Identification of an endochitinase cDNA clone from barley aleurone cells.

A barley aleurone cDNA library was screened using (32)P-labeled cDNA prepared by reverse transcription of mRNA from aleurone layers treated in the presence or absence of gibberellic acid (GA). Besides α-amylase cDNA clones, another set of clones representing an abundant mRNA in aleurone cells was identified. Messenger RNA hybrid-selected by a prototype clone of this group (clone 10) was translated in vitro to yield a 36 kDa protein. Analysis of the DNA sequence and the predicted amino acid sequence of the protein product of this clone indicates that this gene codes for a protein with homology to endochitinases from tobacco and bean. In addition, the predicted amino acid sequence includes a stretch that is closely related to a cyanogen bromide cleavage fragment from an endochitinase isolated from barley endosperm. The structural genes for endochitinase are present as multiple copies on barley chromosome 1. mRNA detectable by this clone increases in abundance in barley aleurone cells incubated in the absence and in the presence of GA. Western blot analysis of proteins from aleurone and endosperm tissues indicates the presence of multiple endochitinases differing in molecular size. Possible mechanisms for the occurrence of multiple forms of endochitinases and their biological significance are discussed.