Fig. 2

Positive regulation of poplar tolerance to salt stress by PtoRD26 dependent on ABA signaling. A The salt tolerance of 45-day-old PtoRD26-RNAi (L2 and L6), WT and PtoRD26.1-OE (L1 and L17) poplars in the soil treated by irrigating with 300 mM NaCl solution. B The malondialdehyde (MDA) content and activity of catalase (CAT) in leaves of different poplar genotypes (A) after salt treatment. C The Na⁺ content of poplar leaves (A) after salt treatment. D The salt tolerance of PtoRD26-RNAi, WT, and PtoRD26.1-OE cuttings in the WPM solid medium supplemented with 150 mM NaCl or 150 mM NaCl plus 10 μM FLU. E The MDA content and EL of the poplar cuttings (D) grown in WPM medium with NaCl. F The MDA content and EL of the poplar cuttings (D) in WPM medium with both NaCl and FLU. 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 Co-expression network of stress-related genes constructed from data of 62 poplar transcriptomes. We generated transcriptomic data of 17 samples from triploid poplar and 9 samples from P. abla var. pyramidalis, and collected 36 other transcriptomic data of P. abla var. pyramidalis that have been released in NCBI. PtoRD26 and a R2R3 MYB transcription factor named SRMT showing co-expression relationships with stress-associated genes. H The qPCR analysis determined the expression level of PtoHB7, PtoERD7, PtoCIPK21, PtoPUB79, and SRMT in the PtoRD26 overexpression, RNAi, and WT lines with or without salt treatment for 4 h, respectively. The qPCR primers of each gene can detect all alleles simultaneously. The expression level of SRMT was enhanced in the PtoRD26.1 overexpression poplars but reduced in the RNAi lines compared to the WT. Letters above bars represent statistically significant differences between groups (P < 0.05) as determined by one-way ANOVA Duncan’s test