Transcriptome changes associated with cold acclimation in leaves of olive tree (Olea europaea L.)

Olea europaea L. ssp. sativa is an evergreen fruit tree well adapted to the climate conditions of the Mediterranean basin. Its cultivation in northern regions may expose the plants to cold and frost damages during winter, although the maturation of olive fruit in cool environments may provide olive oil with peculiar qualitative characteristics. Thisworkaimsatstudyingshort-andlong-termtranscriptional changes occurring in leaves of olive trees cv. Leccino exposed to a progressive lowering of temperatures, till −4 °C. Followinga RNA-Seqanalysis, a leaf transcriptome comprising 44,332 transcripts has been de novo assembled and 5464 differentially expressed genes (DEGs) identified. Transcriptomic data identified almost all the typical components of the known and conserved molecular repertoire of the plant cold response, including changes in membrane composition-related genes, induction of cold-regulated genes (cor), and transcription factors, and downregulation of photosynthesis-relatedgenes.Besidestheknowncomponents of cold response, we also identified some specific features characterizing the cold response of olive tree. Indeed, during cold acclimation, olive tree leaves induced genes of the glutathione cycle, polyamine and flavonoid pathways, likely to support reactive oxygen species (ROS) scavenging, as well as genes of the raffinose and trehalose biosynthetic pathways to sustain the accumulation of osmolytes. Further, the signaling pathway of abscisic acid (ABA) was strongly implicated, while induction of genes responsible for synthesis of callose and lignins indicated changes in composition of cell wall. In parallel to the transcriptome analysis, a CBF-like transcript has been identified and its expression profile studied in the reference cv. Leccino as well as in seven cvs. differing for cold tolerance.