Rice class III chitinase homologues isolated by random cloning of rice cDNAs.

We obtained seven kinds of cDNA clones putatively identified as encoding class III chitinases from cDNA libraries constructed from dichlorophenoxyacetic acid (2,4-D)- and benzyl adenine (BA)- treated rice callus. Putative amino acid sequences encoded in these cDNA clones were compared with those of known chitinases of other plants. Two clones coded for homologues that show high similarity to class III chitinases. These clones contained the common glutamic acid at the active site and were classified as true homologues. The other five clones, however, showed relatively low similarity to class III chitinases and their active sites contained aspartic acid instead of glutamic acid. These clones may correspond to relatives of a super family of class III chitinases. The location of the genes coding for these homologues on the rice genome has been determined by genetic linkage analysis with restriction fragment length polymorphism.