Genetically engineeredFusariumas 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.

Multiple facets of response to fungicides – the influence of azole treatment on expression of key mycotoxin biosynthetic genes and candidate resistance factors in the control of resistant Fusarium strains

“…Importantly, our results are consistent with earlier works of Ochiai et al (2007), stating that non-lethal doses of triazole fungicides activate the Tri5 gene (trichothecene synthase) in Fusarium graminearum. Similar research performed on Fusarium verticillioides and Fusarium proliferatum strains has shown that sublethal doses of fungicides in combination with mild water stress and temperatures less than 35°C, significantly induced Fum1 expression with slight differences in both species (Marín et al 2013).…”

“…Miguel et al 2015) and secondary metabolite accumulation (e.g. Ochiai et al 2007;Mateo et al 2011;Marín et al 2013). The possible influence on the activity of the biosynthetic genes responsible for the production of mycotoxins can thus affect the efficiency of fungicidal treatments in controlling mycotoxin producers.…”

“…In context of the fungicidal treatments, there is a lot of evidence that non-lethal amounts of fungicides, could lead to increased mycotoxin biosynthesis (as evidenced in gene expression patterns). According to the past results of Ochiai et al (2007), suboptimal doses of triazole fungicides can transcriptionally activate the Tri5 gene (trichothecene synthase) in Fusarium graminearum. Similar results were obtained in the experiments investigating the influence of sodium propionate and potassium adsorbate on the expression of the Penicillium verrucosum ochratoxin polyketide synthase gene (Schmidt-Heydt et al 2007).…”

Study of metabolite profiles in winter wheat cultivars induced by Fusarium infection

“…It is very difficult to refer to this fact in view of the results collected so far. The observed differences between contents of fungal metabolites and phenolic acids between the population of K and OCH samples may be explained by the fact that sublethal concentrations of fungicides trigger trichothecene biosynthesis (Ochiai et al 2007;Müllenborn et al 2008). On the other hand, all fungicides (prothioconazole, tebuconazole, metconazole and prothioconazole + tebuconazole) used in the study reduced FHB index and deoxynivalenol (DON) levels according to Amarasinghe et al (2013).…”

Low pH regulates the production of deoxynivalenol by Fusarium graminearum

“…In Aspergillus nidulans, endogenous and exogenous oxylipids differentially regulate sterigmatocystin and penicillin production (Tsitsigiannis & Keller, 2006). A number of recent reports have also implicated various compounds, such as H 2 O 2 , NaCl, azole fungicides, magnesium, carbon source and a large number of phytochemicals, in both positive and negative regulation of trichothecene production in vitro (Boutigny et al, 2008;Jiao et al, 2008;Ochiai et al, 2007;Pinson-Gadais et al, 2008;Ponts et al, 2006). However, in these studies the amount of DON produced in culture does not appear to approach the levels observed in infected heads, where concentrations can exceed 500 p.p.m.…”