Micropropagation and genetically modified plants are produced through tissue culture techniques. New genes are introduced into single plant cells that are growing in culture. Each cell then replicates and is eventually made to regenerate into a complete plant with the introduced genes by the application of appropriate plant hormones.
In addition to the genes that comprise its genome, the genetic make-up of an organism also includes its epigenome. This can be defined as a genome modified with small groups of molecules such as methylation or acetylation, that influence the levels of expression of the encoded protein. In other words these groups act as epigenetic signals.
Now, work at four laboratories, namely, at the University of California, Howard Hughes Medical Institute, LA, Ohio State University and the Biotechnology Center at the University of Delaware carried out by nine geneticists show that the epigenome is altered by subjecting plant cells to tissue culture conditions. This work by Stroud and eight of his associates reported in elite.elifesciences clearly established the differences by using high throughput sequencing analysis of normal and tissue culture derived plant cells. They generated whole-genome, single-nucleotide resolution maps of DNA methylation in several regenerated rice lines and found that regenerated plants produced in culture showed less methylation than control plants. This pattern of methylation was produced only if the plant cells were subjected to tissue culture and was independent of genetic transformation with inserted genes. The changes were relatively over-represented around the promoter sequences of genes—regions of DNA that act as binding sites for the enzymes that transcribe DNA into RNA—and were accompanied by changes in gene expression. Importantly, progenies of the originally regenerated plant frequently also inherited the changes in methylation status. These results are likely to be a part of the explanation for the phenomenon called somaclonal variation, first observed before the era of modern biotechnology, in which plants regenerated from tissue culture sometimes showed heritable alterations in the phenotype of the plant.