Cold acclimation and floral development in almond bud break: insights into the regulatory pathways

Abstract

In temperate fruit trees, seasonal dormancy and cold acclimation have a major impact on blooming time and, consequently, fruit production. To gain insight into the still unclear molecular processes underlying blooming, expression of genes putatively involved in the cold response was studied in almond (Prunus dulcis Mill.), which is the earliest fruit tree in the family Rosaceae to bloom. The transcript levels of two C-repeat binding factor (PdCBF) genes and one of their putative targets, PdDehydrin1 (PdDHN1), were analysed in flower buds and shoot internodes during seasonal dormancy up to bud break. In parallel, expression of candidate genes related to flower development was also followed. In a 2-year study, PdCBF2 showed a progressive increase in transcript abundance during the autumn in close correlation with cold acclimation, while high transcript levels of PdCBF1 and PdDHN1 were already found by summer. After bud break, with temperatures still within the chilling range, both PdCBF genes and PdDHN1 were found to sharply reduce transcription in flower buds and internodes, suggesting damping of CBF-mediated cold signalling during growth resumption, in correlation with cold hardiness decline. Flower bud break was also followed by a decrease in the expression of PdGA20OX, a candidate gene involved in gibberellin biosynthesis, and an increase in the expression of two homeotic genes related to floral organ development, PdMADS1 and -3. These genes may also be relevant players in the regulation of anthesis in this model Rosaceae species.

De Novo Transcriptome Assembly and Comparative Analysis of Differentially Expressed Genes in Prunus dulcis Mill. in Response to Freezing Stress

“…Different studies evaluated the frost injury in almond trees, however, molecular processes involved in the cold response are poorly investigated in this plant [23]. Although, Barros et al [23] recently demonstrated the role of PdCBF2 in cold acclimation of almond, to our current knowledge, there is no study on the molecular responses of almond to frost stress.…”

Prunus transcription factors: breeding perspectives

“…Another class of TFs belonging to the CBF family has been well-documented as being related to cold response and acclimation in peach, almond, apricot, cherry, and Japanese apricot (Kitashiba et al, 2002; Owens et al, 2002; Tittarelli et al, 2009; Li et al, 2009; Barros et al, 2012a,b; Trainin et al, 2013; Zhang et al, 2013; Guo et al, 2014). CBF proteins belong to the CBF/DRE binding ( DREB ) sub-family of the Apetala2-ethylene responsive factor (AP2/ERF) (Nakano et al, 2006).…”

“…These results were attributed to the great variation among CBF genes, which can explain the variation in cold tolerance among P. mume populations. Interestingly, CBF -specific CTR/DRE cis elements in promoters of peach PpDAM 5 and PpDAM 6 genes were also found, suggesting their association with a CBF-regulon (Barros et al, 2012b). …”

“…Plants respond to low temperatures by altering the expression of thousands of genes including TFs (Chinnusamy et al, 2007). In almond, Barros et al (2012b) showed that a progressive increase in the transcript abundance of PdCBF2 ( Prunus dulcis C-repeat binding factor) during autumn was closely related to cold acclimation. The AP2 domain is also considered a regulatory element that stimulates transcription in response to low temperatures in plants (Díaz-Martín et al, 2005).…”

“…The AP2 domain is also considered a regulatory element that stimulates transcription in response to low temperatures in plants (Díaz-Martín et al, 2005). The CBF genes belong to the AP2/EREBD multigene superfamily of TFs, and their relationship to cold response and acclimation in Prunus species is well-documented (Tittarelli et al, 2009; Barros et al, 2012a,b; Trainin et al, 2013). CBF genes are considered key regulators of cold acclimation, and the overexpression of CBF 1, 2 , or 3 is capable of improving freezing tolerance in A. thaliana plants (Owens et al, 2002).…”