Molecular cloning and ethylene-inducible expression of Chib1 chitinase from soybean (Glycine max (L.) Merr.)

A soybean seed-specific PR-8 chitinase, named Chib2, has a markedly extende d C-terminal segment compared to other plant Chib1 homologues of the PR-8 c hitinase family known to date. To further characterize the molecular structure and the expression pattern of this chitinase family, we cloned two typical Chib1-similar cDNAs (Chib1- 1 and Chib1-2) from soybeans by PCR-cloning techniques. The deduced primary sequence of Chib1-1 chitinase is composed of a signal peptide segment (26 amino acid residues) and a mature 273 amino acid sequence (calculated molec ular mass 28,794, calculated pI 3.7). This Chib1-1 enzyme is more than 90% identical to Chib1-2 chitinase but is below 50% identical to Chib2 enzyme. Thus, we confirmed the occurrence of two distinct classes, Chib1 and Chib2 in the plant PR-8 chitinase family. The Chib1 genes, interrupted by one int ron, were found to be up-regulated in response to ethylene in stems and lea ves, but scarcely expressed in developing soybean seeds. Chib1 chitinases m ay be responsible for protecting the plant body from various pathogenic att acks.