Leucine metabolism regulates TRI6 expression and affects deoxynivalenol production and virulence in Fusarium graminearum

TRI6 is a positive regulator of the trichothecene gene cluster and the production of trichothecene mycotoxins (deoxynivalenol [DON] and acetylated forms such as 15-ADON) in the cereal pathogen F. graminearum. As a global transcriptional regulator, TRI6 expression is modulated by nitrogen-limiting conditions, sources of nitrogen and carbon, pH, and light. However, the mechanism by which these diverse environmental factors affect TRI6 expression remains under-explored. In our effort to understand how nutrients affect TRI6 regulation, comparative digital expression profiling was performed with a wildtype F. graminearum and a Δtri6 mutant strain, grown in nutrient-rich conditions. Analysis showed that TRI6 negatively regulates genes of the branched-chain amino acid (BCAA) metabolic pathway. Feeding studies with deletion mutants of MCC, encoding methylcrotonyl-CoA-carboxylase, one of the key enzymes of leucine metabolism, showed that addition of leucine specifically down regulated TRI6 expression and reduced 15-ADON accumulation. Constitutive expression of TRI6 in the Δmcc mutant strain restored 15-ADON production. A combination of cellophane breach assays and pathogenicity experiments on wheat demonstrated that disrupting the leucine metabolic pathway significantly reduced disease. These findings suggest a complex interaction between one of the primary metabolic pathways with a global regulator of mycotoxin biosynthesis and virulence in F. graminearum. Triplicate samples of digital gene expression profiling data for the Tri6 mutant and wildtype strains were compared. **Please note that the raw data files for the current study are no longer available, and therefore are not included in the submission.