C-4 ISOFORM OF NADP-MALATE DEHYDROGENASE - CDNA CLONING AND EXPRESSION IN LEAVES OF C-4, C-3, AND C-3-C-4 INTERMEDIATE SPECIES OF FLAVERIA

In C-4 plants of the NADP-malic enzyme type, an abundant, mesophyll cell-localized NADP-malate dehydrogenase (MDH) acts to convert oxaloacetate, the initial product of carbon fixation, to malate before it is shuttled to the bundle sheath. Since NADP-MDH has different but important roles in leaves of C-3 and C-4 plants, we have cloned and characterized a nearly full-length cDNA encoding NADP-MDH from Flaveria trinervia (C-4) to permit comparative structure/expression studies within the genus Flaveria. The dicot genus Flaveria includes C-3-C-4 intermediate species, as well as C-3 and C-4 species. We show that the previously noted differences in NADP-MDH activity levels among C-3, C-4, and C-3-C-4 Flaveria species are in part due to interspecific differences in mRNA accumulation. We also show that the NADP-MDH gene appears to be present as a single copy among different Flaveria species, suggesting that a pre-existing gene has been reregulated during the evolution from C-3 to C-4 plants to accommodate the abundance and localization requirements of the C-4 cycle.