title: A plastid-localized glycogen synthase kinase 3 modulates stress tolerance and carbohydrate metabolism.
abstract: Glycogen synthase kinase 3 (GSK-3) was originally identified as a regulator of glycogen synthesis in mammals. Like starch in plants, glycogen is a polymer of glucose, and serves as an energy and carbon store. Starch is the main carbohydrate store in plants. Regulation of starch metabolism, in particular in response to environmental cues, is of primary importance for carbon and energy flow in plants but is still obscure. Here, we provide evidence that MsK4, a novel Medicago sativa GSK-3-like kinase, connects stress signalling with carbon metabolism. MsK4 was found to be a plastid-localized protein kinase that is associated with starch granules. High-salt stress rapidly induced the in vivo kinase activity of MsK4. Metabolic profiling of MsK4 over-expressor lines revealed changes in sugar metabolism, including increased amounts of maltose, the main degradation product of starch in leaves. Plants over-expressing MsK4 showed improved tolerance to salt stress. Moreover, under high-salinity conditions, MsK4-over-expressing plants accumulated significantly more starch and showed modified carbohydrate content compared with wild-type plants. Overall, these data indicate that MsK4 is an important regulator that adjusts carbohydrate metabolism to environmental stress.
authors.affiliation: Gregor Mendel Institute of Molecular Plant Biology, Austrian Academy of Sciences, Vienna Biocenter, A-1030 Vienna, Austria.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kempa
authors.forename: Wilfried
authors.initials: W
authors.lastname: Rozhon
authors.forename: Jozef
authors.initials: J
authors.lastname: Samaj
authors.forename: Alexander
authors.initials: A
authors.lastname: Erban
authors.forename: Frantisek
authors.initials: F
authors.lastname: Baluska
authors.forename: Thomas
authors.initials: T
authors.lastname: Becker
authors.forename: Joachim
authors.initials: J
authors.lastname: Haselmayer
authors.forename: Enrico
authors.initials: E
authors.lastname: Schleiff
authors.forename: Joachim
authors.initials: J
authors.lastname: Kopka
authors.forename: Heribert
authors.initials: H
authors.lastname: Hirt
authors.forename: Claudia
authors.initials: C
authors.lastname: Jonak
mesh_terms: D050260:Carbohydrate Metabolism; D018506:Gene Expression Regulation, Plant / Q000187:drug effects; D038362:Glycogen Synthase Kinase 3 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism* / Q000502:physiology*; D053858:Metabolic Networks and Pathways; D018087:Plastids / Q000201:enzymology*; D012492:Salts / Q000494:pharmacology; D015398:Signal Transduction / Q000502:physiology; D013213:Starch / Q000378:metabolism
chemical_list: D012492:Salts; D013213:Starch; D038362:Glycogen Synthase Kinase 3