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Fruit trees from temperate and boreal regions have developed specific physiological mechanisms in order to adapt their development and growth to seasonal changing conditions. One of these mechanisms is the winter bud dormancy, which protects tree meristems against low temperatures. In apple trees (Malus domestica), cold temperatures induce bud dormancy at the end of summer/beginning of the fall. During winter, buds stay dormant and will not resume growth until they are exposed to a certain period of cold known as chilling requirement. Once chilling requirement is satisfied, dormancy is released and buds can resume growth (budbreak) and initiate flowering in response to warm temperatures in spring. In the model plant species Arabidopsis thaliana, it has been shown that small RNAs are involved in the temperature-mediated control of flowering time. Small RNAs also modulate temperature responses in woody plant species, such as grapevine, poplar and pear. However, it remains unclear how small RNAs are involved in the temperature-mediated control of dormancy and budbreak timing in fruit tree species. Therefore, in this work we aimed at identifying small RNAs potentially implicated in dormancy and budbreak using apple as a fruit tree model. For this purpose, we performed a small RNA sequencing on bud samples during a dormancy time-course experiment. This experiment resulted in the identification of 373 different potential micro RNAs (miRNAs), including 105 already known apple miRNAs. From them, thirty-nine were differentially expressed during the dormancy progression, suggesting their role in this process. The possible targets were identified in silico and classified according to their potential molecular function. Remarkably, targets of the identified miRNAs were related to growth control and hormonal signaling, cell wall modification, global transcriptional and post-transcriptional regulation, among other significant pathways. In conclusion, we identified several apple miRNAs and their targets that are potentially involved in genetic networks controlling dormancy and budbreak in fruit tree species. |
