scholarly journals Reduced Virulence Caused by Meiotic Instability of the TOX2 Chromosome of the Maize Pathogen Cochliobolus carbonum

2000 ◽  
Vol 13 (1) ◽  
pp. 80-87 ◽  
Author(s):  
John W. Pitkin ◽  
Anastasia Nikolskaya ◽  
Joong-Hoon Ahn ◽  
Jonathan D. Walton
Keyword(s):  
Cyclic Peptide ◽  
Normal Growth ◽  
Pathogenic Fungi ◽  
Housekeeping Genes ◽  
Toxin Production ◽  
In Planta ◽  
Cochliobolus Carbonum ◽  
Hc Toxin ◽  
Reduced Rate ◽  
Functional Copy

The mechanisms by which pathogenic fungi evolve are poorly understood. Production of the host-selective cyclic peptide HC-toxin is controlled by a complex locus, TOX2, in the plant pathogen Cochliobolus carbonum. Crosses between toxin-producing (Tox2+) and toxin-nonproducing (Tox2-) isolates, as well as crosses between isolates in which the TOX2 genes were on chromosomes of different size, yielded progeny that had lost one or more copies of one or more of the TOX2 genes. Of approximately 200 progeny analyzed, eight (4%) had lost at least one TOX2 gene. All of them still had at least one functional copy of all of the known genes required for HC-toxin production (HTS1, TOXA, TOXC, and TOXE). Most deletion strains could be explained by simple chromosome breaks resulting in the loss of major contiguous portions (0.8 to 1.4 Mb) of the 3.5-Mb TOX2 chromosome, whereas others had more complicated patterns. All deletion strains had normal growth and were fertile, indicating that the 1.4 Mb of DNA contained no essential housekeeping genes. Most strains were also still virulent (Tox2+), but two had a novel phenotype of reduced virulence (RV), characterized by smaller lesions that expanded at a reduced rate and an inability to colonize plants systemically. Although the RV strains made no detectable HC-toxin in culture, the RV phenotype was dependent on the presence of a functional copy of HTS1, which encodes the central enzyme in HC-toxin biosynthesis. We propose that the RV strains still make a low level of HC-toxin, at least in planta, and that this is due to the loss of one or more genes that contribute to, but are not absolutely required for, HC-toxin synthesis.

scholarly journals A Fatty Acid Synthase Gene in Cochliobolus carbonum Required for Production of HC-Toxin, Cyclo(d-Prolyl-l-Alanyl- d-Alanyl- l-2-Amino-9,10-Epoxi-8-Oxodecanoyl)

1997 ◽  
Vol 10 (2) ◽  
pp. 207-214 ◽  
Author(s):  
Joong-Hoon Ahn ◽  
Jonathan D. Walton
Keyword(s):  
Fatty Acid ◽  
Fatty Acid Synthase ◽  
Cyclic Peptide ◽  
Decanoic Acid ◽  
Toxin Production ◽  
Gene Encoding ◽  
Cochliobolus Carbonum ◽  
Primary Amino ◽  
Hc Toxin

The fungal maize pathogen Cochliobolus carbonum produces a phytotoxic and cytostatic cyclic peptide, HC-toxin, of structure cyclo(D-prolyl-L-alanyl-D-alanyl-L-Aeo), in which Aeo stands for 2-amino-9,10-epoxi-8-oxodecanoic acid. Here we report the isolation of a gene, TOXC, that is present only in HC-toxin-producing (Tox2+) fungal strains. TOXC is present in most Tox2+ strains in three functional copies, all of which are on the same chromosome as the gene encoding HC-toxin synthetase. When all copies of TOXC are mutated by targeted gene disruption, the fungus grows and sporulates normally in vitro but no longer makes HC-toxin and is not pathogenic, indicating that TOXC has a specific role in HC-toxin production and hence virulence. The TOXC mRNA is 6.5 kb and the predicted product has 2,080 amino acids and a molecular weight of 233,000. The primary amino acid sequence is highly similar (45 to 47% identity) to the β subunit of fatty acid synthase from several lower eukaryotes, and contains, in the same order as in other β subunits, domains predicted to encode acetyl transferase, enoyl reductase, dehydratase, and malonyl-palmityl transferase. The most plausible function of TOXC is to contribute to the synthesis of the decanoic acid backbone of Aeo.

