CHARACTERIZATION OF A CLASS-I CHITINASE GENE AND OF WOUND-INDUCIBLE, ROOT AND FLOWER-SPECIFIC CHITINASE EXPRESSION IN BRASSICA-NAPUS

Complementary and genomic DNAs coding for a Brassica napus chitinase h ave been cloned and sequenced. The genomic DNA contains one intron and encodes a 322-amino acid basic chitinase with a 20-amino acid N-termi nal signal peptide followed by a 40-amino acid cysteine-rich domain, l inked by a hinge region to the main domain of the enzyme. The sequence of the cDNAs is identical to the exon sequence deduced from the genom ic DNA. A probe derived from this gene identified a 1.2-kb transcript present in high amount in roots, moderate in floral tissues and low in stems and leaves. The synthesis of these transcripts is regulated dur ing development and is induced in roots by wounding and ethephon. This type of chitinase is encoded by two sequences in Brassica napus, as s hown either by Southern hybridizations or by genomic amplification and sequencing using the polymerase chain reaction. These genes are homol ogous to one sequence found in the Brassica oleracea genome.