Enhancing stress tolerance represents a critical objective in the genetic improvement of poplar trees. Populus × euramericana 'Bofeng 3' is a nationally certified elite poplar variety that was approved as a premium pulpwood variety for the southern area of Northeastern China. This variety grows quickly, has good yield, and resists frost; however, its weaker drought and salt tolerance limits its broader use in diverse environments. The aim of this study is to understand the genetic basis of the fast growth and stress-adaptation traits of this variety and to provide support for future molecular breeding efforts. We present a chromosome-scale genome assembly of Populus × euramericana 'Bofeng 3', totaling 445.53 Mb, of which with 90.39% is anchored to 19 chromosomes, containing 33,309 protein-coding genes and 45.36% repetitive elements. Comparative genomics showed that 'Bofeng 3' has expanded gene families related to photosynthesis and metabolism, and contracted families involved in stress responses, distinguishing it from other Populus species. Under drought (9137 leaf, 9403 root differentially expressed genes (DEGs)) and salt stress (2840 leaf, 3807 root DEGs), trend analysis revealed specific expression patterns. Several unique and expanded genes, including those for photosynthetic proteins, peroxidases, gamma-aminobutyric acid metabolism, and disease resistance, showed stress-responsive trends. Weighted gene co-expression network analysis identified five modules (three positive, two negative) that significantly correlated with photosynthetic traits, highlighting key candidates such as bZIP transcription factors and auxin/indole acetic acid genes. This study determined the genetic basis underlying the rapid growth traits of Populus × euramericana 'Bofeng 3', while providing genomic resources to establish a robust foundation for future gene editing and molecular breeding studies, including critical candidate genetic resources for developing superior drought- and salt-tolerant poplar varieties via targeted genome editing technologies.
Keywords: Populus × euramericana ‘Bofeng 3’; comparative genomics; drought tolerances; genome; salt resistance; transcriptome.