Combined transcriptomic and metabolomic approaches provide new insights into C/N partitioning in roots of Arabidopsis thaliana

Balance between carbon and nitrogen metabolism is a requirement for the sustained growth of organisms. In plant leaves, this balance is achieved by inter-relationships between photosynthesis, respiration and amino acid metabolism in a photoperiod dependent manner. The GS/GOGAT cycle is a well understood mechanism in plants known to serve as a cross-road between carbon and nitrogen metabolism. Non-photosynthetic tissues (e.g., roots, germinating seeds), however, lack a sufficient supply of carbon skeletons under high nitrogen conditions and hence may resort to other mechanisms, along with the GS/GOGAT cycle, to achieve the desired carbon/nitrogen balance. Considering the importance of asparagine as a major storage form of nitrogen, this study elucidates carbon and nitrogen partitioning within Arabidopsis roots upon asparagine treatment. Here, we propose a potential role for the GAT1_2.1 enzyme in hydrolyzing glutamine to glutamate which can serve as a carbon skeleton for channeling carbon to the TCA cycle, under high nitrogen conditions. Transcriptome analysis revealed a 4.3 fold upregulation of a class I glutamine amidotransferase, GAT1_2.1; GAT1_2.1 was shown to be highly responsive to nitrogen levels and has a root specific expression in Arabidopsis. Metabolite profiling data further strengthened the transcriptome data and suggest a major reprogramming of C and N metabolites to sustain TCA cycle.