Differential expression of Trichoderma harzianum chitinases during mycoparasitism

The chitinolytic system of the biocontrol agent Trichoderma harzianum is made up of two β-1,4-N-acetylglucosaminidases and four endochitinases. The expression of the various N-acetylglucosaminidases and endochitinases during mycoparasitism was found to be regulated in a very specific and finely tuned manner that was affected by the host. When T. harzianum was antagonizing Sclerotium rolfsii, an N-acetylglucosaminidase of 102 kDa (CHIT 102) was the first to be induced. As early as 12 h after contact, its activity diminished, and another N-acetyl-glucosaminidase of 73 kDa (CHIT 73) was expressed at high levels. However, when T. harzianum was antagonizing Rhizoctonia solani, the chitinase expression patterns differed considerably. Twelve hours after contact, CHIT 102 activity was elevated, and the activities of three additional endochitinases 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 gradually increased. The differential expression of T. harzianum chitinases may influence the overall antagonistic ability of the fungus against a specific host.