title: How Chlamydomonas handles nitrate and the nitric oxide cycle.
abstract: The green alga Chlamydomonas is a valuable model system capable of assimilating different forms of nitrogen (N). Nitrate (NO3-) has a relevant role in plant-like organisms, first as a nitrogen source for growth and second as a signalling molecule. Several modules are necessary for Chlamydomonas to handle nitrate, including transporters, nitrate reductase (NR), nitrite reductase (NiR), GS/GOGAT enzymes for ammonium assimilation, and regulatory protein(s). Transporters provide a first step for influx/efflux, homeostasis, and sensing of nitrate; and NIT2 is the key transcription factor (RWP-RK) for mediating the nitrate-dependent activation of a number of genes. Here, we review how NR participates in the cycle NO3- →NO2- →NO →NO3-. NR uses the partner protein amidoxime-reducing component/nitric oxide-forming nitrite reductase (ARC/NOFNiR) for the conversion of nitrite (NO2-) into nitric oxide (NO). It also uses the truncated haemoglobin THB1 in the conversion of nitric oxide to nitrate. Nitric oxide is a negative signal for nitrate assimilation; it inhibits the activity and expression of high-affinity nitrate/nitrite transporters and NR. During this cycle, the positive signal of nitrate is transformed into the negative signal of nitric oxide, which can then be converted back into nitrate. Thus, NR is back in the spotlight as a strategic regulator of the nitric oxide cycle and the nitrate assimilation pathway.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Victoria
authors.initials: V
authors.lastname: Calatrava
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Chamizo-Ampudia
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Emanuel
authors.initials: E
authors.lastname: Sanz-Luque
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Francisco
authors.initials: F
authors.lastname: Ocaña-Calahorro
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Angel
authors.initials: A
authors.lastname: Llamas
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Fernandez
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Campus de Rabanales y Campus Internacional de Excelencia Agroalimentario (CeiA3), Edif. Severo Ochoa, Universidad de Córdoba, Spain.
authors.forename: Aurora
authors.initials: A
authors.lastname: Galvan
mesh_terms: D020418:Algal Proteins / Q000378:metabolism*; D002696:Chlamydomonas / Q000378:metabolism*; D050901:Nitrate Reductase / Q000378:metabolism*; D009569:Nitric Oxide / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D058458:Nitrogen Cycle
chemical_list: D020418:Algal Proteins; D009573:Nitrites; D009569:Nitric Oxide; D050901:Nitrate Reductase
keywords: Chlamydomonas; NO cycle; nitrate reductase.; nitric oxide