Plant pathology

Several of the toxigenic fungal species we work with in our group are also plant pathogens. By their infection of crops they contaminate food and feed with mycotoxins, potentially harmful to humans and animals.

Understanding the biology of the pathogen and the production of mycotoxins during infection and storage is an important part of our focus to safeguard food and feed and ultimately, human and animal health.

The plant pathology related work within the group is mainly dealing with the fungal pathogenesis, fungal genetics, and mycotoxin production of fungi causing Fusarium head blight in small grain cereals (i.e. Fusarium graminearum, Fusarium avenaceum and Fusarium langsethiae).

F. graminearum constitutes a global problem when it comes to cereal infection and mycotoxin contaminations, causing great losses in yield and grain quality and compromising food and feed safety. Norway is no exception, and oats and wheat are the most significantly affected crops. F. graminearum infects the grain through rain splash of conidia from crop debris and soil, as well as through the air. During infection the mycotoxin deoxynivalenol (DON) is produced in large amounts and is a virulence factor necessary for spreading within the plant tissue. DON has additional adverse effects on animals and humans if ingested, causing feed refusal and vomiting in acute doses, and affecting the immune system and gastro intestinal tract. F. graminearum also produces the DON precursors 3-ADON and 15-ADON, and the infected plant is converting part of the DON to the less toxic DON-3-glucoside (DON-3-G) as part of its resistance machinery.  All of these metabolites and others are focus for our research.

In the NFR-funded project MycoProcess, we have studied the distribution and relative amounts of the DON metabolites within the oat grain and investigated their behavior during various processes leading to oat flakes, porridge, sourdough fermentation and regular yeast fermentation. In agreement with data published from other groups we find that the relative amount of DON compared to DON-3-G is highest in the hulls whereas bran is enriched with DON-3-G relative to DON. Matrix effects and biotic and abiotic interaction factors during processing further determine the relative amounts of the various DON metabolites in the product. This is important research in order to maintain control of mycotoxin levels in cereal products and gain knowledge about mycotoxin exposure to the public.

In order to study DON and various known and yet unknown forms of this molecule we are, together with Section of Chemistry,  setting up our own production system of 14C-labeled DON. This will allow us to continue studies of this metabolite both in planta and in animal in vitro and in vivo systems.

F. langsethiae is another Fusarium species frequently contaminating cereal crops, mainly in Northern Europe and the UK. F. langsethiae is far less aggressive than F. graminearum, however, maintains a position as an important food and feed contaminant due to production of the very potent mycotoxins T-2 and HT-2. There is still limited knowledge about F. langsethiae pathogenesis and biochemical potential, and within the strategic institute project FUNtox, our group has engaged in two projects trying to learn more about this fungus.

Genome sequencing of F. langsethiae has revealed a great potential for secondary metabolite biosynthesis.  One of the polyketide synthases, DEP5, is involved in the biosynthetic pathway of the small polyketide depudecin. The depudecin biosynthetic pathway is conserved within only few fungal species and F. lansethiae is the only FHB causing species where the pathway is intact.  Based on multiple approaches we are working to elucidate the role of this mycotoxin in F. langsethiae biology as well as assessing whether it poses a threat to food safety.  With various molecular methods we are investigating the biosynthetic potential for this metabolite, and together with Section of Chemistry we are setting up a method for chemical detection.

In another project we are using a metabolomics approach to investigate competition between F. langsethiae and F. graminearum. From co-culturing  of F. langsethiae strains with F. graminearum we identified eight F. langsethiae strains with ability to form an inhibition zone facing the F. graminearum colony. Using metabolomics methods we are now investigating three compounds that are specifically expressed in F. langsethiae during this interaction.

Fusarium avenaceum is a ubiquitious generalist found in most Norwegian cereal crops, often together with other Fusarium species. Among the metabolites produced by this fungus are enniatins and 2-Amino-14,16-dimethyloctadecan-3-ol (AOD). These mycotoxins are not under the same strict legislations as DON and T-2/HT-2, however may be found in considerable amounts in grain. The fact that the mycotoxins often come in combination with e.g. DON makes them important to study with respect to cocktail effects.

In a FUNtox-project we have in collaboration with several international research groups, identified the biosynthetic pathway for AOD in F. avenaceum. The project has been a collaborative effort involving bioinformatics, generation of fungal knock outs, chemical testing and plant pathogenesis of AOD mutants. FUNtox is also funding toxicological studies of AOD using in vitro cell assays.

An entirely different fungal plant pathogen with great impact is Calviceps purpurea and other Claviceps spp. causing ergot in several grasses in addition to rye, wheat and barley. The fungus takes over the seeds and develops robust survival organs called sclerotia. These organs contain highly neurotoxic mycotoxins with a vasoconstrictive activity, which eventually will cause gangrene and bloss of extremeties if ingested in chronic amounts. Wild game such as elk and deer are, from time to time, found with detached claws or ears due to grassing on contaminated grass. In an ended project we have mapped the population of Claviceps spp. in Norwegian grasses and related it to their mycotoxin profile. Surveys on ergot alkaloids in cereal grain are continuing through chemical testing of crops every year.

Effects of these plant diseases on human and animal health are closely related to the mycotoxins produced in planta and during storage, and the effects vary with the extent of infection and the specific mycotoxins involved. One important area of research is toxicology, investigating effects of mycotoxin exposure on in vitro cell systems as well as animal in vivo systems.  Another important area is risk assessment, dealing with the likelihood of mycotoxin intoxicosis in relation to intake, occurrence and toxicity of the respective mycotoxins. These are described in separate sections.