title: Important roles of drought- and cold-inducible genes for galactinol synthase in stress tolerance in Arabidopsis thaliana.
abstract: Raffinose family oligosaccharides (RFO) accumulating during seed development are thought to play a role in the desiccation tolerance of seeds. However, the functions of RFO in desiccation tolerance have not been elucidated. Here we examine the functions of RFO in Arabidopsis thaliana plants under drought- and cold-stress conditions, based on the analyses of function and expression of genes involved in RFO biosynthesis. Sugar analysis showed that drought-, high salinity- and cold-treated Arabidopsis plants accumulate a large amount of raffinose and galactinol, but not stachyose. Raffinose and galactinol were not detected in unstressed plants. This suggests that raffinose and galactinol are involved in tolerance to drought, high salinity and cold stresses. Galactinol synthase (GolS) catalyses the first step in the biosynthesis of RFO from UDP-galactose. We identified three stress-responsive GolS genes (AtGolS1, 2 and 3) among seven Arabidopsis GolS genes. AtGolS1 and 2 were induced by drought and high-salinity stresses, but not by cold stress. By contrast, AtGolS3 was induced by cold stress but not by drought or salt stress. All the GST fusion proteins of GST-AtGolS1, 2 and 3 expressed in Escherichia coli had galactinol synthase activities. Overexpression of AtGolS2 in transgenic Arabidopsis caused an increase in endogenous galactinol and raffinose, and showed reduced transpiration from leaves to improve drought tolerance. These results show that stress-inducible galactinol synthase plays a key role in the accumulation of galactinol and raffinose under abiotic stress conditions, and that galactinol and raffinose may function as osmoprotectants in drought-stress tolerance of plants.
authors.affiliation: Laboratory of Plant Molecular Biology, RIKEN Tsukuba Institute, 3-1-1 Koyadai, Tsukuba, Ibaraki 305-0074, Japan.
authors.forename: Teruaki
authors.initials: T
authors.lastname: Taji
authors.forename: Chieko
authors.initials: C
authors.lastname: Ohsumi
authors.forename: Satoshi
authors.initials: S
authors.lastname: Iuchi
authors.forename: Motoaki
authors.initials: M
authors.lastname: Seki
authors.forename: Mie
authors.initials: M
authors.lastname: Kasuga
authors.forename: Masatomo
authors.initials: M
authors.lastname: Kobayashi
authors.forename: Kazuko
authors.initials: K
authors.lastname: Yamaguchi-Shinozaki
authors.forename: Kazuo
authors.initials: K
authors.lastname: Shinozaki
mesh_terms: D000064:Acclimatization / Q000235:genetics* / Q000502:physiology; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins; D002240:Carbohydrate Sequence; D003080:Cold Temperature; D004187:Disaccharides / Q000737:chemistry / Q000378:metabolism; D004190:Disasters; D004926:Escherichia coli / Q000235:genetics; D005700:Galactosyltransferases / Q000235:genetics* / Q000378:metabolism; D015870:Gene Expression; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010802:Phylogeny; D018526:Plant Transpiration / Q000235:genetics / Q000502:physiology; D030821:Plants, Genetically Modified; D011887:Raffinose / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D012492:Salts; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D017386:Sequence Homology, Amino Acid; D012987:Soil / Q000032:analysis; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014867:Water / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C114578:DREB1A protein, Arabidopsis; D004187:Disaccharides; D012492:Salts; D012987:Soil; D014157:Transcription Factors; D014867:Water; C013536:6 beta-galactinol; D005700:Galactosyltransferases; C096645:inositol 1-alpha-galactosyltransferase; D011887:Raffinose