title: Sugar-mediated transcriptional regulation of the Gap gene system and concerted photosystem II functional modulation in the microalga Scenedesmus vacuolatus.
abstract: Partial cDNAs corresponding to the GapA, GapC and GapN genes that encode the three different glyceraldehyde-3-phosphate dehydrogenases (GAPDHs) of the green microalga Scenedesmus vacuolatus SAG 211-8b have been cloned and characterized. Northern blot experiments, as well as immunoblots and activity measurements, demonstrate a differential regulation by sugars of the components of the algal Gap gene system. Addition of glucose or other metabolizable sugars to photoautotrophic cultures promoted a drastic repression of the GapA gene and depletion to negligible levels of the corresponding GAPDHA, a chloroplastic protein involved in photosynthetic CO2 assimilation. By contrast, expression of the GapC and GapN genes encoding their cytosolic counterparts involved in glycolysis was enhanced. However, no down-regulation of the GapA gene by glucose took place in the dark, indicating that the observed effect is associated with sugar assimilation in the light. Likewise, glucose promoted in illuminated algal cultures a severe decrease of photosystem II functionality, estimated by O2 evolution activity, thermoluminescence emission and D1 protein level, while again, no effect was observed in the dark. On the basis of the correlation found between photosystem II performance and sugar transcriptional regulation of the GapA gene, a scenario of sugar-mediated regulation of photosynthetic metabolism in microalgae is proposed that will help to explain the so-called glucose bleaching effect in photosynthetic eukaryotes.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Universidad de Sevilla-CSIC, 41092, Seville, Spain.
authors.forename: Federico
authors.initials: F
authors.lastname: Valverde
authors.forename: José M
authors.initials: JM
authors.lastname: Ortega
authors.forename: Manuel
authors.initials: M
authors.lastname: Losada
authors.forename: Aurelio
authors.initials: A
authors.lastname: Serrano
mesh_terms: D020418:Algal Proteins / Q000378:metabolism*; D000595:Amino Acid Sequence; D001665:Binding Sites; D050260:Carbohydrate Metabolism; D002734:Chlorophyll / Q000378:metabolism; D005786:Gene Expression Regulation; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000378:metabolism; D044444:Scenedesmus / Q000235:genetics* / Q000378:metabolism*; D016415:Sequence Alignment; D013997:Time Factors; D014158:Transcription, Genetic
chemical_list: D020418:Algal Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D002734:Chlorophyll; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases