Isolated polynucleotides and polypeptides encoded thereby are described, together with the use of those products for making transgenic plants with increased nitrogen use efficiency. The present invention further relates to nucleotide sequences and the use of those nucleotide sequences in the genetic-engineering of plants to display enhanced nitrogen assimilatory and utilization capacities, grow larger, more efficiently or rapidly, and/or have enriched nitrogen contents in vegetative and/or reproductive plant parts and/or increased biomass. More particularly, this invention relates to producing transgenic plants engineered to have altered expression of key components in the nitrogen assimilation and utilization pathways. The engineered plants may be productively cultivated under conditions of low nitrogen fertilizer input or in nitrogen poor soils. Alternatively, the engineered plants may be used to achieve faster growing or maturing crops, higher crop yields and/or more nutritious products under ideal cultivation conditions.