Developing economically viable, scalable, and sustainable technologies for the conversion of lignocellulosic polysaccharides to liquid fuels is widely seen as a centerpiece of the global bioeconomy, ...and a key part of a multi-pronged approach to achieve carbon neutrality. Here we identify technology challenges and opportunities to achieve this promise. An overview of feedstocks, processes and products indicates that (1) biorefining at a scale sufficient to meaningfully impact climate change will likely involve fuels as the primary products, chemicals and biomaterials as co-products, and lignocellulose as the preferred feedstock; (2) microbial processing of cellulosic biomass will likely occur in the presence of solids, rather than involving solids-free sugar syrups, giving rise to challenges and constraints distinctive to lignocellulose; (3) anaerobic processing involves much lower costs than aerobic processing, making it more promising for fuel production; and (4) anaerobic production at high yields and broth titers has to date been reported only for molecules with ≤4 carbons. Some anaerobic bacteria are substantially more effective at polysaccharide deconstruction than aerobic fungi. Processes based on these microbes have great potential for cost reduction but require substantial research-driven advances. A mechanistic, functional group approach to product tolerance and inhibition is presented, separation technologies applicable to different product classes are surveyed, and perspectives are offered on opportunities to decrease product inhibition and the cost of product recovery. Pathways and research opportunities are considered for chemo-catalytic conversion of anaerobic fermentation products to larger fuel molecules. Fuel properties are considered for a broad range of biologically-derived products in relation to their suitability for various transport applications. Strategic perspectives are presented drawing on these diverse topics and insights. For multiple compounding reasons, features of small molecules make it less expensive to produce them biologically compared to large molecules, and this is particularly true for production from lignocellulose. Yet the fuels the world would most value producing from lignocellulosic biomass to address climate stabilization are large molecules compatible with heavy-duty, difficult-to-electrify transport applications. Hybrid processes wherein lignocellulose is converted biologically to small molecule intermediates and then converted chemo-catalytically to larger fuel molecules are a promising approach to reconciling this discrepancy.
Hybrid processes, featuring biological conversion of lignocellulose to small molecules followed by chemo-catalytic conversion to larger molecules suitable for difficult-to-electrify transport modes, are a promising route to biomass-derived fuels in demand for climate stabilization.
Dear Editor,
Willows （Salix） and poplars （Populus） are known worldwide as woody species with diverse uses 1, 2. Although these two genera diverged from each other around the early Eocene 3, they ...share numerous traits, including the same chromosome number of 2n = 38 and the common ＇Salicoid＇ genome duplication with a high macrosynteny 4, 5.
Carbon dioxide (CO2) is a major greenhouse gas contributing to changing climatic conditions, which is a grand challenge affecting the security of food, energy, and environment. Photosynthesis plays ...the central role in plant-based CO2 reduction. Plants performing CAM (crassulacean acid metabolism) photosynthesis have a much higher water use efficiency than those performing C3 or C4 photosynthesis. Therefore, there is a great potential for engineering CAM in C3 or C4 crops to enhance food/biomass production and carbon sequestration on arid, semiarid, abandoned, or marginal lands. Recent progresses in CAM plant genomics and evolution research, along with new advances in plant biotechnology, have provided a solid foundation for bioengineering to convert C3/C4 plants into CAM plants. Here, we first discuss the potential strategies for CAM engineering based on our current understanding of CAM evolution. Then we describe the technical approaches for engineering CAM in C3 and C4 plants, with a focus on an iterative four-step pipeline: (1) designing gene modules, (2) building the gene modules and transforming them into target plants, (3) testing the engineered plants through an integration of molecular biology, biochemistry, metabolism, and physiological approaches, and (4) learning to inform the next round of CAM engineering. Finally, we discuss the challenges and future opportunities for fully realizing the potential of CAM engineering.
Transgenic Poplar Designed for Biofuels Bryant, Nathan D.; Pu, Yunqiao; Tschaplinski, Timothy J. ...
