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. 2023 Jul 18;14:4285. doi: 10.1038/s41467-023-39930-3

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© The Author(s) 2023

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 6 — a Growth phenotypes of lac19 lac25 lc32 triple mutant. Bar, 40 mm. b, c Statistics analysis of plant height (b) and basal diameter (c) of the poplar plants (a). The upper and lower whiskers represent the maximum and minimum values, respectively. The upper, lower and middlebox lines represent the two quartiles and median of values in each group. All P-values are from two-tailed Student’s t-tests, and n represents 10 trees sampled respectively from each line. d Fluorescence microscopy of cell walls of WT, lac19 lac25 lac32, lac25 lac32, lac19 lines exposed to TrCBM1-GFP. 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. Pf, phloem fiber; xy, xylem. Scale bars, 20 μm. e Histograms showing relative green fluorescence intensity of TrCBM1-GFP. Values are means ± SD (n = 3. All P-values are from two-tailed Student’s t-tests. n represents 3 trees sampled respectively from WT and the mutants). f CRM images of lac19 lac25 lac32 vessels, showing lignin deposition. Scale bars, 10 μm. Arrows indicate cell corners of WT and lac19 lac25 lac32 tested in g. g Spectra analysis of vessel cell corners in f. The grey dotted-line box represents lignin Raman spectra and is enlarged in the right panel of g. h A proposed model for the role of miR408 in regulating poplar lignification and saccharification efficiency. Monolignols are synthesized in the cytoplasm and then exported to the apoplast, oxidized and integrated into the secondary cell wall. This polymerization process is initiated by laccases, which can be down-regulated by miR408. When LAC19, LAC25 and LAC32 were down-regulated, the polymerization of monolignols is repressed, resulting in decreased lignin content and molecular weight, leading to less polymer–polymer cross-linking of lignin and cellulose, and exposing more cellulose scaffold, with increased wall porosity and reduced wall cohesiveness, which allows increased enzyme access to biomass during saccharification in miR408_OX poplar. Source data are provided as a Source Data file.