Characterization of genes relevant to the biological functionality and transcriptional regulation of the ZmNADP-ME3 malic enzyme

Introduction: ZmNADP-ME3 is a maize NADP-dependent malic enzyme that catalyses the oxidative decarboxylation of malate and is expressed almost exclusively during kernel development and in response to ABA hormone-mediated stresses. Although the ZmNADP-ME3 transcript is found at high levels in embryo and endosperm, the enzyme activity was significantly higher in embryos. In addition, it could be verified that the activity is maximal 20 days after pollination. The presence of ZmNADP-ME3 was also studied by Western blots. Although the reaction it catalyses is well characterized, its biological role is still unknown. To further study the function of ZmNADP-ME3, a meta-analysis of genes co-expressed in different tissues and stages of maize kernel maturation was performed. As a result, genes strongly linked to ZmNADP-ME3 were identified that could provide clues to the processes in which this malic enzyme participates. In addition, we searched for conserved motifs in the promoters of the co-expressed genes to determine whether they respond to a common signalling pathway. These results, together with those previously obtained on transcription factors that bind to the ZmNADP-ME3 promoter, provide relevant information on the expression networks in which the ZmNADP-ME3 protein is involved.