Characterization of a full-length cDNA clone encoding glutamine synthetase from rubber tree latex

Abstract

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 respectively with cytosolic and chloroplastic GS published sequences. These homologies and the lack of N-terminal leader peptide sequence strongly suggested that this clone encodes a cytosolic glutamine synthetase. Southern blot analysis demonstrated the existence of an intron(s) and suggested that the rubber tree GS is encoded by a small multigene family. The 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.