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A Comprehensive Analysis of the NADP-Malic Enzyme Gene Family of Arabidopsis

Wheeler, Mariel C. Gerrard, Tronconi, Marcos A., Drincovich, María F., Andreo, Carlos S., Flůgge, Ulf-Ingo, Maurino, Verónica G.
Plant physiology 2005 v.139 no.1 pp. 39-51
Arabidopsis thaliana, plant proteins, malic enzyme, isozymes, complementary DNA, tissue distribution, plastids, recombinant fusion proteins, gene expression, embryo (plant), embryogenesis, seed germination, transfer DNA, insertional mutagenesis, protein structure, enzyme activity, plant biochemistry, plant genetics, nucleotide sequences
The Arabidopsis (Arabidopsis thaliana) genome contains four genes encoding putative NADP-malic enzymes (MEs; AtNADP-ME1-ME4). NADP-ME4 is localized to plastids, whereas the other three isoforms do not possess any predicted organellar targeting sequence and are therefore expected to be cytosolic. The plant NADP-MEs can be classified into four groups: groups I and II comprising cytosolic and plastidic isoforms from dicots, respectively; group III containing isoforms from monocots; and group IV composed of both monocots and dicots, including AtNADP-ME1. AtNADP-MEs contained all conserved motifs common to plant NADP-MEs and the recombinant isozymes showed different kinetic and structural properties. NADP-ME2 exhibits the highest specific activity, while NADP-ME3 and NADP-ME4 present the highest catalytic efficiency for NADP and malate, respectively. NADP-ME4 exists in equilibrium of active dimers and tetramers, while the cytosolic counterparts are present as hexamers or octamers. Characterization of T-DNA insertion mutant and promoter activity studies indicates that NADP-ME2 is responsible for the major part of NADP-ME activity in mature tissues of Arabidopsis. Whereas NADP-ME2 and -ME4 are constitutively expressed, the expression of NADP-ME1 and NADP-ME3 is restricted by both developmental and cell-specific signals. These isoforms may play specific roles at particular developmental stages of the plant rather than being involved in primary metabolism.