Arabidopsis Thaliana Essay Example

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The floral organs in Arabidopsis thaliana are determined by various classes of genes, either expressed individually or in combination. These genes, which play a role in the identification of floral organs, can be found in Appendix – Table 1. The ABC model describes three types of interactions among these gene classes: intraclass, interclass, and cadastral interactions. Intraclass interactions occur among members of the same gene class, such as the interaction between AP1 and AP2 resulting in sepal formation.

The cooperation or positivity of intraclass interaction is determined for class A and B genes, respectively (Howell 1998). Conversely, interclass interaction refers to the interaction between members of different classes in the same flower regions (Howell 1998). This type of interaction is observed in whorls 2 and 3, where the interaction between class A and B genes in whorl 2 results in petal formation, while the interaction between class B and C in whorl 3 leads to stamen formation.

Cadastral interaction refers to the competitive interaction between members of different classes within a flower (Howell 1998). This interaction can be observed in the interaction of class A genes with class C genes, where the expression of one gene inhibits the expression of the other within the same whorl (Masson 2004). Table 1 in the appendix provides evidence of this cadastral interaction, as it shows that class A and class C genes are not simultaneously present in the same whorl.

Although the ABC model was initially presented as the standard for flower development, it has certain limitations in its application. There are further intricacies observed in the genetic aspects of floral development that cannot be entirely accounted

for by this model. These limitations encompass variations in the maintenance of the A function, duplicated regulation of the ABC system, and division of genetic function. In maize and petunia plants, genes AP1 and AP2, which also exist in Arabidopsis, do not produce the A function protein as they do in Arabidopsis.

In addition, no A function gene has been discovered in Antirrhinum, which indicates that the ABC model is insufficient to explain the incomplete conservation of the A function. Ongoing studies on Arabidopsis SEPALLATA (SEP) genes, a group of MADS box genes, have shed light on the limitations of the ABC system and the partitioning of genetic function. The formation of flowers composed solely of sepal-like organs is observed in triple null mutants lacking SEP1 to SEP3.

However, when studying homologs of the SEP class in other plants like Gerbera, it is observed that these homologs have different functions. These functions are related to the development of the condensed disk-like asteraceous inflorescence and the different floral forms that grow on it. An example of genetic function partitioning can be seen in the SEP-like gene that controls the C function in the staminal whorl of flowers on the outer part of the inflorescence, while another SEP homolog controls the C function only in the carpels of the inner flowers (Access Science 2002).

The MADS domain is a DNA binding and dimerization domain found in both yeast transcription factor MCM1 and mammal transcription factor SRF (Serum Response Factor). In Arabidopsis, the MADS family is represented by AP1, AP3, PI, and AG genes. However, the AP2 gene does not produce a MADS domain protein and

does not follow a specified pattern of expression (Weigel and Meyerowitz 1996). Previous studies have shown that MADS domain transcription factors bind to promoter elements containing a core CArG domain. These factors play a role in flower development and are likely responsible for activating the expression of a distinct set of downstream genes.