Sugar release and growth of biofuel crops are improved by downregulation of pectin biosynthesis

Abstract

Cell walls in crops and trees have been engineered for production of biofuels and commodity chemicals, but engineered varieties often fail multi-year field trials and are not commercialized. We engineered reduced expression of a pectin biosynthesis gene (Galacturonosyltransferase 4, GAUT4) in switchgrass and poplar, and find that this improves biomass yields and sugar release from biomass processing. Both traits were maintained in a 3-year field trial of GAUT4-knockdown switchgrass, with up to sevenfold increased saccharification and ethanol production and sixfold increased biomass yield compared with control plants. We show that GAUT4 is an α-1,4-galacturonosyltransferase that synthesizes homogalacturonan (HG). Downregulation of GAUT4 reduces HG and rhamnogalacturonan II (RGII), reduces wall calcium and boron, and increases extractability of cell wall sugars. Decreased recalcitrance in biomass processing and increased growth are likely due to reduced HG and RGII cross-linking in the cell wall.

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Figure 1: Saccharification yield from switchgrass, rice, and poplar GAUT4-KD lines and bioconversion of switchgrass GAUT4-KD to ethanol.
Figure 2: Growth and yield of switchgrass, rice, and poplar GAUT4-KD transgenic lines.
Figure 3: HG:GalAT activity of Arabidopsis (AtGAUT4), poplar (PdGAUT4), and switchgrass (PvGAUT4) recombinant GAUT4 transiently expressed in N. benthamiana and HG:GalAT activity in switchgrass WT and KD lines.
Figure 4: Model of GAUT4 function in cell wall extractability, porosity and cell size, and hypothesis for mechanism of GAUT4-KD in recalcitrance and plant growth.
Figure 5: Pectin-mediated wall cross-linking is reduced in the PvGAUT4-KD cell walls.

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Acknowledgements

We thank CCRC Analytical Services for glycosyl residue linkage analysis, W. Rottmann for leading the Populus transformation, L. Gunter for validation of Populus constructs, I. Gelineo-Albersheim for submission of BESC transformation pipeline file and, along with K. Hunt, for help in establishing the poplar greenhouse growth conditions, E. Chandler, R. Amos, and K. Engle for preparation of endopolygalacturonase, and B. Rockwell and C. Treager for assistance with cell wall isolation and extraction. We also thank B. Wolfe, M. Laxton, and the UT field staff for assistance with data collection and general field maintenance, and R. Millwood for assistance with the USDA APHIS BRS permit regulations. The work was primarily supported by BioEnergy Science Center grant DE-PS02-06ER64304, and partially by the Center for Bioenergy Innovation. The BioEnergy Science Center and the Center for Bioenergy Innovation are US Department of Energy Bioenergy Research Centers, supported by the Office of Biological and Environmental Research in the Department of Energy's Office of Science. The research was also partially funded by the Department of Energy Center Grant DE-SC0015662. The CCRC series of plant cell wall glycan-directed antibodies were generated with the support from the US National Science Foundation Plant Genome Program (grants DBI-0421683 and IOS-0923992).

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Authors

Contributions

A.K.B. participated in all aspects of the study, including line selection, plant phenotyping, expression study, tissue handling and distribution, and cell wall analysis, and wrote the manuscript. M.A.A. performed molecular cloning and generated heterologous expression constructs for poplar and switchgrass genes; designed and performed heterologous expression and enzymatic activity assays; and wrote the manuscript. M.L., C.G.Y., and Y.P. performed the cellulose analyses. H.L.B., M.M., and C.N.S. carried out and analyzed the switchgrass field study. Y.-C.L., J.-Y.Z., and H.R. carried out molecular cloning and production of RNAi plasmid for switchgrass and rice. I.M.B. performed some of the cell wall analyses. A.L.B., Z.R.K., and P.R.L. performed switchgrass and rice transformations and propagated transgenic plants. S.P. and M.G.H. performed and analyzed the glycome profiling analysis. B.S.D. performed the stereomicrograph measurement of switchgrass biomass water uptake. S.S.M. and D.R. participated in growth, sampling and analysis of the plants. K.Y., O.A.T., M.R., A.D., and J.N. carried out the ethanol fermentation analyses. K.W. carried out molecular cloning and production of the RNAi plasmid for poplar. C.C. performed Populus transformation and propagated transgenic plants. X.Y. contributed bioinformatic information for construction of poplar gene constructs. L.T. performed molecular cloning and produced heterologous expression construct of Arabidopsis gene. R.W.S. conducted high-throughput pyrolysis molecular beam mass spectrometry (py-MBMS) lignin assays. E.L.G. and A.Z. coordinated analysis of samples through the BioEnergy Science Center (BESC) high-throughput MBMS and saccharification pipelines. G.B.T. performed high-throughput recalcitrance pipeline through BESC. S.R.D. guided overall high-throughput saccharification pipeline through BESC and provided data analysis. W.A.P. guided the switchgrass and rice transformation pipeline and provided data analysis. M.K.U. guided cloning and production of RNAi vectors for switchgrass and rice. J.R.M. and B.H.D. guided the overall ethanol assay and interpreted the ethanol data. M.F.D. developed and provided leadership for the MBMS pipeline through BESC. R.S.N. directed the BESC transformation pipeline and coordinated analyses through the pipeline. A.J.R. coordinated and analyzed cellulose research. D.M. conceived of the study, coordinated the research, and contributed to the interpretation of results, and drafting and finalizing of the manuscript. All authors read and approved the final manuscript.

