title: Tiered regulation of sulfur deprivation responses in Chlamydomonas reinhardtii and identification of an associated regulatory factor.
abstract: During sulfur (S) deprivation, the unicellular alga Chlamydomonas reinhardtii exhibits increased expression of numerous genes. These genes encode proteins associated with sulfate (SO4(2-)) acquisition and assimilation, alterations in cellular metabolism, and internal S recycling. Administration of the cytoplasmic translational inhibitor cycloheximide prevents S deprivation-triggered accumulation of transcripts encoding arylsulfatases (ARS), an extracellular polypeptide that may be important for cell wall biosynthesis (ECP76), a light-harvesting protein (LHCBM9), the selenium-binding protein, and the haloperoxidase (HAP2). In contrast, the rapid accumulation of transcripts encoding high-affinity SO4(2-) transporters is not affected. These results suggest that there are two tiers of transcriptional regulation associated with S deprivation responses: the first is protein synthesis independent, while the second requires de novo protein synthesis. A mutant designated ars73a exhibited low ARS activity and failed to show increases in ECP76, LHCBM9, and HAP2 transcripts (among others) in response to S deprivation; increases in transcripts encoding the SO4(2-) transporters were not affected. These results suggest that the ARS73a protein, which has no known activity but might be a transcriptional regulator, is required for the expression of genes associated with the second tier of transcriptional regulation. Analysis of the ars73a strain has helped us generate a model that incorporates a number of complexities associated with S deprivation responses in C. reinhardtii.
authors.affiliation: Department of Plant Biology, Carnegie Institution for Science, Stanford, California 94305, USA. maksoy1@stanford.edu
authors.forename: Munevver
authors.initials: M
authors.lastname: Aksoy
authors.forename: Wirulda
authors.initials: W
authors.lastname: Pootakham
authors.forename: Steve V
authors.initials: SV
authors.lastname: Pollock
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Moseley
authors.forename: David
authors.initials: D
authors.lastname: González-Ballester
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Grossman
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D001192:Arylsulfatases / Q000235:genetics / Q000378:metabolism*; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics / Q000502:physiology; D002701:Chloramphenicol / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D048028:DNA, Algal / Q000235:genetics; D003609:Dactinomycin / Q000494:pharmacology; D015870:Gene Expression; D018506:Gene Expression Regulation, Plant; D008040:Genetic Linkage; D008954:Models, Biological; D016254:Mutagenesis, Insertional; D010641:Phenotype; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism; D013455:Sulfur / Q000172:deficiency* / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D048028:DNA, Algal; D012333:RNA, Messenger; D013431:Sulfates; D003609:Dactinomycin; D002701:Chloramphenicol; D013455:Sulfur; D003513:Cycloheximide; D001192:Arylsulfatases