PsnWRKY70 Negatively Regulates NaHCO₃ Tolerance in Populus

Poplar is an important afforestation and ornamental tree species in Northeast China. The distribution area of saline-alkali land is approximately 765 hm² in Northeast China. The breeding of saline-alkali-resistant transgenic trees could be an effective method of afforestation in saline-alkali land. WRKY transcription factors play a crucial role in abiotic stress. In this study, we analyzed the genetic stability of the two-year-old PsnWRKY70 transgenic poplars. The results showed that PsnWRKY70 of transgenic poplars had been expressed stably and normally at the mRNA level. The gene interference expression (RE) lines had no significant effect on the growth of PsnWRKY70 under NaHCO₃ stress, and the alkali damage index of RE lines was significantly lower than that of WT and overexpression (OE) lines at day 15 under NaHCO₃ stress. POD activity was significantly higher in RE lines than in WT. The MDA content of the RE line was lower than that of the WT line. Transcriptome analysis showed that RE lines up-regulated genes enriched in cell wall organization or biogenesis pathway-related genes such as EXPA8, EXPA4, EXPA3, EXPA1, EXPB3, EXP10, PME53, PME34, PME36, XTH9, XTH6, XTH23, CESA1, CESA3, CES9; FLA11, FLA16 and FLA7 genes. These genes play an important role in NaHCO₃ stress. Our study showed that the interference expression of the PsnWRKY70 gene can enhance the tolerance of NaHCO₃ in poplar.