High quality haplotype-resolved genome assemblies of Populus tomentosa Carr., a stabilized interspecific hybrid species that is widespread in Asia

Populus has a wide ecogeographical range spanning the Northern Hemisphere, and exhibits abundant distinct species and hybrids globally. Populus tomentosa Carr. is widely distributed and cultivated in the eastern region of Asia, where it plays multiple important roles in forestry, agriculture, conservation, and urban horticulture. Reference genomes are available for several Populus species, however, our goals were to produce a very high quality de novo, chromosome-level genome assembly in P. tomentosa genome that could serve as a reference for evolutionary and ecological studies of hybrid speciation. Here, combining long-read sequencing and Hi-C scaffolding, we present a high-quality, haplotype-resolved genome assembly. The genome size was 740.2 Mb, with a contig N50 size of 5.47 Mb and a scaffold N50 size of 46.68 Mb, consisting of 38 chromosomes, as expected with the known diploid chromosome number (2n=2x=38). A total of 59,124 protein-coding genes were identified. Phylogenomic analyses revealed that P. tomentosa is comprised of two distinct subgenomes, which we deomonstrate is likely to have resulted from hybridization between Populus adenopoda as the female parent and Populus alba var. pyramidalis as the male parent, approximately 3.93 Mya. Although highly colinear, significant structural variation was also found between the two subgenomes. Our study provides a valuable resource for ecological genetics and forest biotechnology.