Targeting of glutamine synthetase to the mitochondria of transgenic tobacco

• Published in: Plant molecular biology 1990-01, Vol.15 (6), p.895-904
• Main Authors: Hemon, P. (Warwick Univ., Coventry (UK). Dept. of Biological Sciences), Robbins, M.P, Cullimore, J.V
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Biological and medical sciences; Biological Transport; Cell physiology; Fabaceae - enzymology; Fabaceae - genetics; Fundamental and applied biological sciences. Psychology; Genes, Plant; Genes, Synthetic; Genetic Vectors; GLUTAMATE AMMONIA LIGASE; Glutamate-Ammonia Ligase - genetics; Glutamate-Ammonia Ligase - metabolism; GLUTAMINA SINTETASA; GLUTAMINE SYNTHETASE; H super(+)-transporting ATP synthase; Isoenzymes - genetics; Isoenzymes - metabolism; Membrane and intracellular transports; MITOCHONDRIA; Mitochondria - metabolism; MITOCHONDRIE; MITOCONDRIA; Molecular and cellular biology; Molecular Sequence Data; Mosaic Viruses - genetics; NICOTIANA; Nicotiana - genetics; Nicotiana - metabolism; Nicotiana plumbaginifolia; PHASEOLUS VULGARIS; PLANTAS TRANSGENICAS; PLANTE TRANSGENIQUE; Plants, Medicinal; Plants, Toxic; Promoter Regions, Genetic; Protein Processing, Post-Translational; PROTEINAS; PROTEINE; PROTEINS; Proton-Translocating ATPases - genetics; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; TRANSGENIC PLANTS
• ISSN: 0167-4412; 1573-5028
• DOI: 10.1007/bf00039428

Two transgenic tobacco lines were genetically engineered to contain chimaeric genes encoding the glutamine synthetase (GS) gamma polypeptide of Phaseolus vulgaris (French bean), expressed from the cauliflower mosaic virus 35S promoter. One (MIT-1) contained two copies of a construct including the first 60 amino acids of the Nicotiana plumbaginifolia beta-F1 ATPase to target the GS polypeptide to the mitochondrion. The other (CYT-4) contained a single copy of a cytosolic GS construct. Leaves of in vitro plantlets expressed the constructs and contained a novel GS polypeptide, which assembled into active GS isoenzymes constituting about 25% of the total GS activity. In in vitro plantlets of MIT-1, but not CYT-4, the novel polypeptide was found to be associated with the mitochondria. Moreover in MIT-1, the size of the novel polypeptide was not that predicted of the precursor (44.9 kDa) but was about 39 kDa, the same size as the authentic GS gamma polypeptide in CYT-4. These results are consistent with the precursor being imported into the mitochondria and cleaved near the fusion junction between the two sequences. These experiments have therefore shown that the presequence of the beta-F1 ATPase has successfully targeted the GS gamma polypeptide to the mitochondria of transgenic tobacco where it has assembled into an active isoenzyme. However, in fully regenerated plants growing photoautotrophically in growth-room conditions, although the constructs were still expressed, the gamma polypeptide did not accumulate to the same levels as in in vitro plantlets and new isoenzyme activities were now barely detectable. Moreover in leaves of the mature MIT-1 plants, the gamma polypeptide was found to be associated with the insoluble fraction of the mitochondria. The results of these experiments are discussed.