Chitinase Gene Expression during Mycoparasitic Interaction ofTrichoderma harzianumwith Its Host

Zeilinger, S., Galhaup, C., Payer, K., Woo, S. L., Mach, R. L., Fekete, C., Lorito, M., and Kubicek, C. P. 1999. Chitinase gene expression during mycoparasitic interaction ofTrichoderma harzianumwith its host.Fungal Genetics and Biology26,131–140. For monitoring chitinase expression during mycoparasitism ofTrichoderma harzianum in situ,we constructed strains containing fusions of green fluorescent protein (GFP) to the 5′-regulatory sequences of theT. harzianum nag1(N-acetyl-β-d-glucosaminidase-encoding) andech42(42-kDa endochitinase-encoding) genes. Confronting these strains withRhizoctonia solaniled to induction of gene expression before (ech42) or after (nag1) physical contact. A 12-kDa cut-off membrane separating the two fungi abolishedech42expression, indicating that macromolecules are involved in its precontact activation. Noech42expression was triggered by culture filtrates ofR. solanior by placingT. harzianumonto plates previously colonized byR. solani.Instead, high expression occurred upon incubation ofT. harzianumwith the supernatant ofR. solanicell walls digested with culture filtrates or purified endochitinase 42 (CHIT42, encoded byech42) fromT. harzianum.The chitinase inhibitor allosamidin blockedech42expression and reduced inhibition ofR. solanigrowth during confrontation. The results indicate thatech42is expressed before contact ofT. harzianumwithR. solaniand its induction is triggered by soluble chitooligosaccharides produced by constitutive activity of CHIT42 and/or other chitinolytic enzymes.