title: Endonucleolytic activation directs dark-induced chloroplast mRNA degradation.
abstract: Plastid mRNA stability is tightly regulated by external signals such as light. We have investigated the biochemical mechanism responsible for the dark-induced decrease of relative half-lives for mRNAs encoding photosynthetic proteins. Protein fractions isolated from plastids of light-grown and dark-adapted plants correctly reproduced an RNA degradation pathway in the dark that is downregulated in the light. This dark-dependent pathway is initiated by endonucleolytic cleavages in the petD mRNA precursor substrate proximal to a region that can fold into a stem-loop structure. Polynucleotide phosphorylase (PNPase) polyadenylation activity was strongly increased in the protein fraction isolated from plastids in dark-adapted plants, but interestingly PNPase activity was not required for the initiation of dark-induced mRNA degradation. A protein factor present in the protein fraction from plastids of light-grown plants could inactivate the endonuclease activity and thereby stabilize the RNA substrate in the protein fraction from plastids of dark-adapted plants. The results show that plastid mRNA stability is effectively controlled by the regulation of a specific dark-induced RNA degradation pathway.
authors.affiliation: Institute of Plant Sciences, Swiss Federal Institute of Technology, ETH Zentrum, LFW E51.1, Universitätstrasse 2, CH-8092 Zürich, Switzerland. sacha.baginsky@ipw.biol.ethz.ch
authors.forename: Sacha
authors.initials: S
authors.lastname: Baginsky
authors.forename: Wilhelm
authors.initials: W
authors.lastname: Gruissem
mesh_terms: D020413:3' Untranslated Regions; D003573:Cytochrome b Group / Q000235:genetics / Q000378:metabolism; D045346:Cytochrome b6f Complex; D003624:Darkness; D004722:Endoribonucleases / Q000378:metabolism*; D004789:Enzyme Activation; D018506:Gene Expression Regulation, Plant; D008027:Light; D010940:Plant Proteins / Q000032:analysis; D026723:Polyadenylation; D011117:Polyribonucleotide Nucleotidyltransferase / Q000502:physiology; D012322:RNA Precursors / Q000737:chemistry / Q000378:metabolism; D020871:RNA Stability; D018747:RNA, Chloroplast / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism
chemical_list: D020413:3' Untranslated Regions; D003573:Cytochrome b Group; D010940:Plant Proteins; D012322:RNA Precursors; D018747:RNA, Chloroplast; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C084072:petD protein, cytochrome b(6)f complex; D045346:Cytochrome b6f Complex; D011117:Polyribonucleotide Nucleotidyltransferase; D004722:Endoribonucleases