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Abstract
Fusarium trichothecenes are fungal toxins that cause disease on infected plants and, more importantly, health problems for humans and animals that consume infected fruits or vegetables. Unfortunately, there are few methods for controlling mycotoxin production by fungal pathogens. In this study, we isolated and characterized sixteen Fusarium strains from naturally infected potato plants in the field. Pathogenicity tests were carried out in the greenhouse to evaluate the virulence of the strains on potato plants as well as their trichothecene production capacity, and the most aggressive strain was selected for further studies. This strain, identified as F. sambucinum, was used to determine if trichothecene gene expression was affected by the symbiotic Arbuscular mycorrhizal fungus (AMF) Glomus irregulare. AMF form symbioses with plant roots, in particular by improving their mineral nutrient uptake and protecting plants against soil-borne pathogens. We found that that G. irregulare significantly inhibits F. sambucinum growth. We also found, using RT-PCR assays to assess the relative expression of trichothecene genes, that in the presence of the AMF G. irregulare, F. sambucinum genes TRI5 and TRI6 were up-regulated, while TRI4, TRI13 and TRI101 were down-regulated. We conclude that AMF can modulate mycotoxin gene expression by a plant fungal pathogen. This previously undescribed effect may be an important mechanism for biological control and has fascinating implications for advancing our knowledge of plant-microbe interactions and controlling plant pathogens.
Highlights
Secondary metabolites are compounds produced by many organisms including filamentous fungi
We addressed three specific points: i) trichothecene production by F. sambucinum using molecular and chemical approaches; ii) effect of the Arbuscular mycorrhizal fungus (AMF) G. irregulare on the growth of trichothecene-producing F. sambucinum in vitro; and iii) G. irregulare-induced modulation of trichothecene gene expression in F. sambucinum
We chose F. sambucinum strain T5 as a model for this study because it was the most aggressive strain when tested on potato plants, inducing a rapid wilting and yellowing that resulted in plant death (Figure S2)
Summary
Secondary metabolites are compounds produced by many organisms including filamentous fungi These compounds include pigments, toxins, plant growth regulators, antibiotics and numerous compounds used for pharmaceutical purposes [1]. The fungal genus Fusarium (teleomorph: Giberrella) consists of over 70 species, many of which are plant pathogens, and some species can produce secondary metabolites, known as mycotoxins, that are toxic to humans and animals [1,4]. Trichothecene biosynthetic gene clusters have been characterized in F. graminearum and F. sporotrichioides, [1,7]. In both species, there is a core cluster of 12 genes that are involved in the biosynthesis, regulation or transport of trichothecenes. The biosynthetic pathway for all trichothecenes begins with a cyclization of farnesyl pyrophosphate to produce the hydrocarbon trichodiene [8]
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