Expression patterns of cytoplasmic pyruvate, orthophosphate dikinase of rice (C-3) and maize (C-4) in a C-3 plant, rice

Two types of mRNAs are transcribed from the C-4-type pyruvate, orthophosphate dikinase gene (Pdk) with different sizes, which encode chloroplastic and cytoplasmic forms of the enzyme. The two transcripts are produced by two independent promoters and this unusual dual promoter system is also found in the C-4-like Pdk gene of the C-3 plant, rice. In order to elucidate the expression pattern of the cytoplasmic transcript from the maize C-4-type and rice C-4-like Pdk genes, we have produced chimeric constructs with the beta-glucuronidase (GUS) reporter gene under the control of the cytoplasmic promoters and introduced the constructs into rice. Both cytoplasmic promoters directed GUS expression in non-photosynthetic organs, such as endosperm and roots, in transgenic rice plants, while expression was low in photosynthetic organs. These results indicate that the organ-specific localization of the cytoplasmic enzyme is similar in C-3 and C-4 plants. The results also suggest the possibility that the cytoplasmic enzyme has a similar function(s) in non-photosynthetic organs both in C-3 and C-4 plants.