First insights into the biological role of the major NADP-malic enzyme of Arabidopsis thaliana

BADIA, M. B.; ARIAS, C. L.; TRONCONI, M. A.; MAURINO, V. G.; ANDREO, C. S.; DRINCOVICH, M. F.; GERRARD WHEELER, M. C.

Buenos Aires

Workshop; Fronteras en Biociencias; 2012

MINCyT-SOCIEDAD MAX PLANCK

NAD(P)-malic enzymes (NAD(P)-ME) catalyze the reversible oxidative decarboxylation of L-malate to pyruvate, CO2 and NAD(P)H. NAD(P)-ME are well known for their prominent role in C4 plants, although the biological function of non-photosynthetic isoforms remains elusive. In the C3 dicot species Arabidopsis thaliana, ME is present as a multigene family. The Arabidopsis genome encodes two NAD-ME and four NADP-ME isoforms, which differ in their cellular localization and expression pattern, and may participate in specific biological functions instead of representing functional redundancy. In this work, knock-out mutant and overexpressing lines in cytosolic NADP-ME2, the isoform that mostly contributes to the malic enzyme activity in all organs of the plant, are being analyzed in order to elucidate possible biological roles of this isozyme. These plants have a 14-fold decrease and an 8-fold increase, respectively, in total leaf NADP-ME activity relative to the wild type. Interestingly, both lines showed a decreased expression of the other constitutive members of the ME family. In addition, the plants with increased NADP-ME activity showed changes in the expression and activity of another malate metabolism related enzyme, the malate dehydrogenase. This line also presented a mild phenotype and was significantly more sensitive to osmotic stress. Although loss-of-function mutant of NADP-ME2 exhibited a typical vegetative and reproductive development under normal or stress conditions, it showed an altered content of organic acids and sugars. Overall, the depletion or the gain of NADP-ME2 activity produces changes in gene expression, enzymatic activity and metabolite levels which reflect the relevance of this enzyme in plant organic acids metabolism.