Overexpressing a Fungal CeGDH Gene Improves Nitrogen Utilization and Growth in Rice.

In lower organisms, NADP(H)-dependent glutamate dehydrogenases (GDHs) have high affinities to ammonium and play important roles in nitrogen assimilation. Glutamate dehydrogenases in higher plants have lower affinities for ammonium so their nitrogen is mainly assimilated as ammonium by the glutamine synthetase (GS)/glutamate synthase (GOGAT) pathway. In present study, an NADP(H)-dependent glutamate dehydrogenase gene (CeGDH) was cloned from the fungus Cylindrocarpon ehrenbergii (Ce) and ectopically expressed in rice (Oryza sativa L. 'Kitaake'). Meanwhile, the enzyme activity of CeGDH was detected and the effects of CeGDH in transgenic rice were analyzed. The determination of enzymatic activity in vitro showed that CeGDH's aminating activity is higher than its deaminating activity, which was also confirmed by the results of enzymatic activity in vivo in CeGDH transgenic rice. These results suggested that the CeGDH is inclined to convert 2-Oxoglutarate to glutamate. Additionally, the nitrogen assimilation ability and grain yield were analyzed in CeGDH transgenic plants. The hydroponic experiments revealed that the shoot and root lengths and nitrogen contents were improved obviously in transgenic plants compared with the wild-type under low-nitrogen conditions at seedling stage. In field conditions, the agronomic traits analysis showed that panicle numbers and grain yields of the transgenic plants also increased significantly under low-nitrogen conditions. These results demonstrated that the introduction of CeGDH into rice could enhance nitrogen utilization, improve growth, and increase grain yields, especially in low nitrogen fertility. [ABSTRACT FROM AUTHOR]