Poplar Genomics: An Introduction

The genus Populus L. (poplar) comprises 32 individual species belonging to six sections according to classical taxonomy (Abaso, Turanga, Populus, Leucoides, Aigeiros, Tacamahaca). Poplars form a monophyletic group within the family Salicaceae and are possibly descended from a single ancestor in what is now North America, more specifically Mexico. Poplars are mostly dioecious and diploid, but with important exceptions. Sexual dimorphism is not widespread but has been observed for aspens (section Populus). Species boundaries in poplars are sometimes very fluid; intrasectional and sometimes intersectional hybridization may occur when species exist in sympatry. Poplar arguably has the most advanced genomics resources of any forest tree species, with reference-quality genome assemblies for multiple species. Poplar is also the model for studying the genomics of wood formation. Poplar is also increasingly becoming a model for ecological genomics as the genus includes many keystone species, and conservation of several of these species is becoming a concern due to undesirable gene flow from exotic species into their natural habitat or due to their decline driven by climate change. This Chapter covers the following sections for poplar, (1) general introduction to the genus; (2) phylogenomics; (3) hybridization; (4) polyploidy; (5) dioecy/dimorphism; (6) genomic resources, with most up-to-date information.