Analysis of promoter activity for the gene encoding pyruvate orthophosphate dikinase in stably transformed C4 Flaveria species

The C-4 enzyme pyruvate orthophosphate dikinase is encoded by a single gene, Pdk, in the C-4 plant Flaveria trinervia. This gene also encodes enzyme isoforms located in the chloroplast and in the cytosol that do not have a function in C-4 photosynthesis. Our goal is to identity cis-acting DNA sequences that regulate the expression of the gene that is active in the C-4 cycle. We fused 1.5 kb of a 5' flanking region from the Pdk gene, including the entire 5' untranslated region, to the uidA reporter gene and stably transformed the closely related C-4 species Flaveria bidentis. beta-Glucuronidase (GUS) activity was detected at high levels in leaf mesophyll cells. GUS activity was detected at lower levels in bundle-sheath cells and stems and at very low levels in roots. This lower-level GUS expression was similar to the distribution of mRNA encoding the nonphotosynthetic form of the enzyme. We conclude that cis-acting DNA sequences controlling the expression of the C-4 form in mesophyll cells and the chloroplast form in other tells and organs are colocated within the same 5' region of the Pdk gene.