The genome of Draba nivalis shows signatures of adaptation to the extreme environmental stresses of the Arctic.

Michael D Nowak,Anne K Brysting,Martin A Lysak,Audun Schrøder‐Nielsen,Xinyi Guo,Christian Brochmann,Siri Birkeland,Tanja Slotte,Rimjhim Roy Choudhury,Christian Parisod,Marco Fracassetti,Abel Gizaw,Loren Rieseberg,Anna Lovisa S Gustafsson,Terezie Mandáková

doi:10.1111/1755-0998.13280

Abstract

The Arctic is one of the most extreme terrestrial environments on the planet. Here, we present the first chromosome‐scale genome assembly of a plant adapted to the high Arctic, Draba nivalis (Brassicaceae), an attractive model species for studying plant adaptation to the stresses imposed by this harsh environment. We used an iterative scaffolding strategy with data from short‐reads, single‐molecule long reads, proximity ligation data, and a genetic map to produce a 302 Mb assembly that is highly contiguous with 91.6% assembled into eight chromosomes (the base chromosome number). To identify candidate genes and gene families that may have facilitated adaptation to Arctic environmental stresses, we performed comparative genomic analyses with nine non‐Arctic Brassicaceae species. We show that the D. nivalis genome contains expanded suites of genes associated with drought and cold stress (e.g., related to the maintenance of oxidation‐reduction homeostasis, meiosis, and signaling pathways). The expansions of gene families associated with these functions appear to be driven in part by the activity of transposable elements. Tests of positive selection identify suites of candidate genes associated with meiosis and photoperiodism, as well as cold, drought, and oxidative stress responses. Our results reveal a multifaceted landscape of stress adaptation in the D. nivalis genome, offering avenues for the continued development of this species as an Arctic model plant.

Highlights

The Arctic accounts for ~10% of Earth's land surface, and the combination of high latitude and regional climate patterns make it one of the harshest terrestrial environments on the planet
In a recent study of its transcriptome, we identified numerous candidate genes for Arctic adaptation illuminating its potential as an Arctic model species (Birkeland et al, 2020)
Exploring the functional annotations of the 2,958 genes of the expanded gene families (EGFs), we found 158 significantly enriched Biological process (BP) gene ontology (GO) annotations including several functions highlighting how this species was able to adapt to Arctic habitats (Figure 6b; Tables S10–S12)

Summary

| INTRODUCTION

The Arctic accounts for ~10% of Earth's land surface, and the combination of high latitude and regional climate patterns make it one of the harshest terrestrial environments on the planet. We present the chromosome-scale genome assembly of Draba nivalis, a perennial diploid with a circum-Arctic distribution This species is ideal for studying the evolution of environmental stress tolerance in plants because it occurs in the high Arctic where extremes in temperature, light regime, and low water availability are ever-present. Draba is the largest genus in the Brassicaceae with > 390 species, which mainly occur in Arctic and alpine regions (Jordon-Thaden et al, 2013). Many of these species, including D. nivalis, form dense and hairy cushions as protection from wind and cold, and are strongly autogamous to secure reproduction in their pollinator-poor environments (Brochmann, 1993). The availability of many Brassicaceae genome assemblies enabled us to conduct comparative analyses of chromosomal evolution and functional genomics, to shed light on the genomic characteristics of a plant adapted to the extreme abiotic stresses of the Arctic

| MATERIALS AND METHODS

Findings

| DISCUSSION