Agamous is a C class gene, a transcription factor responsible for activating genes involved in stamen and carpel development.
|
|
AGAMOUS (AG) is a homeotic gene and MADS-box transcription factor from Arabidopsis thaliana. The TAIR AGI number is AT4G18960.
|
|
Consider the evolution of the C-region gene AGAMOUS (AG). It is expressed in today's flowers in the stamens, and the carpel, which are reproductive organs. It's ancestor in gymnosperms also has the same expression pattern. Here, it is expressed in the strobili, an organ that produces pollens or ovules.
|
|
Another example is that of the toad-flax, Linaria vulgaris, which has two kinds of flower symmetries: radial and bilateral. These symmetries are due to epigenetic changes in just one gene called CYCLOIDEA. The large number of petals in roses has probably been a result of human selection. Arabidopsis thaliana has a gene called AGAMOUS that plays an important role in defining how many petals and sepals and other organs are generated.
|
|
A double-flowered variety of Marsh Marigold was discovered and cultivated in Austria in the late 16th century, becoming a valued garden plant. The first documented double-flowered mutant of Arabidopsis, a model organism for plant development and genetics, was recorded in 1873. The mutated gene likely responsible for the phenotype, AGAMOUS, was cloned and characterized in 1990 in Elliot Meyerowitz's lab as part of his study of molecular mechanisms of pattern formation in flowers.
|
|
Plant hormones play an important part in the process, with the gibberellins having a particularly important role. There are many signals that regulate the molecular biology of the process. The following three genes in Arabidopsis thaliana possess both common and independent functions in floral transition: FLOWERING LOCUS T (FT), LEAFY (LFY), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1, also called AGAMOUS-LIKE20). SOC1 is a MADS-box-type gene, which integrates responses to photoperiod, vernalization and gibberellins.
|
|
Some MADS-box genes of flowering plants have homeotic functions like the HOX genes of animals. The floral homeotic MADS-box genes (such as AGAMOUS and DEFICIENS) participate in the determination of floral organ identity according to the ABC model of flower development. Another function of MADS-box genes is flowering time determination. In Arabidopsis thaliana the MADS box genes SOC1 and Flowering Locus C (FLC) have been shown to have an important role in the integration of molecular flowering time pathways.
|
|
Mutations in this gene give rise to the floral meristem obtaining an indeterminate fate, and many floral organs keep on getting produced. We have flowers like roses, carnations and morning glory, for example, that have very dense floral organs. These flowers have been selected by horticulturists since long for increased number of petals. Researchers have found that the morphology of these flowers is because of strong mutations in the AGAMOUS homolog in these plants, which leads to them making a large number of petals and sepals.
|
|
Serum response factor is a member of the MADS (MCM1, Agamous, Deficiens, and SRF) box superfamily of transcription factors. This protein binds to the serum response element (SRE) in the promoter region of target genes. This protein regulates the activity of many immediate early genes, for example c-fos, and thereby participates in cell cycle regulation, apoptosis, cell growth, and cell differentiation. This gene is the downstream target of many pathways; for example, the mitogen-activated protein kinase pathway (MAPK) that acts through the ternary complex factors (TCFs).
|
|
They are usually recessive, although the double flower mutation in carnations exhibits incomplete dominance. In Arabidopsis, which has been used as a model for understanding flower development, the double-flower gene AGAMOUS encodes a protein responsible for tissue specification of stamen and carpel flower segments. When both copies of the gene are deleted or otherwise damaged, developing flowers lack the signals to form stamen and carpel segments. Regions which would have formed stamens instead default to petals and the carpel region develops into a new flower, resulting in a recursive sepal- petal-petal pattern.
|
|
In A. thaliana, the C function is derived from one MADS-box type gene called AGAMOUS (AG), which intervenes both in the establishment of stamen and carpel identity as well as in the determination of the floral meristem. Therefore, the AG mutants are devoid of androecium and gynoecium and they have petals and sepals in their place. In addition, the growth in the centre of the flower is undifferentiated, therefore the petals and sepals grow in repetitive verticils. The PLENA (PLE) gene is present in A. majus, in place of the AG gene, although it is not an ortholog.
|
|
A. thaliana has been extensively studied as a model for flower development. The developing flower has four basic organs: sepals, petals, stamens, and carpels (which go on to form pistils). These organs are arranged in a series of whorls: four sepals on the outer whorl, followed by four petals inside this, six stamens, and a central carpel region. Homeotic mutations in A. thaliana result in the change of one organ to another—in the case of the agamous mutation, for example, stamens become petals and carpels are replaced with a new flower, resulting in a recursively repeated sepal-petal-petal pattern.
|
|
The gene which Superman interacts with (APETALA3) is a member of the B-Function group of the ABC model of flower development, which is typically responsible for the development of Stamen and Petals. Other important members of the ABC model of flower development include APETALA1, APETALA2, AGAMOUS, and PISTILATA. Superman has not been found to interact with any of these other genes. SUPERMAN (SUP) and SUPERMAN-like genes such as APETALA2 work as a protein complex regulators with other corepressors known as TOPLESS (TPL) and a Histone Deacetylase 19 (HD19) in order to repress transcriptional functions in plants Krogan, N. T., Hogan, K., & Long, J. A. (2012).
|
|
Botanists and biologists began to research A. thaliana in the early 1900s, and the first systematic description of mutants was done around 1945. TAIR: About Arabidopsis A. thaliana is now widely used for studying plant sciences, including genetics, evolution, population genetics, and plant development. Although A. thaliana has little direct significance for agriculture, it has several traits that make it a useful model for understanding the genetic, cellular, and molecular biology of flowering plants. A double flower mutant of arabidopsis, first documented in 1873 The first mutant in A. thaliana was documented in 1873 by Alexander Braun, describing a double flower phenotype (the mutated gene was likely Agamous, cloned and characterized in 1990).
|
|
Functional domains of the floral regulator AGAMOUS: characterization of the DNA binding domain and analysis of dominant negative mutations. Mizukami, Y., Huang, H., Tudor, M., Hu, Y., Ma, H. Plant Cell (1996) AP2 also makes up another compound called ANT, which is composed of two AP2 domains homologous with the DNA binding domain of ethylene response element binding proteins.The AINTEGUMENTA gene of Arabidopsis required for ovule and female gametophyte development is related to the floral homeotic gene APETALA2. Klucher, K.M., Chow, H., Reiser, L., Fischer, R.L. Plant Cell (1996) Another study by Maes, T. titled Petunia Ap2-like genes and their role in flower and seed development, discovered three AP2-like proteins from petunia and by studying their expression patterns in situ hybridization: PhAP2A, PhAP2B, and PhAP2C.
|
|
In A. thaliana, function A is mainly represented by two genes APETALA1 (AP1) and APETALA2 (AP2) AP1 is a MADS-box type gene, while AP2 belongs to the family of genes that contains AP2, which it gives its name to and which consists of transcription factors that are only found in plants. AP2 has also been shown to complex with the co-repressor TOPLESS (TPL) in developing floral buds to repress the C-class gene AGAMOUS (AG). However, AP2 is not expressed in the shoot apical meristem (SAM), which contains the latent stem cell population throughout the adult life of Arabidopsis, and so it is speculated that TPL works with some other A-class gene in the SAM to repress AG.AP1 functions as a type A gene, both in controlling the identity of sepals and petals, and it also acts in the floral meristem. AP2 not only functions in the first two verticils, but also in the remaining two, in developing ovules and even in leaves.
|
|