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The Superman gene (also SUPERMAN or SUP) in the plant Arabidopsis thaliana which 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 because of this, the related gene KRYPTONITE and the related Clark Kent alleles were named accordingly. The superman gene encodes a transcription factor, which binds to the DNA via a zinc finger binding motif. Similar, homologous genes are known in the petunia and snapdragon, which are also involved in flower development, although in both cases there are important differences from the functioning in Arabidopsis. Superman is expressed early on in flower development, in the region of cells which would normally grow into the female reproductive organ (the pistil) of the flower. Superman regulates this development indirectly by interacting with the genes of the ABC model of flower development in a variety of ways, often repressing their expression.

Gene Function
SUPERMAN encodes a protein (which shares the name Superman) containing a zinc finger region and a leucine zipper region, which both suggest DNA interaction and transcription factor activity. The protein Superman acts as an indirect regulator of floral homeotic genes, controlling the development of the flowers of Arabidopsis thaliana. These flowers develop in four whorls, which are concentric groups of cells branching off of the growing meristem. The Superman protein acts in the fourth whorl of flowers, which would normally develop into the pistil. The protein normally binds to the DNA and restricts the effect of another gene called APETALA3 in the fourth whorl, leaving APETALA3 expression only present in the second and third whorls. APETALA3 is a gene normally associated with the development of a stamen in the third whorl. Therefore, by APETALA3 restriction in the fourth whorl, we allow for the development of other organs in such as the pistil, instead of stamen development.

Loss of Function Mutation
A mutation named the sup-1 mutation suppresses SUPERMAN gene function, resulting in a lack of repression of APETALA3 in the fourth whorl. This results in flowers that carry extra stamens, which develop instead of the pistil that would normally be developing in the fourth whorl. For the sup-1 mutation, more extreme stamen development is seen from a homozygous mutation than a heterozygous mutation. Additionally, these sup-1 mutations have been seen to directly cause asymmetric growth of the ovules that do manage to form, regardless of APETALA3.

Epigenetic Changes
Superman has been found to undergo to epigenetic cytosine methylation, which represses its' transcriptional activity. This methylation is carried out by the gene called KRYPTONITE, which codes for a methyltransferase. A Superman gene that has undergone methylation is referred to as a Clark Kent (clk) allele. The exact location of the methylation varies and defines which clk allele we define the plant as having. So far, there are 7 identified clk epialleles (numbered clk1-clk7), each one representing an altered versions of the Superman gene which lacks function. Whereas most cases of cytosine methylation in plants tend to be located in the promoter of transcription, the cytosine methylation of Superman actually occurs within the gene, just after the promoter.

These Clark Kent alleles can be inherited. However, this change is unstable, and through natural mutation will often revert back to the normal functioning gene at a rate of about 3% per generation.

Interaction with the ABC Model of Flower Development
"main article: ABC model of flower development"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 the genes APETALA1, APETALA2, AGAMOUS, and PISTILATA. Superman has not been found to interact as strongly with any of these other genes.

Homologues in Other Species
This pattern of flower development is conserved across many plants, so homologues of Superman and APETALA3 have been found in other plants. For instance APETALA3 has homologue DIFICIENS in the Snapdragon, Antirrhinum majus and SUPERMAN has homologue PhSUP1 in the Petunia, Petunia hybrida, and OCTANDRA in Antirrhinum majus . The functions of these homologues are not the same however.