Transcriptome analysis of endodormant and ecodormant flower buds in early- and late-flowering almond cultivars

Flower bud dormancy in temperate fruit tree species, like almond [Prunus dulcis (Mill.) D.A. Webb], is a survival mechanism that ensures flowering will occur under suitable weather conditions for successful flower development, pollination and fruit set. Dormancy is divided into three sequential phases: paradormancy, endodormancy and ecodormancy. During the winter, buds need cultivar-specific chilling requirements to overcome endodormancy and heat requirements to activate the machinery to flower in the ecodormancy phase. One of the main factors that enables the transition from endodormancy to ecodormancy is transcriptome reprogramming. In this work, three almond cultivars with different chilling requirements and flowering times were monitored by RNA sequencing during the endodormancy release of flower buds. Candidate endodormancy and ecodormancy genes were identified, and differentially expressed genes (DEGs) associated with metabolic switches, cell-to-cell transport, cell wall remodeling, phytohormone signaling and pollen development were commonly found in the general endodormancy release processes. This information may be used for the development of dormancy molecular markers, increasing the efficiency of temperate fruit tree breeding programs in a climate change context.