title: Salt stress induces internalization of plasma membrane aquaporin into the vacuole in Arabidopsis thaliana.
abstract: Salt stress is a major environmental stress for plants, causing hyperosmotic, ionic and drought-like stresses. Plasma membrane intrinsic protein 2;1 (PIP2;1), which forms a water channel that regulates water flux thorough the plasma membrane (PM), is constitutively trafficked between the PM and the trans-Golgi network (TGN) in Arabidopsis thaliana. Salt stress is known to relocalize PIP2;1 to intracellular compartments, probably to decrease the water permeability of the root. However, the destination of internalized PIP2;1 and the mechanism by which PIP2;1 is internalized remain unclear. Here, we examined the effects of salt stress and inhibitors of endocytosis on the intracellular localization of green fluorescent protein-fused PIP2;1 (GFP-PIP2;1) in Arabidopsis thaliana root epidermal cells. Salt stress decreased the fluorescence of GFP-PIP2;1 at the PM and increased it in the vacuolar lumen as shown by staining of the vacuolar membrane. The internalization of PIP2;1 was suppressed by an inhibitor of clathrin-mediated endocytosis and by inhibitors of two kinases that appear to have roles in salt stress, phosphatidylinositol 3-kinase (PI3K) and phosphatidylinositol 4-kinase (PI4K). Inhibiting PI4K suppressed the salt-induced endocytosis of GFP-PIP2;1 at the PM, whereas inhibiting PI3K suppressed the trafficking of GFP-PIP2;1 after its internalization. These results suggest that salt stress induces the internalization of PIP2;1 from the PM to the vacuolar lumen, and that these processes are dependent on clathrin, PI3K and PI4K.
authors.affiliation: Laboratory of Plant Molecular Genetics, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan.
authors.forename: Masamichi
authors.initials: M
authors.lastname: Ueda
authors.affiliation: Laboratory of Plant Molecular Genetics, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan; Japan Science and Technology Agency (JST), CREST, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan.
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Tsutsumi
authors.affiliation: Laboratory of Plant Molecular Genetics, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo, 113-8657, Japan; Japan Science and Technology Agency (JST), CREST, 4-1-8 Honcho Kawaguchi, Saitama, 332-0012, Japan. Electronic address: amfuji@mail.ecc.u-tokyo.ac.jp.
authors.forename: Masaru
authors.initials: M
authors.lastname: Fujimoto
mesh_terms: D020346:Aquaporins / Q000378:metabolism*; D017360:Arabidopsis / Q000187:drug effects* / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000378:metabolism*; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D012965:Sodium Chloride / Q000008:administration & dosage*; D014617:Vacuoles / Q000187:drug effects / Q000378:metabolism*
chemical_list: D020346:Aquaporins; D029681:Arabidopsis Proteins; C491680:plasma membrane intrinsic protein 2 Arabidopsis; D012965:Sodium Chloride
keywords: Aquaporin; Arabidopsis; Clathrin; Endocytosis; Salt stress