A polyketide synthase is required for fungal virulence and production of the polyketide T-toxin.
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.
Yang
G
G
Department of Plant Pathology, Cornell University, Ithaca, New York 14853, USA.
Rose
M S
MS
Turgeon
B G
BG
Yoder
O C
OC
D000595:Amino Acid Sequence; D001483:Base Sequence; D005656:Fungal Proteins / Q000737:chemistry*; D005658:Fungi / Q000472:pathogenicity*; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D009183:Mycotoxins / Q000737:chemistry*; D016415:Sequence Alignment; D003313:Zea mays / Q000201:enzymology*
D005656:Fungal Proteins; D009097:Multienzyme Complexes; D009183:Mycotoxins; C091329:Tox1 protein, Cochliobolus heterostrophus