Location: Food and Feed Safety ResearchTitle: Evolution of polyketide synthesis in a Dothideomycete forest pathogen
|OZTURK, I - Massey University
|CHETTRI, PRANAV - Massey University
|DUPONT, PIERRE-YVES - Massey University
|BARNES, IRENE - University Of Pretoria
|MCDOUGAL, REBECCA - New Zealand Forest Research Institute
|SIM, ANDRE - Massey University
|BRADSHAW, ROSIE - Massey University
Submitted to: Fungal Genetics and Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/5/2017
Publication Date: 7/6/2017
Citation: Ozturk, I.K., Chettri, P., Dupont, P-Y., Barnes, I., McDougal, R.L., Moore, G.G., Sim, A., Bradshaw, R.E. 2017. Evolution of polyketide synthesis in a Dothideomycete forest pathogen. Fungal Genetics and Biology. 106:42-50.
Interpretive Summary: Polyketides, such as aflatoxin, are amongst the best-studied mycotoxins. Whole genome sequencing of fungi has enabled identification of complete genome sets of polyketide synthase (PKS) genes, and characterisation of many of these is in progress. The pine needle pathogen Dothistroma septosporum produces dothistromin, a polyketide related to aflatoxin. It is unusual in having a fragmented gene cluster in which dothistromin genes are spread over six loci on one chromosome instead of being clustered in one location. It is also unusual among pathogenic fungi in having a small number of PKS genes in its genome, with only two other functional PKS genes predicted in addition to the dothistromin PKS.
Technical Abstract: Fungal secondary metabolites have many important biological roles and some, like the toxic polyketide aflatoxin, have been intensively studied at the genetic level. Complete sets of polyketide synthase (PKS) genes can now be identified in fungal pathogens by whole genome sequencing and studied in order to predict the biosynthetic potential of those fungi. The pine needle pathogen Dothistroma septosporum is predicted to have only three functional PKS genes, a small number for a hemibiotrophic fungus. One of these genes is required for production of dothistromin, a polyketide virulence factor related to aflatoxin, whose biosynthetic genes are dispersed across one chromosome rather than being clustered. Here we evaluated the evolution of the other two genes, and their predicted gene clusters, using phylogenetic and population analyses. DsPks1 and its gene cluster are quite conserved among related fungi, while DsPks2 appears to be novel. The DsPks1 protein was predicted to be required for dihydroxynaphthalene (DHN) melanin biosynthesis but functional analysis of DsPks1 mutants showed that D. septosporum produced mainly dihydroxyphenylalanine (DOPA) melanin, which is produced by a PKS-independent pathway. Although the secondary metabolites made by these two PKS genes are not known, comparisons between strains of D. septosporum from different regions of the world revealed that both PKS core genes are under negative selection and we suggest they may have important cryptic roles in planta.