Brassinosteroid overproduction improves lignocellulose quantity and quality to maximize bioethanol yield under green-like biomass process in transgenic poplar

Abstract

Background: As a leading biomass feedstock, poplar plants provide enormous lignocellulose resource convertible for biofuels and bio-chemicals. However, lignocellulose recalcitrance particularly in wood plants, basically causes a costly bioethanol production unacceptable for commercial marketing with potential secondary pollution to the environment. Therefore, it becomes important to reduce lignocellulose recalcitrance by genetic modification of plant cell walls, and meanwhile to establish advanced biomass process technology in woody plants. Brassinosteroids, plantspecific steroid hormones, are considered to participate in plant growth and development for biomass production, but little has been reported about brassinosteroids roles in plant cell wall assembly and modification. In this study, we generated transgenic poplar plant that overexpressed DEETIOLATED2 gene for brassinosteroids overproduction. We then detected cell wall feature alteration and examined biomass enzymatic saccharification for bioethanol production under various chemical pretreatments.Results: Compared with wild type, the PtoDET2 overexpressed transgenic plants contained much higher brassinosteroids levels. The transgenic poplar also exhibited significantly enhanced plant growth rate and biomass yield by increasing xylem development and cell wall polymer deposition. Meanwhile, the transgenic plants showed significantly improved lignocellulose features such as reduced cellulose crystalline index and degree of polymerization values and decreased hemicellulose xylose/arabinose ratio for raised biomass porosity and accessibility, which led to integrated enhancement on biomass enzymatic saccharification and bioethanol yield under various chemical pretreatments. In contrast, the CRISPR/Cas9-generated mutation of PtoDET2 showed significantly lower brassinosteroids level for reduced biomass saccharification and bioethanol yield, compared to the wild type. Notably, the optimal green-like pretreatment could even achieve the highest bioethanol yield by effective lignin extraction in the transgenic plant. Hence, this study proposed a mechanistic model elucidating how brassinosteroid regulates cell © The Author(s) 2020. 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' Full list of author information is available at the end of the article wall modification for reduced lignocellulose recalcitrance and increased biomass porosity and accessibility for high bioethanol production. Conclusions:This study has demonstrated a powerful strategy to enhance cell...

LACCASE14 is required for the deposition of guaiacyl lignin and affects cell wall digestibility in poplar

“…Dried and milled poplar was used for analysis of sugar yield. Chemical pretreatment and sequential enzymatic hydrolysis were performed as described previously with minor modifications [45][46][47]. For H 2 SO 4 pretreatment: the well-mixed biomass samples were treated with 6 mL 4% H 2 SO 4 at 120 °C for 20 min, then shaken under 150 rpm at 50 °C for 2 h. For NaOH pretreatment: the well-mixed biomass samples were incubated with 6 mL 4% NaOH shaken at 50 °C for 2 h. After pretreatments, the pretreated residues were washed with distilled water for 3-5 times until pH 7.0 for following enzymatic hydrolysis.…”

Comparative Analysis of Herbaceous and Woody Cell Wall Digestibility by Pathogenic Fungi

“…Despite great progress in investigating PCW recalcitrance, few studies have compared the enzymatic digestibility of herbaceous and woody biomass by pathogenic fungi. Different woody and herbaceous biomass have distinguishable PCW compositions, polymer features, and structures [ 8 , 9 ]. For instance, substitutions on xylans, the major component of the secondary cell walls (SCWs) of dicotyledonous and grass plants, are diverse and vary phylogenetically [ 10 , 11 ].…”

Ecologically adaptable Populus simonii is specific for recalcitrance‐reduced lignocellulose and largely enhanced enzymatic saccharification among woody plants

“…However, after 10% CaO pretreatment, the P. simonii sample showed the most reduction by 42%, resulting in the lowest cellulose DP value measured in the CaO pretreatment residue from P. simonii sample. Recent studies have indicated that reduced cellulose DP could provide more reducing ends of β-1,4-glucans for efficient enzymatic hydrolysis of lignocellulose in both grassy plants and woody plants (Alam et al, 2019;Cheng et al, 2018;Fan et al, 2020;Huang et al, 2015;Li et al, 2018), the most reduction on cellulose DP is consistent with the highest hexoses yield achieved in the P. simonii sample. To confirm this finding, we observed lignocellulose morphogenesis of two Populus species (P. simonii and P. deltoides) using scanning electronic microscopy (Figure 5b).…”

“…Thus, selection of the desirable woody plants becomes a promising solution for mild and green‐like biomass pretreatment and efficient enzymatic saccharification toward cost‐effective bioethanol production. Furthermore, genetic modification of lignocellulose has been implemented to originally reduce recalcitrance in bioenergy woody plants (Fan et al., 2017, 2020; Huang et al., 2019; Li et al., 2018; Straub et al., 2019; Wang et al., 2016; Wu et al., 2019).…”