scholarly journals 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

2002 ◽  
Vol 15 (9) ◽  
pp. 883-893 ◽  
Author(s):  
Mark S. Rose ◽  
Sung-Hwan Yun ◽  
Thipa Asvarak ◽  
Shun-Wen Lu ◽  
O. C. Yoder ◽  
...  
Keyword(s):  
Polyketide Synthase ◽  
Pathogenic Fungus ◽  
Toxin Production ◽  
Cochliobolus Heterostrophus ◽  
Wild Type ◽  
Targeted Disruption ◽  
Transfer Event ◽  
High Virulence ◽  
Genes Encoding ◽  
Encoding Genes

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 aceto-acetate decarboxylase-encoding genes) and RED1 (similar to genes encoding members of the medium-chain dehydro-genase/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.

scholarly journals Two Polyketide Synthase-Encoding Genes Are Required for Biosynthesis of the Polyketide Virulence Factor, T-toxin, by Cochliobolus heterostrophus

2006 ◽  
Vol 19 (2) ◽  
pp. 139-149 ◽  
Author(s):  
Scott E. Baker ◽  
Scott Kroken ◽  
Patrik Inderbitzin ◽  
Thipa Asvarak ◽  
Bi-Yu Li ◽  
...  
Keyword(s):  
Polyketide Synthase ◽  
Toxin Production ◽  
Carbon Chain ◽  
Cochliobolus Heterostrophus ◽  
Maize Production ◽  
High Virulence ◽  
Encoding Gene ◽  
Corn Leaf Blight ◽  
Encoding Genes ◽  
Sequencing Procedure

Cochliobolus heterostrophus race T, causal agent of southern corn leaf blight, requires T-toxin (a family of C35 to C49 polyketides) for high virulence on T-cytoplasm maize. Production of T-toxin is controlled by two unlinked loci, Tox1A and Tox1B, carried on 1.2 Mb of DNA not found in race O, a mildly virulent form of the fungus that does not produce T-toxin, or in any other Cochliobolus spp. or closely related fungus. PKS1, a polyketide synthase (PKS)-encoding gene at Tox1A, and DEC1, a decarboxylase-encoding gene at Tox1B, are necessary for T-toxin production. Although there is evidence that additional genes are required for Ttoxin production, efforts to clone them have been frustrated because the genes are located in highly repeated, A+T-rich DNA. To overcome this difficulty, ligation specificity-based expression analysis display (LEAD), a comparative amplified fragment length polymorphism/gel fractionation/capillary sequencing procedure, was applied to cDNAs from a near-isogenic pair of race T (Tox1+) and race O (Tox1-) strains. This led to discovery of PKS2, a second PKS-encoding gene that maps at Tox1A and is required for both Ttoxin biosynthesis and high virulence to maize. Thus, the carbon chain of each T-toxin family member likely is assembled by action of two PKSs, which produce two polyketides, one of which may act as the starter unit for biosynthesis of the mature T-toxin molecule.

scholarly journals Toxin-deficient mutants from a toxin-sensitive transformant of Cochliobolus heterostrophus.

Genetics ◽  
1994 ◽  
Vol 137 (3) ◽  
pp. 751-757
Author(s):  
G Yang ◽  
B G Turgeon ◽  
O C Yoder
Keyword(s):  
Fragment Length Polymorphism ◽  
Signal Sequence ◽  
Single Gene ◽  
Toxin Production ◽  
Cochliobolus Heterostrophus ◽  
Polygalacturonic Acid ◽  
Wild Type ◽  
Transformation Vector ◽  
Screening Procedures ◽  
Restriction Fragment Length

Abstract Tox1 is the only genetic element identified which controls production of T-toxin, a linear polyketide involved in the virulence of Cochliobolus heterostrophus to its host plant, corn. Previous attempts to induce toxin-deficient (Tox-) mutants, using conventional mutagenesis and screening procedures, have been unsuccessful. As a strategy to enrich for Tox- mutants, we constructed a Tox1+ strain that carried the corn T-urf13 gene (which confers T-toxin sensitivity) fused to a fungal mitochondrial signal sequence; the fusion was under control of the inducible Aspergillus nidulans pelA promoter which, in both A. nidulans and C. heterostrophus, is repressed by glucose and induced by polygalacturonic acid (PGA). We expected that a transformant carrying this construction would be sensitive to its own toxin when the T-urf13 gene was expressed. Indeed, the strain grew normally on medium containing glucose but was inhibited on medium containing PGA. Conidia of this strain were treated with ethylmethanesulfonate and plated on PGA medium. Among 362 survivors, 9 were defective in T-toxin production. Authenticity of each mutant was established by the presence of the transformation vector, proper mating type, and a restriction fragment length polymorphism tightly linked to the Tox1+ locus. Progeny of each mutant crossed to a Tox1+ tester segregated 1:1 (for wild type toxin production vs. no or reduced toxin production), indicating a single gene mutation in each case. Progeny of each mutant crossed to a Tox1- tester segregated 1:1 (for no toxin production vs. no or reduced toxin production) indicating that each mutation mapped at the Tox1 locus. Availability of Tox- mutants will permit mapping in the Tox1 region without interference from a known Tox1 linked translocation breakpoint.

