title: Functional analysis of an Arabidopsis thaliana abiotic stress-inducible facilitated diffusion transporter for monosaccharides.
abstract: Sugars play indispensable roles in biological reactions and are distributed into various tissues or organelles via transporters in plants. Under abiotic stress conditions, plants accumulate sugars as a means to increase stress tolerance. Here, we report an abiotic stress-inducible transporter for monosaccharides from Arabidopsis thaliana that is termed ESL1 (ERD six-like 1). Expression of ESL1 was induced under drought and high salinity conditions and with exogenous application of abscisic acid. Promoter analyses using beta-glucuronidase and green fluorescent protein reporters revealed that ESL1 is mainly expressed in pericycle and xylem parenchyma cells. The fluorescence of ESL1-green fluorescent protein-fused protein was detected at tonoplast in transgenic Arabidopsis plants and tobacco BY-2 cells. Furthermore, alanine-scanning mutagenesis revealed that an N-terminal LXXXLL motif in ESL1 was essential for its localization at the tonoplast. Transgenic BY-2 cells expressing mutated ESL1, which was localized at the plasma membrane, showed an uptake ability for monosaccharides. Moreover, the value of K(m) for glucose uptake activity of mutated ESL1 in the transgenic BY-2 cells was extraordinarily high, and the transport activity was independent from a proton gradient. These results indicate that ESL1 is a low affinity facilitated diffusion transporter. Finally, we detected that vacuolar invertase activity was increased under abiotic stress conditions, and the expression patterns of vacuolar invertase genes were similar to that of ESL1. Under abiotic stress conditions, ESL1 might function coordinately with the vacuolar invertase to regulate osmotic pressure by affecting the accumulation of sugar in plant cells.
authors.affiliation: Laboratory of Plant Molecular Physiology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Tokyo 113-8657, Japan.
authors.forename: Kohji
authors.initials: K
authors.lastname: Yamada
authors.forename: Yuriko
authors.initials: Y
authors.lastname: Osakabe
authors.forename: Junya
authors.initials: J
authors.lastname: Mizoi
authors.forename: Kazuo
authors.initials: K
authors.lastname: Nakashima
authors.forename: Yasunari
authors.initials: Y
authors.lastname: Fujita
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
authors.forename: Kazuko
authors.initials: K
authors.lastname: Yamaguchi-Shinozaki
mesh_terms: D020816:Amino Acid Motifs / Q000502:physiology; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000096:biosynthesis* / Q000235:genetics; D001692:Biological Transport / Q000502:physiology; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D015967:Gene Expression Regulation, Viral / Q000502:physiology*; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D009997:Osmotic Pressure / Q000502:physiology; D013312:Stress, Physiological / Q000502:physiology*; D052584:Xylem / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D009004:Monosaccharide Transport Proteins