Expression patterns of cytoplasmic pyruvate, orthophosphate dikinase of rice (C3) and maize (C4) in a C3 plant, rice

Abstract

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 pro duced by two independent promoters and this unusual dual promoter system is also found in the C_4-like Pdk gene of the C₃ 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 ß-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 cyto-plasmic enzyme is similar in C₃ and C₄ plants. The results also suggest the possibility that the cytoplasmic enzyme has a similar function(s) in non-photosynthetic organs both in C₃ and C₄ plants.