title: Loss of Mitochondrial Malate Dehydrogenase Activity Alters Seed Metabolism Impairing Seed Maturation and Post-Germination Growth in Arabidopsis.
abstract: Mitochondrial malate dehydrogenase (mMDH; EC 1.1.1.37) has multiple roles; the most commonly described is its catalysis of the interconversion of malate and oxaloacetate in the tricarboxylic acid cycle. The roles of mMDH in Arabidopsis (Arabidopsis thaliana) seed development and germination were investigated in mMDH1 and mMDH2 double knockout plants. A significant proportion of mmdh1mmdh2 seeds were nonviable and developed only to torpedo-shaped embryos, indicative of arrested seed embryo growth during embryogenesis. The viable mmdh1mmdh2 seeds had an impaired maturation process that led to slow germination rates as well as retarded post-germination growth, shorter root length, and decreased root biomass. During seed development, mmdh1mmdh2 showed a paler green phenotype than the wild type and exhibited deficiencies in reserve accumulation and reduced final seed biomass. The respiration rate of mmdh1mmdh2 seeds was significantly elevated throughout their maturation, consistent with the previously reported higher respiration rate in mmdh1mmdh2 leaves. Mutant seeds showed a consistently higher content of free amino acids (branched-chain amino acids, alanine, serine, glycine, proline, and threonine), differences in sugar and sugar phosphate levels, and lower content of 2-oxoglutarate. Seed-aging assays showed that quiescent mmdh1mmdh2 seeds lost viability more than 3 times faster than wild-type seeds. Together, these data show the important role of mMDH in the earliest phases of the life cycle of Arabidopsis.
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
authors.forename: Yun Shin
authors.identifier: 0000-0003-2866-3693
authors.initials: YS
authors.lastname: Sew
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
authors.forename: Elke
authors.identifier: 0000-0002-1879-9012
authors.initials: E
authors.lastname: Ströher
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia 6009, Australia.
authors.forename: Ricarda
authors.identifier: 0000-0002-0906-8525
authors.initials: R
authors.lastname: Fenske
authors.affiliation: Australian Research Council Centre of Excellence in Plant Energy Biology, University of Western Australia, Crawley, Western Australia 6009, Australia harvey.millar@uwa.edu.au.
authors.forename: A Harvey
authors.identifier: 0000-0001-9679-1473
authors.initials: AH
authors.lastname: Millar
mesh_terms: D000596:Amino Acids / Q000378:metabolism; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D055786:Gene Knockout Techniques; D018525:Germination; D007656:Ketoglutaric Acids / Q000378:metabolism; D008291:Malate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000502:physiology
chemical_list: D000596:Amino Acids; D029681:Arabidopsis Proteins; D007656:Ketoglutaric Acids; D008291:Malate Dehydrogenase