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.
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.
Rose
Mark S
MS
Department of Plant Pathology, Cornell University, Ithaca, NY 14853, USA.
Yun
Sung-Hwan
SH
Asvarak
Thipa
T
Lu
Shun-Wen
SW
Yoder
O C
OC
Turgeon
B Gillian
BG
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*
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