title: Towards understanding peroxisomal phosphoregulation in Arabidopsis thaliana.
abstract: This work identifies new protein phosphatases and phosphatase-related proteins targeting peroxisomes, and raises the question of a novel protein import pathway from ER to peroxisomes involving peroxisomal targeting signal type 1 (PTS1) Plant peroxisomes are essential for several processes, for example lipid metabolism, free radical detoxification, development, and stress-related functions. Although research on peroxisomes has been intensified, reversible phosphorylation as a control mechanism in peroxisomes is barely studied. Therefore, it is crucial to identify all peroxisomal proteins involved in phosphoregulation. We here started with protein phosphatases, and searched the Arabidopsis thaliana genome for phosphatase-related proteins with putative peroxisomal targeting signals (PTS). Five potential peroxisomal candidates were detected, from which four were confirmed to target peroxisomes or have a functional PTS. The highly conserved Ser-Ser-Met> was validated for two protein phosphatase 2C (PP2C) family members (POL like phosphatases, PLL2 and PLL3) as a functional peroxisomal targeting signal type 1 (PTS1). Full-length PLL2 and PLL3 fused with a reporter protein targeted peroxisomes in two plant expression systems. A putative protein phosphatase, purple acid phosphatase 7 (PAP7), was found to be dually targeted to ER and peroxisomes and experiments indicated a possible trafficking to peroxisomes via the ER depending on peroxisomal PTS1. In addition, a protein phosphatase 2A regulator (TIP41) was validated to harbor a functional PTS1 (Ser-Lys-Val>), but the full-length protein targeted cytosol and nucleus. Reverse genetics indicated a role for TIP41 in senescence signaling. Mass spectrometry of whole seedlings and isolated peroxisomes was employed, and identified new putative phosphorylated peroxisomal proteins. Previously, only one protein phosphatase, belonging to the phospho-protein phosphatase (PPP) family, was identified as a peroxisomal protein. The present work implies that members of two other main protein phosphatase families, i.e. PP2C and PAP, are also targeting peroxisomes.
authors.affiliation: Faculty of Science and Technology, Centre for Organelle Research, University of Stavanger, N-4036, Stavanger, Norway. amr.kataya@uis.no.
authors.forename: Amr R A
authors.initials: AR
authors.lastname: Kataya
authors.affiliation: Faculty of Science and Technology, Centre for Organelle Research, University of Stavanger, N-4036, Stavanger, Norway.
authors.forename: Edit
authors.initials: E
authors.lastname: Schei
authors.affiliation: Faculty of Science and Technology, Centre for Organelle Research, University of Stavanger, N-4036, Stavanger, Norway. Cathrine.lillo@uis.no.
authors.forename: Cathrine
authors.initials: C
authors.lastname: Lillo
mesh_terms: D000135:Acid Phosphatase / Q000235:genetics / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant / Q000235:genetics*; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D020675:Peroxisomes / Q000201:enzymology*; D010766:Phosphorylation; D000071636:Protein Phosphatase 2C / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals / Q000235:genetics; D021381:Protein Transport; D036226:Seedlings / Q000201:enzymology / Q000235:genetics
chemical_list: D029681:Arabidopsis Proteins; D006023:Glycoproteins; D021382:Protein Sorting Signals; C091137:purple acid phosphatase; D000071636:Protein Phosphatase 2C; D000135:Acid Phosphatase
keywords: POL like phosphatases (PLL2, PLL3); Peroxisome targeting signal type 1 (PTS1); Peroxisomes; Protein phosphatase 2C (PP2C); Protein phosphatases; Purple acid phosphatase 7; Signaling; β-Oxidation