Trends in plant science,
September 2020, 2020-09-00, 20200901, 2020-09-01, Letnik:
25, Številka:
9
Journal Article
Recenzirano
Odprti dostop
Members of the genus Populus (i.e., cottonwood, hybrid poplar) represent a promising source of lignocellulosic biomass for biofuels. However, one of the major factors negatively affecting poplar’s ...efficient conversion to biofuel is the inherent recalcitrance to enzymatic saccharification due to cell wall components such as lignin. To this effect, there have been efforts to modify gene expression to reduce biomass recalcitrance by changing cell wall properties. Here, we review recent genetic modifications of poplar that led to change cell wall properties and the resulting effects on subsequent pretreatment efficacy and saccharification. Although genetic engineering’s impacts on cell wall properties are not fully predictable, recent studies have shown promising improvement in the biological conversion of transgenic poplar to biofuels.
The cell wall properties of poplar can be altered by modifying gene expression. Modifying the expression of lignin, hemicellulose, and cellulose biosynthesis genes have both been demonstrated to have an impact on poplar’s natural recalcitrance to enzymatic saccharification.Lignin is typically cited as the primary contributor to recalcitrance. However, as modifying gene expression usually results in multifaceted effects on cell wall chemistry, it is difficult to attribute improved saccharification to any single factor.As examined in this review, the effects (or interaction of effects) from genetic engineering on poplar have, in some cases, resulted in drastic improvements in saccharification efficiency.
A characteristic feature of plant cells is the ability to form callus from parenchyma cells in response to biotic and abiotic stimuli. Tissue culture propagation of recalcitrant plant species and ...genetic engineering for desired phenotypes typically depends on efficient in vitro callus generation. Callus formation is under genetic regulation, and consequently, a molecular understanding of this process underlies successful generation for propagation materials and/or introduction of genetic elements in experimental or industrial applications. Herein, we identified 11 genetic loci significantly associated with callus formation in Populus trichocarpa using a genome-wide association study (GWAS) approach. Eight of the 11 significant gene associations were consistent across biological replications, exceeding a chromosome-wide-log10 (p) = 4.46 p = 3.47E-05 Bonferroni-adjusted significance threshold. These eight genes were used as hub genes in a high-resolution co-expression network analysis to gain insight into the genome-wide basis of callus formation. A network of positively and negatively co-expressed genes, including several transcription factors, was identified. As proof-of-principle, a transient protoplast assay confirmed the negative regulation of a Chloroplast Nucleoid DNA-binding-related gene (Potri.018G014800) by the LEC2 transcription factor. Many of the candidate genes and co-expressed genes were 1) linked to cell division and cell cycling in plants and 2) showed homology to tumor and cancer-related genes in humans. The GWAS approach based on a high-resolution marker set, and the ability to manipulate targets genes in vitro, provided a catalog of high-confidence genes linked to callus formation that can serve as an important resource for successful manipulation of model and non-model plant species, and likewise, suggests a robust method of discovering common homologous functions across organisms.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
Crassulacean acid metabolism (CAM) is an important photosynthetic pathway in diverse lineages of plants featuring high water-use efficiency and drought tolerance. A big challenge facing the ...CAM research community is to understand the function of the annotated genes in CAM plant genomes. Recently, a new genome editing technology using CRISPR/Cas9 has become a more precise and powerful tool than traditional approaches for functional genomics research in C3 and C4 plants. In this study, we explore the potential of CRISPR/Cas9 to characterize the function of CAM-related genes in the model CAM species Kalanchoë fedtschenkoi. We demonstrate that CRISPR/Cas9 is effective in creating biallelic indel mutagenesis to reveal previously unknown roles of blue light receptor phototropin 2 (KfePHOT2) in the CAM pathway. Knocking out KfePHOT2 reduced stomatal conductance and CO2 fixation in late afternoon and increased stomatal conductance and CO2 fixation during the night, indicating that blue light signaling plays an important role in the CAM pathway. Lastly, we provide a genome-wide guide RNA database targeting 45 183 protein-coding transcripts annotated in the K. fedtschenkoi genome.