Corresponding author

Correspondence to Debra Mohnen.

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Competing interests

The strategy to produce improved biomass as described in this paper has been included in a patent application. C. C. and K.W. are employees of ArborGen Inc., a global provider of conventional and next-generation plantation tree seedling products for the forestry industry.

Integrated supplementary information

Supplementary Figure 1 Phylogenetic tree of GAUT Protein Family and gene model, RNAi construct, and relative transcript abundance of GAUT4 in switchgrass, rice and poplar knockdown (KD) lines.

Phylogenetic tree of GAUT Protein Family members of Arabidopsis thaliana TAIR10 (green), Populus trichocarpa v3.0 (purple), Oryza sativa v7.0 (blue), and Panicum virgatum v1.1 (red) from Phytozome 11.0 (https://phytozome.jgi.doe.gov/) showing relationship between amino acid sequences. The tree was constructed by the Neighbor-Joining method using MEGA6 [Tamura, K., Stecher, G., Peterson, D., Filipski, A. & Kumar, S. MEGA6: Molecular Evolutionary Genetics Analysis version 6.0. Mol Biol Evol 30, 2725-2729 (2013)]. Potri.016G001700, Pavir.J36995 and LOC_Os08g23780 (marked by red arrows) are named GAUT4 for P. trichocarpa, P. virgatum and O. sativa, respectively. (B) Gene models for OsGAUT4 (LOC_Os08g23780) and PtGAUT4 (Potri.016G001700) from Phytozome 11.0 Oryza sativa v7.0 and Populus trichocarpa v3.0, respectively. Gray boxes indicate the 5’ and 3’ untranslated regions; green and orange boxes indicate exons in rice and poplar, respectively; and lines indicate introns. nt: nucleotides. The indicated RNAi targeted sequence was 443 bp and 200 bp for rice and poplar, respectively. The sequences used for quantitative RT-PCR are indicated by arrows. (C) Schematic representation of pANIC12A [Mann, D.G. et al. Gateway-compatible vectors for high-throughput gene functional analysis in switchgrass (Panicum virgatum L.) and other monocot species. Plant Biotechnol J 10, 226-236 (2012)] and pAGSM552 [Biswal, A.K. et al. Downregulation of GAUT12 in Populus deltoides by RNA silencing results in reduced recalcitrance, increased growth and reduced xylan and pectin in a woody biofuel feedstock. Biotechnol Biofuels 8, 41 (2015)] RNAi expression vectors containing an inverted repeat (indicated by opposing black arrows) of PvGAUT4 and PtGAUT4 RNAi target sequence, respectively. Since the switchgrass and rice RNAi target sequences share 88% identity, the pANIC12A-PvGAUT4 construct was used to transform both switchgrass and rice. (D) Relative transcript levels of PvGAUT4 and its homologs as determined by quantitative RT-PCR of RNA extracted from the first (top) leaf of greenhouse-grown, 3-month-old R1 stage tillers of switchgrass WT and PvGAUT4-KD lines (2A, 2B, and 4A). The expression of PvGAUT4 in WT was set to 1 and switchgrass CYP5 was used as a reference gene. n = 8. (E) Relative transcript levels of OsGAUT4 and its homologs as determined by quantitative RT-PCR analysis of RNA from the first (top) leaf from greenhouse-grown 3-month-old WT and OsGAUT4-KD lines 2A, 2B, 7A, 7B. The expression of OsGAUT4 in rice WT was set to 1 and actin was used as a reference gene. n = 6. (F) Relative transcript levels of PdGAUT4 and its homologs as determined by quantitative RT-PCR analysis of stem xylem RNA from greenhouse-grown 3-month-old poplar WT, vector controls (V.Control-1-8) and PdGAUT4-KD lines (AB23.1 to AB23.15; transcript levels of the homologs were only determined for lines AB23.2, AB23.5, and AB23.12). Expression of PdGAUT4 in poplar WT was set to 1 and 18S rRNA was used as a reference gene. n = 6. (G) Relative transcript levels of PvGAUT4 as determined by quantitative RT-PCR analysis of RNA extracted from R1-stage tillers of field-grown switchgrass WT and PvGAUT4-KD lines harvested over three years of the field experiment, and normalized to switchgrass Ubiquitin (UBI) as the reference gene. n = 3. Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. Statistical analysis was with one-way ANOVA followed by Fisher’s least significant difference method; *P < 0.05, **P < 0.001.

