Fig. 1. Overexpression of miR408 enhances biomass yield, cell wall accessibility and saccharification efficiency in poplar.

a Growth phenotypes of miR408 overexpression and knockout lines. Bar, 15 cm. b, c Comparisons of plant height and basal stem diameter for the above lines. The upper and lower whiskers represent the maximum and minimum values, respectively. The upper, lower and middle box lines represent the two quartiles and median of values in each group. All P-values are from two-tailed Student’s t-tests, n represents 11 to 21 trees sampled respectively from WT (n = 21), miR408_OX #1 (n = 13), #5 (n = 11), #6 (n = 11), miR408_cr #8 (n = 11), #18 (n = 11) and #20 (n = 11). d Comparison of vascular cambium zones and xylem area. Scale bar, 50 μm (upper); 100 μm (down). xy, xylem; ca, cambium; ph, phloem. Ten samples each were analyzed with similar results. e Fluorescence microscopy of cell walls exposed to TrCBM1-GFP from WT, miR408_OX #1, miR408_cr #20 and CCR2-RNAi tissue cultured lines. The CCR2-RNAi line was used as the positive control. TrCBM1 specifically recognizes cellulose and the probe exhibits green fluorescence. Autofluorescence (red) under UV shows lignin and the merged images highlight the negative correlation between probe binding and autofluorescence. Scale bars, 100 μm. f Fluorescence microscopy of transverse sections of one-year-old natural dried poplar stems from WT and miR408_OX exposed to dye-bound cellulases for 24 h. The overexpression lines showed much stronger green fluorescence than WT. Scale bars, 100 μm. Xy, xylem; pi, pith. g, h Histograms showing relative green fluorescence intensity of TrCBM1-GFP (g) and dye-bound cellulase (h). i Saccharification efficiency of WT and miR408_OX plants without pretreatment. Values are presented as means ± SD (n = 3, All P-values are from two-tailed Student’s t-tests; n represents 3 transgenic lines, and three replicate samples were carried out for each transgenic line). Source data are provided as a Source Data file.