scholarly journals Characterization of Inhibitor-Resistant Histone Deacetylase Activity in Plant-Pathogenic Fungi

2002 ◽  
Vol 1 (4) ◽  
pp. 538-547 ◽  
Author(s):  
Dipnath Baidyaroy ◽  
Gerald Brosch ◽  
Stefan Graessle ◽  
Patrick Trojer ◽  
Jonathan D. Walton
Keyword(s):  
Histone Deacetylase ◽  
Cyclic Peptide ◽  
Hdac Inhibitors ◽  
Pathogenic Fungi ◽  
Alternaria Brassicicola ◽  
Resistant Isolate ◽  
Protection Factor ◽  
Hdac Activity ◽  
Crude Extracts ◽  
Hc Toxin

ABSTRACT HC-toxin, a cyclic peptide made by the filamentous fungus Cochliobolus carbonum, is an inhibitor of histone deacetylase (HDAC) from many organisms. It was shown earlier that the HDAC activity in crude extracts of C. carbonum is relatively insensitive to HC-toxin as well as to the chemically unrelated HDAC inhibitors trichostatin and D85, whereas the HDAC activity of Aspergillus nidulans is sensitive (G. Brosch et al., Biochemistry 40:12855-12863, 2001). Here we report that HC-toxin-resistant HDAC activity was present in other, but not all, plant-pathogenic Cochliobolus species but not in any of the saprophytic species tested. The HDAC activities of the fungi Alternaria brassicicola and Diheterospora chlamydosporia, which also make HDAC inhibitors, were resistant. The HDAC activities of all C. carbonum isolates tested, except one non-toxin-producing isolate, were resistant. In a cross between a sensitive isolate and a resistant isolate, resistance genetically cosegregated with HC-toxin production. When fractionated by anion-exchange chromatography, extracts of resistant and sensitive isolates and species had two peaks of HDAC activity, one that was fully HC-toxin resistant and a second that was larger and sensitive. The first peak was consistently smaller in extracts of sensitive fungi than in resistant fungi, but the difference appeared to be insufficiently large to explain the differential sensitivities of the crude extracts. Differences in mRNA expression levels of the four known HDAC genes of C. carbonum did not account for the observed differences in HDAC activity profiles. When mixed together, resistant extracts protected extracts of sensitive C. carbonum but did not protect other sensitive Cochlibolus species or Neurospora crassa. Production of this extrinsic protection factor was dependent on TOXE, the transcription factor that regulates the HC-toxin biosynthetic genes. The results suggest that C. carbonum has multiple mechanisms of self-protection against HC-toxin.

scholarly journals Intraspecies Interaction of Fusarium graminearum Contributes to Reduced Toxin Production and Virulence

2015 ◽  
Vol 28 (11) ◽  
pp. 1256-1267 ◽  
Author(s):  
Sean Walkowiak ◽  
Christopher T. Bonner ◽  
Li Wang ◽  
Barbara Blackwell ◽  
Owen Rowland ◽  
...  
Keyword(s):  
Fusarium Graminearum ◽  
Pathogenic Fungus ◽  
Pathogenic Fungi ◽  
Toxin Production ◽  
In Planta ◽  
Head Blight ◽  
Trichothecene Mycotoxin ◽  
Yield And Quality ◽  
Potential Interactions

