''Superman'' is a plant gene in ''

Arabidopsis thaliana ''Arabidopsis thaliana'', the thale cress, mouse-ear cress or arabidopsis, is a small flowering plant native to Eurasia and Africa. ''A. thaliana'' is considered a weed; it is found along the shoulders of roads and in disturbed land. A winter a ...

'', that plays a role in controlling the boundary between

stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...

and

carpel Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...

development in a flower. It is named for the comic book character

Superman Superman is a superhero who appears in American comic books published by DC Comics. The character was created by writer Jerry Siegel and artist Joe Shuster, and debuted in the comic book ''Action Comics'' #1 (cover-dated June 1938 and publi ...

, and the related genes '' kryptonite (gene)'' and clark kent were named accordingly (although, appropriately, the latter turned out to just be another form of ''superman''). It encodes a

transcription factor In molecular biology, a transcription factor (TF) (or sequence-specific DNA-binding factor) is a protein that controls the rate of transcription of genetic information from DNA to messenger RNA, by binding to a specific DNA sequence. The fu ...

(specifically a C2H2 type

zinc finger protein A zinc finger is a small protein structural motif that is characterized by the coordination of one or more zinc ions (Zn2+) in order to stabilize the fold. It was originally coined to describe the finger-like appearance of a hypothesized structu ...

). Homologous genes are known in the

petunia ''Petunia'' is genus of 20 species of flowering plants of South American origin. The popular flower of the same name derived its epithet from the French, which took the word ''petun'', meaning "tobacco," from a Tupi–Guarani language. A tende ...

and

snapdragon ''Antirrhinum'' is a genus of plants commonly known as dragon flowers, snapdragons and dog flower because of the flowers' fancied resemblance to the face of a dragon that opens and closes its mouth when laterally squeezed. They are native to r ...

, 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 stamen whorl adjacent to the carpel whorl. It interacts with the other genes of the ABC model of flower development in a variety of ways.

Gene function

''Superman'' encodes a

. This protein binds to the DNA through a zinc finger binding motif acts as a regulator of floral

homeotic gene In evolutionary developmental biology, homeotic genes are genes which regulate the development of anatomical structures in various organisms such as echinoderms, insects, mammals, and plants. Homeotic genes often encode transcription factor proteins ...

s, controlling the development of the flowers of ''

'' plants. ''Arabidopsis thaliana'' flowers develop in four whorls, which are concentric groups of cells branching off of the growing

meristem The meristem is a type of tissue found in plants. It consists of undifferentiated cells (meristematic cells) capable of cell division. Cells in the meristem can develop into all the other tissues and organs that occur in plants. These cells conti ...

. ''Superman'' has been found to act in the fourth whorl of flowers, which would normally develop into

Carpels Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...

. Superman normally restricts the effect of another gene called (APETALA3) in the fourth

whorl A whorl ( or ) is an individual circle, oval, volution or equivalent in a whorled pattern, which consists of a spiral or multiple concentric objects (including circles, ovals and arcs). Whorls in nature File:Photograph and axial plane floral ...

, 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, so by its restriction, we allow for the development of other organs in the fourth whorl (such as the

Pistil Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...

). A mutation which completely removes superman gene function would result in flowers that carry extra

s, replacing the pistils which would normally be developing in the fourth whorl. This mutation was named the sup-1 mutation. For the sup-1 mutation, More extreme stamen development is seen from a homozygous mutation than a heterozygous mutation.

Interaction with the 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 The ABC model of flower development is a scientific model of the process by which flowering plants produce a pattern of gene expression in meristems that leads to the appearance of an organ oriented towards sexual reproduction, a flower. There ...

, which is typically responsible for the development of

Stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...

and

Petal Petals are modified Leaf, leaves that surround the reproductive parts of flowers. They are often advertising coloration, brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the ''c ...

s. 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

Epigenetic changes to Superman

Superman has been found to undergo to

epigenetic In biology, epigenetics is the study of stable phenotypic changes (known as ''marks'') that do not involve alterations in the DNA sequence. The Greek prefix '' epi-'' ( "over, outside of, around") in ''epigenetics'' implies features that are "o ...

modifications. Specifically, cytosine methylation (attachment of methyl radicals to cytosine bases), which represses its transcriptional activity. This methylation brings about the Clark Kent (clk) epialleles, which are a set of altered versions of the Superman gene lacking function. Whereas most cases of cytosine methylation in plants tend to happen in the Promoter of transcription, the cytosine methylation of Superman happens within the gene, just after the promoter. The exact location of the methylation varies, but defines which clk epiallele we define the plant as having; so far there are 7 identified clk epialleles (numbered clk1-clk7). These Clark Kent alleles can be inherited, but often, through mutation, will revert to the natural gene at a rate of about 3% per generation.

References

{{Superman Arabidopsis thaliana genes Flowers Superman