Epigenetic variation amongst polyploidy crop species

Abstract

Many agronomically important crop species such as wheat are (or were once) polyploid, with at least one round of whole genome duplication occurring before domestication. This genetic buffering or redundancy allows for sequence divergence, and in turn the development of functional variations between duplicated genes (homoeologues). Homoeologues may encode proteins with different properties and plant breeders have successfully used this genetic resource to introduce new genetic diversity into breeding populations. However duplicated genes are also subject to extensive epigenetic control and are therefore not always equally expressed. The preferential bias in the expression or the silencing of a specific homoeologue may be heritable and can be stable across many generations. There is also mounting evidence to suggest that selective homoeologue expression occurs in response to stresses such as salinity and may be specific to individual pathways or processes. Importantly, this type of epigenetic variation may segregate within a breeding population and is readily observed in newly synthesised polyploid hybrids. It is now known that heritable phenotypic characteristics are determined by a combination of both genotype and epigenotype. Therefore the epigenome of polyploid crop species such as wheat and cotton represents a potent new source of diversity for agronomically important traits such as those linked to abiotic stress, secondary metabolite synthesis and fibre development. This text describes the characterisation of epigenetic variation in polyploidy crop species and its potential for exploitation by breeders for crop improvement.