Fig. 6

Treatments with DNA methylation inhibitor disrupt P. americana growth promotion induced by inoculation with strains PGP41 and PGP5. A, B Aerial part of P. americana under different treatments at day 3 (A) and day 30 (B). The plants were treated with zebularine (Zeb), a DNA methylation inhibitor, to investigate the role of DNA methylation in the growth-promoting process. Zeb, Zeb-treated samples; Non-Zeb, samples without Zeb treatment. C, D Heatmaps based on relative transcript abundances (log2 fold change detected by comparisons of treated vs. control samples) of genes involved in maintaining DNA methylation (C) and genes randomly selected from the overlapping DEGs and DMRs showed in Fig. 5 (D). For both the DNA methylation-related genes and the DEG-DMRs overlapped genes, Zeb treatments caused misregulation of these gene expressions in Zeb-treated roots compared to non-Zeb-treated plants (some upregulated genes in non-Zeb-treated plants showed downregulation in Zeb-treated plants and vice versa). Red, increased transcript abundance; blue, decreased transcript abundance. The relative transcript abundances of Zeb samples were obtained by qRT-PCR; the primers used are listed in Table S3. Asterisks indicate significant differences (P < 0.05). E, F Comparison of inoculation-induced P. americana growth promotion with and without Zeb treatment at day 3 (E, n = 3) and day 30 (F, n ≥ 8). The weights and lengths of both shoots and roots are shown. Different letters indicate significant differences (Duncan’s test, P < 0.05). G The inoculation-induced P. Americana growth promotion by strains PGP41 and PGP5 were detected at day 60 (n ≥ 8), showing long-time growth promotion induced by inoculations at early phase