Eukaryotic DNA is tightly packed into chromatin, a DNA–protein structure that exists as transcriptionally permissive euchromatin or repressive heterochromatin. Post-translational modification of histones plays a key role in regulating chromatin dynamics. Short peptides derived from various sources are known to function as epigenetic modulators; however, their mechanisms of action are poorly understood. We addressed this issued by investigating the effect of peptide AEDL on chromatin structure in tobacco (Nicotiana tabacum L.), a commercially important plant species. The chromatin of tobacco interphase cells is characterized by the presence of zones of transcriptionally active domains and particular domains of condensed chromatin of cells that partially coincide with heterochromatin zones. Chromatin decondensation and the formation of euchromatin, accompanied by the activation of genes expression activity, are a determining factor in responses to stressful effects. Our results show that plants grown in the presence of 10 ?7 M peptide AEDL transformed condensed chromatin domains from 45% in control cells to 25%. Histone modifications, which constitute the so-called histone code, play a decisive role in the control of chromatin structure. Fluorescence quenching experiments using fluorescein isothiocyanate-labeled histones revealed that the linker histone H1 and complexes of core H3 and H1 histones with DNA bound to peptide AEDL in a 1: 1 molar ratio. The peptide was found to bind to the N-terminal lysine residue of H1 and the lysine residue at position 36 of the H3 C terminus. These interactions of histones H1 and H3 with AEDL peptide loosened the tightly packed chromatin structure, getting transcriptionally active euchromatin. Our findings provide novel insight into the mechanism of gene regulation by short peptides and have implications for breeding more resistant or productive varieties of tobacco and other crops.
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