The pea rbcS-3A enhancer-like element directs cell-specific expression in transgenic tobacco

Summary

The pea rbcS-3A gene codes for the small subunit of ribulose-1,5-bisphosphate carboxylase and its expression is regulated by light, tissue type and stage of development. Analysis in transgenic tobacco plants has shown that the upstream region contains an enhancer-like element which can confer light-regulated and organ-specific expression upon a reporter gene (Fluhr et al. 1986a). Here we address the question of whether the enhancer specifies not only organ specificity, but also expression in the correct cell types. In situ immunofluorescence and microdissection were used on transgenic tobacco plants containing the rbcS-3A enhancer fused to a reporter gene consisting of the cauliflower mosaic virus 35S promoter and the bacterial gene encoding chloramphenicol acetyltransferase (CAT). CAT levels are high in leaf mesophyll cells, but in the epidermis expression is restricted to guard cells. In the midrib, of the leaf and in the stem, there is considerable signal in the chlorenchyma and in the phloem region. This pattern of expression closely correlates with the distribution of the endogenous RbcS polypeptides and with the presence of chlorophyll. Our results demonstrate that the rbcS-3A enhancer-like element possesses all the necessary DNA sequences for expression in the correct cell types.