Submitted to: Journal of Food Additives & Contaminants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 26, 2007
Publication Date: October 1, 2007
Citation: Proctor, R., Butchko, R.A., Brown, D.W., Moretti, A. 2007. Functional characterization, sequence comparisons and distribution of a polyketide synthase gene required for perithecial pigmentation in some Fusarium species. Journal of Food Additives & Contaminants. 24(10):1076-1087. Interpretive Summary: Fungi in the genus Fusarium can infect and cause diseases on maize, wheat, and other crops. In infected grain of crops, these fungi can also produce mycotoxins, chemical compounds that are harmful to human and animal health. Fungi, including Fusarium species, produce polyketides, a structurally diverse class of chemical compounds that are formed via the same basic biochemical process. The class of enzymes that catalyze this biochemical process are called polyketide synthases (PKSs). As part of our efforts to assess the potential of polyketide production as targets to control crop diseases and mycotoxin contamination problems caused by Fusarium, we characterized the PGL1 gene, one of 15 PKS-encoding genes previously identified in the maize ear rot fungus Fusarium verticillioides. Mutants of the fungus in which PGL1 was inactivated produced colorless sexual fruiting bodies rather than the black fruiting bodies produced by normal strains of the fungus. This result confirms that PGL1 is required for production of a dark pigment in sexual fruiting bodies of Fusarium, as previously shown in the maize, wheat, and barley pathogen Fusarium graminearum. We showed that PGL1 occurs widely in the genus Fusarium; it was detected in all 42 Fusarium species examined. In F. graminearum, spores produced in the sexual fruiting bodies contribute to the initiation of disease epidemics. PGL1 is involved in the spore formation process. Thus, PGL1 is a potential target to control Fusarium graminearum-induced disease epidemics and the mycotoxin contamination problems that can result from such epidemics.
Technical Abstract: Polyketides are a structurally diverse class of secondary metabolites that are produced by bacteria, fungi, plants and animals. The fungal genus Fusarium includes agronomically important plant pathogenic and mycotoxin-producing species, and produces numerous polyketides. In this study, we further characterized a polyketide synthase-encoding gene (PKS3 = PGL1) that was previously identified in F. graminearum and F. verticillioides. Disruption of the F. verticillioides PGL1 indicated that it is required for production of the dark pigment in perithecial walls, as previously shown in F. graminearum. A third PGL1 orthologue was identified in the genomic sequence of N. haematococca (anamorph F. solani f. sp. pisi). Analysis of the carboxy-terminal end of the deduced PGL1 proteins indicated that they had a functional domain more closely related to dehydrogenases/reductases than to the thioesterase domain present in relatively closely related PKS genes. Comparison of the genomic regions flanking PGL1 in F. graminearum, F. verticillioides, and N. haematococca revealed that the extent of gene synteny in this region was greater between F. graminearum and F. verticillioides than between either of these species and N. haematococca. Southern analysis indicated that PGL1 occurs widely within the genus Fusarium including species with no known sexual stage.