Phosphorylation by MPK6 A conserved transcriptional modification mediates nitrate reductase activation and NO production?

Nitrate reductase is a central enzyme of nitrogen assimilation in plants. In a recent work, we have revealed MPK6 could phosphorylate Arabidopsis NIA2 at the serine 627 in hinge 2 region, this phosphorylation may represent a rapid activation mechnism when plant need excessive nitrate reduction. Interestingly, all eukaryotic NRs have conserved docking sequence in their FAD domains, and many plant NR proteins have the conserved MAPK phosphorylation site. Those indicated that phosphorylation of NR protein by MAP kinase cascade may be conserved in different species. We noticed that the phosphorylation of S627 residue by MPK6 have a specially influence on the NO generation. Although no homology of mammalian NOS has been identified in high plants, NR may still share a similar regulation mechanism with mammalian NOS.