Knock-down of protein phosphatase 2A subunit B'γ promotes phosphorylation of CALRETICULIN 1 in Arabidopsis thaliana. 2011

Andrea Trotta, and Grzegorz Konert, and Moona Rahikainen, and Eva-Mari Aro, and Saijaliisa Kangasjärvi
Department of Biochemistry and Food Chemistry, University of Turku, Turku, Finland.

Controlled protein dephosphorylation by protein phosphatase 2A (PP2A) regulates diverse signaling events in plants. Recently, we showed that a specific B’γ regulatory subunit of PP2A mediates basal repression of immune reactions in Arabidopsis thaliana. Knock-down pp2a-b’γ mutants display constitutive defense reactions and premature yellowing conditionally under moderate light intensity. Here we show that knock-down of PP2A-B’γ renders CALRETI CULIN 1 (CRT 1) highly phosphorylated. Calreticulins are ER-resident chaperonins that operate in the unfolded protein response to prevent ER-stress, components of which are differentially regulated at mRNA level in pp2a-b’γ leaves. We speculate that in dephosphorylated state, CRT 1 promotes the degradation of unfolded proteins in ER. Our findings suggest that in wild type plants, dephosphorylation of CRT 1 is mediated by PP2A-B’γ dependent signaling effects. In pp2a-b’γ, strong phosphorylation of CRT 1 may partially imbalance the quality control of protein folding, thereby eliciting ER-stress and premature yellowing in leaves.

