The nectary-specific pattern of expression of the tobacco Nectarin I promoter is regulated by multiple promoter elements

The major protein secreted into the nectar of tobacco plants (Nectarin I) is a germin-like protein that has superoxide dismutase activity. We have isolated the gene encoding Nectarin I (NECI) and analyzed the expression of a chloramphenicol acetyl transferase (CAT) marker gene driven by its promoter in transgenic plants. Transgenic plant lines that expressed the CAT gene under control of the full-length NECI promoter showed high levels of CAT expression in mature floral nectaries. Tissue specificity of NECI-CAT expression demonstrated that the construct was expressed uniquely in nectaries with a small level of expression in ovary. Further, analysis of its temporal expression showed that the construct is expressed uniquely during those times when nectar is actively being secreted from flowers. An examination of the transcription start site verified that the initiation site of the NECI-CAT mRNA in transgenic plants is identical with that of the native gene in vivo. Two promoter deletion constructs were also prepared and analyzed. Analysis in transgenic plants revealed that the nectary-specific expression is the result of multiple promoter elements and suggests that nectar secretion and flower opening may be coordinately regulated.