Abstract
Trichoderma brevicrassum strain TC967 is a novel biological control agent (BCA) against the plant pathogen Rhizoctonia solani and promotes plant growth. MAPK (mitogen-activated protein kinase) cascades were involved in biocontrol by Trichoderma, but functions of each MAPK in regulating biocontrol have not been characterized in one Trichoderma. In this study, we assembled and annotated the genome of strain TC967, and identified its three MAPK gene sequences. Functions of Fus3-, Slt2- and Hog1-MAPK in strain TC967 were dissected. The three MAPKs were all involved in hyphal growth. The Hog1-MAPK was essential for conidiation and tolerance to hyperosmotic stress. The Fus3- and Slt2-MAPK both mediated cell-wall integrity (CWI) and activities of chitinase and protease. The Fus3- and Hog1-MAPK mediated response to oxidative stress. Our biocontrol assays demonstrated that the Fus3- and Slt2-MAPK mutants were considerably more effective in disease control than the wild-type strain. RNA-seq analysis revealed that MAPK collectively played a major role in regulating biocontrol-related gene expressions, including of the genes in charge of secondary metabolism, fungal cell wall-degrading enzymes (FCWDEs) and small secreted cysteine-rich proteins (SSCPs).
Author summary Soil-born fungal pathogens pose an emerging threat to crop production. Trichoderma brevicrassum strain TC967 has the ability to control the notorious phytopathogen Rhizoctonia solani and promote plant growth. In this study, we explored the functions of three-types of MAPK in mediating biocontrol process, and uncovered that Fus3-, Slt2- and Hog1-MAPK are involved in hyphal growth, conidiation, tolerance to hyperosmotic stress, cell-wall integrity, activities of chitinase and protease, and response to oxidative stress. Biocontrol ability of strain TC967 was accelerated after deletion of the Fus3- and Slt2-MAPK genes. MAPK collectively played a major role in regulating biocontrol-related gene expressions as revealed by RNA-seq analysis. To our knowledge, this is the first report of the functions of MAPKs in regulating biocontrol in one Trichoderma. Our results provide a reference for improvement of biocontrol ability of Trichoderma strains from the view of MAPK cascades.
Competing Interest Statement
The authors have declared no competing interest.
