CHARACTERIZATION OF A FULL-LENGTH CDNA CLONE ENCODING GLUTAMINE-SYNTHETASE FROM RUBBER TREE LATEX

A full-length cDNA clone (HbGs) encoding glutamine synthetase (GS, EC 6.3.1.2) was isolated from a Lambda Zap II library of ethylene-treated Hevea brasiliensis latex. Sequence analysis of this clone revealed an open reading frame corresponding to a 356 amino acid polypeptide. The deduced amino acid sequence showed 80-96% and 76% identity respective ly with cytosolic and chloroplastic GS published sequences. These homo logies and the lack of N-terminal leader peptide sequence strongly sug gested that this clone encodes a cytosolic glutamine synthetase. South ern blot analysis demonstrated the existence of an intron(s) and sugge sted that the rubber tree GS is encoded by a small multigene family. T he short-term kinetics of ethylene action on gene expression revealed marked accumulation of the corresponding GS mRNA in the latex cells of ethylene-treated newly tapped trees, compared to non-treated controls . Additionally, tapping itself was shown to slightly stimulate GS gene expression.