Genetic control of floral size and proportions.

Floral size is an ecologically important trait related to pollination success and genetic fitness. Independently of the sexual reproduction strategy, in many plants, floral size seems to be controlled by several genetic programs that are to some extent independent of vegetative growth. Flower size seems to be governed by at least two independent mechanisms, one controlling floral architecture that affects organ number and a second one controlling floral organ size. Different organ-dependent growth control may account for the final proportions of a flower as a whole. Genes controlling floral organ identity, floral symmetry and organ polarity as well as auxin and gibberellin response, also play a role in establishing the final size and architecture of the flower. The final size of an organ seems to be controlled by a systemic signal that might in some cases overcome transgenic modifications of cell division and expansion. Nevertheless, modification of basic processes like cell wall deposition might produce important changes in the floral organs. The coordination of the direction of cell division and expansion by unknown mechanisms poses a challenge for future research.