Genetically engineered<i>Fusarium</i>as a tool to evaluate the effects of environmental factors on initiation of trichothecene biosynthesis

Abstract

Fusarium graminearum was engineered for expression of enhanced green fluorescent protein gene (egfp) as a reporter regulated in a manner similar to Tri5, a key pathway gene in trichothecene biosynthesis. Using the transgenic fungus, it was found that the reporter gene was induced to express in aerial hyphae developed on trichothecene noninducing medium YG solidified by agar. Unexpectedly, the transcriptional activation of egfp was markedly suppressed by adding NaCl that does not significantly affect fungal growth. As suggested by these findings, wild-type F. graminearum that formed aerial hyphae on YG agar plates produced trichothecenes and the production was effectively suppressed by adding 1% NaCl to the agar. To evaluate the effects of abiotic stress on the expression of trichothecene biosynthesis (Tri) genes, a sensitive plate assay was established using GYEP medium (which very weakly induces trichothecene production) solidified with gellan gum. Using this assay, triazole fungicides were shown to cause transcriptional activation of egfp at sublethal concentrations. Indeed, trichothecene production significantly increased when F. graminearum was grown in rice medium (which moderately induces trichothecene) amended with low doses of tebuconazole. The real-time monitoring system described here may help predict the risks of trichothecene contamination by the fungus under various environmental conditions.