Ancient asymmetries in the evolution of flowers

Dorsoventral asymmetry in flowers is thought to have evolved many times ind ependently as a specialized adaptation to animal pollinators [1, 2]. To und erstand how such a complex trait could have arisen repeatedly, we have comp ared the expression of a gene controlling dorsoventral asymmetry in Antirrh inum with its counterpart in Arabidopsis, a distantly related species with radially symmetrical flowers. We found that the Arabidopsis gene is express ed asymmetrically in floral meristems, even though they are destined to for m symmetrical flowers. This suggests that, although the flowers of the comm on ancestor were probably radially symmetrical, they may have had an incipi ent asymmetry, evident at the level of early gene activity, which could hav e been recruited many times during evolution to generate asymmetric flowers .