Fusarium graminearum is a pathogenic fungus that causes Fusarium head blight in wheat and lowers the yield and quality of grains by contamination with the trichothecene mycotoxin deoxynivalenol. The fungi coexist and interact with several different fusaria as well as other plant pathogenic fungi and bacteria in the field. In Canada, F. graminearum exists as two main trichothecene chemotypes: 3-acetyldeoxynivalenol and 15-acetyldeoxynivalenol. To understand the potential interactions between two isolates of these chemotypes, we conducted coinoculation studies both in culture and in planta. The studies showed that intraspecies interaction reduces trichothecene yield in culture and disease symptoms in wheat. To elucidate the genes involved in the intraspecies interaction, expression profiling was performed on RNA samples isolated from coinoculated cultures, and potential genes were identified by using the genome sequences of the respective isolates.

scholarly journals Cloning and Mapping of a Putative Barley NADPH-Dependent HC-Toxin Reductase

1997 ◽  
Vol 10 (2) ◽  
pp. 234-239 ◽  
Author(s):  
F. Han ◽  
A. Kleinhofs ◽  
A. Kilian ◽  
S. E. Ullrich
Keyword(s):  
Plant Species ◽  
Chromosome 9 ◽  
Immature Embryos ◽  
Chromosome 1 ◽  
Grass Species ◽  
Cochliobolus Carbonum ◽  
Wide Range ◽  
Young Leaves ◽  
High Conservation ◽  
Hc Toxin

The NADPH-dependent HC-toxin reductase (HCTR), encoded by Hm1 in maize, inactivates HC-toxin produced by the fungus Cochliobolus carbonum, and thus confers resistance to the pathogen. The fact that C. carbonum only infects maize (Zea mays) and is the only species known to produce HC-toxin raises the question: What are the biological functions of HCTR in other plant species? An HCTR-like enzyme may function to detoxify toxins produced by pathogens which infect other plant species (R. B. Meeley, G. S. Johal, S. E. Briggs, and J. D. Walton, Plant Cell, 4:71–77, 1992). Hm1 homolog in rice (Y. Hihara, M. Umeda, C. Hara, Q. Liu, S. Aotsuka, K. Toriyama, and H. Uchimiya, unpublished) and HCTR activity in barley, wheat, oats and sorghum have been reported (R. B. Meeley and J. D. Walton, Plant Physiol. 97:1080–1086, 1993). To investigate the sequence conservation of Hm1 and HCTR in barley and the possible relationship of barley Hm1 homolog to the known disease resistance genes, we cloned and mapped a barley (Hordeum vulgare) Hm1-like gene. A putative full-length cDNA clone, Bhm1-18, was isolated from a cDNA library consisting of mRNA from young leaves, inflorescences, and immature embryos. This 1,297-bp clone encodes 363 amino acids which show great similarity (81.6%) with the amino acid sequence of HM1 in maize. Two loci were mapped to barley molecular marker linkage maps with Bhm1-18 as the probe; locus A (Bhm1A) on the long arm of chromosome 1, and locus B (Bhm1B) on the short arm of chromosome 1 which is syntenic to maize chromosome 9 containing the Hm2 locus. The Bhm1-18 probe hybridized strongly to a Southern blot of a wide range of grass species, indicating high conservation of HCTR at the DNA sequence level among grasses. The HCTR mRNA was detected in barley roots, leaves, inflorescences, and immature embryos. The conservation of the HCTR sequence, together with its expression in other plant species (R. B. Meeley and J. D. Walton, Plant Physiol. 97:1080–1086, 1993), suggests HCTR plays an important functional role in other plant species.

scholarly journals Antimicrobial activity of extracellular metabolites from antagonistic bacteria isolated from potato (Solanum phureja) crops

2014 ◽  
Vol 40 (3) ◽  
pp. 212-220 ◽  
Author(s):  
Sinar David Granada García ◽  
Antoni Rueda Lorza ◽  
Carlos Alberto Peláez
Keyword(s):  
Antimicrobial Activity ◽  
Cyclic Peptide ◽  
Biological Activities ◽  
Pathogenic Fungi ◽  
Antagonistic Activity ◽  
Solanum Phureja ◽  
Dual Culture ◽  
Crude Extracts ◽  
Extracellular Metabolites