Supplementary Figure 2 Saccharification yield from poplar control and PdGAUT4-KD lines, and lignin content and S/G ratio from switchgrass and poplar control and KD lines.

(A) Glucose release, (B) xylose release, and (C) total sugar release of poplar WT, vector control, and PdGAUT4-KD lines grown in the greenhouse. (D) Total lignin content and (E) lignin S/G ratio of switchgrass WT and PvGAUT4-KD lines (2A, 2B, and 4A) grown in the greenhouse. (F) Total lignin content and (G) lignin S/G ratio of poplar WT, vector control, and PdGAUT4-KD lines grown in the greenhouse. For poplar, n = 25 for WT; n = 10-15 (as indicated on the graphs) for vector control (V.Control-1-8) and PdGAUT4-KD lines (AB23.1-AB23.15). For switchgrass, n = 5. (H) Total lignin content and (I) lignin S/G ratio of switchgrass WT and PvGAUT4-KD lines grown in the field over the 3-year field experiment and harvested at the end of the season. n = 3. Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. Significance P values are expressed as *P < 0.05, **P < 0.001. Statistical analysis was by one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison test in Statistica 5.0 for greenhouse data and by Fisher’s least significant difference method for field data.

Supplementary Figure 3 Plant morphology and dry matter accumulation in greenhouse-grown switchgrass PvGAUT4-KD lines and disease severity in field-grown lines.

(A) Height, (B) number of tillers, and (C) dry aerial biomass of 60-day-old WT and PvGAUT4-KD lines grown in 1-gallon (4 L) pots in the greenhouse, n = 10. (D) Tiller growth phenotype, (E) height of tillers in panel D, (F) photo of tiller width, (G) width of tillers in panel F and (H) internode length of WT and PvGAUT4-KD 9-week-old plants grown in 5-gallon pots in the greenhouse, n = 25. Arrows in panel F indicate the location of the 4th internodes. (I) Number of tillers, (J) width of tiller 4th internode, and (K) plant height of WT and PvGAUT4-KD lines grown in 5-gallon pots in the greenhouse, n = 20. Statistical analysis of the greenhouse data was using one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison test in Statistica 5.0. (L) Photograph of field-grown WT and PvGAUT4-KD switchgrass at mid- and end-of-season during a 3-year field trial (2013-2015). (M) Rust (Puccinia emaculata) (small lesions) and Bipolaris (large lesions) disease symptoms in WT and PvGAUT4-KD lines grown in the field (photos were taken in year 3 - August 24, 2015). Visual assessment identified more Bipolaris-induced leaf lesions in WT compared to PvGAUT4-KD lines. (N, O) Quantification of Puccinia emaculata rust disease severity in year 2 (N) and year 3 (O) field experiments. There was no significant difference between PvGAUT4-KD lines and WT, except for lines 2A and 2B in the last measurement of year 2 (Julian date 232). For the field data, the experimental unit (n) was a distinct plot that consisted of four genetically-identical clones of a single transgenic event (n = 3). Means within each time point were compared using one-way ANOVA followed by Fisher’s least significant difference method for field data. All data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05, **P < 0.001.

