title: Selective induction and subcellular distribution of ACONITASE 3 reveal the importance of cytosolic citrate metabolism during lipid mobilization in Arabidopsis.
abstract: Arabidopsis thaliana has three genes that encode distinct aconitases (ACO), but little is known about the function of each isoenzyme during plant development. In newly emerged seedlings of Arabidopsis, transcript and protein levels for ACO3 were selectively induced to yield more than 80% of total aconitase activity. Characterization of knockout mutants for each of the three ACOs suggests a major role for only ACO3 in citrate metabolism. The aco3 mutant showed delayed early seedling growth, altered assimilation of [14C]acetate feeding and elevated citrate levels, which were nearly 4-fold greater than in wild-type, aco1 or aco2. However, both ACO1 and ACO2 are active in seedlings as shown by inhibition of aco3 growth by the toxin monofluoroacetate, and altered [14C]acetate assimilation and metabolite levels in aco1 and aco2. Relative levels of fumarate and malate differed between aco2 and aco3, indicating metabolically isolated pools of these metabolites in seedlings. Our inability to enrich ACO protein through mitochondria isolation, and the reduced cytosolic ACO activity of the iron-sulfur centre assembly mutant atm3-1, indicated a cytosolic localization of ACO3 in 3-day-old seedlings. Subsequently, we determined that more than 90% of ACO3 was cytosolic. We conclude that ACO3 is cytosolic in young seedlings and functions in citrate catabolism consistent with the operation of the classic glyoxylate and not direct catabolism of citrate within mitochondria.
authors: *Institut National de la Recherche Agronomique/Université de Bordeaux, UMR 1332 Biologie du Fruit et Pathologie, 33882 Villenave d'Ornon, France.
authors: Mark A
authors: MA
authors: Hooks
authors: †School of Chemistry, Manchester Interdisciplinary Biocentre, University of Manchester, 131 Princess Street, Manchester M1 7ND, U.K.
authors: J William
authors: JW
authors: Allwood
authors: ‡John Innes Centre and University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7UH, U.K.
authors: Joanna K D
authors: JK
authors: Harrison
authors: §Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenburg 1, 14476 Golm, Germany.
authors: Joachim
authors: J
authors: Kopka
authors: §Max-Planck-Institut für Molekulare Pflanzenphysiologie, Am Mühlenburg 1, 14476 Golm, Germany.
authors: Alexander
authors: A
authors: Erban
authors: Royston
authors: R
authors: Goodacre
authors: ‡John Innes Centre and University of East Anglia, Norwich Research Park, Colney Lane, Norwich NR4 7UH, U.K.
authors: Janneke
authors: J
authors: Balk
mesh_terms: D000154:Aconitate Hydratase / Q000235:genetics / Q000378:metabolism*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D019343:Citric Acid / Q000378:metabolism*; D003600:Cytosol / Q000201:enzymology / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant; D006038:Glyoxylates / Q000378:metabolism; D008053:Lipid Mobilization; D021381:Protein Transport
chemical_list: D029681:Arabidopsis Proteins; D006038:Glyoxylates; D019343:Citric Acid; D000154:Aconitate Hydratase; C031150:glyoxylic acid