Abstract
Flower bud dormancy in temperate fruit tree species, such as almond [Prunus dulcis (Mill.) D.A. Webb], is a survival mechanism that ensures that 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 (CRs) 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, we therefore monitored three almond cultivars with different CRs and flowering times by RNA sequencing during the endodormancy release of flower buds and validated the data by quantitative real-time PCR in two consecutive seasons. We were thus able to identify early and late flowering time candidate genes in endodormant and ecodormant almond flower buds associated with metabolic switches, transmembrane transport, cell wall remodeling, phytohormone signaling and pollen development. These candidate genes were indeed involved in the overcoming of the endodormancy in almond. 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.
Highlights
IntroductionIn almond [Prunus dulcis (Mill.) D.A. Webb], kernels are the main commercial component (Gradziel and Martínez-Gómez 2013), and they can be consumed fresh, processed or as a functional food (Musa-Veloso et al 2016)
As mentioned in the results section, expression differences among cultivars were mainly observed in the AB state (Figure S1 available as Supplementary data at Tree Physiology Online), when at least 40% of the chilling requirements (CRs) of each cultivar had accumulated but phenological evolution assessed by the forcing method did not account for dormancy release
The natural progression from endodormancy to ecodormancy of a traditional early flowering almond cultivar (Desmayo Largueta) versus two extra/ultra-late flowering almond cultivars (Penta and Tardona) from our Almond Breeding Program was monitored by gene expression in flower buds, identifying potential dormancy-associated candidate genes related to sugar synthesis and mobilization, lipid peroxidation, coumarate metabolism, transmembrane transport, cell wall remodeling and abscisic acid (ABA) synthesis and signaling
Summary
In almond [Prunus dulcis (Mill.) D.A. Webb], kernels are the main commercial component (Gradziel and Martínez-Gómez 2013), and they can be consumed fresh, processed or as a functional food (Musa-Veloso et al 2016). Almond breeding programs are focused on obtaining new cultivars that are more productive, have a higher fruit quality and are adapted to different environmental conditions. Flowering time (Martinez-Gomez et al 2017), self-compatibility (Sánchez-Pérez et al 2004) and kernel sweetness (Sánchez-Pérez et al 2019) are the main traits breeders that are focused on. Flowering time, which depends on the weather conditions with a combination of chill and heat requirements, is essential for the simultaneous crosspollination of self-incompatible cultivars; it is key in avoiding the loss of crops due to late frosts. Essential for floral development (Sánchez-Pérez et al 2012)
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