Distinct roles of Histone Methyltransferases Acdot1 and AcrmtA in growth regulation, secondary metabolism and stress response in Aspergillus carbonarius

Histone methyltransferases are involved in gene expression regulation by modulating the methylation of histone residues. We investigated the role of the histone methyltransferases Acdot1 and AcrmtA in the mycotoxigenic fungus Aspergillus carbonarius, obtaining knockout or overexpression mutants through Agrobacterium tumefaciens mediated transformation (ATMT). Aspergillus carbonarius is responsible for grape-bunch rots, representing the major source of Ochratoxin A (OTA) contamination on grapes. In morphogenesis assay, deletion of Acdot1 or AcrmtA upregulated the growth only on a minimal medium. In mycotoxin biosynthesis, the role of the genes was different and strongly affected byculture conditions. In liquid culture, ΔAcdot1 increased OTA production on rich media (+41%) as compared to wild type (WT), while ΔAcrmtA reduced OTA biosynthesis in both rich (-43%) and minimal media (-93%). OTA production in OErmtA was like WT on both media, while a lower OTA amount was reported for OEdot1 only on a minimal medium (-74%). The expression of AcOTAp450 (otaC), AcOTAnrps (otaB), AcOTAhal (otaD), key genes of the OTA biosynthetic pathway, was reduced in the ΔAcrmtA. In the presence of oxidative stress, ΔAcdot1 or ΔAcrmtA were slightly inhibited in growth and increased OTA production (+34% and +59%, respectively), while, on the contrary, WT resulted slightly upregulated in mycelium growth. In conclusion, Acdot1 and AcrmtA are differently involved in the growth, mycotoxin biosynthesis, and stress response in A. carbonarius. Due to its involvement in OTA biosynthesis regulation, especially AcrmtA represents a potential target for preventing OTA contamination.