ThHog1 controls the hyperosmotic stress response in Trichoderma harzianum

Area of Science:

• Mycology
• Molecular Biology
• Stress Physiology

Background:

• Trichoderma harzianum is a versatile mycoparasitic fungus.
• Environmental stresses induce gene expression changes in T. harzianum.
• The high-osmolarity glycerol (HOG) pathway is critical for osmotic stress response in fungi.

Purpose of the Study:

• To characterize the hog1 gene in T. harzianum and its role in stress response.
• To investigate the function of the ThHog1 protein in osmotic and oxidative stress.
• To explore the involvement of ThHog1 in fungal interactions and pathogenicity.

Main Methods:

• Transcript profiling under hyperosmotic shock.
• Gene complementation assays in Saccharomyces cerevisiae.
• Construction and analysis of hog1 mutant strains (allele substitution and gene silencing).
• Phosphorylation and subcellular localization studies of ThHog1 protein using GFP fusion.
• Stress cross-resistance experiments and assessment of antagonistic activity against plant pathogens.

Main Results:

• The T. harzianum hog1 gene complemented a yeast hog1 deletion mutant, exhibiting distinct features.
• ThHog1 protein is phosphorylated and localized to the nucleus under osmotic and oxidative stress.
• A hog1-silenced strain showed high sensitivity to osmotic stress and reduced antagonistic activity.
• The hog1(F315S) mutant strain displayed high resistance to cyclosporin A, suggesting pathway crosstalk.
• Mutant strains exhibited reduced antagonistic activity against Phoma betae and Colletotrichum acutatum.

Conclusions:

• The ThHog1 protein plays a primary role in hyperosmotic stress response in T. harzianum.
• ThHog1 is also involved in oxidative stress response and fungus-fungus interactions.
• The hog1 pathway is linked to calcineurin signaling and influences antagonistic capabilities against plant pathogens.