ChLae1 and ChVel1 Regulate T-toxin Production, Virulence, Oxidative Stress Response, and Development of the Maize Pathogen Cochliobolus heterostrophus

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.

A Novel Type Pathway-Specific Regulator and Dynamic Genome Environments of a Solanapyrone Biosynthesis Gene Cluster in the Fungus Ascochyta rabiei

“…Putative transformants were initially selected by their hygromycin resistance, and PCR analysis was conducted to verify integration of the plasmid by a single crossover at the native sol4 genomic locus (see Fig. S2 in the supplemental material), as described earlier (55). The resulting transformants carried two copies of the sol4 gene; one was driven by the inducible pelA promoter, and the other was driven by the native sol4 promoter.…”

VeA Regulates Conidiation, Gliotoxin Production, and Protease Activity in the Opportunistic Human Pathogen Aspergillus fumigatus

“…For example, we found that the F. verticillioides veA null mutant fails to produce disease in seedlings grown from seeds infected with a veA deletion mutant (57). Deletion of veA also reduced plant pathogenicity in Aspergillus flavus (27), A. parasiticus (16), F. fujikuroi (96), F. graminearum (54), and Cochliobolus heterostrophus (99), among others. Importantly, a recent study has shown for the first time that VeA also influences pathogenicity in animals by the opportunistic pathogenic fungus Histoplasma capsulatum (49).…”

“…VeA is found in numerous fungal species, particularly in Ascomycetes (57). Orthologs of VeA in other fungi have also been demonstrated to regulate secondary metabolism: for example, aflatoxin in Aspergillus flavus and Aspergillus parasiticus (16,26), fumonisin and fusarins in Fusarium verticillioides (56) and F. fujikori, where it was also found to regulate gibberellins and bikaverin (96), trichothecenes in Fusarium graminearum (54), dothistromin in Dothistroma septosporum (19), penicillin in A. nidulans (38), cephalosporin C in Acremonium chrysogenum (25), polyketide ML-236B (substrate in pravastatin production) in Penicillium citrinum (5), and T-toxin in Cochliobolus heterostrophus (99), among others.…”

WetA Is Required for Conidiogenesis and Conidium Maturation in the Ascomycete Fungus Fusarium graminearum

“…These reverse genetic studies analyzed well-known regulators of conidiogenesis, such as the fluffy genes, which are activators of the central development pathway genes brlA, abaA, and wetA (2,4,(13)(14)(15)(16). The sensory and regulatory functions of velvet complexes have been well described (4,17,18), and their orthologs have been characterized in many fungi (19)(20)(21)(22)(23)(24)(25)(26)(27).…”