On the origin of floral morphological novelties

Floral morphological novelties, like homeotic changes of whorl 1 organs, can easily arise by modifying existing regulatory networks. Ectopic expression of B-function MADS-box genes in whorl 1 leads to a replacement of sepals by petals, as is found in the Liliaceae. In cases where leaf-like sepals or even inflated calyces develop, which ultimately envelop the mature fruit as in Physalis, ectopic expression of a vegetative MADS-box gene seems to be responsible. Current knowledge concerning the origin of such morphological novelties is reviewed. (C) 2004 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.