CONICET | Buscador de Institutos y Recursos Humanos

Based on their carbon fixation mechanism, vascular plants can be classified as C3, C4 or CAM. In maize, a C4 species, malate is the primary photosynthate in mesophyll cells that is subsequently decarboxylated by NADP-Malic Enzyme (NADP-ME) in bundle sheath cells. This raise in CO2/O2 ratio diminishes the oxigenase activity of RuBisCO and energy wasting. NADP-ME family is an excellent model to study evolution of C4 enzymes. In maize, it has been described that ZmME2 is the closest isoform related to that involved in C4 cycle (ZmME1). The kinetic characteristics of ZmME1 y ZmME2 are well correlated with their photosynthetic and non-photosynthetic functions, respectively. The most active form of ZmME1 is tetrameric, while the most abundant form of ZmME2 is dimeric, as has been shown by studies in recombinant systems. In this work we studied the structural bases related to the oligomeric state of these isoforms. Additionally, we analyzed the effect of the expression of ZmME1 on the metabolism of a C3 species. The full-length cDNA encoding ZmME1 was constitutively expressed in Arabidopsis thaliana. An increase in the plastidic NADP-ME activity led to a green pale phenotype and altered photosynthetic metabolism in plants growing in short days. Additionally, dark-induced senescence of intact plants progressed more rapidly in transgenic plants compared to the wild type. These results clearly support that the emergence of C4 pathway was a coordinated multienzyme event that involved not only novel isoforms but also new metabolic homeostasis.