Genome-wide identiffcation of the WRKY gene family in poplar and the positive role of PsnWRKY95 in response to cadmium stress

WRKY is a crucial transcription factor family in plants, participating in a variety of physiological processes and stress responses. In this study, we identified 102 WRKY genes from the poplar genome, randomly distributed on 18 chromosomes and one scaffold, and classified them into three subgroups based on phylogenetic analysis. Members of the same subgroup form similar structures due to their shared relatively conservative domains. All poplar WRKY proteins are hydrophilic, located in the cell nucleus, and form target relationships with a large number of miRNAs, with their promoter containing a large number of stress defense elements. The expansion of the poplar WRKY family mainly occurs through segmental duplication, and they also have abundant cross-species collinearity. Based on RNA-Seq, we identified 83 WRKYs significantly respond to cadmium (Cd) stress. Subsequently, we conducted a study on WRKY95, which was significantly up-regulated in the roots, stems, and leaves under Cd stress. Under cadmium toxicity, the plant height of PsnWRKY95-overexpressing plants increased by 16%-26% compared with the wild type (WT), the root length increased by 12%-27% compared with WT, the peroxidase (POD) activity was 28%-51% higher than that of WT, the chlorophyll content increased by 15%-29% compared with WT, the malondialdehyde (MDA) content decreased by 13%-32% compared with WT, and the electrical conductivity decreased by 9%-20% compared with WT, with the expression levels of POD and HMA1 in the overexpressing plants also being higher than those in WT. Results from yeast experiments demonstrated that PsnWRKY95 can improve Cd tolerance by specifically binding to cadmium (Cd) resistance element G-box, activating the reactive oxygen clearance ability and downstream target gene. This study comprehensively analyzes the basic data of WRKYs, identifying their response to Cd stress and specifically analyzes the stress-resistant function of PsnWRKY95, providing clues for understanding the molecular mechanism of WRKYs resistance to Cd.