Winter dormancy is an adaptative mechanism that temperate and boreal trees have developed to protect their meristems against low temperatures. In apple trees (Malus domestica), cold temperatures induce bud dormancy at the end of summer/beginning of the fall. Apple buds stay dormant during winter until they are exposed to a period of cold, after which they can resume growth (budbreak) and initiate flowering in response to warmer temperatures in spring. It is well-known that small RNAs modulate temperature responses in many plant species, but however, how small RNAs are involved in genetic networks of temperature-mediated dormancy control in fruit tree species remains unclear. Here, we have made use of a recently developed ARGONAUTE (AGO)-purification technique to isolate small RNAs from apple buds. A small RNA-seq experiment resulted in the identification of 17 micro RNAs (miRNAs) that change their pattern of expression in apple buds during dormancy. Furthermore, the functional analysis of their predicted target genes suggests a main role of the 17 miRNAs in phenylpropanoid biosynthesis, gene regulation, plant development and growth, and response to stimulus. Finally, we studied the conservation of the Arabidopsis thaliana regulatory miR159-MYB module in apple in the context of the plant hormone abscisic acid homeostasis.

The biotrophic oomycete Plasmopara viticola is the causal agent of downy mildew, one of the major grapevine diseases. We report here a successful strategy to cross compatible strains of this pathogen and obtain a large viable progeny. We used this method to study the offspring between two P. viticola strains able to overcome two major grapevine resistance factors (Rpv3, Rpv10). Thanks to the genomic resources now available, we will genotype this progeny to build an unprecedented linkage map and uncover the genomic bases of grapevine resistance breakdown displayed by P. viticola virulent strains.