Abstract
BackgroundAs 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, plant-specific 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.ResultsCompared 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 wall modification for reduced lignocellulose recalcitrance and increased biomass porosity and accessibility for high bioethanol production.ConclusionsThis study has demonstrated a powerful strategy to enhance cellulosic bioethanol production by regulating brassinosteroid biosynthesis for reducing lignocellulose recalcitrance in the transgenic poplar plants. It has also provided a green-like process for biomass pretreatment and enzymatic saccharification in poplar and beyond.
Highlights
As a leading biomass feedstock, poplar plants provide enormous lignocellulose resource convertible for biofuels and bio-chemicals
By comparing various chemical pretreatments, we find out an optimal technique relatively economical and environment-friendly for high bioethanol production
Using public expression profiling data, we found that PtoDET2 is mainly expressed in wood tissues, while accumulated lower in buds, leaves, and roots (Fig. 1a)
Summary
As a leading biomass feedstock, poplar plants provide enormous lignocellulose resource convertible for biofuels and bio-chemicals. It becomes important to reduce lignocellulose recalcitrance by genetic modification of plant cell walls, and to establish advanced biomass process technology in woody plants. Compared with grasses, woody plants have higher lignin content because of their growth behavior of becoming physically larger and stronger. This makes woody biomass, that from softwood species, more recalcitrant to microbial and enzymatic hydrolysis, further leading to an unacceptable cost for using woody biomass as biofuels [6]. Overcoming the recalcitrance of woody biomass is promising in biofuel production
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