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ChLae1 and ChVel1 regulate T-toxin production, virulence, oxidative stress response, and development of the maize pathogen Cochliobolus heterostrophus.

Wu D, Oide S, Zhang N, Choi MY, Turgeon BG - PLoS Pathog. (2012)

Bottom Line: T-toxin production is significantly increased in the dark in wild type (WT), whereas Chvel1 and Chlae1 mutant toxin levels are much reduced in the dark compared to WT.Deletion of ChLAE1 or ChVEL1 reduces tolerance to H(2)O(2).ChLae1 and ChVel1 repress expression of 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis genes, and, accordingly, melanization is enhanced in Chlae1 and Chvel1 mutants, and reduced in OE strains.

View Article: PubMed Central - PubMed

Affiliation: Dept. of Plant Pathology & Plant-Microbe Biology, Cornell University, Ithaca, New York, USA.

ABSTRACT
LaeA and VeA coordinate secondary metabolism and differentiation in response to light signals in Aspergillus spp. Their orthologs, ChLae1 and ChVel1, were identified in the maize pathogen Cochliobolus heterostrophus, known to produce a wealth of secondary metabolites, including the host selective toxin, T-toxin. Produced by race T, T-toxin promotes high virulence to maize carrying Texas male sterile cytoplasm (T-cms). T-toxin production is significantly increased in the dark in wild type (WT), whereas Chvel1 and Chlae1 mutant toxin levels are much reduced in the dark compared to WT. Correspondingly, expression of T-toxin biosynthetic genes (Tox1) is up-regulated in the dark in WT, while dark-induced expression is much reduced/minimal in Chvel1 and Chlae1 mutants. Toxin production and Tox1 gene expression are increased in ChVEL1 overexpression (OE) strains grown in the dark and in ChLAE1 strains grown in either light or dark, compared to WT. These observations establish ChLae1 and ChVel1 as the first factors known to regulate host selective toxin production. Virulence of Chlae1 and Chvel1 mutants and OE strains is altered on both T-cms and normal cytoplasm maize, indicating that both T-toxin mediated super virulence and basic pathogenic ability are affected. Deletion of ChLAE1 or ChVEL1 reduces tolerance to H(2)O(2). Expression of CAT3, one of the three catalase genes, is reduced in the Chvel1 mutant. Chlae1 and Chvel1 mutants also show decreased aerial hyphal growth, increased asexual sporulation and female sterility. ChLAE1 OE strains are female sterile, while ChVEL1 OE strains are more fertile than WT. ChLae1 and ChVel1 repress expression of 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis genes, and, accordingly, melanization is enhanced in Chlae1 and Chvel1 mutants, and reduced in OE strains. Thus, ChLae1 and ChVel1 positively regulate T-toxin biosynthesis, pathogenicity and super virulence, oxidative stress responses, sexual development, and aerial hyphal growth, and negatively control melanin biosynthesis and asexual differentiation.

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Repression of asexual sporulation in the dark and under cycling conditions is compromised in Chlae1 and Chvel1 mutants growing vegetatively.A. Quantification of asexual spores from cultures grown under constant light, 12 hour light/dark cycle, and dark conditions. Error bars are standard deviation. Asterisks represent p-value <0.05 in T-test analysis in which each mutant strain was compared with the corresponding WT C4 strain under the same conditions. Asexual sporulation is repressed in WT in the dark or under the light cycling conditions, while this was not observed for the Chlae1 mutant. Absence of ChVEL1 augments asexual sporulation regardless of the light condition. B. Cultures grown on CMX plates under constant light, 12 hour light/dark cycle and constant dark conditions. Note that in the dark, WT C4 is white and fluffy reflecting aerial hyphal growth and production of very few conidia, while Chlae1 and Chvel1 mutants are pigmented. Alternating light and dark conidial banding pattern of the WT strain C4 in middle panel indicates that conidiation of the WT strain is responsive to light. This banding pattern is absent or much reduced in the Chvel1 mutant, but still evident in the Chlae1 mutant. C. Side view of plates of WT strain C4, and the Chlae1 and Chvel1 mutants grown in constant light or dark on CMX. Note aerial hyphae on plates of WT, especially from the dark. In contrast, the surface of the Chlae1 mutant is very flat while the Chvel1 mutant shows a small amount of aerial hyphae. Thus Lae1 appears to play a greater role in promoting aerial hyphae growth than Vel1.
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ppat-1002542-g006: Repression of asexual sporulation in the dark and under cycling conditions is compromised in Chlae1 and Chvel1 mutants growing vegetatively.A. Quantification of asexual spores from cultures grown under constant light, 12 hour light/dark cycle, and dark conditions. Error bars are standard deviation. Asterisks represent p-value <0.05 in T-test analysis in which each mutant strain was compared with the corresponding WT C4 strain under the same conditions. Asexual sporulation is repressed in WT in the dark or under the light cycling conditions, while this was not observed for the Chlae1 mutant. Absence of ChVEL1 augments asexual sporulation regardless of the light condition. B. Cultures grown on CMX plates under constant light, 12 hour light/dark cycle and constant dark conditions. Note that in the dark, WT C4 is white and fluffy reflecting aerial hyphal growth and production of very few conidia, while Chlae1 and Chvel1 mutants are pigmented. Alternating light and dark conidial banding pattern of the WT strain C4 in middle panel indicates that conidiation of the WT strain is responsive to light. This banding pattern is absent or much reduced in the Chvel1 mutant, but still evident in the Chlae1 mutant. C. Side view of plates of WT strain C4, and the Chlae1 and Chvel1 mutants grown in constant light or dark on CMX. Note aerial hyphae on plates of WT, especially from the dark. In contrast, the surface of the Chlae1 mutant is very flat while the Chvel1 mutant shows a small amount of aerial hyphae. Thus Lae1 appears to play a greater role in promoting aerial hyphae growth than Vel1.

