Trichostatin A Triggers an Embryogenic Transition in Arabidopsis Explants via an Auxin-Related Pathway.

Barbara Wójcikowska,Joanna Morończyk,Jagna Karcz,Tomasz Nodzyński,Malwina Botor,Małgorzata D Gaj,Anna Maria Wójcik

doi:10.3389/fpls.2018.01353

Abstract

Auxin is an important regulator of plant ontogenies including embryo development and the exogenous application of this phytohormone has been found to be necessary for the induction of the embryogenic response in plant explants that have been cultured in vitro. However, in the present study, we show that treatment of Arabidopsis explants with trichostatin A (TSA), which is a chemical inhibitor of histone deacetylases, induces somatic embryogenesis (SE) without the exogenous application of auxin. We found that the TSA-treated explants generated somatic embryos that developed efficiently on the adaxial side of the cotyledons, which are the parts of an explant that are involved in auxin-induced SE. A substantial reduction in the activity of histone deacetylase (HDAC) was observed in the TSA-treated explants, thus confirming a histone acetylation-related mechanism of the TSA-promoted embryogenic response. Unexpectedly, the embryogenic effect of TSA was lower on the auxin-supplemented media and this finding further suggests an auxin-related mechanism of TSA-induced SE. Congruently, we found a significantly increased content of indolic compounds, which is indicative of IAA and an enhanced DR5::GUS signal in the TSA-treated explants. In line with these results, two of the YUCCA genes (YUC1 and YUC10), which are involved in auxin biosynthesis, were found to be distinctly up-regulated during TSA-induced SE and their expression was colocalised with the explant sites that are involved in SE. Beside auxin, ROS were extensively accumulated in response to TSA, thereby indicating that a stress-response is involved in TSA-triggered SE. Relevantly, we showed that the genes encoding the transcription factors (TFs) that have a regulatory function in auxin biosynthesis including LEC1, LEC2, BBM, and stress responses (MYB118) were highly up-regulated in the TSA-treated explants. Collectively, the results provide several pieces of evidence about the similarities between the molecular pathways of SE induction that are triggered by TSA and 2,4-D that involve the activation of the auxin-responsive TF genes that have a regulatory function in auxin biosynthesis and stress responses. The study suggests the involvement of histone acetylation in the auxin-mediated release of the embryogenic program of development in the somatic cells of Arabidopsis.

Highlights

Epigenetic modifications of DNA and histones are believed to play a pivotal role in controlling the development processes in animals and plants
In order to examine the role of histone acetylation in the epigenetic control of the embryogenic transition that was induced in the somatic plant cells, the effect of trichostatin A (TSA) was assessed in the immature zygotic embryo (IZE) explants of Arabidopsis that were cultured in vitro
We found that 42–61% of the explants treated with 0.1–1.0 μM of TSA underwent somatic embryogenesis (SE) induction and that an average of 27 of the embryo-like structures were produced per explant (Figure 2A)

Summary

Introduction

Epigenetic modifications of DNA and histones are believed to play a pivotal role in controlling the development processes in animals and plants (reviewed by Feng et al, 2010; Lauria and Rossi, 2011). The acetylation of lysine residues on the N-terminal tails of histones results in the removal of their positive charge, which alters the histone-histone and histone-DNA interaction and changes the accessibility of DNA to the chromatin-binding proteins (Turner, 2000). Two families of antagonistically acting enzymes, histone acetyltransferases (HATs) and histone deacetylases (HDACs), are responsible for the dynamic changes in the state of histone acetylation. The interplay between the HAT and HDAC enzymes contributes to the control of many biological processes including embryo development, seed dormancy and germination, morphogenesis, light signaling and flowering of Arabidopsis (reviewed by Boycheva et al, 2014; Wang et al, 2014). Histone acetylation has been postulated to regulate the transcription of the genes that control the stress responses (Liu et al, 2014) and plant-to-plant interactions (Venturelli et al, 2015)

Methods

Results

Conclusion