A NEW CLASS OF TOBACCO CHITINASES HOMOLOGOUS TO BACTERIAL EXO-CHITINASES DISPLAYS ANTIFUNGAL ACTIVITY

A novel chitinase gene of tobacco was isolated and characterized by DN A sequence analysis of a genomic clone and a cDNA clone. Comparative s equence analysis of both clones showed an identity of 94%. The protein s encoded by these sequences do not correspond to any of the previousl y characterized plant chitinases of classes I-IV and are designated as class V chitinases. Comparison of the chitinase class V peptide seque nce with sequences in the Swiss Protein databank revealed significant sequence similarity with bacterial exo-chitinases from Bacillus circul ans, Serratia marcescens and Streptomyces plicatus. It was demonstrate d that class V chitinase gene expression is induced after treatment of tobacco with different forms of stress, like TMV-infection, ethylene treatment, wounding or ultraviolet irradiation. Two related chitinase class V proteins of 41 and 43 kDa were purified from Samsun NN tobacco leaves inoculated with tobacco mosaic virus. The proteins were purifi ed by Chelating Superose chromatography and get filtration. In vitro a ssays demonstrated that class V chitinases have endo-chitinase activit y and exhibit antifungal activity toward Trichoderma viride and Altern aria radicina. In addition, it was shown that class V chitinase acts s ynergistically with tobacco class I beta-1,3-glucanase against Fusariu m solani germlings.