Mentions: To assess the role of ChLae1 and ChVel1 in asexual development during vegetative growth, Chlae1, Chvel1 mutants and WT strains were grown on complete medium with xylose (CMX) as carbon source under constant light, constant dark and 12 hour light/dark cycling conditions for 8 to 10 days, and number of conidia measured. The WT strain produced the most conidia in constant light, very few in constant dark, an intermediate number in cycling conditions (Figure 6A). The Chlae1 mutant was relieved from this dark-responsive repression and produced numbers of conidia similar to WT in light, under all conditions. Asexual development by the Chvel1 mutant, however, was significantly increased compared to WT in all light conditions (Figure 6A) as for asexual development on cross plates, described above (Figures 5A, C). Note, however, that the dark-responsive repression of asexual sporulation was still observable for the Chvel1 mutant, but not for the Chlae1 mutant. The WT strain had a very clear banding rhythm (reflecting periods of conidiation) under 12 hour light/dark cycling conditions, whereas the Chvel1 mutant exhibited almost no banding (Figure 6B). WT showed significant development of aerial hyphae in dark, but this was much reduced in the Chlae1 and Chvel1 mutants (Figures 6B, C).


ChLae1 and ChVel1 regulate T-toxin production, virulence, oxidative stress response, and development of the maize pathogen Cochliobolus heterostrophus.

Wu D, Oide S, Zhang N, Choi MY, Turgeon BG - PLoS Pathog. (2012)

Repression of asexual sporulation in the dark and under cycling conditions is compromised in Chlae1 and Chvel1 mutants growing vegetatively.A. Quantification of asexual spores from cultures grown under constant light, 12 hour light/dark cycle, and dark conditions. Error bars are standard deviation. Asterisks represent p-value <0.05 in T-test analysis in which each mutant strain was compared with the corresponding WT C4 strain under the same conditions. Asexual sporulation is repressed in WT in the dark or under the light cycling conditions, while this was not observed for the Chlae1 mutant. Absence of ChVEL1 augments asexual sporulation regardless of the light condition. B. Cultures grown on CMX plates under constant light, 12 hour light/dark cycle and constant dark conditions. Note that in the dark, WT C4 is white and fluffy reflecting aerial hyphal growth and production of very few conidia, while Chlae1 and Chvel1 mutants are pigmented. Alternating light and dark conidial banding pattern of the WT strain C4 in middle panel indicates that conidiation of the WT strain is responsive to light. This banding pattern is absent or much reduced in the Chvel1 mutant, but still evident in the Chlae1 mutant. C. Side view of plates of WT strain C4, and the Chlae1 and Chvel1 mutants grown in constant light or dark on CMX. Note aerial hyphae on plates of WT, especially from the dark. In contrast, the surface of the Chlae1 mutant is very flat while the Chvel1 mutant shows a small amount of aerial hyphae. Thus Lae1 appears to play a greater role in promoting aerial hyphae growth than Vel1.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3285592&req=5