scholarly journals Six New Genes Required for Production of T-Toxin, a Polyketide Determinant of High Virulence of Cochliobolus heterostrophus to Maize

2010 ◽  
Vol 23 (4) ◽  
pp. 458-472 ◽  
Author(s):  
Patrik Inderbitzin ◽  
Thipa Asvarak ◽  
B. Gillian Turgeon
Keyword(s):  
Evolutionary History ◽  
Phylogenetic Profile ◽  
Toxin Production ◽  
Gene Signature ◽  
Cochliobolus Heterostrophus ◽  
Male Sterile ◽  
Toxin A ◽  
New Genes ◽  
Unknown Protein ◽  
High Virulence

Southern Corn Leaf Blight, one of the worst plant disease epidemics in modern history, was caused by Cochliobolus heterostrophus race T, which produces T-toxin, a determinant of high virulence to maize carrying Texas male sterile cytoplasm. The genetics of T-toxin production is complex and the evolutionary origin of associated genes is uncertain. It is known that ability to produce T-toxin requires three genes encoded at two unlinked loci, Tox1A and Tox1B, which map to the breakpoints of a reciprocal translocation. DNA associated with Tox1A and Tox1B sums to about 1.2 Mb of A+T rich, repeated DNA that is not found in less virulent race O or other Cochliobolus species. Here, we describe identification and targeted deletion of six additional genes, three mapping to Tox1A and three to Tox1B. Mutant screens indicate that all six genes are involved in T-toxin production and high virulence to maize. The nine known Tox1 genes encode two polyketide synthases (PKS), one decarboxylase, five dehydrogenases, and one unknown protein. Only two have a similar phylogenetic profile. To trace evolutionary history of one of the core PKS, DNA from more than 100 Dothideomycete species were screened for homologs. An ortholog (60% identity) was confirmed in Didymella zeae-maydis, which produces PM-toxin, a polyketide of similar structure and biological specificity as T-toxin. Only one additional Dothideomycete species, the dung ascomycete Delitschia winteri harbored a paralog. The unresolved evolutionary history and distinctive gene signature of the PKS (fast-evolving, discontinuous taxonomic distribution) leaves open the question of lateral or vertical transmission.

Function and chromosomal location of the Cochliobolus heterostrophus TOX1 locus

1995 ◽  
Vol 73 (S1) ◽  
pp. 1071-1076 ◽  
Author(s):  
B. G. Turgeon ◽  
M. Kodama ◽  
G. Yang ◽  
M.S. Rose ◽  
S.W. Lu ◽  
...  
Keyword(s):  
Polyketide Synthase ◽  
Chromosomal Location ◽  
Genetic Locus ◽  
Single Gene ◽  
Molecular Genetic ◽  
Cochliobolus Heterostrophus ◽  
Male Sterile ◽  
Genetic Analyses ◽  
High Virulence ◽  
The Difference

Conventional genetic analyses have firmly established that the difference in virulence between race T and O of the corn pathogen Cochliobolus heterostrophus is determined by a single genetic locus called Tox1, which also controls production of T-toxin, a polyketide specifically toxic to corn with Texas male sterile (T) cytoplasm. More recently, molecular genetic analyses have revealed that Tox1 is not a single gene but rather at least two genetic loci situated on two different chromosomes. DNA at both of these loci is required for the biosynthesis of T-toxin and for the high virulence of race T to corn carrying T-cytoplasm. One of the loci encodes a polyketide synthase that is necessary for the assembly of the T-toxin molecule. Key words: polyketide, restriction enzyme mediated integration (REMI), host-specific toxin, corn, fungus, virulence.

scholarly journals Deletion of all Cochliobolus heterostrophus Monofunctional Catalase-Encoding Genes Reveals a Role for One in Sensitivity to Oxidative Stress but None with a Role in Virulence

2003 ◽  
Vol 16 (11) ◽  
pp. 1013-1021 ◽  
Author(s):  
Barbara Robbertse ◽  
O. C. Yoder ◽  
Anita Nguyen ◽  
Conrad L. Schoch ◽  
B. Gillian Turgeon
Keyword(s):  
Oxidative Stress ◽  
Hydrogen Peroxide ◽  
Signal Sequence ◽  
Large Subunit ◽  
Small Subunit ◽  
Cochliobolus Heterostrophus ◽  
Wild Type ◽  
Enhanced Sensitivity ◽  
Encoding Genes ◽  
Harmful Effects

