Signalling cascades integrating light-enhanced nitrate metabolism.
In higher plants, light is crucial for regulation of nitrate uptake, translocation and assimilation into organic compounds. Part of this metabolism is tightly coupled to photosynthesis because the enzymes involved, nitrite reductase and glutamate synthase, are localized to the chloroplasts and receive reducing power from photosynthetic electron transport. However, important enzymes in nitrate acquisition and reduction are localized to cellular compartments other than chloroplasts and are also up-regulated by light, i.e. transporters in cell and organellar membranes and nitrate reductase in the cytosol. This review describes the different light-dependent signalling cascades regulating nitrate metabolism at the transcriptional as well as post-transcriptional level, and how reactions in different compartments of the cell are co-ordinated. Essential players in this network are phytochrome and HY5 (long hypocotyls 5)/HYH (HY5 homologue)-dependent signalling pathways, the energy-related AMPK (AMP-activated protein kinase) protein kinase homologue SNRK1 (sucrose non-fermenting kinase 1-related kinase), chloroplastic thioredoxins and the prokaryotically originated PII protein. A complex light-dependent network of regulation emerges, which appears to be necessary for optimal nitrogen assimilation and for avoiding the accumulation of toxic intermediates and side products, such as nitrite and reactive oxygen compounds.
Lillo
Cathrine
C
Centre for Organelle Research, Faculty of Science and Technology, University of Stavanger, 4036 Stavanger, Norway. cathrine.lillo@uis.no
D055372:AMP-Activated Protein Kinases; D017360:Arabidopsis / Q000502:physiology; D029681:Arabidopsis Proteins / Q000502:physiology; D050976:Basic-Leucine Zipper Transcription Factors / Q000502:physiology; D002352:Carrier Proteins / Q000502:physiology; D054479:Chloroplast Thioredoxins / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism; D002940:Circadian Rhythm; D004268:DNA-Binding Proteins; D029382:Dicarboxylic Acid Transporters / Q000502:physiology; D017343:Genes, Plant / Q000528:radiation effects; D005974:Glutamate-Ammonia Ligase / Q000502:physiology; D008027:Light; D009097:Multienzyme Complexes / Q000502:physiology; D050901:Nitrate Reductase / Q000502:physiology; D009566:Nitrates / Q000378:metabolism*; D009572:Nitrite Reductases / Q000502:physiology; D009573:Nitrites / Q000378:metabolism; D009687:Nuclear Proteins / Q000502:physiology; D051922:PII Nitrogen Regulatory Proteins / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000502:physiology; D010834:Phytochrome / Q000502:physiology*; D018521:Plant Physiological Phenomena / Q000528:radiation effects*; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D015398:Signal Transduction / Q000528:radiation effects*
D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D002352:Carrier Proteins; D054479:Chloroplast Thioredoxins; D004268:DNA-Binding Proteins; D029382:Dicarboxylic Acid Transporters; C109254:HY5 protein, Arabidopsis; C457459:HYH protein, Arabidopsis; D009097:Multienzyme Complexes; D009566:Nitrates; D009573:Nitrites; D009687:Nuclear Proteins; D051922:PII Nitrogen Regulatory Proteins; D010834:Phytochrome; D009572:Nitrite Reductases; D050901:Nitrate Reductase; C071570:SNF1-related protein kinases; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D010749:Phosphoprotein Phosphatases; D005974:Glutamate-Ammonia Ligase