Functional characterization, sequence comparisons and distribution of a polyketide synthase gene required for perithecial pigmentation in some Fusarium species

Polyketides are a structurally diverse class of secondary metabolites produced by bacteria, fungi, plants and animals. The fungal genus Fusarium includes agronomically important plant pathogenic and mycotoxin- producing species and produces numerous polyketides. The study 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 the 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 protein indicated that it had a functional domain related to dehydrogenases/reductases that is sometimes present in non- ribosomal peptide synthetases. 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 blot analysis indicated that PGL1 occurs widely within the genus Fusarium including species with no known sexual stage.