CLONING OF A CDNA FOR A CHITINASE HOMOLOG WHICH LACKS CHITIN-BINDING SITES AND IS DOWN-REGULATED BY WATER-STRESS AND WOUNDING

A cDNA clone (pLP6) of a gene which is repressed under water deficit w as isolated from a loblolly pine (Pinus taeda L.) cDNA library and cha racterized. The predicted polypeptide encoded by pLP6 bears strong res emblance to a number of Class I chitinases. However, LP6 lacks most of the amino-terminal and, consequently the signal peptide, cysteine-ric h chitin-binding domain and glycine/proline-rich 'hinge' region, diagn ostic of Class I chitinases, are absent. Although the cDNA is similar in size to its mRNA, the long open reading frame encoding the LP6 prot ein commences halfway through the mRNA, implying a 5'-untranslated reg ion of over 700 nucleotides. Subfragments from the 5' end of pLP6 hybr idize to the same mRNA as do probes consisting of the entire cDNA. Rev erse transcription(RT)-PCR experiments confirm that the cDNA derives f rom a single mRNA molecule. Analysis of the 5'-UTR revealed six upstre am open reading frames and four inverted repeat structures. Expression of the pLP6 gene is repressed by water deficit stress and wounding. P ossible functions and origin of this gene are discussed.