Histone Methyltransferases AcDot1 and AcRmtA Are Involved in Growth Regulation, Secondary Metabolism, and Stress Response in Aspergillus carbonarius

Histone post-translational modifications (HPTMs) can affect gene expression by rearranging chromatin structure. Between these, histone methylation is one of the most studied in filamentous fungi, and different conserved domains coding for methyltransferase were found in Aspergillus spp. genomes. In this work, the role of the histone methyltransferases AcDot1 and AcRmtA in the mycotoxigenic fungus Aspergillus carbonarius was investigated, obtaining knockout or overexpression mutants through Agrobacterium tumefaciens-mediated transformation (ATMT). A. carbonarius is responsible for grape-bunch rot, representing the major source of ochratoxin A (OTA) contamination on grapes. In vivo conditions, the deletion of Acdot1 or AcrmtA resulted in upregulation of growth when the isolates were cultivated on a minimal medium. The influence of Acdot1 on the OTA biosynthesis was differently affected by culture conditions. On rich media, an increase in OTA accumulation was observed, while on minimal medium, lower OTA concentrations were reported. The deletion of AcrmtA always resulted in lower OTA accumulation. However, the expression of OTA biosynthesis genes was regulated by both histone methyltransferases. Of the six analyzed OTA genes, three of them showed altered expression in the knockout mutants, and otaB and otaR1 were common between both mutants. Furthermore, both AcDot1 and AcRmtA play a role in oxidative stress response, induced by 1 mM hydrogen peroxide, by modulating growth, conidiation and OTA biosynthesis. Neither the deletion nor the overexpression of the Acdot1 or AcrmtA affected virulence, while both the sporulation and OTA production were negatively affected in vivo by the deletion of AcrmtA.