DIFFERENTIAL EXPRESSION OF TRICHODERMA-HARZIANUM CHITINASES DURING MYCOPARASITISM

The chitinolytic system of the biocontrol agent Trichoderma harzianum is made up of two beta-1,4-N-acetylglucosaminidases and four endochiti nases. The expression of the various N-acetylglucosaminidases and endo chitinases during mycoparasitism was found to be regulated in a very s pecific and finely tuned manner that was affected by the host. When ?: harzianum was antagonizing Sclerotium rolfsii, an N-acetylglucosamini dase of 102 kDa (CHIT 102) was the first to be induced. As early as 12 h after contact, its activity diminished, and another N-acetylglucosa minidase of 73 kDa (CHIT 73) was expressed at high levels. However, wh en T. harzianum was antagonizing Rhizoctonia solani, the chitinase exp ression patterns differed considerably. Twelve hours after contact, CH IT 102 activity was elevated, and the activities of three additional e ndochitinases at 52 kDa (CHIT 52), 42 kDa (CHIT 42), and 33 kDa (CHIT 33) were detected. As the antagonistic interaction proceeded, CHIT 102 activity decreased, whereas the activity of the endochitinases gradua lly increased. The differential expression of T. harzianum chitinases may influence the overall antagonistic ability of the fungus against a specific host.