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.

Epigenetic Regulation of Auxin-Induced Somatic Embryogenesis in Plants

“…In the majority of reports, an inverse relationship has been observed between the embryogenic competence of explants/culture and the DNA methylation level. Accordingly, the hypomethylation of DNA seems to be associated with the early stages of embryogenic induction, and the embryogenic cultures have a lower level of 5mC than the non-embryogenic cultures (reviewed in [25]). However, the hypomethylation of DNA is not specific to the embryogenic induction and seems to be related to a general process of tissue dedifferentiation because both the embryogenic culture and non-embryogenic calli of Arabidopsis had a decreased 5mC content [24,138].…”

“…The contrasting effects of a demethylation agent, 5-azacitidine (5-AzaC), treatment on the embryogenic response of plant tissue offer further evidence that a complex set of exo-and endogenous culture factors rather than the induction of embryonic development per se appear to shape the global DNA methylation level in in vitro cultured tissue. Accordingly, 5-AzaC treatment has been recommended for improving the embryogenic capacity of cultures derived from poorly responding plant explants and the genotypes of in vitro recalcitrant plant species [25] including the recovery of the SE potential in aged cultures of Theobroma cacao [140]. However, the 5-AzaC treated explants of Arabidopsis showed a significantly reduced SE capacity [24].…”

“…The specific epigenetic marks that activate and repress gene transcription are indicated in green and red, respectively. Arrows and circle-shaped ends show the activation or repression of gene expression, respectively [14][15][16][17][18][19][20][21][22][23][24][25][26][27]. ( miRNAs, which are products of the MIRNA genes, are small (19 to 24 nucleotides long), single-stranded non-coding RNA molecules that regulate both the state of the chromatin-associated with their targets and the availability of the encoded transcripts for protein translation [26].…”

Target of Rapamycin Regulates Genome Methylation Reprogramming to Control Plant Growth in Arabidopsis

“…In plants, genome-wide demethylation caused by methylation inhibitor azacitidine leads to growth retardation, malformations, and changes in the flowering time or flower sexuality (Fieldes et al, 2005;Marfil et al, 2012). Interestingly, azacitidine can increase amounts of somatic embryos in somatic embryogenesis stage, indicating that DNA demethylation caused by azacitidine promotes the reprogramming of gene expression, acquisition of totipotency and initiation of embryogenesis in explant (Osorio-Montalvo et al, 2018).…”

“…The TOR signaling pathway is a central regulator in regulating cell growth, homeostasis, proliferation and metabolism (Dobrenel et al, 2016;Saxton and Sabatini, 2017;Shi et al, 2018). DNA methylation is an epigenetic mechanism that plays key roles in genome integrity, suppression of transposon, gene expression and somatic embryogenesis in plants (Osorio-Montalvo et al, 2018;Zhang et al, 2018). However, it has not been reported whether TOR directly or indirectly regulates the methylation level of genome DNA to control plant growth and development.…”