ThHog1 controls the hyperosmotic stress response in Trichoderma harzianum

Abstract

Trichoderma harzianum is a widespread mycoparasitic fungus, able to successfully colonize a wide range of substrates under different environmental conditions. Transcript profiling revealed a subset of genes induced in T. harzianum under hyperosmotic shock. The hog1 gene, a homologue of the MAPK HOG1 gene that controls the hyperosmotic stress response in Saccharomyces cerevisiae, was characterized. T. harzianum hog1 complemented the hog1D mutation in S. cerevisiae, but showed different features to yeast alleles: improved osmoresistance by expression of the hog1 allele and a lack of lethality when the hog1 F315S allele was overexpressed. ThHog1 protein was phosphorylated in T. harzianum under different stress conditions such as hyperosmotic or oxidative stress, among others. By using a ThHog1-GFP fusion, the protein was shown to be localized in nuclei under these stress conditions. Two mutant strains of T. harzianum were constructed: one carrying the hog1 F315S allele, and a knockdown hog1-silenced strain. The silenced strain was highly sensitive to osmotic stress, and showed intermediate levels of resistance against oxidative stress, indicating that the main role of ThHog1 protein is in the hyperosmotic stress response. Stress cross-resistance experiments showed evidences of a secondary role of ThHog1 in oxidative stress. The strain carrying the hog1 F315S allele was highly resistant to the calcineurin inhibitor cyclosporin A, which suggests the existence of links between the two pathways. The two mutant strains showed a strongly reduced antagonistic activity against the plant pathogens Phoma betae and Colletotrichum acutatum, which points to a role of ThHog1 protein in fungus-fungus interactions.

Mitogen-Activated Protein Kinase hog1 in the Entomopathogenic FungusBeauveria bassianaRegulates Environmental Stress Responses and Virulence to Insects

“…Expression of the hydrophobin-encoding genes hyd1 and hyd2 in the ⌬Bbhog1 mutant and the wild-type strain. Real-time RT-PCR was used to determine the relative levels of expression of hyd1 and hyd2 using Bgpd, ␤-tubulin, and 18S rRNA as loading controls to normalize samples by a method described previously (52) (11). Here we found that Bbhog1 was an important virulence determinant of B. bassiana and influenced at least three aspects of infection, spore viability, adherence to the insect cuticle, and appressorium formation.…”

“…For instance, deletion of HOG1-encoding genes in Candida albicans (44), Neurospora crassa (58), Magnaporthe grisea (12), and Colletotrichum lagenarium (29) causes a defect in adaptation to highosmolarity conditions. A hog1-silenced strain of Trichoderma harzianum was highly sensitive to osmotic stress and showed intermediate levels of sensitivity to oxidative stress (11). HOG1 MAP kinase is activated by high osmolarity, oxidative stress, and UV stress in Debaryomyces hansenii (47).…”

“…Inactivation of HOG1 orthologs in M. grisea, N. crassa, and C. lagenarium results in increased resistance to the phenylpyrrole fungicide fludioxonil (12,29,58). A T. harzianum strain overexpressing the hog1(F315S) allele was highly resistant to the calcineurin inhibitor cyclosporine A, which suggests that there are links between the two pathways (11). In addition, HOG1 orthologs participating in fungal pathogen-host interactions have been demonstrated to be present in the plant pathogen Mycosphaerella graminicola and the mycoparasitic fungus T. harzianum.…”

“…Deletion of the HOG1 kinase gene in M. graminicola results in mutants that are nonpathogenic to the host plant (35). In T. harzianum, either hyperactivation [with the hog1(F315S) allele] or silencing (using RNA interference) of a HOG1 protein leads to strongly reduced antagonistic activity against some plant fungal patho-gens (11). These results suggested that HOG1 MAPKs might provide a clue for understanding the regulatory mechanism that responds to environmental stresses in fungi and fungal pathogenesis.…”

Marine Isolates of Trichoderma spp. as Potential Halotolerant Agents of Biological Control for Arid-Zone Agriculture

“…In Saccharomyces cerevisiae, the main pathway involved in sensing changes in Na ϩ concentrations and in responding to them is known as the HOG signaling pathway, which controls the expression of others osmoresponsive genes. The hog1 gene homologue was isolated and characterized from T. harzianum (5) and was shown to be important for the hyperosmotic stress response but also for fungus-fungus interactions.…”