title: Floridoside and isofloridoside are synthesized by trehalose 6-phosphate synthase-like enzymes in the red alga Galdieria sulphuraria.
abstract: Compatible solutes are small molecules that are involved in acclimation to various abiotic stresses, especially high salinity. Among the red algae, the main photosynthetic products floridoside and isofloridoside (galactosylglycerols) are known also to contribute to the osmotic acclimation of cells. However, the genes encoding (iso)floridoside biosynthetic enzymes are still unknown. To identify candidate genes, we examined the genome of the floridoside- and isofloridoside-accumulating extremophilic red alga Galdieria sulphuraria belonging to the Cyanidiales. We hypothesized that two candidate genes, Gasu_10960 and Gasu_26940, code for enzymes involved in floridoside and isofloridoside biosynthesis. These proteins comprise a sugar phosphate synthase and a sugar phosphate phosphatase domain. To verify their biochemical activity, both genes were in vitro translated into the entire proteins. The protein translation mixture containing Gasu_10960 synthesized small amounts of isofloridoside, whereas the Gasu_26940 translation mix also produced small amounts of floridoside. Moreover, the expression of Gasu_10960 in a salt-sensitive mutant of the cyanobacterium Synechocystis sp. PCC 6803 resulted in increased salt tolerance as a consequence of the presence of isofloridoside in the complemented cells. Thus, our experiments suggest that the Gasu_26940 and Gasu_10960 genes of G. sulphuraria encode the enzymatically active floridoside and isofloridoside phosphate synthase/phosphatase fusion proteins, respectively, crucial for salt acclimation.
authors.affiliation: Institut für Biowissenschaften, Abteilung Pflanzenphysiologie, Universität Rostock, Albert-Einstein-Straße 3, D-18059, Rostock, Germany.
authors.forename: Nadin
authors.initials: N
authors.lastname: Pade
authors.affiliation: Center of Excellence on Plant Sciences (CEPLAS), Institute of Plant Biochemistry, Heinrich-Heine University, Universitätsstraße 1, D-40225, Düsseldorf, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Linka
authors.affiliation: Institut für Chemie, Universität Rostock, Albert-Einstein-Straße 3, D-18059, Rostock, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Ruth
authors.affiliation: Center of Excellence on Plant Sciences (CEPLAS), Institute of Plant Biochemistry, Heinrich-Heine University, Universitätsstraße 1, D-40225, Düsseldorf, Germany.
authors.forename: Andreas P M
authors.initials: APM
authors.lastname: Weber
authors.affiliation: Institut für Biowissenschaften, Abteilung Pflanzenphysiologie, Universität Rostock, Albert-Einstein-Straße 3, D-18059, Rostock, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Hagemann
mesh_terms: D020418:Algal Proteins / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D057075:Enzyme Assays; D005697:Galactosides / Q000096:biosynthesis*; D008401:Gas Chromatography-Mass Spectrometry; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D005816:Genetic Complementation Test; D005964:Glucosyltransferases / Q000378:metabolism*; D005990:Glycerol / Q000031:analogs & derivatives* / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010802:Phylogeny; D000461:Rhodophyta / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D012965:Sodium Chloride / Q000494:pharmacology
chemical_list: C457479:2-galactopyranosylglycerol; D020418:Algal Proteins; D005697:Galactosides; D012965:Sodium Chloride; C025100:isofloridoside; D005964:Glucosyltransferases; C023180:trehalose-6-phosphate synthase; D005990:Glycerol
keywords: Galdieria sulphuraria; compatible solute; galactosylglycerol; red algae; salt stress; sugar phosphate phosphatase; sugar phosphate synthase