Expression of nitrate assimilation related genes in Chlamydomonas reinhardtii.
The mRNA accumulation pattern of the Chlamydomonas reinhardtii nitrate assimilation-related gene cluster has been elucidated. In ammonium-grown wild-type cells, nit-1 (nitrate reductase, NR), nar-1, nar-2 and nar-3 (nitrate transporter) genes showed very similar kinetics of expression when transferred to nitrate medium. Transcripts of all these genes accumulated transiently in ammonium-grown wild-type cells after a one-hour incubation in nitrogen-free medium, and practically disappeared at about 2 hours. Mutant strains lacking functional nitrate reductase showed similar accumulation kinetics of these transcripts during both nitrate induction and derepression in nitrogen-free media. In contrast to the other nar transcripts, that nar-4, a gene sharing similar sequences with nar-3, accumulated in small amounts in wild-type cells, and only increased after a long nitrate induction period. Nitrate and light showed a strong positive effect on the accumulation of nit-1 gene transcripts. Acetate as a carbon source allowed accumulation of nit-1 mRNA in the dark, indicating the existence of interactions between light and carbon metabolism in nit-1 gene expression. Our data strongly suggest that NR negatively autoregulates its own expression and that of nar genes.
Quesada
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A
Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Spain.
Fernández
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E
D000818:Animals; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D003001:Cloning, Molecular; D005786:Gene Expression Regulation; D007700:Kinetics; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000235:genetics* / Q000378:metabolism; D009566:Nitrates / Q000378:metabolism*; D015183:Restriction Mapping; D014158:Transcription, Genetic
D002352:Carrier Proteins; D009566:Nitrates; D009565:Nitrate Reductases; D050901:Nitrate Reductase