Enhancer sequences from Arabidopsis thaliana obtained by library transformation of Nicotiana tabacum

In this paper we report on the use of a bidirectional enhancer cloning vehicle to isolate and characterize new enhancer sequences from Arabidopsis thaliana. A library of A. thaliana genomic Sau3A segments was constructed in Escherichia coli in the binary plasmid enhancer cloning vehicle pROA97. The T-DNA based vector carries abbreviated TATA regions from the cauliflower mosaic virus 35S transcription unit upstream of two genes. The library was transferred via triparental mating into Agrobacterium tumefaciens. The neomycin phosphotransferase II gene was used for selection of kanamycin-resistant transformed tobacco callus cells. Approximately 1100 transgenic plants were regenerated and assayed for expression of the E. coli beta-glucuronidase (GUS) gene in leaves, stems, roots, or seeds. Plasmids carrying putative enhancer sequences were rescued from the genomes of transgenic plants and the cloned sequences were assayed for enhancer function in genetic selection experiments. Plants were regenerated from the kanamycin-resistant calli obtained in the secondary transformation experiments. Histochemical analysis of GUS activity in the leaf, stem, and root tissues of transgenic plants showed a variety of expression patterns. The DNA sequences are presented of five Arabidopsis segments which confer enhancer function.