Global and local adaptation to aridity in a desert plant Gymnocarpos przewalskii

In order to thrive and survive plant species need to combine stability in the long term and rapid response to environmental challenges in the short term. The former would be reflected by global adaptation across species and the latter by pronounced local adaptation among populations of the same species. It remains unclear how much overlap is to be expected between the parts of the genome associated to these two contrasted adaptation processes. In the present study, we generated a high-quality genome and re-sequenced 177 individuals for Gymnocarpos przewalskii, an important desert plant species from North-West China, to detect local adaptation. To test for global adaptation to aridity at the molecular level we compared genomic data of 15 species that vary in their ability to withstand drought. A total of 118 genes were involved in global adaptation to aridity. Sixty-five G. przewalskii genes were shared across all xerophytic species, of which sixty-three were under stabilizing selection and two under directional selection. While 20% of G. przewalskii genome showed signatures of local adaptation to aridity during population divergence, only 13 of those genes were also under global adaptation. Hence, our results suggest that long-term stability is crucial for adaptation to extreme environmental stress but is only maintained in a small group of highly pleiotropic genes while a rapid response to recent changes elicits a genome-wide response, including gene family expansion. The overlap between the two evolutionary mechanisms appears limited.