Suárez Ramón, Márquez Judith, Shishkova Svetlana, Hernández Georgina
Centro de Investigación sobre Fijación de Nitrógeno - UNAM. Apartado Postal 565-A, Cuernavaca, Mor. Mexico Facultad de Ciencias - UNAM. México D.F. 04510, Mexico Present address: Instituto de Biotecnologia - UNAM. Ap. Postal 520-3, Cuernavaca, Mor. Mexico.
Physiol Plant. 2003 Mar;117(3):326-336. doi: 10.1034/j.1399-3054.2003.00053.x.
Legumes can obtain nitrogen from symbiotic nitrogen fixation in root nodules. The glutamine synthetase/glutamate synthase cycle is responsible for the initial nitrogen assimilation. This work reports the analysis of transgenic Lotus japonicus plants with the chimeric gene containing the alfalfa cytosolic glutamine synthetase (GS1) (EC 6.3.1.2) gene controlled by the Sesbania rostrata leghemoglobin gene promoter (Srglb3p). Surprisingly, all of the transgenic primary transformants analysed were sterile. Two transformants designated GS39 and GS44 were further analysed. GS in nodules of GS39 and GS44 plants was upregulated, at the level of transcript and protein. The transgenic plants had 2-fold higher nodule GS activity and similar root GS activity compared to control plants. The GS39 and GS44 sterile plants showed morphological alterations in pollen grains and in ovules. An increase in GS transcript abundance and enzyme activity was measured during early and late stages of flower development of GS plants. Flowers of GS plants showed higher glutamine content, resulting in an increased glutamine/glutamate ratio. The GS transcript and protein were detected in ovules. These data indicate that overexpression of GS1 in reproductive organs critically affects their development and might be a reason for sterility of L. japonicus plants.
豆科植物可通过根瘤中的共生固氮作用获取氮。谷氨酰胺合成酶/谷氨酸合酶循环负责最初的氮同化。这项工作报道了对转基因日本百脉根植株的分析，该植株带有嵌合基因，此嵌合基因包含受刺槐豆血红蛋白基因启动子（Srglb3p）控制的苜蓿胞质谷氨酰胺合成酶（GS1）（EC 6.3.1.2）基因。令人惊讶的是，所有分析的转基因初代转化体均不育。对两个命名为GS39和GS44的转化体进行了进一步分析。GS39和GS44植株根瘤中的GS在转录本和蛋白质水平上均上调。与对照植株相比，转基因植株的根瘤GS活性高2倍，而根GS活性相似。GS39和GS44不育植株在花粉粒和胚珠上表现出形态改变。在GS植株花发育的早期和晚期均检测到GS转录本丰度和酶活性增加。GS植株的花显示出较高的谷氨酰胺含量，导致谷氨酰胺/谷氨酸比率增加。在胚珠中检测到了GS转录本和蛋白质。这些数据表明，生殖器官中GS1的过表达严重影响其发育，这可能是日本百脉根植株不育的原因。
