Genetic and epigenetic control of dormancy transitions throughout the year in the monoecious cork oak.

Bud dormancy plays a vital role in flowering regulation and fruit production, being highly regulated by endogenous and environmental cues. Deployment of epigenetic modifications and differential gene expression control bud dormancy/break cycles. Information on how these genetic and epigenetic mechanisms are regulated throughout the year is still scarce for temperate trees such as Quercus suber. Here, the expression levels of CENTRORADIALIS-LIKE (CENL) and DORMANCY-ASSOCIATED PROTEIN 1 (QsDYL1) during seasonal cycles of bud development, suggesting that QsCENL may be implicated in growth cessation in Q. suber and that QsDYL1 is a good dormancy marker. As gene expression can be regulated by the activity of chromatin modifiers, we have analysed the expression of these genes and the deposition of epigenetic marks in dormant versus non-dormant bud meristems. The DNA methyl transferases CHROMOMEHTYLASE 3 (QsCMT3) and METHYLTRANSFERASE 1 (QsMET1) were more expressed in the transition between dormancy to bud swelling. QsCMT3 was also highly expressed during the late stages of active bud formation. Conversely, the HISTONE ACETYLTRANSFERASE 1 (QsHAC1) was up-regulated during growth cessation and dormancy when compared to bud swelling. These results indicate that epigenetic regulation is implicated in how bud development progresses in Q. suber, which can be observed in the different profile deposition of the repressive and active marks, 5mC and H3K18Ac/H3K4me, respectively. The identification of bud-specific genetic and epigenetic profiling opens new possibilities to predict the relative rate of dormancy/growth of the bud stages, providing tools to understand how trees respond to the current challenges posed by climate change.