Nussaume L, Vincentz M, Meyer C, Boutin J P, Caboche M
Laboratoire de Biologie Cellulaire, Institut National de la Recherche Agronomique, Centre de Versailles, Versailles, France.
Plant Cell. 1995 May;7(5):611-21. doi: 10.1105/tpc.7.5.611.
Higher plant nitrate reductases (NRs) carry an N-terminal domain whose sequence is not conserved in NRs from other organisms. A gene composed of a full-length tobacco NR cDNA with an internal deletion of 168 bp in the 5' end fused to the cauliflower mosaic virus 35S promoter and appropriate termination signals was constructed and designated as delta NR. An NR-deficient mutant of Nicotiana plumbaginifolia was transformed with this delta NR gene. In transgenic plants expressing this construct, NR activity was restored and normal growth resulted. Apart from a higher thermosensitivity, no appreciable modification of the kinetic parameters of the enzyme was detectable. The post-transcriptional regulation of NR by light was abolished in delta NR transformants. Consequently, deregulated production of glutamine and asparagine was detected in delta NR transformants. The absence of in vitro delta NR activity modulation by ATP suggests the impairment of delta NR phosphorylation and thereby suppression of delta NR post-translational regulation. These data imply that post-transcriptional control of NR expression is important for the flow of the nitrate assimilatory pathway.
高等植物硝酸还原酶（NRs）带有一个N端结构域，其序列在来自其他生物体的硝酸还原酶中并不保守。构建了一个基因，该基因由全长烟草NR cDNA组成，其5'端内部缺失168 bp，并与花椰菜花叶病毒35S启动子和适当的终止信号融合，命名为δNR。用该δNR基因转化了烟草垂花烟草的NR缺陷型突变体。在表达该构建体的转基因植物中，NR活性得以恢复，植物生长正常。除了较高的热敏感性外，未检测到该酶动力学参数有明显改变。在δNR转化体中，光对NR的转录后调控被消除。因此，在δNR转化体中检测到谷氨酰胺和天冬酰胺的失控产生。ATP对δNR体外活性的调节缺失表明δNR磷酸化受损，从而抑制了δNR的翻译后调控。这些数据表明，NR表达的转录后控制对于硝酸同化途径的流动很重要。
