XVI International Botanical Congess

Robinia pseudoacacia, a leguminous, deciduous tree, has lectins in the inner bark (phloem) and the seeds. The inner bark lectin is located in parenchyma cells. We isolated a gene for a 29 kDa subunit of the inner bark lectin and designated it Rplec2. To determine the cis elements concerned with tissue-specific expression of Rplec2, the 5' upstream region (from -793 bp to +26 bp) of the gene was fused to the GUS reporter gene and introduced into tobacco plants. With transformants that showed significant GUS activity, we performed histochemical staining for GUS activity. In the stems, the staining was confined to the internal and external phloems and the parenchyma cells surrounding the external phloem. No staining was observed in leaf mesophyll cells. These results indicate that the 5' upstream region of Rplec2 functions as a promoter that directs phloem-specific expression of the GUS gene in mature transgenic tobacco plants.