Loss-of-function analysis using CRISPR/Cas9-mediated mutagenesis provides new insight into the role of phototropin 2 in crassulacean acid metabolism
Annual plants grow vegetatively at early developmental stages and then transition to the reproductive stage, followed by senescence in the same year. In contrast, after successive years of vegetative ...growth at early ages, woody perennial shoot meristems begin repeated transitions between vegetative and reproductive growth at sexual maturity. However, it is unknown how these repeated transitions occur without a developmental conflict between vegetative and reproductive growth. We report that functionally diverged paralogs FLOWERING LOCUS T1 (FT1) and FLOWERING LOCUS T2 (FT2), products of whole-genome duplication and homologs of Arabidopsis thaliana gene FLOWERING LOCUS T (FT), coordinate the repeated cycles of vegetative and reproductive growth in woody perennial poplar (Populus spp.). Our manipulative physiological and genetic experiments coupled with field studies, expression profiling, and network analysis reveal that reproductive onset is determined by FT1 in response to winter temperatures, whereas vegetative growth and inhibition of bud set are promoted by FT2 in response to warm temperatures and long days in the growing season. The basis for functional differentiation between FT1 and FT2 appears to be expression pattern shifts, changes in proteins, and divergence in gene regulatory networks. Thus, temporal separation of reproductive onset and vegetative growth into different seasons via FT1 and FT2 provides seasonality and demonstrates the evolution of a complex perennial adaptive trait after genome duplication.
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•A strong correlation between guaiacyl-type structures in bio-oils and recalcitrance.•The ratio of syringyl/guaiacyl-type-related structures changes with recalcitrance.•Differences ...between biological and thermal conversion of biomass to biofuels.
Pyrolysis of five poplar samples with differing degrees of recalcitrance was performed; the correlations between the poplar enzymatic hydrolysis glucose yields and the physicochemical properties of pyrolysis product were investigated in this study. Sugar release of five poplar samples varied from 48.1 to 112.3 mg/g for glucose, and 12.0 to 32.4 mg/g for xylose. The yield of pyrolysis products was calculated and the molecular weight distribution of pyrolysis oils was measured by GPC, ranging from 268 to 289 g/mol for its weight-average molecular weight. GC–MS analysis of the bio-oil exhibited a strong correlation between biomass recalcitrance and guaiacyl-type structures in bio-oils. The correlation between biomass recalcitrance and the ratio of syringyl-to-guaiacyl-type-related structures was also assessed. The results from quantitative 31P NMR indicated some correlation between biomass recalcitrance and the guaiacyl hydroxyl groups in bio-oils. These results illustrate correlations and differences between converting biomass to biofuels via the biological and thermal platform.
Microbial communities in plant roots provide critical links between above‐ and belowground processes in terrestrial ecosystems. Variation in root communities has been attributed to plant host effects ...and microbial host preferences, as well as to factors pertaining to soil conditions, microbial biogeography and the presence of viable microbial propagules. To address hypotheses regarding the influence of plant host and soil biogeography on root fungal and bacterial communities, we designed a trap‐plant bioassay experiment. Replicate Populus, Quercus and Pinus plants were grown in three soils originating from alternate field sites. Fungal and bacterial community profiles in the root of each replicate were assessed through multiplex 454 amplicon sequencing of four loci (i.e., 16S, SSU, ITS, LSU rDNA). Soil origin had a larger effect on fungal community composition than did host species, but the opposite was true for bacterial communities. Populus hosted the highest diversity of rhizospheric fungi and bacteria. Root communities on Quercus and Pinus were more similar to each other than to Populus. Overall, fungal root symbionts appear to be more constrained by dispersal and biogeography than by host availability.
Population-level studies enabled by high-throughput phenotyping have revealed significant variation in lignin characteristics including content, S:G:H ratio, inter-unit linkage distributions, and ...molecular weights across multiple plant species. Coupled with genome-wide association mapping studies (GWAS) targeted at linking genetic mutations to phenotype, significant progress has been made in associating putative causal mutations to variation in lignin characteristics. Despite this progress, there are few examples, in which these associations have been molecularly validated to provide new insights into the genetic regulation of lignin biosynthesis. Given a recent report of a GWAS-discovered 5-enolpyruvylshikimate-3-phosphate (EPSP) synthase moonlighting as a transcriptional regulator of lignin biosynthesis, the potential to bridge scientific disciplines in order to uncover hidden elements of lignin biosynthesis has been demonstrated, offering a path to alter lignin characteristics via genetic manipulation in order to expedite lignin valorization. To maximize this potential, however, there is a crucial need for (1) broader surveys of naturally varying diverse plant populations and (2) analytical platforms that can resolve subtle properties at fine chemical and biological scales.
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