Physiological analysis of nitrogen-efficient rice overexpressing alanine aminotransferase under different N regimes

Cereal crop plants have low nitrogen (N) use efficiency, taking up only 30% to 50% of the applied N fertilizers, with the rest having the potential for loss into the environment as N pollution. One way to address this problem is to improve the nitrogen use efficiency of cereal crops using a transgenic approach. We developed alanine aminotransferase overexpressing rice, and we have previously determined that this modification provided an improved nitrogen-use phenotype to the engineered plants. In this study, the transgenic rice were grown in low, medium, and high nitrogen supply, and morphology, plant N levels, enzymatic activity, metabolite levels, and transcriptome response in the roots and shoots at active and maximum tillering at each N level were measured. The transcriptome response was analysed further using MapMan and PageMan to view multiple comparisons. The transgenic rice plants showed improved nitrogen use efficiency at medium and high N supply, but with few significant changes to the amino acid levels or to the transcriptome. The transgenic plants grown in high N showed up-regulation of transcripts associated with photosynthesis, non-melavonate pathway secondary metabolites, protein degradation, and many unknown function transcripts.