Characterization of genes encoding novel peptidases in the biocontrol fungus Trichoderma harzianum CECT 2413 using the TrichoEST functional genomics approach

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Abstract
Proteolytic enzymes (EC 3.4) secreted by Trichoderma strains are receiving increasing attention because of their potential implication in the Trichoderma biocontrol abilities. We have used an expressed sequence tag (EST) approach to identify genes encoding extracellular peptidases in T. harzianum CECT 2413 grown under several biocontrol-related conditions. Based on BlastX results and Gene Ontology annotation, a total of 61 (among 3478) unique sequences (unisequences) were predicted to encode enzymes with peptidase activity, three corresponding to secreted peptidases already known from this Trichoderma strain (PAPA, PRA1 and P6281). Further manual screening based on the functional identity and cellular location of the best matches revealed ten unisequences encoding novel extracellular peptidases. We report the characterization of the corresponding genes as well as a potential orthologous gene of the intracellular peptidase PAPB from T. asperellum. In each case, full-length coding sequences were obtained, and deduced proteins were compared at phylogenetic level with peptidases from other organisms. T. harzianum CECT 2413 novel peptidases included six serine endopeptidases (EC 3.4.21) belonging to the families S1, S8 and S53, three aspartic endopeptidases (EC 3.4.23) of the family A1, one metallo-endopeptidase (EC 3.4.24) of the family M35, and one aminopeptidase (EC 3.4.11) of the family M28. Results obtained by Northern blot analyses demonstrated that the genes within a family are differentially regulated in response to different culture conditions, suggesting that they have diverse functional roles.