Hirel B, Marsolier M C, Hoarau A, Hoarau J, Brangeon J, Schafer R, Verma D P
Laboratoire du Métabolisme et de la Nutrition des Plantes, C.N.R.A., Versailles, France.
Plant Mol Biol. 1992 Oct;20(2):207-18. doi: 10.1007/BF00014489.
Glutamine synthetase (GS; EC 6.3.1.2) is present in different subcellular compartments in plants. It is located in the cytoplasm in root and root nodules while generally present in the chloroplasts in leaves. The expression of GS gene(s) is enhanced in root nodules and in soybean roots treated with ammonia. We have isolated four genes encoding subunits of cytosolic GS from soybean (Glycine max L. cv. Prize). Promoter analysis of one of these genes (GS15) showed that it is expressed in a root-specific manner in transgenic tobacco and Lotus corniculatus, but is induced by ammonia only in the legume background. Making the GS15 gene expression constitutive by fusion with the CaMV-35S promoter led to the expression of GS in the leaves of transgenic tobacco plants. The soybean GS was functional and was located in the cytoplasm in tobacco leaves where this enzyme is not normally present. Forcing this change in the location of GS caused concomitant induction of the mRNA for a native cytosolic GS in the leaves of transgenic tobacco. Shifting the subcellular location of GS in transgenic plants apparently altered the nitrogen metabolism and forced the induction in leaves of a native GS gene encoding a cytosolic enzyme. The latter is normally expressed only in the root tissue of tobacco. This phenomenon may suggest a hitherto uncharacterized metabolic control on the expression of certain genes in plants.
谷氨酰胺合成酶（GS；EC 6.3.1.2）存在于植物的不同亚细胞区室中。它位于根和根瘤的细胞质中，而通常存在于叶片的叶绿体中。GS基因的表达在根瘤和用氨处理的大豆根中增强。我们从大豆（Glycine max L. cv. Prize）中分离出四个编码胞质GS亚基的基因。对其中一个基因（GS15）的启动子分析表明，它在转基因烟草和百脉根中以根特异性方式表达，但仅在豆科植物背景下受氨诱导。通过与CaMV - 35S启动子融合使GS15基因组成型表达，导致GS在转基因烟草植株的叶片中表达。大豆GS具有功能，位于烟草叶片的细胞质中，而该酶通常不存在于此。GS位置的这种改变导致转基因烟草叶片中天然胞质GS的mRNA伴随性诱导。转基因植物中GS亚细胞定位的改变显然改变了氮代谢，并促使叶片中编码胞质酶的天然GS基因的诱导。后者通常仅在烟草的根组织中表达。这种现象可能表明植物中某些基因的表达存在一种迄今未被表征的代谢控制。
