The unfolding drama of flower development: recent results from genetic and molecular analyses.

Abstract

There has been an explosion of information about flower development recently, largely because of genetic and molecular studies in Arabidopsis thaliana and Antirrhihum majus. A number of homeotic genes have been identified that regulate flower development, and models have been proposed for the specification of meristem and floral organ identities. Molecular cloning of many of these genes has allowed the testing of specific predictions of the models but also has led to modifications of a floral organ identity model. Furthermore, several of the floral genes contain a conserved region, the MADS box, which encodes a domain with striking sequence similarity with known transcription factors from human and yeast. Additional MADS box genes have been isolated from several plants; these genes are likely to play important regulatory roles during flower development. The genetic and molecular studies have uncovered many of the components of a complex network of regulatory proteins that directs flower development. Further characterization of these and other yet to be discovered components promises to contribute a great deal to our understanding of the mechanisms controlling flower development. Flowering plants, like other land plants, have vegetative organs such as roots, stems, and leaves, which absorb nutrients and water from the soil, transport them to other parts of the plant, and synthesize organic compounds using the sun's energy. In addition, flowering plants produce elaborate reproductive structures, the flowers, which, following fertilization, become fruits and bear seeds. From the seasoned gardener to the casual observer, from the naturalist to the florist shopper, people have always been fascinated by the enormous variety of flowers, ranging from 2 mm to > 10 cm in length, covering the whole visual spectrum with their colors, and differing in the arrangement of flowers and the symmetry within a flower. How do flowers develop? What genes regulate this complex process? In recent years, rapid advances have been made in addressing these questions, largely as a result of genetic and molecular studies in two distantly related flowering plants, Arabidopsis thaliana, a relative of cauliflower and cabbage, and the snapdragon, Antirrhinum majus.