| The Abc Model Of Flower Development |
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| CATEGORIES ABOUT THE ABC MODEL OF FLOWER DEVELOPMENT | |
| angiosperms | |
| evolutionary biology | |
| genetics | |
| mutation | |
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The ABC model of flower development in Angiosperms was formulated by E. Coen and E. Meyerowitz in 1991.1 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 of Transcription Factors in the different parts of the Flower 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 five Petal s but many Stamen s. Garden roses have a hometic 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.2 Floral organ identity Gene s are therefore divided into three classes, depending on which organs they affect. Mutations in class A genes affect Sepal s and petals. Mutations in class B genes affect petals and stamens, while those in class C affect stamens and Carpel s. All three classes of genes are Homeotic Gene s, which are translated into Protein s. Each protein coded by these genes contains a MADS-box region that allows the protein to bind to DNA and to function as a regulator in DNA Transcription . It is believe 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:
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. SEE ALSO REFERENCES EXTERNAL LINKS |
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