Evidence of chromatin and transcriptional dynamics for cold development in peach flower bud.

• In temperate zones, fruit trees regulate their annual growth cycle to seasonal environmental changes. During the cold season, growth is limited by both environmental and genetic factors. After the exposure to low temperature and fulfillment of chilling requirements, mild temperatures promote the growth and flowering. However, an insufficient chilling exposure may lead to non-uniform blooming, with a negative impact on fruit set. • To gain insights into the flower development in the fruit tree buds, peach is an interesting model, flower and vegetative bud being distinct organs. To understand how flower bud development is regulated, we integrated cytological observations, epigenetic and chromatin genome wide data with transcriptional changes, to identify the main regulatory factors involved in flower development during chilling accumulation. • We demonstrated that there is not growth cessation in peach flower buds during chilling accumulation, but there are changes in transcript level of key genes of hormone metabolism and flower bud development, in distribution of histone modifications (H3K4me3 and H3K27me3), and DNA methylation. • All together our findings indicate that during the cold season flower bud is in a non-dormant status and that the chilling experience allows flower differentiation to be completed.