MOLECULAR CHARACTERIZATION OF 4 CHITINASE CDNAS OBTAINED FROM CLADOSPORIUM-FULVUM-INFECTED TOMATO

Complementary DNA clones encoding acidic and basic isoforms of tomato chitinases were isolated from Cladosporium fulvum-infected leaves. The clones were sequenced and found to encode the 30 kDa basic intracellu lar and the 26 and 27 kDa acidic extracellular tomato chitinases previ ously purified (M.H.A.J. Joosten et al., in preparation). A fourth tru ncated cDNA which appears to encode an extracellular chitinase with 82 % amino acid similarity to the 30 kDa intracellular chitinase was also isolated. Characterization of the clones revealed that the 30 kDa bas ic intracellular protein is a class I chitinase and that the 26 and 27 kDa acidic extracellular proteins which have 85% peptide sequence sim ilarity are class II chitinases. The characterized cDNA clones represe nt four from a family of at least six tomato chitinases. Southern blot analysis indicated that, with the exception of the 30 kDa basic intra cellular chitinase, the tomato chitinases are encoded by one or two ge nes. Northern blot analysis showed that the mRNA encoding the 26 kDa a cidic extracellular chitinase is induced more rapidly during an incomp atible C. fulvum-tomato interaction than during a compatible interacti on. This difference in timing of mRNA induction was not observed for t he 30 kDa basic intracellular chitinase.