Regulation of plant NR activity by reversible phosphorylation, 14-3-3 proteins and proteolysis

This review highlights progress in dissecting how plant nitrate rejuctase ( NR) activity is regulated by Ca2+, protein kinases, protein kinase kinases, protein phosphatases, 14-3-3 proteins and protease(s). The signailing comp onents that regulate NR have also been discovered to target other enzymes o f metabolism, vesicle trafficking and cellular signalling. Extracellular su gars exert a major impact on the 14-3-3-binding status and stability of man y target proteins, including NR in plants, whereas other stimuli affect the regulation of some targets and not others. We thus begin to see how select ive or global switches in cellular behaviour are triggered by regulatory ne tworks in response to different environmental stimuli. Surprisingly, the qu estion of how changes in NR activity actually affect the rate of nitrate as similation is turning out to be a tough problem.