An exploration of LEAFY expression in independent evolutionary origins of rosette flowering in Brassicaceae

Whereas most Brassicaceae produce flowers on an elongated inflorescence, a few lineages produce flowers directly from the vegetative rosette on elongated pedicels. Knowing the extent to which independent origins of rosette flowering involve the same developmental and genetic mechanisms could clarify the constraints acting on plant architectural evolution. Prior work in Idahoa, Ionopsidium, and Leavenworthia suggested that changes in the activity or expression of the flower meristem identity gene, LEAFY (LFY), played a role in all three origins of rosette flowering. Here we studied the developmental morphology of L. crassa and immunolocalization of LFY protein in Leavenworthia and Ionopsidium to further compare independent origins of rosette flowering. Leavenworthia crassa differs from Ionopsidium and Idahoa in producing ebracteate flowers. Flowers are, however, associated with "squamules," here interpreted as stipules of a cryptic bract. LFY was detected in L. crassa flower primordia but not in inflorescence meristems. In contrast, the rosette flowering Io. acaule accumulated LFY protein in the inflorescence meristem, whereas its inflorescence-flowering close relative, Io. prolongoi, did not. Thus, although different cases of rosette flowering likely entailed modifications of the same meristem identity program, distinct developmental genetic mechanisms appear to be involved in each case.