Drought stress priming induces morphological adaptation and methylome changes in apple seedlings.

Developing multiple stress-tolerant crops is the goal of many breeders in the current context of seasonal variability precipitated by the ongoing climate change. Among the most pressing stress, drought is becoming a major concern in many regions of the world. Plant responses to drought have been studied in many species, including perennial plants such as apple trees (Malus domestica); however, the effects of recurrent stress and the potential for stress memory, or priming, remain poorly described. Priming reflects the capacity of plants to “memorize” environmental stress experiences and potentially improve their responses to recurring stress. Such information may be retained through epigenetic modifications of DNA and associated histone proteins. This ability could enable training of plants to face future challenges. In this study, we explored the effects of recurrent drought stress on apple seedling morphology and investigated the epigenetic changes in plants subjected to this treatment. Our results indicate that naïve apple seedlings can be primed upon first exposure to drought stress, and that primed plants respond differently to recurrent stress later in the season. Analyses of differentially methylated regions further indicate that primed plants’ molecular responses differ significantly from plants exposed to drought stress for the first time. Finally, our results suggest that following a winter period, the previously induced priming effect may be partially lost. Overall, our study demonstrates the importance of studying recurrent stress to better understand the memory-associated mechanisms leading to morphological and DNA methylation modifications in perennial plants.