Control of organ asymmetry in flowers of Antirrhinum

Organ asymmetry is thought to have evolved many times independently in plan ts. In Antirrhinum, asymmetry of the flower and its component organs requir es eye and dich gene activity. We show that, like eye, the dich gene encode s a product belonging to the TCP family of DNA-binding proteins that is fir st expressed in the dorsal domain of early floral meristems. However, where as eye continues to be expressed throughout dorsal regions, expression of d ich eventually becomes restricted to the most dorsal half of each dorsal pe tal. This correlates with the effects of dich mutations and ectopic eye exp ression on petal shape, providing an indication that plant organ asymmetry can reflect subdomains of gene activity. Taken together, the results indica te that plant organ asymmetry can arise through a series of steps during wh ich early asymmetry in the developing meristem is progressively built upon.