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, orthophospha te dikinase gene (Pdk) with different sizes, which encode chloroplastic and cytoplasmic forms of the enzyme. The two transcripts are produced by two i ndependent 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 ex pression 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 pro moters 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 photosynthet ic organs. These results indicate that the organ-specific localization of t he cytoplasmic enzyme is similar in C-3 and C-4 plants. The results also su ggest the possibility that the cytoplasmic enzyme has a similar function(s) in non-photosynthetic organs both in C-3 and C-4 plants.