How plants evolved to shape their microbiota is a long-standing question in ecology and evolution. We used natural plant variation and biogeography to dissect how plants evolved along with their microbiota to cope with aridity. To do so, we identified within-genus pairs of Brassicaceae species that are distributed vicariously across Israel’s steep precipitation gradient. This natural distribution offers an excellent framework for studying the evolution of plant-microbe interactions under arid conditions. Through eco-evolutionary common garden experiments, we compared the exudate profiles and microbiomes of these species and the European species Arabidopsis thaliana under drought and salinity stress. We identified drought- and salinity-typical belowground responses, both in the plant’s exudate profiles and in the composition of the root microbiota. In addition, we have generated an extensive bacterial culture collection representing the native microbiota of Israeli desert plants. We will use this collection to dive into the modes by which bacteria protect plants from drought, by using microbiome de-construction and gene deletion experiments. We have demonstrated that drought-adapted plants mount a unique below-ground response to drought conditions. Our next phase of experiments will establish if and to what extent plants evolved to supplement their own genomes with those of their microbiota to cope with challenging environments.
