Expression of photosynthetic genes from the C4 plant, maize, in tobacco.

Previous results from this laboratory have demonstrated the presence of genes for phosphoenolpyruvate carboxylase and pyruvate, orthophosphate dikinase in C3 plants. The structure and light-enhanced expression of these genes is very similar to that of the genes found in the C4 plant, maize. In order to investigate whether or not the regulation of these genes is similar in C3 and C4 plants, we have constructed chimeric genes using beta-glucuronidase as a reporter gene under the control of the maize promoters of the genes for phosphoenolpyruvate carboxylase, pyruvate, orthophosphate dikinase, and the small subunit of ribulose bisphosphate carboxylase (RuBisCO). The chimeric genes were introduced into tobacco, a C3 plant. These genes were expressed primarily in leaf and stem tissue and the expression was enhanced by light. Thus, as in C4 plants, the genes are expressed in a tissue-specific and light-inducible manner in the C3 plant. Since the expression of these genes is restricted to specific cells in leaf tissue of C4 plants, we also investigated the spatial pattern of expression of the chimeric genes using histochemical analysis of beta-glucuronidase activity. High level expression of all of these genes was found in mesophyll cells. This included the small subunit of RuBisCO, which is not expressed in mesophyll cells but in bundle sheath cells in C4 plants. This report describes similarities between C3 and C4 plants in regulating the expression of these genes.