title: An ER-localized form of PV72, a seed-specific vacuolar sorting receptor, interferes the transport of an NPIR-containing proteinase in Arabidopsis leaves.
abstract: Putative vacuolar sorting receptors that bind to the vacuolar targeting signals have been found in various plants; pumpkin PV72, pea BP-80 and Arabidopsis AtELP. PV72 is a seed-specific receptor that is predicted to sort seed storage proteins to protein storage vacuoles. Analysis by surface plasmon resonance showed that the lumenal domain of PV72 bound to an NPIR (a typical vacuolar targeting signal)-containing peptide of the precursor of a cysteine proteinase, AtALEU, in the presence of Ca(2+) (K(D) = 0.1 micro M). To elucidate the receptor-dependent transport of vacuolar proteins in plant cells, we produced transgenic Arabidopsis plants that expressed a fusion protein (PV72-HDEL) composed of the lumenal domain of PV72 and an endoplasmic reticulum (ER)-retention signal, HDEL. The expression of PV72-HDEL induced the accumulation of the AtALEU precursor. The accumulation level of the AtALEU precursor was dependent on that of PV72-HDEL. In contrast, it did not induce the accumulation of a precursor of another cysteine proteinase, RD21, which contains no NPIR. Detailed subcellular localization revealed that both the AtALEU precursor and PV72-HDEL accumulated in the ER fraction. We found that most of the AtALEU precursor molecules formed a complex with PV72-HDEL. The AtALEU precursor might be trapped by PV72-HDEL in the ER and not transported to the vacuoles. This in-planta analysis supports the hypothesis that an Arabidopsis homolog of PV72 functions as a sorting receptor for the NPIR-containing proteinase. The overall results suggest that vacuolar sorting receptors for the protein storage vacuoles and the lytic vacuoles share the similar recognition mechanism for a vacuolar targeting signal.
authors.affiliation: Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan.
authors.forename: Etsuko
authors.initials: E
authors.lastname: Watanabe
authors.forename: Tomoo
authors.initials: T
authors.lastname: Shimada
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamura
authors.forename: Ryo
authors.initials: R
authors.lastname: Matsushima
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Koumoto
authors.forename: Mikio
authors.initials: M
authors.lastname: Nishimura
authors.forename: Ikuko
authors.initials: I
authors.lastname: Hara-Nishimura
mesh_terms: D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D010450:Endopeptidases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000235:genetics; D010455:Peptides / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals / Q000235:genetics*; D021381:Protein Transport / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D012639:Seeds / Q000201:enzymology / Q000235:genetics; D014617:Vacuoles / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; C111597:PAC vesicle 72-kDa protein, Cucurbita; D010455:Peptides; D010940:Plant Proteins; D021382:Protein Sorting Signals; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; C046726:aleurain