Control of Nitrogen Assimilation in Plants through S-nitrosothiols

The inorganic ion nitrate is the primary source of nitrogen for land plants, and the availability of this nutrient in the soil represents a bottleneck in crop yield. To assimilate nitrate, plants employ a variety of transporters and reductases expressed in different tissues and organs to transport and catalyse the sequential reduction of assimilates. Nitrate assimilation is a high-energy consuming process subject to tight metabolic control, which is not yet fully understood. Recently, nitrate assimilation was demonstrated to be regulated by a feedback mechanism involving the free radical nitric oxide (NO). NO primarily acts through covalent attachment to thiol groups of Cys residues, causing S-nitrosylation, a reversible post-translational protein modification. Previous evidence has indicated that S-nitrosylation feedback regulates nitrate transporters and reductases in a novel mechanism involving the production and scavenging of NO. In this review, we will discuss recent advances in the field of nitrate assimilation, focussing on the interplay between this process and NO-mediated redox signaling pathways in plants.