Poplar stems show opposite epigenetic patterns during winter dormancy and vegetative growth

In this study the identification of epigenetic marks of closed and open chromatin states has been performed by immunofluorescence in vibratome-thick sections from poplar stems, followed by quantification of the signal in a representative population of individual nuclei on a confocal microscope. Unlike other methods often used for detection of global DNA methylation levels, the procedure hereby proposed can be applied to a wide range of specimens regardless of the purity and yield of genomic DNA extraction and in a tissue-dependent manner. Using antibodies to 5-methylcytidine and acetylated lysine 8 of histone H4, as reliable indicators of transcription incompatible and compatible chromatin states, respectively, the influence of epigenetic regulation on differential gene expression during the growth and arrest periods in xylem and phloem tissues was assessed. The fluorescence signal of 5-methylcytosine was significantly higher in winter as compared with summer. Conversely, the fluorescence signal for acetylated Lys 8 of histone H4 was significantly higher in summer than in winter in both tissues examined. Collectively, these results put forward an epigenetic control of winter dormancy in poplar stems.