The role of recognition in the induction of specific chitinases during mycoparasitism by Trichoderma harzianum.

The induction of chitinolytic enzymes in the biocontrol agent Trichoderma harzianum during parasitism on Sclerotium rolfsii and the role of fungal-fungal recognition in this process were studied. A change in the chitinolytic enzyme profile was detected during the interaction between the fungi, grown in dual culture on synthetic medium. Before coming into contact with each other, both fungi contained a protein with constitutive 1,4-beta-N-acetylglucosaminidase activity. As early as 12 h after contact, the chitinolytic activity in S. rolfsii disappeared, while that of T. harzianum (a protein with a molecular mass of 102 kDa, CHIT 102) greatly increased. After 24 h of interaction, the activity of CHIT 102 diminished concomitantly with the appearance of a 73 kDa 1,4-beta-N-acetylglucosaminidase, which became clear and strong at 48 h. This phenomenon did not occur if the S. rolfsii mycelium was autoclaved prior to incubation with T. harzianum, suggesting its dependence on vital elements from the host. Cycloheximide inhibited this phenomenon, indicating that de novo synthesis of enzymes is taking place in Trichoderma during these stages of the parasitism. A biomimetic system based on the binding of a purified surface lectin from the host S. rolfsii to nylon fibres was used to dissect the effect of recognition. An increase in CHIT 102 activity was detected, suggesting that the induction of chitinolytic enzymes in Trichoderma is an early event which is elicited by the recognition signal (i.e. lectin-carbohydrate interactions). It is postulated that recognition is the first step in a cascade of antagonistic events which triggers the parasitic response in Trichoderma.