Isolation of an osmotic stress- and abscisic acid-induced gene encoding an acidic endochitinase from Lycopersicon chilense

We have identified one osmotic stress- and abscisic acid-responsive member of the endochitinase (EC 3.2.1.14) gene family from leaves of drought-stressed Lycopersicon chilense plants, a natural inhabitant of extremely arid regions in South America. The 966-bp full-length cDNA (designated 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 mass of 24 943 and pI value of 6.2. Sequence analysis revealed that pcht28 has a high degree of homology with class II chitinases (EC 3.2.1.14) from tomato and tobacco. Expression of the pcht28 protein in Escherichia coli verified that it is indeed a chitinase. Northern blot analysis indicated that this gene has evolved a different pattern of expression from that of other family members reported thus far. It is highly induced by both osmotic stress and the plant hormone abscisic acid. Southern blot analysis of genomic DNA suggested that the pcht28-related genes may form a small multigene family in this species. The efficiency of induction of the gene by drought stress, in leaves and stems, is significantly higher in L. chilense than in the cultivated tomato. It is speculated that, besides its general defensive function, the pcht28-encoded chitinase may play a particular role in plant development or in protecting plants from pathogen attack during water stress.