Adaptation and diversification in the Canary island endemic Descurainia (Brassicaceae)

Abstract

Oceanic archipelagos provide striking examples of plant lineages that have radiated rapidly over steep ecological gradients, often demonstrating remarkable adaptations. Here, we investigate the evolutionary processes behind the diversification and adaptation of the Canary Island Descurainia (Brassicaceae), an island cousin of Arabidopsis. Canary Island Descurainia is comprised of seven species that have rapidly radiated across islands and along an elevation cline, with several species occupying high-elevation habitats. Genotyping-by-sequencing (GBS) was employed to infer the roles ecology, geographical isolation, and hybridisation have played in the diversification of these seven species. At least three geographical shifts and one ecological shift between high- and low elevation species were identified, as well as a putative hybrid origin for one species. A high-quality reference genome was generated for Descurainia millefolia, with a final size of 180 megabases and an N50 of 290 k. Through comparative phylogenomic, we confirmed the placement of Descurainia within Lineage I of Brassicaceae. Through whole-genome re-sequencing, representing the seven species of Canary Island Descurainia, we compare the low-elevation species and high elevation species to identify candidate genes that may incur adaptation to sub-alpine environments. A Gene Ontology (GO) enrichment analysis on positively selected genes (PSGs) revealed genes associated with changes in flowering times and genes likely related to adaptation to the harsher high-elevation environment (for instance, cold and UV tolerance). We further provided evidence that one of our candidate genes incurs drought tolerance through T-DNA knockouts and a greenhouse water stress experiment. Overall, using Canary Island Descurainia as a model, our analyses have helped to understand the evolutionary processes behind the diversification of island plants, as well as broader questions surrounding adaptation.

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Identifiers

ORCID for Amy Clare Jackson: orcid.org/0000-0003-0660-0181

ORCID for Mark Chapman: orcid.org/0000-0002-7151-723X

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