Whole-Genome Resequencing Provides Insights into the Genetic Structure and Evolution of Paulownia spp.

Paulownia trees are grown globally for their robust timber, agroforestry, and effective carbon dioxide drawdown. China possesses rich Paulownia germplasm resources, offering favorable material for the genetic improvement. Understanding the taxonomy and phylogenetic relationships of Paulownia species is essential for the advancement of germplasm innovation. In this study, we re-sequenced 67 typical accessions of 11 species within the Paulownia genus. A total of 16,163,790 high-quality single nucleotide polymorphisms (SNPs) were identified. Based on these markers, these accessions were classified into three groups: P. fortunei and P. lampropylla (Group I); P. tomentosa, P. fargesii, and P. kawakamii (Group II); and P. taiwaniana, P. jianshiensis, P. catalpifolia, P. elongata, P. ichangensis, and P. albiphloea (Group III). Using maximum likelihood estimation, population genetic structure analysis revealed that the 11 species originated from four different ancestral populations. The two predominant breeding species—P. fortunei and P. tomentosa—exhibit divergent origins: P. fortunei arose from hybridization between two ancestral species followed by complex admixture, whereas P. tomentosa retains a predominantly singular ancestral lineage, with traces of P. kawakamii. The genetic diversity (π) of P. tomentosa was 0.002588, which was considerably lower than that of P. fortune (0.004181) suggesting that P. tomentosa is subjected to a stronger breeding selection during the evolution than P. fortune. A total of 59 selected regions and 65 genes were identified by selective sweep analysis. These genes may be involved in biological processes such as morphological development and response to abiotic stress and hormonal activity regulation. These findings provide valuable references for further research on the genetic differentiation and adaptive evolutionary mechanisms of Paulownia species, laying a foundation for future germplasm innovation and variety improvement.