Promoting gene expression in plants by permissive histone lysine methylation

Plants have evolved sophisticated epigenetic regulatory mechanisms to coordinate changes in gene expression during development and in response to environmental stimuli. Epigenetics refers to the modification of DNA and chromatin associated proteins, which affect gene expression and cell function, without changing the genetic code. Such modifications are inherited through cell division or mitosis, and in rare instances through meiosis, although it can be reversible and thus regulatory. Epigenetic modifications are controlled by groups of proteins, such as the family of histone lysine methytransferases (HKMTs). The catalytic core known as the SET domain encodes HKMT activity and either promotes of represses gene expression. A large family of SET domain proteins is present in Arabidopsis where there is growing evidence that two classes of these genes are involved in promoting gene expression in a diverse range of developmental processes. This review will focus on the function of these two classes and the processes that they control and highlight the huge potential this regulatory mechanism has in plants.