title: The role of arabinokinase in arabinose toxicity in plants.
abstract: Plant cell wall polymers are synthesized by glycosyltransferases using nucleotide sugars as substrates. Most UDP-sugars are synthesized from UDP-glucose via de novo pathways but salvage pathways work in parallel to recycle sugars, which have been released during cell wall polymer and glycoprotein turnover. Here we report on the cloning and biochemical analysis of two arabinokinases in Arabidopsis. Arabinokinase is a 100 kDa protein located in the cytosol with a putative N-terminal glycosyltransferase domain and a C-terminal sugar-1-kinase domain. This unique structure is highly conserved in the plant kingdom. Arabinokinase has a high affinity for l-arabinose, which is the only sugar substrate of this GHMP (galactose; homoserine; mevalonate; phosphomevalonate) kinase. Plants that were knocked-out for arabinokinase and the previously described ara1-1 mutant were characterized. The ARA1-1 mutant form of the enzyme carries a point mutation in an α-helix. The mutation is close to the substrate binding site and changes the Km value for arabinose from 80 μm in the wild type to 17 000 μm in ARA1-1. The previous arabinose toxicity explanation is challenged by knockout plants in arabinokinase that accumulate higher levels of arabinose but do not show signs of arabinose toxicity. Analysis of marker genes from sugar signalling pathways (SnRK1 and Tor) suggest that ara1-1 misinterprets its carbon energy status. Although glucose is present in ara1-1 similar to wild type levels, it constitutively changes gene expression as typically found in wild type plants only under starvation conditions. Furthermore, ara1-1 shows increased expression of marker genes for programmed cell death as found in other lesion mimic mutants.
authors.affiliation: Division of Plant Physiology, Department of Cell Biology, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria.|Division of Chemistry and Bioanalytics, Department of Molecular Biology, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria.
authors.forename: Robert
authors.initials: R
authors.lastname: Behmüller
authors.affiliation: Division of Plant Physiology, Department of Cell Biology, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria.
authors.forename: Eva
authors.initials: E
authors.lastname: Kavkova
authors.affiliation: Division of Plant Physiology, Department of Cell Biology, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Düh
authors.affiliation: Division of Chemistry and Bioanalytics, Department of Molecular Biology, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria.
authors.forename: Christian G
authors.initials: CG
authors.lastname: Huber
authors.affiliation: Division of Plant Physiology, Department of Cell Biology, University of Salzburg, Hellbrunner Straße 34, 5020, Salzburg, Austria. raimund.tenhaken@sbg.ac.at.
authors.forename: Raimund
authors.initials: R
authors.lastname: Tenhaken
mesh_terms: D019943:Amino Acid Substitution; D017360:Arabidopsis / Q000737:chemistry / Q000166:cytology / Q000201:enzymology* / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D001089:Arabinose / Q000633:toxicity*; D002473:Cell Wall / Q000737:chemistry / Q000378:metabolism; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D016254:Mutagenesis, Insertional; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins; D036226:Seedlings / Q000737:chemistry / Q000166:cytology / Q000201:enzymology / Q000235:genetics; D013403:Sugar Phosphates / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D011994:Recombinant Proteins; D013403:Sugar Phosphates; C104973:arabinose-1-phosphate; D001089:Arabinose; D016695:Glycosyltransferases; D017853:Phosphotransferases (Alcohol Group Acceptor); C111816:ARA1 protein, Arabidopsis; C000622193:ARA2 protein, Arabidopsis
keywords: Arabidopsis thaliana; GHMP kinase; UDP-sugar; arabinokinase; arabinose toxicity; arabinose-1-phosphate; salvage pathway; sugar phosphates; sugar sensing