The activity of the high-affinity nitrate transport system I (NRT2;1, NAR2) is responsible for the efficient signalling of nitrate assimilation genes in Chlamydomonas reinhardtii.
The expression of nitrite uptake activity and the induction of transcripts from several nitrate assimilation genes (Nii1, Nrt2;1, Nrt2;3, and Nar1) have been analysed in Chlamydomonas reinhardtii Dang. strains bearing several sets of genes encoding nitrate transport systems. Different nitrate concentrations resulted in a differential induction pattern of nitrite uptake activity depending on which particular nitrate transport system was present in the cells, and that was directly related to their relative efficiency for nitrate transport. The presence of the high-affinity nitrate transport system I (NRT2;1, NAR2) made cells able to sense the very low concentrations of nitrate present in culture medium with no added nitrate and to express optimally Nii1, Nrt2;1, Nrt2;3, and Nar1 genes involved in nitrate/nitrite assimilation. In addition, strains lacking nitrate reductase activity overexpressed these gene transcripts as a result of continuous signalling by nitrate, but only those bearing an active system I. This study supports the hypothesis that signalling of nitrate assimilation genes occurs intracellularly in a process dependent on the nitrate uptake activity. The bispecific nitrate/nitrite transport system I with the highest affinity for nitrate is the most efficient one for signalling the expression of nitrate/nitrite assimilation genes in C. reinhardtii.
Rexach
Jesús
J
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Campus de Rabanales, Edif. Severo Ochoa, 14071 Córdoba, Spain.
Llamas
Angel
A
Fernández
Emilio
E
Galván
Aurora
A
D020418:Algal Proteins; D000818:Animals; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic; D047908:Intracellular Signaling Peptides and Proteins; D009154:Mutation; D009565:Nitrate Reductases / Q000235:genetics / Q000378:metabolism; D000091285:Nitrate Transporters; D009566:Nitrates / Q000378:metabolism* / Q000494:pharmacology; D009572:Nitrite Reductases / Q000235:genetics / Q000378:metabolism; D009573:Nitrites / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D020418:Algal Proteins; D027321:Anion Transport Proteins; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; C095726:NIT8 protein, Chlamydomonas reinhardtii; D000091285:Nitrate Transporters; D009566:Nitrates; D009573:Nitrites; D009687:Nuclear Proteins; D010940:Plant Proteins; D015800:Protozoan Proteins; D009565:Nitrate Reductases; D009572:Nitrite Reductases