Supplementary Figure 4 Growth and relative water content of poplar control and PdGAUT4-KD lines.

(A) Plant height and (B) diameter of three-month-old poplar WT, vector control (VC), and PdGAUT4-KD lines. n = 25 for WT; n = 10-15 (as indicated on the graphs) for vector control (V.Control-1-8) and PdGAUT4-KD lines (AB23.1-AB23.15). (C) Plant phenotype of 3-month-old control (WT and VC) lines and PdGAUT4-KD lines AB23.2, AB23.5, AB23.12 and AB23.14 (two plants from each line). (D) Height and (E) radial growth of PdGAUT-KD lines compared to controls over a 9-month growth period. (F) Plant height and (G) stem diameter of 3-month-old, greenhouse-grown PdGAUT4-KD transgenic plants (as % of WT) were plotted against corresponding PdGAUT4 transcript expression levels in xylem tissue, showing negative correlations. Poplar 18S rRNA was used as reference gene in the quantitative RT-PCR transcript expression analysis. (H) Leaf phenotype (6th leaf from the apex) of control (WT and VC) and PdGAUT4-KD lines from 3-month-old plants. (I) Length and (J) width of leaves from different developmental stages of 3-month-old plants. Every other leaf of ten plants was measured starting with the 2nd leaf from the apex. (K and L) Leaf area of (K) developing (10th from apex) and (L) fully expanded (20th from apex) leaves, respectively, of 3-month-old plants. (M) Leaf relative water content (RWC) of WT and PdGAUT4-KD lines. (N) Fresh weight and (O) dry weight of WT and PdGAUT4-KD stems from 3-month-old plants. For panels I-O, n = 10. Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05, **P < 0.001 (one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison test).

Supplementary Figure 5 HG:GalAT activity of Arabidopsis (AtGAUT4), poplar (PdGAUT4), and switchgrass (PvGAUT4) recombinant GAUT4 transiently expressed in N. benthamiana.

(A) Pmole [14C]GalA-radiolabeled HG synthesized by solubilized and partially purified membrane proteins (1 μg protein) from N. benthamiana leaves transiently co-expressing GAUT4 constructs and the silencing suppresor p19 [Voinnet, O., Pinto, Y.M. & Baulcombe, D.C. Suppression of gene silencing: a general strategy used by diverse DNA and RNA viruses of plants. Proc Natl Acad Sci U S A 96, 14147-14152 (1999)], and leaves expressing p19 alone, in 3-hr reactions containing UDP-[14C]GalA and exogenous HG acceptors. (B) Quantitative real time PCR analysis of GAUT4 transgene transcript levels using N. benthamiana 60S ribosomal protein L23 [Liu, D. et al. Validation of reference genes for gene expression studies in virus-infected Nicotiana benthamiana using quantitative real-time PCR. PLoS One 7, e46451 (2012)] as the reference gene. The dotted line indicates the respective transgene transcript expression level in the control samples (transfected only with p19), which is set to 1. (C) Western blot of microsome samples (200 μg protein) using anti-His-tag antibody. Arrow heads, recombinant AtGAUT4 and PdGAUT4 protein bands; arrow, a non-specific protein band. (D) Sensitivity of products synthesized by recombinant Arabidopsis, poplar and switchgrass GAUT4 to digestion by endopolygalacturonase-I (+EPG). Data are duplicate samples from at least two independent experiments (n=4), presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05, **P < 0.01, ***P < 0.001 (ANOVA followed by Tukey’s multiple comparison test).

Supplementary Figure 6 Glycome profiling of switchgrass biomass from WT and PvGAUT4-KD lines.

Switchgrass cell wall (AIR; prepared from WT and PvGAUT4-KD R1 stage tillers) was sequentially extracted using increasingly harsh solvents (indicated in grey boxes at the bottom of the panels) and the wall extracts were subsequently analyzed by ELISA using 155 plant cell wall non-cellulosic glycan-directed monoclonal antibodies (mAbs) as described in Online Methods. Data are presented as heatmaps with the range of strongest ELISA binding response to no binding indicated by a yellow-red-blue-black scale. The mAbs are grouped based on the cell wall glycans they primarily recognize as shown in the color-coded panel on the right side of the heatmaps. The mass amounts of materials recovered in each extraction step are depicted in the bar graphs above the heatmaps. Dotted green boxes outline major areas of the heatmaps where reduced or increased ELISA binding responses were clearly observed in the PvGAUT4-KD lines compared to WT.

