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 the processes of photosynthesis, respiration and amino acid metabolism in a photoperiod dependent manner. The GS/GOGAT cycle is one such mechanism and is highly elucidated in plants to serve as a cross-road between C and N metabolism. Non-photosynthetic tissues (e.g., roots), however, lack a sufficient supply of carbon skeletons under high N conditions and hence may resort to other mechanisms, along with GS/GOGAT cycle, to achieve the aforementioned C/N balance. Our understanding of the pathways involved in this major aspect of plant regulation, is limited. The current research proposes the potential role of an enzyme, GAT1_2.1, in hydrolyzing glutamine to Glu which may serve as carbon skeletons for channeling C to the TCA cycle, under high N conditions, using Arabidopsis as a model. Transcriptome analysis of asparagine treated Arabidopsis roots 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 N status, has a root specific expression in Arabidopsis and is found to be highly co-expressed with Glutamate Dehydrogenase 2 (GDH2). Metabolite profiling data, using gat1_2.1 mutant of Arabidopsis, suggest that in the absence of GAT1_2.1, GABA shunt pathway is activated to replenish the depleted levels of Glu. This Glu may then be deaminated to 2-oxoglutarate by GDH2 and channelled into the TCA cycle thus providing a cross-road between C and N metabolism in roots.