Expression of two major chitinase genes of Trichoderma atroviride (T-harzianum P1) is triggered by different regulatory signals

Regulation of the expression of the two major chitinase genes, ech42 (encod ing the CHIT42 endochitinase) and nag1 (encoding the CHIT73 N-acetyl-beta-D -glucosaminidase), of the chitinolytic system of the mycoparasitic biocontr ol fungus Trichoderma atroviride (= Trichoderma harzianum P1) was investiga ted by using a reporter system based on the Aspergillus niger glucose oxida se. Strains harboring fusions of the ech42 or nag1 5' upstream noncoding se quences with the A. niger goxA. gene displayed a glucose oxidase activity p attern that was consistent under various conditions with expression of the native ech42 and nag1 genes, as assayed by Northern analysis. The expressio n product of goxA in the mutants was completely secreted into the medium, d etectable on Western blots, and quantifiable by enzyme-linked immunosorbent assay. nag1 gene expression was triggered during growth on fungal (Botryti s cinerea) cell walls and on the chitin degradation product N-acetylglucosa mine. N-Acetylglucosamine, di-N-acetylchitobiose, or tri-N-acetylchitotrios e also induced nag1 gene expression when added to mycelia pregrown on diffe rent carbon sources, ech42 expression was also observed during growth on fu ngal cell walls hut, in contrast, was not triggered by addition of chitooli gomers to pregrown mycelia. Significant ech42 expression was observed after prolonged carbon starvation, independent of the use of glucose or glycerol as a carbon source, suggesting that relief of carbon catabolite repression was not involved in induction during starvation. In addition, ech42 gene t ranscription was triggered by physiological stress, such as low temperature , high osmotic pressure, or the addition of ethanol. Four copies of a putat ive stress response element (CCCCT) were found in the ech42 promoter.