Supplementary Figure 7 Glycome profiling of poplar biomass from WT and PdGAUT4-KD lines.

Sequential cell wall extracts were prepared from poplar stem AIR using increasingly harsh solvents (indicated in grey boxes at the bottom of the panels) and subsequently analyzed by ELISA using 155 plant cell wall non-cellulosic glycan-directed monoclonal antibodies (mAbs) as described in Online Methods. Data are presented as heatmaps with the range of strongest ELISA binding response to no binding indicated by a yellow-red-blue-black scale. The mAbs are grouped based on the cell wall glycans they primarily recognize as shown in the color-coded panel on the right side of the heatmaps. The mass amounts of materials recovered in each extraction step are depicted in the bar graphs above the heatmaps. Dotted green boxes outline major areas of the heatmaps where reduced or increased ELISA binding responses were clearly observed in the PdGAUT4-KD lines compared to WT.

Supplementary Figure 8 Transmission electron microscopy of immunogold-labeled switchgrass stem cross-sections.

Transmission electron microscopy was carried out on phloem cell walls in switchgrass stem (R1 stage) cross-sections from WT and PvGAUT4-KD lines. Immunolabeling was with HG-specific antibodies JIM5 (A-D) and JIM7 (E-H). CW – cell wall; CML – compound middle lamellae. Black double-ended arrows indicate cell wall thickness. Scale bars = 0.5 μm. (I-J) Numbers of immunogold particles per μm2 wall area observed as representative of JIM5 and JIM7 epitope abundance in WT and PvGAUT4-KD cell wall cross sections shown in panels A-H. n = 6. Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05, **P < 0.001 (one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison test).

Supplementary Figure 9 Mass of cell wall alcohol insoluble residue (AIR), each sequential AIR extract, and the insoluble pellet from (A) switchgrass R1 stage tillers and (B) poplar stem biomass from control (WT only for switchgrass; WT and vector control for poplar) and GAUT4-KD lines.

(i) Mass of AIR extracted per gram ground dry biomass. [(ii) – (vii)] Amount of material recovered in each fraction following sequential extraction of AIR using increasingly harsh solvents: (ii) 50 mM ammonium oxalate, (iii) 50 mM sodium carbonate, (iv) 1M KOH, (v) 4M KOH, (vi) 100 mM sodium chlorite, and (vii) 4M KOH post-chlorite (PC). (viii) Total amount of material recovered in all AIR extracts combined. (ix) Amount of material remaining in the final insoluble pellet. Data in panels (ii) to (ix) are in mg extract/gram AIR. n = 6. Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05, **P < 0.001 (one-way analysis of variance (ANOVA) followed by Tukey’s multiple comparison test).

Supplementary Figure 10 Physical assessment of switchgrass WT and PvGAUT4-KD biomass.

(A) Stereomicrographs of dry and fully hydrated switchgrass stem sections, showing greater water uptake by the PvGAUT4-KD biomass compared to WT. Sample volumes were calculated from measurements taken directly from the images, with volumes of the hollow central stem core excluded from the volume calculations. Volume differences between the dry and fully hydrated samples are reported as percent changes. Measurements were taken from two stem sections each from two independent stems from two genetically identical clones of a single transgenic event (n = 4). Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. Scale bar = 1 mm. (B and C) Scanning electron micrographs of hot-water pre-treated switchgrass biomass (20 mesh i.e. 0.85 mm; biomass pre-treated at 180°C, for 15 minutes), showing more extensive tissue/cell damage in PvGAUT4-KD biomass compared to WT. Arrows indicate sites of tissue tearing. Scale bars = 50 μm.

Supplementary Figure 11 Characteristics of cellulose extracted from switchgrass WT and PvGAUT4-KD lines.

(A) Number-average (DPn) and weight-average (DPw) degree of polymerization of cellulose. (B) Polydispersity index of cellulose. (C) Cellulose crystallinity index. (D) Distribution coefficient of Direct Orange (DO) dye. All measurements were taken in triplicate from two independently grown biomass samples of three genetically identical clones of a single trangenic event (n = 6). Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05 (one-tailed Student’s t-test).

