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ARS Home » Southeast Area » New Orleans, Louisiana » Southern Regional Research Center » Food and Feed Safety Research » Research » Publications at this Location » Publication #339903

Research Project: Molecular and Environmental Factors Controlling Aflatoxin Reduction by Non-Toxigenic Aspergillus Strains

Location: Food and Feed Safety Research

Title: Evolution of polyketide synthesis in a Dothideomycete forest pathogen

item OZTURK, I - Massey University
item CHETTRI, PRANAV - Massey University
item DUPONT, PIERRE-YVES - Massey University
item BARNES, IRENE - University Of Pretoria
item MCDOUGAL, REBECCA - New Zealand Forest Research Institute
item Moore, Geromy
item SIM, ANDRE - Massey University
item 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.