CONICET | Buscador de Institutos y Recursos Humanos

The Arabidopsis thaliana genome contains two genes encoding the mitochondrial NAD-malic enzyme (NAD-ME), nad-me1 and nad-me2. The encoded proteins, NAD-ME1 and -2, assemble as active homodimers; however, they can also associate to form a heterodimeric enzyme (NAD-MEH) in vivo and in vitro. Although nad-me1 and -2 genes show a similar pattern of expression in mature organs of Arabidopsis, NAD-ME1 and -2 accumulate at different levels in the separate components of floral organ. Such changes in the protein ratio can influence the formation of the three different NAD-ME native associations. Recombinant NAD-ME1, -2 and -H isoforms differ in its interaction with the substrates, L-malate and NAD, and are differentially regulated by intermediates of glycolysis or Krebs cycle, which suggest a specificity of function of each entity in the C4-organic acid metabolism. Another evidence that support this hypothesis arise from the specific expression shown by nad-me genes in plants under different nutritional and ambient conditions. In addition, the analysis of mutant plants lacking of one or both nad-me functional genes revealed in each case a metabolic perturbation that was gene mutated-dependent. On another hand, the metabolic status of the double mutant plant, which not presents detectable NAD-ME activity, was different depending on the light/dark period. In this regard, during the day double mutant exhibit little changes with a higher level of some sugars, while in nocturne period the perturbation is more accentuated with contend of several amino acid enhanced compared to wild type plant. Also, NAD-ME activity in leaves is higher in the dark, because a mayor expression of nad-me genes. These results reveal a major role of mitochondrial NAD-ME in the coordination of the carbon and nitrogen metabolisms during night periods in Arabidopsis.