Identification of genes with a biocontrol function in Trichoderma harzianum mycelium using the expressed sequence tag approach.

Species of Trichoderma are commercially applied as biological control agents against plant fungal pathogens based on different mechanisms, such as the production of antifungal metabolites, competition for space and nutrients and mycoparasitism. But the integrated biocontrol mechanism of Trichoderma harzianum is not well explored at the genetic level. This study aimed to initiate the preliminary development of an expressed sequence tag (EST) database for T. harzianum and thereby gain potentially useful information on Trichoderma gene sequences in order to elucidate the integrated biocontrol mechanism. Partial sequencing of anonymous cDNA clones is a widely used technique for gene identification. A directional cDNA library has been constructed from mycelium of T. harzianum and 3298 clones have been randomly selected, subjected to single-pass sequencing from the 5' end of the vector, and identified by sequence similarity searches against gene sequences in international databases. Of the 3298 mycelium clones, 2174 exhibit similarity to known genes and 451 to known ESTs, while 673 represent novel gene sequences. Analysis of the identified clones indicated sequence similarity to a broad diversity of genes encoding proteins such as enzymes, structural proteins, and regulatory factors. A significant proportion of genes identified in the mycelium were involved in processes related to mycoparasitism and fungicidal metabolites, as would be expected in biocontrol fungus. These results present the successful application of EST analysis in T. harzianum and provide a preliminary indication of gene expression in mycelium.