Histone H3 and H4 acetylation patterns are more dynamic than those of DNA methylation in Brachypodium distachyon embryos during seed maturation and germination

Abstract

The transition of seeds from a dry to a metabolically active state requires significant changes in both the spatial and temporal patterns of gene expression, and this transcriptional reprogramming involves various modifications of the chromatin structure. There are several factors that can greatly influence the structure of chromatin, one of which is the chemical modifications of histone proteins and DNA itself. In this study, we analysed the distribution of three epigenetic markers, i.e. acetylation of histone H4 (H4K16ac) and histone H3 (H3K18ac) as well as DNA methylation (5mC) in Brachypodium distachyon embryos during the four stages of seed development-maturation, desiccation (quiescence), imbibition and germination. Our results indicate that both H4K16ac and H3K18ac are at a very high level in embryos during seed imbibition, but that the patterns of DNA methylation are considerably more stable in embryos during seed development.

Keywords: Brachypodium distachyon embryo; DNA methylation; Epigenetic modifications; H3K18ac; H4K16ac.

Fig. 1

Schematic representation of a longitudinal cross-section through a Brachypodium embryo. Squares within the embryo diagram indicate fragments of scutellum (I), SAM and leaf primordia (II) and RAM (III). Enlargements of these areas are shown in Figs. 3, 4, and 5. cl coleoptile, cr coleorhiza, rc root cap, Rpr RAM and primary root, sc scutellum, Spl SAM and primary leaf

Fig. 2

Immunodetection (green fluorescence) of unmodified H3 in imbibed Brachypodium embryo. Red (artificial colour) fluorescence—DAPI. Red colour of cell walls is caused by their autofluorescence. Scale bar represents 50 μm

Fig. 3

Immunodetection (green fluorescence) of H4K16ac in matured (a, e, i), ‘dry’ (b, f, j), imbibed (c, g, k) and germinating (d, h, l) Brachypodium embryos. Fragments of cross-sections through the scutellum (a–d), SAM (e–h) and RAM (i–l). Red (artificial colour) fluorescence—DAPI. Red colour of cell walls is caused by their autofluorescence. Scale bar represents 20 μm; all photomicrographs were taken at the same magnification

Fig. 4

Immunodetection (green fluorescence) of H3K18ac in matured (a, e, i), ‘dry’ (b, f, j), imbibed (c, g, k) and germinating (d, h, l) Brachypodium embryos. Fragments of cross-sections through the scutellum (a–d), SAM (e–h) and RAM (i–l). Red (artificial colour) fluorescence—DAPI. Red colour of cell walls is caused by their autofluorescence. Scale bar represents 20 μm; all photomicrographs were taken at the same magnification

Fig. 5

Immunodetection (green fluorescence) of 5mC in matured (a, e, i), ‘dry’ (b, f, j), imbibed (c, g, k) and germinating (d, h, l) Brachypodium embryos. Fragments of cross-sections through the scutellum (a–d), SAM (e–h) and RAM (i–l). Red (artificial colour) fluorescence—DAPI. Red colour of cell walls is caused by their autofluorescence. Scale bar represents 20 μm; all photomicrographs were taken at the same magnification