ppat-1002542-g006: Repression of asexual sporulation in the dark and under cycling conditions is compromised in Chlae1 and Chvel1 mutants growing vegetatively.A. Quantification of asexual spores from cultures grown under constant light, 12 hour light/dark cycle, and dark conditions. Error bars are standard deviation. Asterisks represent p-value <0.05 in T-test analysis in which each mutant strain was compared with the corresponding WT C4 strain under the same conditions. Asexual sporulation is repressed in WT in the dark or under the light cycling conditions, while this was not observed for the Chlae1 mutant. Absence of ChVEL1 augments asexual sporulation regardless of the light condition. B. Cultures grown on CMX plates under constant light, 12 hour light/dark cycle and constant dark conditions. Note that in the dark, WT C4 is white and fluffy reflecting aerial hyphal growth and production of very few conidia, while Chlae1 and Chvel1 mutants are pigmented. Alternating light and dark conidial banding pattern of the WT strain C4 in middle panel indicates that conidiation of the WT strain is responsive to light. This banding pattern is absent or much reduced in the Chvel1 mutant, but still evident in the Chlae1 mutant. C. Side view of plates of WT strain C4, and the Chlae1 and Chvel1 mutants grown in constant light or dark on CMX. Note aerial hyphae on plates of WT, especially from the dark. In contrast, the surface of the Chlae1 mutant is very flat while the Chvel1 mutant shows a small amount of aerial hyphae. Thus Lae1 appears to play a greater role in promoting aerial hyphae growth than Vel1.
Mentions: To assess the role of ChLae1 and ChVel1 in asexual development during vegetative growth, Chlae1, Chvel1 mutants and WT strains were grown on complete medium with xylose (CMX) as carbon source under constant light, constant dark and 12 hour light/dark cycling conditions for 8 to 10 days, and number of conidia measured. The WT strain produced the most conidia in constant light, very few in constant dark, an intermediate number in cycling conditions (Figure 6A). The Chlae1 mutant was relieved from this dark-responsive repression and produced numbers of conidia similar to WT in light, under all conditions. Asexual development by the Chvel1 mutant, however, was significantly increased compared to WT in all light conditions (Figure 6A) as for asexual development on cross plates, described above (Figures 5A, C). Note, however, that the dark-responsive repression of asexual sporulation was still observable for the Chvel1 mutant, but not for the Chlae1 mutant. The WT strain had a very clear banding rhythm (reflecting periods of conidiation) under 12 hour light/dark cycling conditions, whereas the Chvel1 mutant exhibited almost no banding (Figure 6B). WT showed significant development of aerial hyphae in dark, but this was much reduced in the Chlae1 and Chvel1 mutants (Figures 6B, C).

Bottom Line: T-toxin production is significantly increased in the dark in wild type (WT), whereas Chvel1 and Chlae1 mutant toxin levels are much reduced in the dark compared to WT.Deletion of ChLAE1 or ChVEL1 reduces tolerance to H(2)O(2).ChLae1 and ChVel1 repress expression of 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis genes, and, accordingly, melanization is enhanced in Chlae1 and Chvel1 mutants, and reduced in OE strains.

View Article: PubMed Central - PubMed

Affiliation: Dept. of Plant Pathology & Plant-Microbe Biology, Cornell University, Ithaca, New York, USA.

ABSTRACT
LaeA and VeA coordinate secondary metabolism and differentiation in response to light signals in Aspergillus spp. Their orthologs, ChLae1 and ChVel1, were identified in the maize pathogen Cochliobolus heterostrophus, known to produce a wealth of secondary metabolites, including the host selective toxin, T-toxin. Produced by race T, T-toxin promotes high virulence to maize carrying Texas male sterile cytoplasm (T-cms). T-toxin production is significantly increased in the dark in wild type (WT), whereas Chvel1 and Chlae1 mutant toxin levels are much reduced in the dark compared to WT. Correspondingly, expression of T-toxin biosynthetic genes (Tox1) is up-regulated in the dark in WT, while dark-induced expression is much reduced/minimal in Chvel1 and Chlae1 mutants. Toxin production and Tox1 gene expression are increased in ChVEL1 overexpression (OE) strains grown in the dark and in ChLAE1 strains grown in either light or dark, compared to WT. These observations establish ChLae1 and ChVel1 as the first factors known to regulate host selective toxin production. Virulence of Chlae1 and Chvel1 mutants and OE strains is altered on both T-cms and normal cytoplasm maize, indicating that both T-toxin mediated super virulence and basic pathogenic ability are affected. Deletion of ChLAE1 or ChVEL1 reduces tolerance to H(2)O(2). Expression of CAT3, one of the three catalase genes, is reduced in the Chvel1 mutant. Chlae1 and Chvel1 mutants also show decreased aerial hyphal growth, increased asexual sporulation and female sterility. ChLAE1 OE strains are female sterile, while ChVEL1 OE strains are more fertile than WT. ChLae1 and ChVel1 repress expression of 1,8-dihydroxynaphthalene (DHN) melanin biosynthesis genes, and, accordingly, melanization is enhanced in Chlae1 and Chvel1 mutants, and reduced in OE strains. Thus, ChLae1 and ChVel1 positively regulate T-toxin biosynthesis, pathogenicity and super virulence, oxidative stress responses, sexual development, and aerial hyphal growth, and negatively control melanin biosynthesis and asexual differentiation.

Show MeSH
Related in: MedlinePlus