Editing Botany (section)

=== Epigenetics ===
{{Main|Epigenetics}}
[[Epigenetics]] is the study of heritable changes in [[gene expression|gene function]] that cannot be explained by changes in the underlying [[DNA sequence]]{{sfn|Bird|2007|pp = 396–398}} but cause the organism's genes to behave (or "express themselves") differently.{{sfn|Hunter|2008}} One example of epigenetic change is the marking of the genes by [[DNA methylation]] which determines whether they will be expressed or not. Gene expression can also be controlled by repressor proteins that attach to [[silencer (DNA)|silencer]] regions of the DNA and prevent that region of the DNA code from being expressed. Epigenetic marks may be added or removed from the DNA during programmed stages of development of the plant, and are responsible, for example, for the differences between anthers, petals and normal leaves, despite the fact that they all have the same underlying genetic code. Epigenetic changes may be temporary or may remain through successive [[cell division]]s for the remainder of the cell's life. Some epigenetic changes have been shown to be [[Heritability|heritable]],{{sfn|Spector|2012|p = 8}} while others are reset in the germ cells.

Epigenetic changes in [[Eukaryote|eukaryotic]] biology serve to regulate the process of [[cellular differentiation]]. During [[morphogenesis]], [[totipotent]] [[stem cells]] become the various [[pluripotent]] [[cell line]]s of the [[embryo]], which in turn become fully differentiated cells. A single fertilised egg cell, the [[zygote]], gives rise to the many different [[plant cell]] types including [[parenchyma]], [[vessel element|xylem vessel elements]], [[phloem]] sieve tubes, [[guard cell]]s of the [[epidermis (botany)|epidermis]], etc. as it continues to [[mitosis|divide]]. The process results from the epigenetic activation of some genes and inhibition of others.{{sfn|Reik|2007|pp = 425–432}}

Unlike animals, many plant cells, particularly those of the [[ground tissue#Parenchyma|parenchyma]], do not terminally differentiate, remaining totipotent with the ability to give rise to a new individual plant. Exceptions include highly lignified cells, the [[ground tissue#Sclerenchyma|sclerenchyma]] and xylem which are dead at maturity, and the phloem sieve tubes which lack nuclei. While plants use many of the same epigenetic mechanisms as animals, such as [[chromatin remodeling|chromatin remodelling]], an alternative hypothesis is that plants set their gene expression patterns using positional information from the environment and surrounding cells to determine their developmental fate.{{sfn|Costa|Shaw|2007|pp = 101–106}}

Epigenetic changes can lead to [[paramutation]]s, which do not follow the Mendelian heritage rules. These epigenetic marks are carried from one generation to the next, with one allele inducing a change on the other.{{sfn|Cone|Vedova|2004}}