The
ABC model of flower development in angiosperms was formulated by E. Coen and
Elliot MeyerowitzElliot Meyerowitz is a U.S. biologist. He is currently George W. Beadle Professor of Biology and Chair, Division of Biology at the California Institute of Technology....
in 1991. 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
flowerA flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds...
regulates the development of floral organs.
Two key observations have led to the ABC model.
The
ABC model of flower development in angiosperms was formulated by E. Coen and
Elliot MeyerowitzElliot Meyerowitz is a U.S. biologist. He is currently George W. Beadle Professor of Biology and Chair, Division of Biology at the California Institute of Technology....
in 1991. 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
flowerA flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds...
regulates the development of floral organs.
Two key observations have led to the ABC model. First, the discovery of
homeoticHox genes are a group of related genes that specify the anterior-posterior axis and segment identity of metazoan organisms during early embryonic development...
mutations in which one organ develops in a location normally occupied by a different organ. Wild
roseA rose is a perennial flower shrub or vine of the genus Rosa, within the family Rosaceae, that contains over 100 species and comes in a variety of colours. The species form a group of erect shrubs, and climbing or trailing plants, with stems that are often armed with sharp prickles...
s, for example, have only five
petalA petal is one member or part of the corolla of a flower. The corolla is the name for all of the petals of a flower; the inner perianth whorl, term used when this is not the same in appearance as the outermost whorl and is used to attract pollinators based on its bright color...
s but many
stamenThe stamen is the male organ of a flower. Each stamen generally has a stalk called the filament , and, on top of the filament, an anther , and pollen sacs,...
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.
Floral organ identity
geneA gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cells and pass genetic traits to offspring...
s are therefore divided into three classes, depending on which organs they affect. Mutations in class A genes affect
sepalA sepal is a part of the flower of angiosperms . Sepals in most flowers are green and lie under the more conspicuous petals. As a collective unit the sepals form a calyx, whereas the collection of petals is called the corolla...
s and petals. Mutations in class B genes affect petals and stamens, while those in class C affect stamens and carpels. All three classes of genes are
homeotic geneHox genes are a group of related genes that specify the anterior-posterior axis and segment identity of metazoan organisms during early embryonic development...
s, which are translated into
proteinProteins are organic compounds made of amino acids arranged in a linear chain and folded into a globular form. The amino acids in a polymer chain are joined together by the peptide bonds between the carboxyl and amino groups of adjacent amino acid residues...
s. Each protein coded by these genes contains a
MADS-boxMADS box is a conserved sequence motif found in a family of transcription factors, the MADS-box protein family. The length of the MADS-box reported by various researchers varies somewhat, but typical lengths are in the range of 168 to 180 base pairs....
region that allows the protein to bind to
DNADeoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms and some viruses. The main role of DNA molecules is the long-term storage of information...
and to function as a regulator in DNA
transcriptionTranscription, or RNA synthesis, is the process of creating an equivalent RNA copy of a sequence of DNA. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as a complementary language that can be converted back and forth from DNA to RNA in the presence of the correct enzymes...
. It is believed that these genes are master controlling genes, regulating the action of other genes that will control organ development.
Known ABC genes by class
from Antirrhinum and Arabidopsis
|
Antirrhinum Antirrhinum is a genus of plants commonly known as snapdragons from the flowers' fancied resemblance to the face of a dragon that opens and closes its mouth when laterally squeezed...
|
ArabidopsisArabidopsis thaliana , is a small flowering plant native to Europe, Asia, and northwestern Africa. A spring annual with a relatively short life cycle, Arabidopsis is popular as a model organism in plant biology and genetics...
|
| Class A |
SQUAMOSA (SQUA) LIPLESS1 (LIP1) LIPLESS2 (LIP2) |
APETALA2 Apetala 2 ' is a gene coding for a member of a large family of plant-specific transcription factors, the AP2/EREBP family, from Arabidopsis thaliana which plays a role in the ABC model of flower development.In the A...
(AP2) APETALA1 (AP1) |
| Class B |
DEFICIENS (DEF) GLOBOSA (GLO) |
APETALA3 (AP3) PISTILLATA (PI) |
| Class C |
PLENA (PLE) FARINELLI (FAR) |
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
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds...
- MADS-box
MADS box is a conserved sequence motif found in a family of transcription factors, the MADS-box protein family. The length of the MADS-box reported by various researchers varies somewhat, but typical lengths are in the range of 168 to 180 base pairs....
- Mutation
In biology, a mutation is a randomly derived change to the nucleotide sequence of the genetic material of an organism.Mutations can be caused by copying errors in the genetic material during cell division, or by exposure to mutagens , or can be induced by the organism itself, by cellular processes...
- Plant evolutionary developmental biology
Evolutionary developmental biology refers to the study of developmental programs and patterns from an evolutionary perspective. It seeks to understand the various influences shaping the form and nature of life on the planet. Evo-devo arose as a separate branch of science only in the last decade...
- Superman (gene)
Superman is a plant gene in Arabidopsis thaliana that plays a role in controlling the boundary between stamen and carpel development in a flower. It is named for the comic book character Superman, and the related genes kryptonite and clark kent were named accordingly...
External links