title: A decarboxylase encoded at the Cochliobolus heterostrophus translocation-associated Tox1B locus is required for polyketide (T-toxin) biosynthesis and high virulence on T-cytoplasm maize.
abstract: Genes at two unlinked loci (Tox1A and Tox1B) are required for production of the polyketide T-toxin by Cochliobolus heterostrophus race T, a pathogenic fungus that requires T-toxin for high virulence to maize with T-cytoplasm. Previous work indicated that Tox1A encodes a polyketide synthase (PKS1) required for T-toxin biosynthesis and for high virulence. To identify genes at Tox1B, a wild-type race T cDNA library was screened for genes missing in the genome of a Tox1B deletion mutant. The library was probed, first with a 415-kb NotI restriction fragment from the genome of the Tox1B mutant, then with the corresponding 560-kb fragment from the genome of wild type. Two genes, DEC1 (similar to acetoacetate decarboxylase-encoding genes) and RED1 (similar to genes encoding members of the medium-chain dehydrogenase/reductase superfamily), were recovered. Targeted disruption of DEC1 drastically reduced both T-toxin production and virulence of race T to T-cytoplasm maize, whereas specific inactivation of RED1 had no apparent effect on T-toxin production (as determined by bioassay) or on virulence. DEC1 and RED1 map within 1.5 kb of each other on Tox1B chromosome 6;12 and are unique to the genome of race T, an observation consistent with the hypothesis that these genes were acquired by C. heterostrophus via a horizontal transfer event.
authors.affiliation: Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA.
authors.forename: Mark S
authors.initials: MS
authors.lastname: Rose
authors.forename: Sung-Hwan
authors.initials: SH
authors.lastname: Yun
authors.forename: Thipa
authors.initials: T
authors.lastname: Asvarak
authors.forename: Shun-Wen
authors.initials: SW
authors.lastname: Lu
authors.forename: O C
authors.initials: OC
authors.lastname: Yoder
authors.forename: B Gillian
authors.initials: BG
authors.lastname: Turgeon
mesh_terms: D000595:Amino Acid Sequence; D001203:Ascomycota / Q000201:enzymology / Q000235:genetics* / Q000472:pathogenicity; D001692:Biological Transport / Q000235:genetics; D002262:Carboxy-Lyases / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D003593:Cytoplasm / Q000378:metabolism; D018076:DNA, Complementary / Q000235:genetics; D005656:Fungal Proteins / Q000096:biosynthesis* / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D009183:Mycotoxins / Q000096:biosynthesis* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction / Q000235:genetics; D014774:Virulence / Q000235:genetics; D003313:Zea mays / Q000382:microbiology*
chemical_list: D018076:DNA, Complementary; D005656:Fungal Proteins; D009183:Mycotoxins; C086673:RED1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; C091329:Tox1 protein, Cochliobolus heterostrophus; D002262:Carboxy-Lyases