Overexpression of an NADP(H)-dependent glutamate dehydrogenase gene, TrGDH, from Trichurus improves nitrogen assimilation, growth status and grain weight per plant in rice.

As glutamate dehydrogenases (GDHs) of microorganisms usually have higher affinity for NH₄⁺ than do those of higher plants, it is expected that ectopic expression of these GDHs can improve nitrogen assimilation in higher plants. Here, a novel NADP(H)-GDH gene (TrGDH) was isolated from the fungus Trichurus and introduced into rice (Oryza sativa L.). Investigation of kinetic properties in vitro showed that, compared with the rice GDH (OsGDH4), TrGDH exhibited higher affinity for NH₄⁺ (K_m = 1.48 ± 0.11 mM). Measurements of the NH₄⁺ assimilation rate demonstrated that the NADP(H)-GDH activities of TrGDH transgenic lines were significantly higher than those of the controls. Hydroponic experiments revealed that the fresh weight, dry weight and nitrogen content significantly increased in the TrGDH transgenic lines. Field trials further demonstrated that the number of effective panicles, 1,000-grain weight and grain weight per plant of the transgenic lines were significantly higher than those of the controls, especially under low-nitrogen levels. Moreover, glutelin and prolamine were found to be markedly increased in seeds from the transgenic rice plants. These results sufficiently confirm that overexpression of TrGDH in rice can improve the growth status and grain weight per plant by enhancing nitrogen assimilation. Thus, TrGDH is a promising candidate gene for maintaining yields in crop plants via genetic engineering.