A Polyketide Synthase Is Required for Fungal Virulence and Production of the Polyketide T-Toxin

Abstract

Race T of the fungal pathogen Cochliobolus heterostrophus is highly virulent toward Texas male sterile (T) maize and differs from its relative, race O, at a locus (Tox1) that is responsible for the production of T-toxin, a family of linear long-chain (C35 to E41) polyketides. In a previous study, the restriction enzyme-mediated integration procedure was used to mutagenize and tag Tox1. Here, we report that the DNA recovered from the insertion site of one mutant encodes a 7.6-kb open reading frame (2530 amino acids) that identifies a multifunctional polyketide synthase (PKS)-encoding gene (PKS1) with six catalytic domains arranged in the following order, starting at the N terminus: beta-ketoacyl synthase, acyltransferase, dehydratase, enoyl reductase, beta-ketoacyl reductase, and acyl carrier protein. PKS1 is interrupted by four apparent introns (74, 57, 49, and 41 bp) and exists in the genome as a single copy surrounded by highly repetitive, A + T-rich DNA. When PKS1 in race T was inactivated by targeted gene disruption, T-toxin production and high virulence were eliminated, indicating that this PKS is required for fungal virulence. Race O strains, which do not produce T-toxin, lack a detectable homolog of PKS1, suggesting that race T may have acquired PKS1 by horizontal transfer of DNA rather than by vertical inheritance from an ancestral strain.

Localization and Transcriptional Responses of Chrysoporthe austroafricana in Eucalyptus grandis Identify Putative Pathogenicity Factors

“…In this study, we identified two NRPS candidates ( Table 2 ). PKSs are also associated with the biosynthesis of toxins in Cochliobolus heterostrophus, Cercospora nicotianae, Botrytis Cinerea , and Gibberella fujikuroi (Yang et al, 1998; Proctor et al, 1999; Choquer et al, 2005; Dalmais et al, 2011). In this study, the expression of two PKS genes only in the susceptible host environment may contribute to the proliferation of C. austroafricana .…”

Phylogenomic analysis of type I polyketide synthase genes in pathogenic and saprobic ascomycetes

“…The diversity of PKS genes and PKs found in Pezizomycotina led to speculation, including our own (6,43), that HGT is involved in generating and maintaining this diversity (ref. 44 and references therein).…”

“…To address these questions, we performed phylogenetic analyses on the amino acid sequences of KS domains encoded by all previously characterized fungal PKS genes and by all putative PKS genes extracted from genomic sequences of five taxonomically diverse fungal species in the Ascomycota, subphylum Pezizomycotina (4) [the saprobe Neurospora crassa (5); the maize pathogens Cochliobolus heterostrophus (Bipolaris maydis) (6,7) and Gibberella moniliformis (Fusarium verticillioides) (8); the cereal pathogen Gibberella zeae (Fusarium graminearum) (8); and the cosmopolitan dicot pathogen Botryotinia fuckeliana (Botrytis cinerea) (8)]. We also searched for PKS genes in the genomes of three earlier diverging ascomycetes [Saccharomyces cerevisiae (9), the plant pest Eremothecium (Ashbya) gossypii (10), (both in the Saccharomycotina), and the yeast saprobe Schizosaccharomyces pombe (11) (Taphrinomycotina)].…”

A Penicillium freii gene that is highly similar to the β‐keto‐acyl synthase domain of polyketide synthase genes from other fungi

“…These genes are involved in the Penicillium freii IBT 3464 from the culture collection at the biosynthesis of mycotoxins such as 6-methylsalicylic acid Department of Biotechnology, Technical University of (Beck et al 1990 ;Fujii et al 1996), sterigmatocystin (Yu Denmark, Lyngby, was used throughout these studies. The and Leonard 1995), aflatoxin (Chang et al 1995 ;Feng and strain was grown on Czapek yeast autolysate agar or broth Leonard 1995), T-toxin (Yang et al 1996), and in the biosyn- (Pitt 1979). Xanthomegnin was detected by the TLC-agar thesis of a polyketide precursor to a green spore pigment plug method (Filtenborg et al 1983).…”