E2 ubiquitin-conjugating enzymes (UBCs) are pivotal components of the plant ubiquitination machinery, mediating substrate specificity in the ubiquitin-proteasome system (UPS) and integrating with kinase cascades, hormone signaling (e.g., ABA, BR), and metabolic pathways to regulate stress responses and proteostasis. While genome-wide characterization of the UBC gene family has been reported in herbaceous models, including 48 members in Arabidopsis , 48 in rice, and 75 in maize, a comprehensive analysis in woody perennial species such as Populus —crucial for long-term stress adaptation and secondary growth—remains lacking. Here, we report the first systematic genome-wide identification and characterization of 74 PtrUBC genes in Populus trichocarpa , including gene structures, conserved motifs, phylogenetic relationships, duplication events, cis-regulatory elements and expression profiles under diverse abiotic stresses. Functional assays demonstrated that PtUBC42 overexpression enhanced salt tolerance in Populus tomentosa , whereas CRISPR/Cas9 knockout conferred hypersensitivity. Mechanistically, PtUBC42 localizes to the endoplasmic reticulum (ER) and positively regulates salt-responsive and brassinosteroid (BR) pathway genes. This study hypothesizes that PtrUBC members, particularly PtUBC42 , serve as key nodes linking ubiquitination with stress signaling networks in woody plants. Our findings provide a foundation for molecular breeding of salt-tolerant poplars. • Genome-wide analysis identified 74 PtrUBC genes; a unified nomenclature was established. • Endoplasmic Reticulum (ER)-localized PtUBC42 acts as a positive regulator, enhancing salt tolerance in poplar. • Overexpression of PtUBC42 mitigated salt damage; CRISPR/Cas9 knockout lines were hypersensitive. • PtUBC42 enhances salt tolerance by modulating brassinosteroid (BR) signaling.
Liu et al. (Fri,) studied this question.