Review article : Epigenetics : History, present status and future perspective

Abstract

Epigenetics refers to the heritable changes in the pattern
of gene expression resulting from the modification of DNA
bases, histone proteins and/or non-coding-RNA biogenesis
without altering the underlying nucleotide sequence.
Genome-wide epigenetic variations are being reported
which are often associated with variation in gene
expression. Many of these changes occur during
developmental processes and stress exposures. Both, the
level of gene expression and the epigenetic changes may
relapse to the pre-stress state shortly after removal of the
stress. One of the common mechanisms involved in
epigenetic changes is methylation of 5th carbon by the
action of the enzyme DNA methyltransferase. In addition,
histone proteins are post-translationally modified which
may affect transcription, DNA replication, chromosome
segregation/condensation, and/or DNA repair process.
Small-RNA (particularly small-interfering RNAs) play a
crucial role in DNA methylation via RNA-directed DNA
methylation (RdDM) pathway. The epigenetic changes in
plants induced by aforesaid processes can be inherited
over the generations in the form of epialleles. Epigenetic
change in genes caused by DNA methylation and/or histone
modifications during plant development often results in
phenotypic changes. It is becoming increasingly evident,
that epigenetic changes have important roles to play in
acclimatization, stress tolerance, adaptation, and evolution
processes. With the growing reports on epigenetic changes
affecting gene expression, it would be worth investigating
the epigenetic machinery of gene regulation in plants, and
their possible utilization in crop improvement. This review
focuses on the historical development and basics of
epigenetics followed by the present status and future
prospects in crop improvement.