- ABC Model of Flower Development
The ABC model of flower development in
angiosperms was formulated by E. Coen andElliot Meyerowitz in 1991. [cite journal |last=Coen |first=Henrico S. |coauthors=Elliot M. Meyerowitz |year=1991 |title=The war of the whorls: Genetic interactions controlling flower development |journal=Nature |volume=353 |issue= |pages=31–37 |doi=10.1038/353031a0] This model is built on the observation of mutants with defects in floral organ development. The ABC model summarizes how the presence or absence of different classes oftranscription factors in the different parts of theflower regulates the development of floral organs.Two key observations have led to the ABC model. First, the discovery of homeotic mutations in which one organ develops in a location normally occupied by a different organ. Wild
rose s, for example, have only fivepetal s but manystamen s. Garden roses have a homeotic gene that causes some of the potential stamens to develop into petals instead. Second, each of the genes that affect the identity of organs in flowers has an effect on "two" groups of flower organs, affecting petals "and" sepals or affecting petals "and" stamens.cite book |last=Fosket |first=Donald E. |title=Plant Growth and Development: A Molecular Approach |year=1994 |publisher=Academic Press |location=San Diego |isbn=0-12-262430-0| pages=498-509]Floral organ identity
gene s are therefore divided into three classes, depending on which organs they affect. Mutations in class A genes affectsepal s and petals. Mutations in class B genes affect petals and stamens, while those in class C affect stamens andcarpel s. All three classes of genes arehomeotic gene s, which are translated intoprotein s. Each protein coded by these genes contains aMADS-box region that allows the protein to bind toDNA and to function as a regulator in DNA transcription. It is believed that these genes are master controlling genes, regulating the action of other genes that will control organ development.The ABC model proposes that class A genes alone are responsible for the development of sepals, but act together with class B genes to effect petal development. Class C genes alone are responsible for initiating the development of carpels, but act together with class B genes to determine the development of stamens. Support for a dual gene interaction with class B genes comes from the nature of class B mutants. A defective B gene leads to the absence of petals and stamens; in their places develop additional sepals and carpels. Similar organ replacement occurs when other classes of genes undergo mutation.
Summary:
*The expression of A genes induces the development ofsepals .
*The expression of B genes together with A genes induces the development ofpetals .
*The expression of B genes together with C genes induces the development ofstamens .
*The expression of C genes induces the development ofcarpels .In 2004 the characterization of "sepallata1,2,3" triple mutant in "Arabidopsis" has led to the formulation of the ABCE model, which consider the importance of class E genes for the development of the floral organs.
ee also
*
Flower
*MADS-box
*Mutation
*Plant evolutionary developmental biology
*Superman (gene) References
External links
* [http://biology.kenyon.edu/courses/biol114/Chap13/Chapter_12C.html Flower Development]
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