A NOVEL PATHOGEN-INDUCIBLE AND WOUND-INDUCIBLE TOBACCO (NICOTIANA-TABACUM) PROTEIN WITH ANTIFUNGAL ACTIVITY

A novel pathogen- and wound-inducible antifungal protein of 20 kD was purified from tobacco (Nicotiana tabacum) Samsun NN leaves inoculated with tobacco mosaic virus (TMV). The protein, designated CBP20, was pu rified by chitin-affinity chromatography and gel filtration. In vitro assays demonstrated that CBP20 exhibits antifungal activity toward Tri choderma viride and Fusarium solani by causing lysis of the germ tubes and/or growth inhibition. In addition it was shown that CBP20 acts sy nergistically with a tobacco class I chitinase against F. solani and w ith a tobacco class 1 beta-1,3-glucanase against F. solani and Alterna ria radicina. Analysis of the protein and corresponding cDNAs revealed that CBP20 contains an N-terminal chitin-binding domain that is prese nt also in the class I chitinases of tobacco, the putative wound-induc ed (WIN) proteins of potato, WIN1: and WIN2, and several plant lectins . The C-terminaI domain of CBP20 showed high identity with tobacco pat hogenesis-related (PR) proteins, PR-4a and PR-4b, tomato PR-P2, and po tato WIN1 and WIN2. CBP20 is synthesized as a preproprotein, which is processed into the mature protein by the removal of an N-terminal sign al peptide and a C-terminal propeptide, most likely involved in the va cuolar targeting of the protein. The intracellular localization of CBP 20 and its induction upon TMV infection and wounding indicate that CBP 20 is the first class I PR-4 type protein purified.