Genome of , a close relative of , shows ecological adaptation to high altitude.

, a close relative of and , grows on the Qinghai-Tibet Plateau (QTP) about 4,000 m above sea level and represents an attractive model system for studying speciation and ecological adaptation in extreme environments. We assembled a draft genome sequence of 234.72 Mb encoding 27,019 genes and investigated its origin and adaptive evolutionary mechanisms. Phylogenomic analyses based on 4,586 single-copy genes revealed that is most closely related to (estimated divergence 8.8 to 12.2 Mya), whereas both species form a sister clade to and , from which they diverged between 12.7 and 17.2 Mya. LTR retrotransposons in proliferated shortly after the dramatic uplift and climatic change of the Himalayas from the Late Pliocene to Pleistocene. Compared with closely related species, showed significant contraction and pseudogenization in gene families associated with disease resistance and also significant expansion in gene families associated with ubiquitin-mediated proteolysis and DNA repair. We identified hundreds of genes involved in DNA repair, ubiquitin-mediated proteolysis, and reproductive processes with signs of positive selection. Gene families showing dramatic changes in size and genes showing signs of positive selection are likely candidates for 's adaptation to intense radiation, low temperature, and pathogen-depauperate environments in the QTP. Loss of function at the S-locus, the reason for the transition to self-fertilization of , might have enabled its QTP occupation. Overall, the genome sequence of provides insights into the mechanisms of plant adaptation to extreme environments.