Figure 1.

Salt-induced expression of miR390 in poplar LRs. A, Time-course assay of mature miR390 expression under salt stress. Four-week-old wild-type seedlings grown on Woody Plant Medium (WPM) were subjected to 200 mm NaCl for 0, 6, 12, and 24 h, and total roots were collected for RNA extraction. The miR390 expression level was determined by stem-loop RT-qPCR. The U6 snRNA was used as a reference to normalize the expression data of miR390. Asterisks indicate significant differences with respect to the value for 0 h (one-way ANOVA followed by Dunnett’s test for pairwise comparisons: *, P < 0.05 and **, P < 0.01; n = 3). B, Histological staining of the LR tip of transgenic poplar harboring the GUS reporter gene driven by the promoter of miR390a under salt treatment. Four-week-old wild-type seedlings were subjected to 200 mm NaCl for 6 h for GUS staining. Bar = 500 μm. C, Quantitative measurement of salt-induced GUS activity driven by the miR390a promoter in the reporter line. Salt treatment was performed as indicated in B. The values under mock treatment were normalized to 1. Error bars represent sd. Asterisks indicate significant differences with respect to the control (Student’s t test: **, P < 0.01; n = 4).