A FLOWER-SPECIFIC MYB PROTEIN ACTIVATES TRANSCRIPTION OF PHENYLPROPANOID BIOSYNTHETIC GENES

Synthesis of flavonoid pigments in flowers requires the coordinated ex pression of genes encoding enzymes in the phenylpropanoid biosynthetic pathway. Some cis-elements involved in the transcriptional control of these genes have been defined. We report binding of petal-specific ac tivities from tobacco and Antirrhinum majus (snapdragon) to an element conserved in promoters of phenylpropanoid biosynthetic genes and impl icated in expression in flowers. These binding activities were inhibit ed by antibodies raised against Myb305, a flower-specific Myb protein previously cloned from Antirrhinum by sequence homology. Myb305 bound to the same element and formed a DNA-protein complex with the same mob ility as the Antirrhinum petal protein in electrophoretic mobility shi ft experiments. Myb305 activated expression from its binding site in y east and in tobacco protoplasts. In protoplasts, activation also requi red a G-box-like element, suggesting co-operation with other elements and factors. The results strongly suggest a role for Myb305-related pr oteins in the activation of phenylpropanoid biosynthetic genes in flow ers. This is consistent with the genetically demonstrated role of plan t Myb proteins in the regulation of genes involved in flavonoid synthe sis.