L-Threonine and its analogue added to autoclaved solid medium suppress trichothecene production by Fusarium graminearum.

Fusarium graminearum produces trichothecene mycotoxins under certain nutritional conditions. When L-Thr and its analogue L-allo-threonine were added to brown rice flour solid medium before inoculation, trichothecene production after 4 days of incubation was suppressed. A time-course analysis of gene expression demonstrated that L-Thr suppressed transcription of Tri6, a trichothecene master regulator gene, and a terpene cyclase Tri5 gene. Regulation of trichothecene biosynthesis by altering major primary metabolic processes may open up the possibility to develop safe chemicals for the reduction of mycotoxin contamination might be developed.

Hydroxylations of trichothecene rings in the biosynthesis of Fusarium trichothecenes: evolution of alternative pathways in the nivalenol chemotype.

Fusarium sporotrichioides genes FsTri11, FsTri13, and FsTri1 encode cytochrome P450 monooxygenases (CYPs) responsible for hydroxylations at C-15, C-4, and C-8 of the trichothecene skeleton, respectively. However, the corresponding genes of nivalenol (NIV)-chemotype Fusarium graminearum remain to be functionally elucidated. In this study, we characterized the roles of these CYPs in NIV biosynthesis. Analyses of the metabolites of the F. graminearum Fgtri11- mutant, a disruptant of FgTri11 encoding isotrichodermin (ITD) C-15 hydroxylase, revealed a small amount of NIV-type trichothecenes suggesting that an alternative C-15 hydroxylase partially complemented FgTRI11p. In contrast, the C-7/C-8 hydroxylations depended solely on FgTRI1p, as suggested by the metabolite profiles of the Fgtri11- Fgtri1- double gene disruptant. Disruption of FgTri1 in both the wild-type and Fgtri13- mutant backgrounds revealed that FgTRI13p exhibits marginal activity toward calonectrin (CAL) and that it was the only C-4 hydroxylase. In addition, feeding experiments demonstrated that the C-4 hydroxylation of a 7-hydroxytrichothecene lacking C-8 ketone was extremely limited. The marginal activity of FgTRI13p toward CAL was advantageous for the C-7/C-8 hydroxylation steps in NIV biosynthesis, as transformation of a C-4 oxygenated trichothecene lacking C-7/C-8 modifications into NIV-type trichothecenes was quite inefficient. The significance of hydroxylation steps in the evolution of Fusarium trichothecenes is discussed.