GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE EXPRESSION IN TRICHODERMA-HARZIANUM IS REPRESSED DURING CONIDIATION AND MYCOPARASITISM

A glyceraldehyde-3-phosphate dehydrogenase (gpd) cDNA was isolated fro m the filamentous fungus Trichoderma harzianum in the course of a sear ch for light-regulated genes in this organism. There is apparently onl y one copy of gpd in the T. harzianum genome, and its sequence is most similar to that of other filamentous ascomycetes. Trichoderma grows i n the soil as a saprophyte or mycoparasite. A brief pulse of blue ligh t, or nutrient depletion, induces sporulation, which is accompanied by altered patterns of abundance of specific polypeptides. Mycoparasitic development is also accompanied by changes in gene expression. The ab undance of gpd mRNA decreased strongly during sporulation, and was low est in samples consisting of mature conidiophores and conidia. When T. harzianum was grown in the presence of cell walls of the phytopathoge n Rhizoctonia solani, the gpd mRNA level was much lower than in simila r cultures grown on glucose. The repression of gpd, which is usually c onsidered a constitutively expressed gene, may be part of the switch t o sporulation or to the simulated mycoparasitic state. The implication s of these findings for the use of gpd promoters to confer high consti tutive expression are discussed.