UI MeSH Term Description Entries
D010766 Phosphorylation The introduction of a phosphoryl group into a compound through the formation of an ester bond between the compound and a phosphorus moiety. Phosphorylations
D004721 Endoplasmic Reticulum A system of cisternae in the CYTOPLASM of many cells. In places the endoplasmic reticulum is continuous with the plasma membrane (CELL MEMBRANE) or outer membrane of the nuclear envelope. If the outer surfaces of the endoplasmic reticulum membranes are coated with ribosomes, the endoplasmic reticulum is said to be rough-surfaced (ENDOPLASMIC RETICULUM, ROUGH); otherwise it is said to be smooth-surfaced (ENDOPLASMIC RETICULUM, SMOOTH). (King & Stansfield, A Dictionary of Genetics, 4th ed) Ergastoplasm,Reticulum, Endoplasmic
D015398 Signal Transduction The intracellular transfer of information (biological activation/inhibition) through a signal pathway. In each signal transduction system, an activation/inhibition signal from a biologically active molecule (hormone, neurotransmitter) is mediated via the coupling of a receptor/enzyme to a second messenger system or to an ion channel. Signal transduction plays an important role in activating cellular functions, cell differentiation, and cell proliferation. Examples of signal transduction systems are the GAMMA-AMINOBUTYRIC ACID-postsynaptic receptor-calcium ion channel system, the receptor-mediated T-cell activation pathway, and the receptor-mediated activation of phospholipases. Those coupled to membrane depolarization or intracellular release of calcium include the receptor-mediated activation of cytotoxic functions in granulocytes and the synaptic potentiation of protein kinase activation. Some signal transduction pathways may be part of larger signal transduction pathways; for example, protein kinase activation is part of the platelet activation signal pathway. Cell Signaling,Receptor-Mediated Signal Transduction,Signal Pathways,Receptor Mediated Signal Transduction,Signal Transduction Pathways,Signal Transduction Systems,Pathway, Signal,Pathway, Signal Transduction,Pathways, Signal,Pathways, Signal Transduction,Receptor-Mediated Signal Transductions,Signal Pathway,Signal Transduction Pathway,Signal Transduction System,Signal Transduction, Receptor-Mediated,Signal Transductions,Signal Transductions, Receptor-Mediated,System, Signal Transduction,Systems, Signal Transduction,Transduction, Signal,Transductions, Signal
D017360 Arabidopsis A plant genus of the family BRASSICACEAE that contains ARABIDOPSIS PROTEINS and MADS DOMAIN PROTEINS. The species A. thaliana is used for experiments in classical plant genetics as well as molecular genetic studies in plant physiology, biochemistry, and development. Arabidopsis thaliana,Cress, Mouse-ear,A. thaliana,A. thalianas,Arabidopses,Arabidopsis thalianas,Cress, Mouse ear,Cresses, Mouse-ear,Mouse-ear Cress,Mouse-ear Cresses,thaliana, A.,thaliana, Arabidopsis,thalianas, A.
D054648 Protein Phosphatase 2 A phosphoprotein phosphatase subtype that is comprised of a catalytic subunit and two different regulatory subunits. At least two genes encode isoforms of the protein phosphatase catalytic subunit, while several isoforms of regulatory subunits exist due to the presence of multiple genes and the alternative splicing of their mRNAs. Protein phosphatase 2 acts on a broad variety of cellular proteins and may play a role as a regulator of intracellular signaling processes. PPP2CA Phosphatase,PPP2CB Phosphatase,Protein Phosphatase 2, Catalytic Subunit,Protein Phosphatase 2, Catalytic Subunit, alpha Isoform,Protein Phosphatase 2, Catalytic Subunit, beta Isoform,Protein Phosphatase 2, Regulatory Subunit,Protein Phosphatase 2, Regulatory Subunit A, alpha Isoform,Protein Phosphatase 2, Regulatory Subunit A, beta Isoform,Protein Phosphatase 2, Regulatory Subunit B, alpha Isoform,Protein Phosphatase 2, Regulatory Subunit B, beta Isoform,Protein Phosphatase 2, Regulatory Subunit B, delta Isoform,Protein Phosphatase 2, Regulatory Subunit B, gamma Isoform,Protein Phosphatase 2A, Catalytic Subunit, alpha Isoform,Protein Phosphatase 2A, Catalytic Subunit, beta Isoform,Protein Phosphatase 2A, Regulatory Subunit A , alpha Isoform,Protein Phosphatase 2A, Regulatory Subunit A, beta Isoform,Protein Phosphatase 2A, Regulatory Subunit B, alpha Isoform,Protein Phosphatase 2A, Regulatory Subunit B, beta Isoform,Protein Phosphatase 2A, Regulatory Subunit B, delta Isoform,Protein Phosphatase 2A, Regulatory Subunit B, gamma Isoform,Protein Phosphatase-2A,Serine Threonine Protein Phosphatase 2A Catalytic Subunit beta Isoform,Serine-Threonine-Protein Phosphatase 2A Catalytic Subunit alpha Isoform,Phosphatase, PPP2CA,Phosphatase, PPP2CB,Protein Phosphatase 2A,Serine Threonine Protein Phosphatase 2A Catalytic Subunit alpha Isoform
D055785 Gene Knockdown Techniques The artificial induction of GENE SILENCING by the use of RNA INTERFERENCE to reduce the expression of a specific gene. It includes the use of DOUBLE-STRANDED RNA, such as SMALL INTERFERING RNA and RNA containing HAIRPIN LOOP SEQUENCE, and ANTI-SENSE OLIGONUCLEOTIDES. Gene Knock Down Techniques,Gene Knock Down,Gene Knock-Down,Gene Knock-Down Techniques,Gene Knockdown,Gene Knock Downs,Gene Knock-Down Technique,Gene Knock-Downs,Gene Knockdown Technique,Gene Knockdowns,Knock Down, Gene,Knock Downs, Gene,Knock-Down Technique, Gene,Knock-Down Techniques, Gene,Knock-Down, Gene,Knock-Downs, Gene,Knockdown Technique, Gene,Knockdown Techniques, Gene,Knockdown, Gene,Knockdowns, Gene,Technique, Gene Knock-Down,Technique, Gene Knockdown,Techniques, Gene Knock-Down,Techniques, Gene Knockdown
D029681 Arabidopsis Proteins Proteins that originate from plants species belonging to the genus ARABIDOPSIS. The most intensely studied species of Arabidopsis, Arabidopsis thaliana, is commonly used in laboratory experiments. Arabidopsis thaliana Proteins,Thale Cress Proteins,Proteins, Arabidopsis thaliana,thaliana Proteins, Arabidopsis
D037282 Calreticulin A multifunctional protein that is found primarily within membrane-bound organelles. In the ENDOPLASMIC RETICULUM it binds to specific N-linked oligosaccharides found on newly-synthesized proteins and functions as a MOLECULAR CHAPERONE that may play a role in PROTEIN FOLDING or retention and degradation of misfolded proteins. In addition calreticulin is a major storage form for CALCIUM and functions as a calcium-signaling molecule that can regulate intracellular calcium HOMEOSTASIS. 55-kDa High-Affinity Calcium Binding Protein,CAB-63,CBP3 (Liver),Calcium-Binding Protein-3,Calregulin,ERp60,HACBP,cC1qR Protein,55 kDa High Affinity Calcium Binding Protein,Calcium Binding Protein 3

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