The genome of the maize pathogen Cochliobolus heterostrophus encodes three unlinked monofunctional catalase-encoding (CAT) genes that singly or in combination could offer protection against the harmful effects of oxidative stress. Phylogenetic analysis placed the CAT2 and CAT3 proteins in a cluster with large subunit catalases (CAT3 has a secretory signal sequence and was grouped with known secreted catalases), whereas CAT1 clustered with small subunit catalases. Single, double, and triple cat mutants were created and screened for sensitivity to hydrogen peroxide and altered virulence on maize. All mutants deficient in CAT3 had enhanced sensitivity to hydrogen peroxide, as compared with wild type or with mutants deficient in CAT1, CAT2, or both. All catalase-deficient mutants had normal virulence to maize. Thus, the secreted CAT3 protein protects the fungus from oxidative stress during vegetative growth, but members of this enzyme family, alone or in combination, are not essential for virulence.

scholarly journals The Toxin Cercosporin is a Virulence Factor for Infection of Coffee by Cercospora coffeicola

2019 ◽  
Author(s):  
A. G. C. Souza ◽  
S. Herrero ◽  
M. E. Daub
Keyword(s):  
Virulence Factor ◽  
Polyketide Synthase ◽  
Production Systems ◽  
Toxin Production ◽  
Wild Type ◽  
Minas Gerais State ◽  
Mycelial Plug ◽  
Polyketide Synthase Gene ◽  
Cercospora Coffeicola

ABSTRACTBrown eye spot, caused by Cercospora coffeicola, causes significant losses in both quality and quantity of coffee production. As many Cercospora spp. produce the photoactivated toxin cercosporin, this study aimed to determine the role of cercosporin in C. coffeicola pathogenesis by creating disruption mutants unable to produce the toxin. Six C. coffeicola isolates from Brazilian fields, representing organic and conventional production systems in the Minas Gerais state, were evaluated for their ability to produce cercosporin in vitro. Toxin production varied among isolates, ranging from 3.5 – 25.3 µM/ 5 mm mycelial plug; production was undetectable in one isolate. The C. coffeicola homolog of the polyketide synthase gene (CTB1) involved in cercosporin production was amplified using a degenerate primer strategy. The 7044 nt ccCTB1 gene sequence was 90.3% identical to the cnCTB1 gene in Cercospora nicotianae and encoded a putative protein of 2196 amino acids with 98.2% similarity and 97.5% identity to its counterpart in C. nicotianae. Transformation of two isolates of C. coffeicola with a CTB1 disruption construct resulted in the recovery of six ctb1 disruption mutants. All of the ctb1 disruptants were deficient in cercosporin production. Disruption mutants did not differ significantly from the wild type for either growth or sporulation, but were significantly altered in virulence on coffee. As compared to wild type, time to lesion development was significantly increased and numbers of lesions were significantly decreased in coffee plants inoculated with ctb1 disruption mutants. These results show that cercosporin toxin is a virulence factor for C. coffeicola infection of coffee.

scholarly journals Draft Genome Sequences of Campylobacter jejuni Strains Isolated from Poultry

2020 ◽  
Vol 9 (7) ◽  
Author(s):  
Basanta R. Wagle ◽  
Daya Marasini ◽  
Indu Upadhyaya ◽  
Sandip Shrestha ◽  
Komala Arsi ◽  
...  
Keyword(s):  
Campylobacter Jejuni ◽  
Broiler Chickens ◽  
Draft Genome ◽  
Toxin Production ◽  
Intestinal Colonization ◽  
Wild Type ◽  
Genome Sequences ◽  
Content Type ◽  
Genes Encoding ◽  
Production Stress

Four wild-type Campylobacter jejuni strains isolated from the cecal contents of broiler chickens were sequenced. The average genome size was 1,622,170 bp, with 1,667 to 1,761 coding sequences and 47 to 51 RNAs. Multiple genes encoding motility, intestinal colonization, toxin production, stress tolerance, and multidrug resistance were present in all the strains.

scholarly journals Molecular characterization of clinical carbapenem-resistant Enterobacterales from Qatar

2021 ◽  
Author(s):  
Fatma Ben Abid ◽  
Clement K. M. Tsui ◽  
Yohei Doi ◽  
Anand Deshmukh ◽  
Christi L. McElheny ◽  
...  
Keyword(s):  
Common Species ◽  
Clinical Samples ◽  
Whole Genome ◽  
E Coli ◽  
Carbapenem Resistant ◽  
Genes Encoding ◽  
Encoding Genes ◽  
Sequence Types ◽  
Common Sequence

AbstractOne hundred forty-nine carbapenem-resistant Enterobacterales from clinical samples obtained between April 2014 and November 2017 were subjected to whole genome sequencing and multi-locus sequence typing. Klebsiella pneumoniae (81, 54.4%) and Escherichia coli (38, 25.5%) were the most common species. Genes encoding metallo-β-lactamases were detected in 68 (45.8%) isolates, and OXA-48-like enzymes in 60 (40.3%). blaNDM-1 (45; 30.2%) and blaOXA-48 (29; 19.5%) were the most frequent. KPC-encoding genes were identified in 5 (3.6%) isolates. Most common sequence types were E. coli ST410 (8; 21.1%) and ST38 (7; 18.4%), and K. pneumoniae ST147 (13; 16%) and ST231 (7; 8.6%).

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