Thermal-responsive genetic and epigenetic regulation of cluster controlling dormancy and chilling requirement in peach floral buds.

The () gene cluster in peach serves as a key regulatory hub on which the seasonal temperatures act and orchestrate dormancy onset and exit, chilling response and floral bud developmental pace. Yet, how different temperature regimes interact with and regulate the six linked genes remains unclear. Here, we demonstrate that chilling downregulates in dormant floral buds with distinct patterns and identify as the most abundantly expressed one. We reveal multiple epigenetic events, with tri-methyl histone H3 lysine 27 (H3K27me3) induced by chilling specifically in and , a 21-nt sRNA in and a ncRNA induced in 4. Such induction is inversely correlated with downregulation of their cognate s. We also show that the six s were hypermethylated, associating with the production of 24-nt sRNAs. Hence, the chilling-responsive dynamic of the different epigenetic elements and their interactions likely define distinct expression abundance and downregulation pattern of each . We further show that the expression of the five s remains steadily unchanged or continuously downregulated at the ensuing warm temperature after chilling, and this state of regulation correlates with robust increase of sRNA expression, H3K27me3 and CHH methylation, which is particularly pronounced in . Such robust increase of repressive epigenetic marks may irreversibly reinforce the chilling-imposed repression of s to ensure flower-developmental programming free from any residual inhibition. Taken together, we reveal novel information about genetic and epigenetic regulation of the cluster in peach, which will be of fundamental significance in understanding of the regulatory mechanisms underlying chilling requirement and dormancy release, and of practical application for improvement of plasticity of flower time and bud break in fruit trees to adapt changing climates.