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Microbiology 153 (2007), 2137-2147; DOI  10.1099/mic.0.2006/005462-0
© 2007 Society for General Microbiology

The MAP kinase TVK1 regulates conidiation, hydrophobicity and the expression of genes encoding cell wall proteins in the fungus Trichoderma virens

Artemio Mendoza-Mendoza{dagger}, Teresa Rosales-Saavedra, Carlos Cortés, Verónica Castellanos-Juárez, Pedro Martínez and Alfredo Herrera-Estrella

Laboratorio Nacional de Genómica para la Biodiversidad, Centro de Investigación y de Estudios Avanzados, Campus Guanajuato, Apartado Postal 629, 36500, Irapuato, Guanajuato, Mexico

Correspondence
Alfredo Herrera-Estrella
aherrera{at}ira.cinvestav.mx

Mitogen-activated protein (MAP) kinases modulate morphological and genetic processes, which determine cell fate. The tvk1 gene encodes a MAP kinase of Trichoderma virens and its deletion promotes an unusual conidiation phenotype in submerged culture. Here, it is reported that the morphology, physiology and expression of genes encoding cell wall proteins from Trichoderma are significantly affected by Tvk1. Morphological changes were evident in the cell walls of aerial conidia produced by a MAPK null mutant when compared to those produced by the wild-type. Unexpectedly, conidia produced in submerged culture by the {Delta}tvk1 strain were highly hydrophobic, whereas in aerial conidia hydrophobicity was severely reduced. In addition, the {Delta}tvk1 strain was unable to break the liquid–air interface when the fungus grew in rich medium; however, when it grew in minimal medium the fungus produced large filaments which were much more efficient at breaking the interface than the wild-type. Through cDNA subtractive hybridization between the wild-type and {Delta}tvk1 grown in submerged culture, five genes encoding hydrophobin-like proteins and two additional genes encoding cell wall proteins were identified. Four hydrophobin-encoding genes (Tv-hfb1, Tv-srh1, tv-cfth1 and Tv-qid3) and a gene encoding a clock-controlled-like protein (Tv-ccg14/TvSm1) were upregulated in {Delta}tvk1, whereas genes encoding a cell wall protein (tv-qid74) and an additional hydrophobin (tv-hfb3) were absent in the mutant strain. Clear differences in gene expression were shown during conidiation and emergence from the liquid–air interface, suggesting different functions of the corresponding proteins in these two phenomena. The results support a model in which Tvk1 regulates morphology and genes encoding cell wall proteins during development of Trichoderma.

Abbreviations: MAP, mitogen-activated protein; SEM, scanning electron microscopy; TEM, transmission electron microscopy

{dagger}Present address: Max-Planck-Institut für Terrestrische Mikrobiologie, D-35043 Marburg, Germany.






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Copyright © 2007 Society for General Microbiology.