title: Integration of chloroplast nucleic acid metabolism into the phosphate deprivation response in Chlamydomonas reinhardtii.
abstract: Cell survival depends on the cell's ability to acclimate to phosphorus (P) limitation. We studied the chloroplast ribonuclease polynucleotide phosphorylase (PNPase), which consumes and generates phosphate, by comparing wild-type Chlamydomonas reinhardtii cells with strains with reduced PNPase expression. In the wild type, chloroplast RNA (cpRNA) accumulates under P limitation, correlating with reduced PNPase expression. PNPase-deficient strains do not exhibit cpRNA variation under these conditions, suggesting that in the wild type PNPase limits cpRNA accumulation under P stress. PNPase levels appear to be mediated by the P response regulator PHOSPHORUS STARVATION RESPONSE1 (PSR1), because in psr1 mutant cells, cpRNA declines under P limitation and PNPase expression is not reduced. PNPase-deficient cells begin to lose viability after 24 h of P depletion, suggesting that PNPase is important for cellular acclimation. PNPase-deficient strains do not have enhanced sensitivity to other physiological or nutrient stresses, and their RNA and cell growth phenotypes are not observed under P stress with phosphite, a phosphate analog that blocks the stress signal. In contrast with RNA metabolism, chloroplast DNA (cpDNA) levels declined under P deprivation, suggesting that P mobilization occurs from DNA rather than RNA. This unusual phenomenon, which is phosphite- and PSR1-insensitive, may have evolved as a result of the polyploid nature of cpDNA and the requirement of P for cpRNA degradation by PNPase.
authors.affiliation: Boyce Thompson Institute for Plant Research, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Shlomit
authors.initials: S
authors.lastname: Yehudai-Resheff
authors.forename: Sara L
authors.initials: SL
authors.lastname: Zimmer
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Komine
authors.forename: David B
authors.initials: DB
authors.lastname: Stern
mesh_terms: D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D016825:Chlamydomonas reinhardtii / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D002736:Chloroplasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D018742:DNA, Chloroplast / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004794:Enzyme Repression / Q000187:drug effects; D005095:Exoribonucleases / Q000378:metabolism; D018628:Gene Dosage; D018745:Genome, Plant / Q000235:genetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D009687:Nuclear Proteins / Q000096:biosynthesis; D010710:Phosphates / Q000172:deficiency*; D017905:Phosphites / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis; D011117:Polyribonucleotide Nucleotidyltransferase / Q000172:deficiency; D020871:RNA Stability / Q000187:drug effects; D018747:RNA, Chloroplast / Q000378:metabolism*; D012293:Rifampin / Q000494:pharmacology; D017386:Sequence Homology, Amino Acid
chemical_list: D018742:DNA, Chloroplast; D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; D010710:Phosphates; D017905:Phosphites; D010940:Plant Proteins; C403075:Psr1 protein, Chlamydomonas; D018747:RNA, Chloroplast; D011117:Polyribonucleotide Nucleotidyltransferase; D005095:Exoribonucleases; C022535:exoribonuclease II; D012293:Rifampin