DNA Methylation/Demethylation Programming During Peach Flower Bud Dormancy Release, Development and Blooming

Peach flower bud development undergoes a long, complex and temperature-dependent regulation process, with  cessation of growth in response to cool temperatures in  late fall, a slow but gradual development during the chilling period in winter and eventually blooming in early spring. It has been demonstrated that the dormant flower buds absolutely require a certain period of accumulative chilling temperature prior to bud break, and warm temperatures for late development and blooming. Thus, chilling and heat requirements constitute unique and important regulatory features for peach flower bud. In this study, we took a deep sequencing approach to investigate epigenetic mechanisms underlying the chilling and heating requirement of peach flower buds. We identified over 2400 differentially methylated genome regions  (DMRs) in  the buds before and after chilling treatment, with 75% of them up-methylated and 25% down-methylated, indicating that the chilling temperature is primarily correlated with increased DNA methylation. We also identified over 17,000 DMRs during the late developmental period between the times that the chilling requirement is met and bloom.  Of the total DMRs identified, 7,201 are located in repetitive and intergenic regions while 10,195 are in intragenic regions, many of which are located in promoter regions. During bloom we found that 97% of the total DMRs identified are down-methylated while only 3% of them are up-methylated, in contrast to that observed during chilling treatment. Our study provides evidence that a robust demethylation program occurs during late flower development and bloom, which is further supported by the transcriptome analysis of a number of genes which are directly and indirectly involved in DNA demethylation and methylation. The potential biological significance of this work will be discussed.