Use of the rice sucrose synthase-1 promoter to direct phloem-specific expression of β-glucuronidase and snowdrop lectin genes in transgenic tobacco plants

The promoter region from the rice sucrose synthase-1 gene (RSs1) was fused with coding sequences for β-glucuronidase (GUS) and snowdrop (Galanthus nivalis) lectin (GNA). Tobacco plants were transformed with these chimaenc genes in order to determine the expression pattern directed by the RSs1 promoter. Histochemical and immunochemical assays demonstrated that the expression of both GUS and GNA was restricted to phloem tissue, and was not observed in any other tissues. This phloem-specific expression pattern was consistent in stem, leaf and root, and in different transgenic plants. Chimaeric genes of RSs 1-GUS and RSs1 GNA were stably inherited in T1 plants. In addition, GNA was detected by immunological assay in the honeydew produced by peach potato aphids (Myzus persicae) feeding on RSs1-GNA transgenic tobacco plants. This provided direct evidence that GNA was not only expressed in the phloem tissue, but was also present in the phloem sap of transgenic tobacco plants. The RSs1 promoter can thus be used to direct expression of an insecticidal protein, such as GNA, in transgenic plants to control phloem sap-feeding insect pests.