Abstract
Despite the high economic and ecological importance of forests, our knowledge of the
genomic evolution of trees under salt stress remains very limited. Here we report the genome
sequence of the desert poplar, Populus euphratica, which exhibits high tolerance to sa lt stress.
Its genome is very similar and collinear to that of the closely related mesophytic congener,
P trichocarpa. However, we find that several gene families likely to be involved in tolerance to
salt stress contain significantly more gene copies within the P euphratica lineage.
Furthermore, genes showing evidence of positive selection are significantly enriched in
functional categories related to salt stress. Some of these genes, and others within the same
categories, are significantly upregulated under salt stress relative to their expression in
another salt-sensitive poplar. Our results provide an important background for understanding
tree adaptation to salt stress and facilitating the genetic improvement of cultivated poplars for
saline soils.
