title: A dual role of tobacco hexokinase 1 in primary metabolism and sugar sensing.
abstract: Hexokinase (HXK) is present in all virtually living organisms and is central to carbohydrate metabolism catalysing the ATP-dependent phosphorylation of hexoses. In plants, HXKs are supposed to act as sugar sensors and/or to interact with other enzymes directly supplying metabolic pathways such as glycolysis, the nucleotide phosphate monosaccharide (NDP-glucose) pathway and the pentose phosphate pathway. We identified nine members of the tobacco HXK gene family and observed that among RNAi lines of these nine NtHXKs, only RNAi lines of NtHXK1 showed an altered phenotype, namely stunted growth and leaf chlorosis. NtHXK1 was also the isoform with highest relative expression levels among all NtHXKs. GFP-tagging and immunolocalization indicated that NtHXK1 is associated with mitochondrial membranes. Overexpression of NtHXK1 resulted in elevated glucose phosphorylation activity in leaf extracts or chloroplasts. Moreover, NtHXK1 was able to complement the glucose-insensitive Arabidopsis mutant gin2-1 suggesting that NtHXK1 can take over glucose sensing functions. RNAi lines of NtHXK1 showed severely damaged leaf and chloroplast structure, coinciding with an excess accumulation of starch. We conclude that NtHXK1 is not only essential for maintaining glycolytic activity during respiration but also for regulating starch turnover, especially during the night.
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research IPK, Corrensstrasse 3, 06466 Gatersleben, Germany.
authors.forename: Young-Min
authors.initials: YM
authors.lastname: Kim
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Nicolas
authors.initials: N
authors.lastname: Heinzel
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Jens-Otto
authors.initials: JO
authors.lastname: Giese
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Julia
authors.initials: J
authors.lastname: Koeber
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Melzer
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Twan
authors.initials: T
authors.lastname: Rutten
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Nicolaus
authors.initials: N
authors.lastname: Von Wirén
authors.affiliation: Department of Biology, Friedrich-Alexander-Universität, Staudtstrasse 5, 91058, Erlangen, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Sonnewald
authors.affiliation: Molecular Plant Nutrition, Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, 06466, Gatersleben, Germany.
authors.forename: Mohammad-Reza
authors.initials: MR
authors.lastname: Hajirezaei
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D050260:Carbohydrate Metabolism; D006593:Hexokinase / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D005810:Multigene Family; D018515:Plant Leaves / Q000201:enzymology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D030821:Plants, Genetically Modified / Q000378:metabolism; D034622:RNA Interference; D014026:Nicotiana / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism
chemical_list: D010940:Plant Proteins; D006593:Hexokinase
keywords: Arabidopsis thaliana; Nicotiana tabacum; gin2-1; hexokinase; starch metabolism