A comprehensive analysis of the NADP-malic enzyme gene family of Arabidopsis

GERRARD WHEELER, M. C.; TRONCONI, M. A.; DRINCOVICH, M. F.; ANDREO, C. S.; FLÜGGE, U. I.; MAURINO, V. G.

PLANT PHYSIOLOGY.

American Society of Plant Physiologists

Año: 2005 vol. 139 p. 39 - 51

0032-0889

The Arabidopsis thaliana genome contains four genes encoding putative NADP-malic enzymes (AtNADP-ME1-4). 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: group I and group II comprising cytosolic and plastidic isoforms from dicots, respectively; group III containing isoforms from monocots and group IV constituted by 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 catalytically efficiency for NADP and malate, respectively. NADP-ME4 exists in an equilibrium of active dimers and tetramers, while the cytosolic counterparts are present as hexamers or octamers. Characterization of T-DNA insertion mutants and promoter activities studies indicate that NADP-ME2 is responsible for the major part of NADP-ME activity in mature tissues of Arabidopsis. Whereas NADP-ME2 and -4 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.