Four rice genes encoding NADP malic enzyme exhibit distinct expression profiles

In plants, the NADP malic enzymes (NADP-MEs) are encoded by small gene families. These NADP-ME gene families are relatively well described in C4 plants but not well studied in C3 plants. In this study, we investigated the NADP-ME gene family in a model C3 monocot plant (rice, Oryza sativa) based on its recently released genomic DNA sequence. We found that the rice NADP-ME family is composed of four members, one plastidic NADP-ME and three cytosolic versions. Although the rice NADP-ME genes identified share a high degree of similarity with one another, one cytosolic NADP-ME (OscytME3) contains several unique amino acid substitutions within highly conserved amino acid regions. Phylogenetic analysis showed that OscytME3 might be derived from a different evolutionary branch than the other three rice genes. Expression analysis of the four rice NADP-ME genes indicated that each had a different tissue-specific and developmental profile, although all four responded to stress stimuli.