title: Knock-down of protein phosphatase 2A subunit B'γ promotes phosphorylation of CALRETICULIN 1 in Arabidopsis thaliana.
abstract: 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.
authors: Department of Biochemistry and Food Chemistry, University of Turku, Turku, Finland.
authors: Andrea
authors: A
authors: Trotta
authors: Grzegorz
authors: G
authors: Konert
authors: Moona
authors: M
authors: Rahikainen
authors: Eva-Mari
authors: EM
authors: Aro
authors: Saijaliisa
authors: S
authors: Kangasjärvi
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D037282:Calreticulin / Q000235:genetics / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D055785:Gene Knockdown Techniques; D010766:Phosphorylation; D054648:Protein Phosphatase 2 / Q000235:genetics* / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D029681:Arabidopsis Proteins; D037282:Calreticulin; D054648:Protein Phosphatase 2