Fusarium metabolites and detoxification reactions: determinants of pathogen virulence and plant resistance?

Many filamentous fungi causing plant diseases have the ability to produce toxic secondary metabolites. So far most of the research has focused on compounds accumulating in infected cereals at toxicologically relevant levels for humans and animals consuming contaminated food or feed. The most important mycotoxin producing pathogens in Europe are species of Fusarium which cause head blight of small grain cereals and ear rot of maize. Only polygenically inherited quantitative differences in resistance exist in plant genetic resources, and the molecular basis of quantitative trait loci improving resistance is unknown. The goal of our project is to get an improved understanding of the role of fungal secondary metabolites in disease development, in order to be able to dissect plant resistance components. We will use the tools of modern genomics and metabolomics to change plant breeding from a solely empirical to a knowledge-based science, which should allow breeding of Fusarium resistant cultivars with low mycotoxin content. Our working hypothesis is that necrotrophic fungal pathogens like Fusarium produce a redundant set to metabolites which can suppress defense responses in plants, causing the broad host range. Bioinformatical analysis of the available full genome sequence of Fusarium graminearum revealed that this organism possesses many genes predicted to code for enzymes involved in secondary metabolite biosynthesis (e.g. 15 polyketide synthases, 20 ribosomal peptide synthases and 17 terpenoid synthases). For most of the genes no corresponding metabolites are known. The goal of our project is to use advanced functional genomics and metabolomics tools to identify new Fusarium metabolites suppressing defense responses triggered by the pathogen and purified elicitor proteins of Fusarium. With such compounds at hand we will explore their mode of action in model plants, and investigate the genome-wide transcriptional response in model and crop plants after challenge with toxins or with the pathogen. We will explore if differences exist in the breeding material regarding the ability to metabolize and detoxify (known and new) Fusarium metabolites. Candidate genes involved in detoxification (and supposedly pathogen resistance) will be validated by analysis of loss of function alleles identified by screening a wheat TILLING population, or by overexpression in transgenic wheat. The interdisciplinary collaboration of scientists integrating fungal genomics and bioinformatics, metabolomics, model and crop plant genomics and plant breeding distinguishes this proposal from other ongoing projects.