MOLECULAR CHARACTERIZATION OF A CDNA CLONE ENCODING GLUTAMINE-SYNTHETASE FROM A GYMNOSPERM, PINUS-SYLVESTRIS

A full-length cDNA clone (pGSP114) encoding glutamine synthetase was i solated from a lambdagt11 library of the gymnosperm Pinus sylvestris. Nucleotide sequence analysis showed that pGSP114 contains an open read ing frame encoding a protein of 357 amino acid residues with a calcula ted molecular mass of 39.5 kDa. The derived amino acid sequence was mo re homologous to cytosolic (GS1) (78-82%) than to chloroplastic (GS2) (71-75%) glutamine synthetase in angiosperms. The lack of N-terminal p resequence and C-terminal extension which define the primary structure of GS2, also supports that the isolated cDNA encodes cytosolic GS. So uthern blot analysis of genomic DNA from P. sylvestris and P. pinaster suggests that GS may be encoded by a small gene family in pine. GS mR NA was more abundant in cotyledons and stems than in roots of both Sco ts and maritime pines. Western blot analysis in P. sylvestris seedling s showed that only one GS polypeptide, similar in size to GS1 in P. pi naster, could be detected in several different tissues. Our results su ggest that cytosolic GS is mainly responsible for glutamine biosynthes is in pine seedlings.