The present invention relates to transgenic plants that have increased nitrogen use efficiency, stress tolerance, and/or alleviating a limitation such that yield is increased, or a combination of these and that have been transformed using a novel vector construct including a synthetic isocitrate dehydrogenase ( icdh) gene that modulates nitrogen use in plants. The invention also relates to stacking the icdh gene with other exogenous or heterologous genes that modulate nitrogen use in the plant, including a N-acetylglutamate kinase gene. The invention also relates to methods of expressing in plants the nucleic acid molecules corresponding to the nucleic acid sequences that modulate nitrogen use in plants or are modulated by nitrogen conditions.
