5-Azacytidine: A Promoter of Epigenetic Changes in the Quest to Improve Plant Somatic Embryogenesis

Abstract

Somatic embryogenesis (SE) is a widely studied process due to its biotechnological potential to generate large quantities of plants in short time frames and from different sources of explants. The success of SE depends on many factors, such as the nature of the explant, the microenvironment generated by in vitro culture conditions, and the regulation of gene expression, among others. Epigenetics has recently been identified as an important factor influencing SE outcome. DNA methylation is one of the most studied epigenetic mechanisms due to its essential role in gene expression, and its participation in SE is crucial. DNA methylation levels can be modified through the use of drugs such as 5-Azacytidine (5-AzaC), an inhibitor of DNA methylation, which has been used during SE protocols. The balance between hypomethylation and hypermethylation seems to be the key to SE success. Here, we discuss the most prominent recent research on the role of 5-AzaC in the regulation of DNA methylation, highlighting its importance during the SE process. Also, the molecular implications that this inhibitor might have for the increase or decrease in the embryogenic potential of various explants are reviewed.

Keywords: 2,4-dichlorophenoxyacetic acid (2,4-D); 5-Azacytidine; DNA methylation; epigenetics; hypomethylation; in vitro; plant tissue culture; somatic embryogenesis.

Figure 1

In plant somatic embryogenesis, genetic (green) and epigenetic (yellow) mechanisms induce the development of embryogenic cells from any explant (cells isolated from the leaves, shoots or roots). Due to the totipotentiality properties of plant cells, a group of embryogenic cells can develop into a complete and functional plantlet.

Figure 2

Differences between direct somatic embryogenesis (SE) and indirect SE during the induction and developmental stages in dicotyledonous and monocotyledonous plants.

Figure 3

(A) Relations between levels of cell differentiation, DNA methylation and embryogenic potential between different kinds of plant tissues used as explants; (B) differences in DNA methylation and embryogenic potential between embryogenic and non-embryogenic callus; (C) dynamics of DNA methylation levels throughout the SE process.

Figure 4

Global DNA methylation, SAM and ethylene dynamics when 2,4-D and 5-AzaC are added to the culture media during the SE process. SAM: S-adenosylmethionine. 2,4-D: 2,4-Dichlophenoxyacetic acid. GDM: global DNA methylation. The purple arrow represents the dynamics of GDM. The red arrow represents the amount of 2,4-D added into the culture medium. The green arrow represents the decrease in endogenous ethylene reported in different studies. The orange arrow represents the increase in the accumulation of endogenous SAM reported in different studies.