Functional characterization of two almond C-repeat-binding factors involved in cold response

Low temperature plays a crucial role in seasonal development of woody plants and may directly impact crop production, more particularly in temperate fruit trees. Given its high genetic variability and adaptability to different climatic conditions, almond (Prunus dulcis Mill.) is an interesting model to understand the mechanisms regulating low temperature sensing in fruit trees. In this paper, we report the cloning and characterization of two genes (PdCBF1 and PdCBF2) belonging to the C-repeat-binding factor (CBF) family of transcription factors. Southern blotting analysis showed that this family is composed of at least five members. In almond shoots propagated in vitro, transcription of these genes was rapidly induced by low temperature, suggesting an involvement in cold acclimation. Transactivation assays showed that PdCBF1 and PdCBF2 could bind to dehydration responsive element/C-repeat containing sequences, as activators of gene expression. In addition, induction of both PdCBFs by cold was higher towards the end of the day, which agreed with the expression pattern of PdDehydrin1, a predicted CBF target gene. Furthermore, PdCBF1 and PdCBF2 were also transiently induced by abscisic acid and drought treatments. Considering the bin mapping analysis that correlated PdCBFs and PdDHN1 (respectively in linkage groups 5 and 7) with two different quantitative trait locicontrolling blooming time, it is relevant to perform further association studies that may validate their effect on this trait.