Genome-Wide Identification of the WOX Gene Family in Three Populus Species and Expression Profiling of Populus euphratica and Populus pruinosa Under Abiotic Stresses

The WUSCHEL-related homeobox (WOX) gene family plays crucial roles in plant growth, development, and stress responses. In this study, a comprehensive genome-wide analysis of WOX genes was conducted in three Populus species, P. euphratica, P. pruinosa, and P. deltoides. A total of 16, 16, and 21 WOX genes were identified, respectively, and classified into three clades (ancient, intermediate, and WUS/modern) based on phylogenetic relationships. Structural analyses revealed highly conserved homeodomain motifs and similar exon–intron organizations, indicating strong evolutionary conservation. Furthermore, synteny analyses demonstrated that whole-genome duplication or segmental duplication events were the primary drivers of WOX gene family expansion, with most duplicated gene pairs undergoing purifying selection. Promoter analysis identified abundant cis-acting elements related to light responsiveness, hormone signaling, and stress responses. Notably, transcriptomic profiling during seed germination under drought and salt stress revealed distinct interspecific expression patterns and temporal dynamics between the two desert poplars. Specifically, members such as PeWox11 and PpWox2 were significantly induced, suggesting their potential involvement in abiotic stress adaptation. These findings provide comprehensive insights into the evolutionary conservation and divergence of WOX genes in Populus, establishing a theoretical foundation for the molecular breeding of stress-tolerant woody plants.