Epistatic Relationship between MGV1 and TRI6 in the Regulation of Biosynthetic Gene Clusters in Fusarium graminearum

Genetic studies have shown that the MAP kinase MGV1 and the transcriptional regulator TRI6 regulate many of the same biosynthetic gene clusters (BGCs) in Fusarium graminearum. This study sought to investigate the relationship between MGV1 and TRI6 in the regulatory hierarchy. Transgenic F. graminearum strains constitutively expressing MGV1 and TRI6 were generated to address both independent and epistatic regulation of BGCs by MGV1 and TRI6. We performed a comparative transcriptome analysis between axenic cultures grown in nutrient-rich and secondary metabolite-inducing conditions. The results indicated that BGCs regulated independently by Mgv1 included genes of BGC52, whereas genes uniquely regulated by TRI6 included the gene cluster (BGC49) that produces gramillin. To understand the epistatic relationship between MGV1 and TRI6, CRISPR/Cas9 was used to insert a constitutive promoter to drive TRI6 expression in the Δmgv1 strain. The results indicate that BGCs that produce deoxynivalenol and fusaoctaxin are co-regulated, with TRI6 being partially regulated by MGV1. Overall, the findings from this study indicate that MGV1 provides an articulation point to differentially regulate various BGCs. Moreover, TRI6, embedded in one of the BGCs provides specificity to regulate the expression of the genes in the BGC.