further studies are needed to finally determine in which specific stressful conditions melanin biosynthetic pathways are activated.