EXPRESSION OF A FLOWER-SPECIFIC MYB PROTEIN IN LEAF-CELLS USING A VIRAL VECTOR CAUSES ECTOPIC ACTIVATION OF A TARGET PROMOTER

The promoter of the bean PAL2 gene (encoding phenylalanine ammonia-lya se; EC 4.3.1.5) is a model for studies of tissue-restricted gene expre ssion in plants. Petal epidermis is one of the tissues in which this p romoter is activated in tobacco. Previous work suggested that a major factor establishing the pattern of PAL2 expression in tobacco petals i s the tissue distribution of a protein closely related to Myb305, whic h is a Myb-like transcriptional activator from snapdragon. In the pres ent work, we show that Myb305 expression in tobacco leaves causes ecto pic activation of the PAL2 promoter. To achieve Myb305 expression in p lanta, a viral expression vector was used. This approach combines the utility of transient assays with the possibility of direct biochemical detection of the introduced factor and may have wider application for studying the function of plant transcription factors.