Epigenetics: History, present status and future perspective

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.