The cycloidea gene can respond to a common dorsoventral prepattern in Antirrhinum.

Dorsoventral asymmetry in flowers of Antirrhinum depends on expression of the cycloidea gene in dorsal regions of floral meristems. To determine how cycloidea might be regulated we analysed its expression in several contexts. We show that cycloidea is activated shortly after floral induction, and that in addition to flowers, cycloidea can be asymmetrically expressed in shoots, even though these shoots show no marked dorsoventral asymmetry. Shoots expressing cycloidea include secondary branches lying just below the inflorescence, and shoots of floricaula mutants. Asymmetric cycloidea expression may also be observed within organ primordia, such as the sepals of terminal flowers produced by centroradialis mutants. Later expression of cycloidea within flowers can be modified by mutations in organ identity genes. Taken together, the results suggest that cycloidea can respond to a common dorsoventral pre-pattern in the apex and that the specific effects of cycloidea on the flower depend on interactions with floral-specific genes.