Chitinase gene expression during mycoparasitic interaction of Trichoderma harzianum with its host

For monitoring chitinase expression during mycoparasitism of Trichoderma ha rzianum in situ, we constructed strains containing fusions of green fluores cent protein (GFP) to the 5'-regulatory sequences of the T, harzianum nag1 (N-acetyl-beta-D-glucosaminidase-encoding) and ech42 (42-kDa endochitinase- encoding) genes. Confronting these strains with Rhizoctonia solani led to i nduction of gene expression before (ech42) or after (nag1) physical contact . A 12-kDa cut-off membrane separating the two fungi abolished ech42 expres sion, indicating that macromolecules are involved in its precontact activat ion. No ech42 expression was triggered by culture filtrates of R. solani or by placing T, harzianum onto plates previously colonized by R, solani, Ins tead, high expression occurred upon incubation of T. harzianum with the sup ernatant of R. solani cell walls digested with culture filtrates or purifie d endochitinase 42 (CHIT42, encoded by ech42) from T. harzianum. The chitin ase inhibitor allosamidin blocked ech42 expression and reduced inhibition o f R. solani growth during confrontation. The results indicate that ech42 is expressed before contact of T. harzianum with R. solani and its induction is triggered by soluble chitooligosaccharides produced by constitutive acti vity of CHIT42 and/or other chitinolytic enzymes. (C) 1999 Academic Press.