title: Expression of novel cytosolic malate dehydrogenases (cMDH) in Lupinus angustifolius nodules during phosphorus starvation.
abstract: During P deficiency, the increased activity of malate dehydrogenase (MDH, EC 1.1.1.37) can lead to malate accumulation. Cytosolic- and nodule-enhanced MDH (cMDH and neMDH, respectively) are known isoforms, which contribute to MDH activity in root nodules. The aim of this study was to investigate the role of the cMDH isoforms in nodule malate supply under P deficiency. Nodulated lupins (Lupinus angustifolius var. Tanjil) were hydroponically grown at adequate P (+P) or low P (-P). Total P concentration in nodules decreased under P deficiency, which coincided with an increase in total MDH activity. A consequence of higher MDH activity was the enhanced accumulation of malate derived from dark CO2 fixation via PEPC and not from pyruvate. Although no measurable neMDH presence could be detected via PCR, gene-specific primers detected two 1kb amplicons of cMDH, designated LangMDH1 (corresponding to +P, HQ690186) and LangMDH2 (corresponding to -P, HQ690187), respectively. Sequencing analyses of these cMDH amplicons showed them to be 96% identical on an amino acid level. There was a high degree of diversification between proteins detected in this study and other known MDH proteins, particularly those from other leguminous plants. Enhanced malate synthesis in P-deficient nodules was achieved via increased anaplerotic CO2 fixation and subsequent higher MDH activities. Novel isoforms of cytosolic MDH may be involved, as shown by gene expression of specific genes under P deficiency.
authors.affiliation: Department of Agronomy, Faculty of Agriculture, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Electronic address: mrl@sun.ac.za.
authors.forename: Marcellous
authors.initials: M
authors.lastname: Le Roux
authors.affiliation: Department of Botany and Zoology, Faculty of Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Electronic address: ephiri@sun.ac.za.
authors.forename: Ethel
authors.initials: E
authors.lastname: Phiri
authors.affiliation: Department of Microbiology, Faculty of Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Electronic address: wesaal@sun.ac.za.
authors.forename: Wesaal
authors.initials: W
authors.lastname: Khan
authors.affiliation: Department of Bioengineering Kafkas University, 36100 Kars, Turkey. Electronic address: msakiroglu@gmail.com.
authors.forename: Muhammet
authors.initials: M
authors.lastname: Sakiroğlu
authors.affiliation: Department of Botany and Zoology, Faculty of Science, University of Stellenbosch, Private Bag X1, Matieland 7602, South Africa. Electronic address: alexvalentine@mac.com.
authors.forename: Alex
authors.initials: A
authors.lastname: Valentine
authors.affiliation: Department of Biomedical Sciences, Faculty of Health and Wellness Science, Cape Peninsula University of Technology, P.O. Box 1906, Bellville 7535, South Africa. Electronic address: khans@cput.ac.za.
authors.forename: Sehaam
authors.initials: S
authors.lastname: Khan
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D003600:Cytosol / Q000201:enzymology; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D018527:Hydroponics; D007527:Isoenzymes; D031297:Lupinus / Q000201:enzymology* / Q000235:genetics; D008291:Malate Dehydrogenase / Q000235:genetics* / Q000378:metabolism; D008293:Malates / Q000378:metabolism*; D008969:Molecular Sequence Data; D009586:Nitrogen Fixation; D010758:Phosphorus / Q000172:deficiency* / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics; D053204:Root Nodules, Plant / Q000201:enzymology / Q000235:genetics; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018076:DNA, Complementary; D018744:DNA, Plant; D007527:Isoenzymes; D008293:Malates; D010940:Plant Proteins; D018749:RNA, Plant; D010758:Phosphorus; C030298:malic acid; D008291:Malate Dehydrogenase
keywords: Cytosolic; Isoforms; Malate dehydrogenase; Nodules; P deficiency