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Abstract

Two osmotic stress- and ABA-responsive members of the endochitinase (EC 3.2.1.14) gene family has been isolated and identified from leaves of drought-stressed Lycopersicon chilense plants. The 966-base-pair insert of pcht28 encodes an acidic chitinase precursor with an amino-terminal signal peptide. The mature protein is predicted to have 229 amino acid residues with a relative molecular weight of 24,943 and pI value of 6.2. The same number in amino acids, molecular and PI value are predicted for the protein encoded by pchtI, despite of a slight variation in the DNA and amino acid sequences. Sequence analysis revealed that pcht28 and pchtI have a high degree of homology with class II chitinases (EC 3.2.1.14) from tobacco. Northern blot analysis indicated that these genes have evolved a completely different pattern of expression from others reported thus far. They are highly induced by both osmotic stress and the plant hormone abscisic acid. Southern blot analysis of genomic DNA suggested that the pcht28- and pchtI-related chitinase is encoded by a small multigene family in this species. Knowing the role of plant chitinase in plant defense against fungal pathogens, it is assumed that, besides their general defensive function, the pcht28- and pchtI-encoded chitinases may play a particular role in protecting plants from pathogen attack during water stress.

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