ABC Model of Flower Development
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2008-06-24T00:07:53Z
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[[Image:ABC flower development.svg|thumb|175px|A diagram of the ABC model in Arabidopsis. Class A genes (blue) affect sepals and petals, class B genes (yellow) affect petals and stamens, class C genes (red) affect stamens and carpels.]]
The '''ABC model of flower development''' in [[angiosperms]] was formulated by E. Coen and [[Elliot Meyerowitz]] in 1991.<ref>{{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}}</ref> 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 gene|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 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.<ref name="Fosket 1994">{{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}}</ref>
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 (genetics)|transcription]]. It is believed that these genes are master controlling genes, regulating the action of other genes that will control organ development.
{| class="wikitable" align="right" style="margin-left:1em"
|+'''Known ABC genes by class<ref name="Fosket 1994" /><br/>from ''Antirrhinum'' and ''Arabidopsis'''''
|-
! style="background:#aaaaff;" align="center" |
! style="background:#aaaaff;" align="center" | ''[[Antirrhinum]]''
! style="background:#aaaaff;" align="center" | ''[[Arabidopsis thaliana|Arabidopsis]]''
|-
! style="background:#ccccff;" align="left" | Class A
| style="background:#ffffff;" align="center" |''SQUAMOSA'' (SQUA)
| style="background:#ffffff;" align="center" |''[[Apetala2|APETALA2]]'' (AP2) ''APETALA1'' (AP1)
|-
! style="background:#ccccff;" align="left" | Class B
| style="background:#ffffff;" align="center" |''DEFICIENS'' (DEF) ''GLOBOSA'' (GLO)
| style="background:#ffffff;" align="center" |''APETALA3'' (AP3) ''PISTILLATA'' (PI)
|-
! style="background:#ccccff;" align="left" | Class C
| style="background:#ffffff;" align="center" |''PLENA'' (PLE) ''FARINELLI'' (FAR)
| style="background:#ffffff;" align="center" |''AGAMOUS'' (AG)
|}
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 of [[sepals]].
*The expression of B genes together with A genes induces the development of [[petals]].
*The expression of B genes together with C genes induces the development of [[stamens]].
*The expression of C genes induces the development of [[carpels]].
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==
*[[Flower]]
*[[MADS-box]]
*[[Mutation]]
*[[Plant evolutionary developmental biology]]
*[[Superman (gene)]]
==References==
<references/>
==External links==
*[http://biology.kenyon.edu/courses/biol114/Chap13/Chapter_12C.html Flower Development]
[[Category:Angiosperms]]
[[Category:Evolutionary biology]]
[[Category:Genetics]]
[[Category:Mutation]]
[[es:Desarrollo floral]]
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