Fig. 4

Positive regulation of poplar tolerance to salt stress by SRMT is dependent on the ABA signaling pathway. A The phenotype of SRMT-RNAi (L4 and L29), WT, and SRMT-OE (L11 and L13) poplars in soil after salt treatment through watering with 300 mM NaCl solution, indicating increased tolerance to salt stress in SRMT.3 overexpressing lines, but decreased salt tolerance in SRMT-RNAi lines. B The MDA content and EL in leaves of three poplar genotypes after salt treatment. C The Na⁺ content in the leaves detached from the SRMT-RNAi, WT, and SRMT.3-OE poplars after salt treatment. D The salt tolerance of SRMT-RNAi, WT, and SRMT.3-OE planted in the WPM solid medium supplemented with 150 mM NaCl, or both 150 mM NaCl and 10 μM fluridone (FLU). The enhanced salt tolerance of transgenic poplars by overexpressing SRMT.3 was eliminated by adding FLU to the medium. E The MDA content and EL in the RNAi, overexpression, and WT lines planted in the WPM solid medium containing 150 mM NaCl indicates results consistent with observations of phenotypes. F The MDA content and EL in different poplar genotypes planted in the WPM solid medium containing 150 mM NaCl and 10 μM FLU were not significantly different. The mean ± s.d. of all data from at least three biological replicates is shown. Asterisks indicate statistically significant differences (two-sided Student’s t test, *P < 0.05, **P < 0.01, ns = not significant). G Venn diagram indicating the DEGs in the SMRT.3 overexpression poplar compared to WT poplars under identical normal condition, and WT treated with 300 mM NaCl compared to the controls (WT treated by ddH₂O). H Heatmap indicating the expression levels of 131 genes of the top 700 upregulated DEGs associated with ABA, drought, and salt stress, etc. in the SRMT.3 overexpression poplar compared to WT. I The qPCR detected expression levels of PtoHB7, PtoERD7, PtoCIPK21, PtoPUB79, and PtoRD26, which were upregulated in SRMT.3-OE lines and downregulated in SRMT-RNAi lines with or without salt treatment for 4 h, respectively. Letters above bars represent statistically significant differences between groups (P < 0.05) as determined by one-way ANOVA Duncan’s test