Regulation of the alternative oxidase Aox1 gene in Chlamydomonas reinhardtii. Role of the nitrogen source on the expression of a reporter gene under the control of the Aox1 promoter.
In higher plants, various developmental and environmental conditions enhance expression of the alternative oxidase (AOX), whereas its induction in fungi is mainly dependent on cytochrome pathway restriction and triggering by reactive oxygen species. The AOX of the unicellular green alga Chlamydomonas reinhardtii is encoded by two different genes, the Aox1 gene being much more transcribed than Aox2. To analyze the transcriptional regulation of Aox1, we have fused its 1.4-kb promoter region to the promoterless arylsulfatase (Ars) reporter gene and measured ARS enzyme activities in transformants carrying the chimeric construct. We show that the Aox1 promoter is generally unresponsive to a number of known AOX inducers, including stress agents, respiratory inhibitors, and metabolites, possibly because the AOX activity is constitutively high in the alga. In contrast, the Aox1 expression is strongly dependent on the nitrogen source, being down-regulated by ammonium and stimulated by nitrate. Inactivation of nitrate reductase leads to a further increase of expression. The stimulation by nitrate also occurs at the AOX protein and respiratory levels. A deletion analysis of the Aox1 promoter region demonstrates that a short upstream segment (-253 to +59 with respect to the transcription start site) is sufficient to ensure gene expression and regulation, but that distal elements are required for full gene expression. The observed pattern of AOX regulation points to the possible interaction between chloroplast and mitochondria in relation to a potential increase of photogenerated ATP when nitrate is used as a nitrogen source.
Baurain
Denis
D
Genetics of Microorganisms, Department of Life Sciences, B22, University of Liège, Sart Tilman, B-4000 Liège, Belgium.
Dinant
Monique
M
Coosemans
Nadine
N
Matagne
René F
RF
D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001192:Arylsulfatases / Q000235:genetics / Q000378:metabolism; D001386:Azides / Q000494:pharmacology; D019069:Cell Respiration / Q000235:genetics / Q000502:physiology; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D003576:Electron Transport Complex IV / Q000378:metabolism; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D017930:Genes, Reporter / Q000235:genetics; D024101:Mitochondrial Proteins; D050901:Nitrate Reductase; D009565:Nitrate Reductases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D009566:Nitrates / Q000494:pharmacology; D009584:Nitrogen / Q000494:pharmacology*; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011993:Recombinant Fusion Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D000099188:Alternative Oxidase
D020418:Algal Proteins; D001192:Arylsulfatases; D001386:Azides; D003576:Electron Transport Complex IV; D024101:Mitochondrial Proteins; D050901:Nitrate Reductase; D009565:Nitrate Reductases; D009566:Nitrates; D009584:Nitrogen; D010088:Oxidoreductases; D010940:Plant Proteins; D000644:Quaternary Ammonium Compounds; D011993:Recombinant Fusion Proteins; D000099188:Alternative Oxidase