Microorganisms for biological control are capable of producing active compounds that inhibit the development of phytopathogens, constituting a promising tool toob tain active principles that could replace synthetic pesticides. This study evaluatedtheability of severalpotentialbiocontrol microorganismsto produce active extracellular metabolites. In vitro antagonistic capability of 50 bacterial isolates from rhizospheric soils of "criolla" potato (Solanum phureja) was tested through dual culture in this plant with different plant pathogenic fungi and bacteria. Isolates that showed significantly higher antagonistic activity were fermented in liquid media and crude extracts from the supernatants had their biological activities assessed by optical density techniques. Inhibitory effecton tested pathogens was observed for concentrations between 0.5% and 1% of crude extracts. There was a correlation between the antimicrobial activity of extracts and the use of nutrient-rich media in bacteria fermentation. Using a bioguided method, a peptidic compound, active against Fusarium oxysporum, was obtained from the 7ANT04 strain (Pyrobaculum sp.). Analysis by nuclear magnetic resonance and liquid chromatography coupled to mass detector evidenced an 11-amino acid compound. Bioinformatic software using raw mass data confirmed the presence of a cyclic peptide conformed by 11 mostly non-standard amino acids.

scholarly journals Antibiotic and Biosurfactant Properties of Cyclic Lipopeptides Produced by Fluorescent Pseudomonas spp. from the Sugar Beet Rhizosphere

2002 ◽  
Vol 68 (7) ◽  
pp. 3416-3423 ◽  
Author(s):  
T. H. Nielsen ◽  
D. Sørensen ◽  
C. Tobiasen ◽  
J. B. Andersen ◽  
C. Christophersen ◽  
...  
Keyword(s):  
Amino Acids ◽  
Biological Control ◽  
Cyclic Peptide ◽  
Agricultural Soils ◽  
Pathogenic Fungi ◽  
Growth Media ◽  
Single Strain ◽  
Cyclic Lipopeptides ◽  
Peptide Moiety

ABSTRACT Cyclic lipopeptides (CLPs) with antibiotic and biosurfactant properties are produced by a number of soil bacteria, including fluorescent Pseudomonas spp. To provide new and efficient strains for the biological control of root-pathogenic fungi in agricultural crops, we isolated approximately 600 fluorescent Pseudomonas spp. from two different agricultural soils by using three different growth media. CLP production was observed in a large proportion of the strains (approximately 60%) inhabiting the sandy soil, compared to a low proportion (approximately 6%) in the loamy soil. Chemical structure analysis revealed that all CLPs could be clustered into two major groups, each consisting of four subgroups. The two major groups varied primarily in the number of amino acids in the cyclic peptide moiety, while each of the subgroups could be differentiated by substitutions of specific amino acids in the peptide moiety. Production of specific CLPs could be affiliated with Pseudomonas fluorescens strain groups belonging to biotype I, V, or VI. In vitro analysis using both purified CLPs and whole-cell P. fluorescens preparations demonstrated that all CLPs exhibited strong biosurfactant properties and that some also had antibiotic properties towards root-pathogenic microfungi. The CLP-producing P. fluorescens strains provide a useful resource for selection of biological control agents, whether a single strain or a consortium of strains was used to maximize the synergistic effect of multiple antagonistic traits in the inoculum.

scholarly journals An Extended Physical Map of the TOX2 Locus of Cochliobolus carbonum Required for Biosynthesis of HC-Toxin

2002 ◽  
Vol 35 (1) ◽  
pp. 31-38 ◽  
Author(s):  
Joong-Hoon Ahn ◽  
Yi-Qiang Cheng ◽  
Jonathan D. Walton
Keyword(s):  
Physical Map ◽  
Cochliobolus Carbonum ◽  
Hc Toxin
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