A mitogen-activated protein kinase Tmk3 participates in high osmolarity resistance, cell wall integrity maintenance and cellulase production regulation in Trichoderma reesei

• Published in: PloS one Vol. 8; no. 8; p. e72189
• Main Authors: Wang, Mingyu, Zhao, Qiushuang, Yang, Jinghua, Jiang, Baojie, Wang, Fangzhong, Liu, Kuimei, Fang, Xu
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 26.08.2013; Public Library of Science (PLoS)
• Subjects: Alternative energy sources; Amino Acid Sequence; Aspergillus nidulans; Biology; Biosynthesis; Biosynthetic Pathways - genetics; Carbon; Cell Wall - enzymology; Cell Wall - genetics; Cell Wall - metabolism; Cell walls; Cellulase; Cellulase - genetics; Cellulase - metabolism; Chitin; Chitin - metabolism; Chitin Synthase - genetics; Chitin Synthase - metabolism; Chitinase; Clonal deletion; Cultivation; Culture media; Defects; Derepression; Energy resources; Enzymes; Eukaryotes; Fungal Proteins - genetics; Fungal Proteins - metabolism; Fungi; Gene expression; Gene Expression Regulation, Developmental - drug effects; Gene Expression Regulation, Enzymologic - drug effects; Gene Expression Regulation, Fungal - drug effects; Genes; Glucan; Glucosyltransferases - genetics; Glucosyltransferases - metabolism; Glycerol; Glycerol - metabolism; Hog1 protein; Integrity; Kinases; Laboratories; Lignocellulose; MAP kinase; Media (culture); Medical research; Mitogen-Activated Protein Kinases - classification; Mitogen-Activated Protein Kinases - genetics; Mitogen-Activated Protein Kinases - metabolism; Molecular Sequence Data; Morphogenesis; Mutation; Oryza; Osmolar Concentration; Osmolarity; Pathways; Phosphorylation; Phylogeny; Physiology; Protein kinase; Proteins; Renewable resources; Restoration; Saccharomyces cerevisiae; Salt Tolerance - genetics; Sensitivity; Sequence Homology, Amino Acid; Signal transduction; Signaling; Sodium chloride; Sodium Chloride - pharmacology; Solid state; Transcription factors; Transduction; Trehalose; Trehalose - biosynthesis; Trichoderma - enzymology; Trichoderma - genetics; Trichoderma - growth & development; Trichoderma reesei; Yeast; China
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0072189

The mitogen-activated protein kinase (MAPK) pathways are important signal transduction pathways conserved in essentially all eukaryotes, but haven't been subjected to functional studies in the most important cellulase-producing filamentous fungus Trichoderma reesei. Previous reports suggested the presence of three MAPKs in T. reesei: Tmk1, Tmk2, and Tmk3. By exploring the phenotypic features of T. reesei Δtmk3, we first showed elevated NaCl sensitivity and repressed transcription of genes involved in glycerol/trehalose biosynthesis under higher osmolarity, suggesting Tmk3 participates in high osmolarity resistance via derepression of genes involved in osmotic stabilizer biosynthesis. We also showed significant downregulation of genes encoding chitin synthases and a β-1,3-glucan synthase, decreased chitin content, 'budded' hyphal appearance typical to cell wall defective strains, and increased sensitivity to calcofluor white/Congo red in the tmk3 deficient strain, suggesting Tmk3 is involved in cell wall integrity maintenance in T. reesei. We further observed the decrease of cellulase transcription and production in T. reesei Δtmk3 during submerged cultivation, as well as the presence of MAPK phosphorylation sites on known transcription factors involved in cellulase regulation, suggesting Tmk3 is also involved in the regulation of cellulase production. Finally, the expression of cell wall integrity related genes, the expression of cellulase coding genes, cellulase production and biomass accumulation were compared between T. reesei Δtmk3 grown in solid state media and submerged media, showing a strong restoration effect in solid state media from defects resulted from tmk3 deletion. These results showed novel physiological processes that fungal Hog1-type MAPKs are involved in, and present the first experimental investigation of MAPK signaling pathways in T. reesei. Our observations on the restoration effect during solid state cultivation suggest that T. reesei is evolved to favor solid state growth, bringing up the proposal that the submerged condition normally used during investigations on fungal physiology might be misleading.