Supplementary Figure 12 Microscopic analysis of poplar wood phloem and xylem tissue.

(A-L) Toluidine blue-stained cross sections of the stem 10th internode (from top) from three-month-old (A-D) WT and PdGAUT4-KD transgenic lines (E-H) AB23.2 and (I-L) AB23.12. (B-D, F-H, J-L) Higher magnification of (B, F, J) phloem tissue, (C, G, K) xylem vessels, and (D, H, L) secondary wood xylem tissue from panels A, E, and I, respectively. Red arrows indicate ray cells. ep: epidermis, co: cortex, sc: sclerenchyma fibers, ph: phloem, c: cambium, xy: xylem, r: xylem ray cells, xp: xylem parenchyma, v: xylem vessel, p: pith. Bar = 50 μm in panels A-D, E-G, I-K; 100 μm in panels H and L. (M-N) Distance across phloem and secondary wood xylem, respectively, in the stem cross sections. (O) Numbers of individual xylem vessel cells per 300 μm2 area of secondary wood xylem. (P) Xylem vessel cell lumen diameter. Data are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. n = 6 for panel M, n = 5 for panels N-P. *P < 0.05, **P < 0.001 (ANOVA followed by Tukey’s multiple comparison test).

Supplementary Figure 13 Size of individual xylem vessel and fiber cells from PdGAUT4-KD and WT debarked and depithed stem wood tissue.

Xylem vessel and fiber cells were separated by maceration of the bottom part of stem (6 cm) from 9-month-old plants. (A) Vessel cell total length, (B) vessel cell lumen length, (C) vessel cell total diameter, (D) fiber cell length, and (E) fiber cell diameter. A total of approximately 100 vessel and 130 fiber cells from three plants of each genotype were measured using an AxioVision camera in a Zeiss Axioplan microscope (Carl Zeiss). Data from two independent experiments (n = 6) are presented as box plots showing the median as well as the 25th and 75th percentiles. Ends of whiskers are set at 1.5*IQR above and below the third and first quartiles, respectively. *P < 0.05, **P < 0.001 (ANOVA followed by Tukey’s multiple comparison test).

Supplementary Figure 14 Field design of the 3-year field-trial of switchgrass WT and PvGAUT4-KD lines.

The field (14.5 m x 23.6 m) was divided into three subplots, which were each further divided into replicate-plots arranged in a completely randomized design within the subplot. The subplot on the upper third of the diagram contains the replicate-plots (green boxes) for the PvGAUT4-KD lines (2A, 2B, and 4A) and the corresponding WT (‘Alamo’-derived parent clone SA7), as well as an additional parental clone (SA37). The replicate-plots were spaced 152 cm apart, and each was planted at 76 cm apart with four vegetatively propagated clones of each line (inset at the upper right hand corner). A border of ‘Alamo’-derived ST1-genotype plants was included to control for shading effects.

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Supplementary Figures 1–14 (PDF 3089 kb)

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Supplementary Tables and Supplementary Notes

Supplementary Table 1 and Supplementary Notes 1–6 (PDF 1044 kb)

Supplementary Table 2

Glycosyl residue composition of cell wall extracts from tillers of switchgrass WT and PvGAUT4-KD plants (XLSX 13 kb)

Supplementary Table 3

Glycosyl residue composition and total carbohydrate in cell wall extracts from WT and PvGAUT4-KD lines (XLSX 12 kb)

Supplementary Table 4

Glycosyl residue composition of cell wall extracts from stems of P. deltoides WT, vector control and PdGAUT4-KD plants (XLSX 14 kb)

Supplementary Table 5

Glycosyl residue composition and total carbohydrate of cell wall extracts from WT and PdGAUT4-KD lines (AB23.2,AB23.5, AB23.12, AB23.14) (XLSX 12 kb)

Supplementary Table 6

Glycosyl linkage analysis of fractionated cell walls from switchgrass WT and PvGAUT4-KD lines (XLSX 12 kb)

Supplementary Table 7

Glycosyl linkage analysis of fractionated cell walls from P.deltoides WT and PdGAUT4-KD lines. (XLSX 11 kb)

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Biswal, A., Atmodjo, M., Li, M. et al. Sugar release and growth of biofuel crops are improved by downregulation of pectin biosynthesis. Nat Biotechnol 36, 249–257 (2018). https://doi.org/10.1038/nbt.4067

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