Abstract
The Dormancy-associated MADS-box (DAM) 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 DAM genes remains unclear. Here, we demonstrate that chilling downregulates DAM1 and DAM3–6 in dormant floral buds with distinct patterns and identify DAM4 as the most abundantly expressed one. We reveal multiple epigenetic events, with tri-methyl histone H3 lysine 27 (H3K27me3) induced by chilling specifically in DAM1 and DAM5, a 21-nt sRNA in DAM3 and a ncRNA induced in DAM4. Such induction is inversely correlated with downregulation of their cognate DAMs. We also show that the six DAMs 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 DAM. We further show that the expression of the five DAMs 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 DAM4. Such robust increase of repressive epigenetic marks may irreversibly reinforce the chilling-imposed repression of DAMs to ensure flower-developmental programming free from any residual DAM inhibition. Taken together, we reveal novel information about genetic and epigenetic regulation of the DAM 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.
Highlights
Dormancy is an adaptation that enables perennial plants to survive unfavorable seasonal stresses
We show that the chilling and successive warm temperatures regulate diverse epigenetic events that may synergically enable Dormancy-associated MADS-box (DAM) rapidly downregulated under the chilling condition and irreversibly repressed during growth seasons, allowing the flower developmental pace successfully proceeded and flower buds breaking at a proper time or season
In the floral and lateral buds, DAM5 and DAM6 were shown to be downregulated by chilling during dormancy release[11,26,29], suggesting that DAM5 and DAM6 are involved in chilling requirement and dormancy release in those buds as well
Summary
Dormancy is an adaptation that enables perennial plants to survive unfavorable seasonal stresses. In contrast to dormant vegetative buds that are believed to primarily arrest at G1 phase of the cell cycle and remain quiescent during the chilling period[10], the dormant peach floral buds undergo morphological changes[11], with evident formation of distinct archesporial cells and epidermis, microsporangium walls and tapetum in the anthers[12,13], and visible ovules in the carpel/gynoecium[14,15,16] These floral morphological changes rarely occur in the fully dormant floral buds maintained at ambient or warm temperatures[11]. Chilling couples the dormancy release with floral developmental programming and only critical stages (e.g. ovule formation) driven through by chilling renders the floral buds capably released from dormancy or competent to grow in spring
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