title: Differential regulation of chloroplast gene expression in Chlamydomonas reinhardtii during photoacclimation: light stress transiently suppresses synthesis of the Rubisco LSU protein while enhancing synthesis of the PS II D1 protein.
abstract: Transfer of Chlamydomonas reinhardtii cells grown photoautotrophically in low light to higher light intensities has a dramatic transient effect on the differential expression of the two major chloroplast encoded photosynthetic proteins. Synthesis of the D1 protein of Photosystem II increases more than 10-fold during the first six hours in high light (HL), whereas synthesis of the large subunit (LSU) of Rubisco drops dramatically within 15 min and only gradually resumes at about 6 h. Synthesis of the chloroplast-encoded ATP synthase beta subunit, the nuclear-encoded Rubisco small subunit and the nuclear-encoded beta-tubulin is not noticeably affected. Up regulation of psbA mRNA translation accounts for a substantial fraction of the increased D1 synthesis, since accumulation of psbA mRNA increases 4.2- and 6.3-fold less than D1 synthesis at 6 and 18 h in HL. Down-regulation of LSU synthesis is not correlated with a reduction in the steady-state level of the rbcL transcript. Primer extension mapping of the 5' ends of the rbcL mRNAs reveals transcripts with start points located at -93 and -168 relative to the first translated ATG. Transfer of low light (LL)-grown cells to HL temporarily decreases the ratio of the -93 to -168 transcripts, but this ratio normalizes after 6 h in HL, coincident with the recovery in the synthesis of LSU. These several distinct effects of temporary light stress were correlated with a rapid, sustained increase in the reduction state of QA, a transient decline in photosynthetic efficiency, a less rapid drop in total chlorophyll content and a delay in cell division.
authors.affiliation: Department of Botany, Duke University, Durham, NC 27708-1000, USA.
authors.forename: M
authors.initials: M
authors.lastname: Shapira
authors.forename: A
authors.initials: A
authors.lastname: Lers
authors.forename: P B
authors.initials: PB
authors.lastname: Heifetz
authors.forename: V
authors.initials: V
authors.lastname: Irihimovitz
authors.forename: C B
authors.initials: CB
authors.lastname: Osmond
authors.forename: N W
authors.initials: NW
authors.lastname: Gillham
authors.forename: J E
authors.initials: JE
authors.lastname: Boynton
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D000818:Animals; D016825:Chlamydomonas reinhardtii / Q000235:genetics* / Q000378:metabolism / Q000528:radiation effects; D002734:Chlorophyll / Q000378:metabolism; D000077194:Chlorophyll A; D002736:Chloroplasts / Q000235:genetics; D005786:Gene Expression Regulation / Q000528:radiation effects*; D008027:Light; D045342:Light-Harvesting Protein Complexes; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000096:biosynthesis* / Q000235:genetics; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D012273:Ribulose-Bisphosphate Carboxylase / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D045332:Photosystem II Protein Complex; D010940:Plant Proteins; D012333:RNA, Messenger; D002734:Chlorophyll; C101625:RbcL protein, plastid; D012273:Ribulose-Bisphosphate Carboxylase; D000077194:Chlorophyll A