Abstract
Somatic embryogenesis (SE), which is a process that involves the in vitro-induced embryogenic reprogramming of plant somatic cells, requires dynamic changes in the cell transcriptome. These changes are fine-tuned by many genetic and epigenetic factors, including posttranslational histone modifications such as histone acetylation. Antagonistically acting enzymes, histone acetyltransferases (HATs) and deacetylases (HDACs), which control histone acetylation in many developmental processes, are believed to control SE. However, the function of specific HAT/HDACs and the genes that are subjected to histone acetylation-mediated regulation during SE have yet to be revealed. Here, we present the global and gene-specific changes in histone acetylation in Arabidopsis explants that are undergoing SE. In the TSA (trichostatin A)-induced SE, we demonstrate that H3 and H4 acetylation might control the expression of the critical transcription factor (TF) genes of a vital role in SE, including LEC1, LEC2 (LEAFY COTYLEDON 1; 2), FUS3 (FUSCA 3) and MYB118 (MYB DOMAIN PROTEIN 118). Within the HATs and HDACs, which mainly positively regulate SE, we identified HDA19 as negatively affecting SE by regulating LEC1, LEC2 and BBM. Finally, we provide some evidence on the role of HDA19 in the histone acetylation-mediated regulation of LEC2 during SE. Our results reveal an essential function of histone acetylation in the epigenetic mechanisms that control the TF genes that play critical roles in the embryogenic reprogramming of plant somatic cells. The results implicate the complexity of Hac-related gene regulation in embryogenic induction and point to differences in the regulatory mechanisms that are involved in auxin- and TSA-induced SE.
Highlights
Chromatin, which is a complex of DNA and histones, plays a central role in controlling the gene expression at the transcriptional level by modulating the accessibility of DNA to the transcription factors (TFs) [1]
An RNAqueous Total RNA Isolation Kit (Thermo Fisher Scientific, Waltham, MA, USA) was used to isolate the total RNA from the immature zygotic embryos (IZEs) explants that had been induced on the EA medium for 0, 5 and 10 days according to the manufacturer’s instructions
We previously indicated that trichostatin A (TSA) treatment resulted in Somatic embryogenesis (SE) induction on an auxin-free medium, which suggests that histone acetylation (Hac) plays a role in the mechanism that controls the embryogenic reprogramming of plant somatic cells [38]
Summary
Chromatin, which is a complex of DNA and histones, plays a central role in controlling the gene expression at the transcriptional level by modulating the accessibility of DNA to the transcription factors (TFs) [1]. In contrast to DNA methylation, the role of the histone modification, including histone acetylation (Hac), in regulating gene expression is less recognised, primarily because of the limited number of available analytical tools [3]. New molecular methods applied in epigenetics have contributed to significant progress in revealing experimental evidence about the essential role of histone modifications, including Hac, in regulating the gene expression in various organisms, including plants [4,5]. During the Hac-mediated regulation of gene expression, histone acetyltransferases (HATs) neutralise the positive charge of lysine in the histone tails, and that, in turn, promotes an “open” and transcriptionally permissive chromatin structure [6]. In order to activate or repress the target gene expression, HATs and HDACs act as a part of the transcriptional complexes and control many developmental processes in plants [8]. In addition to functioning in the transcriptional complexes, HATs and HDACs might control the de/acetylation state of the non-histone proteins [8,9]
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