Heterostructural metal/metal oxides are the very promising substituents of noble‐metal catalysts; however, generation and further stabilization of accessible metal/metal oxide heterojunctions are ...very difficult. A strategy to encapsulate and stabilize Cu/Cu2O nanojunctions in porous organic frameworks in situ is developed by tuning the acrylate contents in copper‐based metal–organic frameworks (Cu‐MOFs) and the pyrolytic conditions. The acrylate groups play important roles on improving the polymerization degree of organic frameworks and generating and stabilizing highly dispersed and accessible Cu/Cu2O heteronanojunctions. As a result, pyrolysis of the MOF ZJU‐199, consisting of three acrylates per ligand, generates abundant heterostructural Cu/Cu2O discrete domains inside porous organic matrices at 350 °C, demonstrating excellent catalytic properties in liquid‐phase hydrogenation of furfural into furfuryl alcohol, which are much superior to the non‐noble metal‐based catalysts.
A strategy to generate and stabilize Cu/Cu2O nanojunctions inside porous organic frameworks is developed by controlled pyrolysis of metal–organic frameworks. This results in a composite material that consists of easily accessed Cu/Cu2O heterojunctions inside porous organic matrices that exhibit excellent catalytic properties in the hydrogenation of furfural into furfuryl alcohol.
A low-cost and green biorefinery will increase the economy and revenue from lignocellulosic biomass. Herein, a biomass-derived deep eutectic solvent (DES) pretreatment was developed to deconstruct ...the recalcitrant structure of Eucalyptus for further cellulose enzymatic hydrolysis and lignin valorization. The DES consisted of biomass-derived chemicals (lactic acid and choline chloride). The results showed that DES pretreatment resulted in notable removal of hemicelluloses and lignin, and drastically reduced “biomass recalcitrance”. Under the optimum conditions (DES ratio: 10 : 1, temperature: 110 °C, time: 6 h), the glucose yield by enzymatic hydrolysis reached 94.3%, which was significantly enhanced 9.8 times compared to that of the original biomass without DES pretreatment. The state-of-the-art analysis indicated that the regenerated lignin exhibited well-preserved structures ( i.e. , β- O -4, β–β linkages) without contaminated carbohydrates, and it had a relatively low and homogeneous molecular weight. All these structural characteristics suggested that lignin has great potential application in its conversion into bio-based chemicals and materials. Besides, it is urgent to develop low-cost recycled DESs as green solvents for sustainable biomass pretreatment. The lifetime and recyclability experiment of the DES solution showed that the recovery yield of the DES was at least 90% and the fundamental structural properties of the recycled DES were almost unchanged throughout the recycling cycles. More importantly, the pretreatment efficiency (delignification and enzymatic saccharification) was still largely maintained after the recycling process. Overall, this work demonstrated that biomass pretreatment with the recycled DES was promising for a low-cost biorefinery to achieve an efficient fractionation of lignocellulosic biomass into fermentable glucose and high-quality lignin with tailored chemical structures.
Summary
Lignified stone cells substantially reduce fruit quality. Therefore, it is desirable to inhibit stone cell development using genetic technologies. However, the molecular mechanisms regulating ...lignification are poorly understood in fruit stone cells. In this study, we have shown that microRNA (miR) miR397a regulates fruit cell lignification by inhibiting laccase (LAC) genes that encode key lignin biosynthesis enzymes. Transient overexpression of PbrmiR397a, which is the miR397a of Chinese pear (Pyrus bretschneideri), and simultaneous silencing of three LAC genes reduced the lignin content and stone cell number in pear fruit. A single nucleotide polymorphism (SNP) identified in the promoter of the PbrmiR397a gene was found to associate with low levels of fruit lignin, after analysis of the genome sequences of sixty pear varieties. This SNP created a TCA element that responded to salicylic acid to induce gene expression as confirmed using a cell‐based assay system. Furthermore, stable overexpression of PbrmiR397a in transgenic tobacco plants reduced the expression of target LAC genes and decreased the content of lignin but did not change the ratio of syringyl‐ and guaiacyl‐lignin monomers. Consistent with reduction in lignin content, the transgenic plants showed fewer numbers of vessel elements and thinner secondary walls in the remaining elements compared to wild‐type control plants. This study has advanced our understanding of the regulation of lignin biosynthesis and provided useful molecular genetic information for improving pear fruit quality.
Summary
Flower and fruit colors are important agronomic traits. To date, there is no forward genetic evidence that the glutathione S‐transferase (GST) gene is responsible for the white flower color ...in peach (Prunus persica). In this study, genetic analysis indicated that the white‐flower trait is monogenetic, is recessive to the non‐white allele, and shows pleiotropic effects with non‐white‐flowered types. The genetic locus underpinning this trait was mapped onto chromosome 3 between 0.421951 and 3.227115 Mb by using bulked segregant analysis in conjunction with whole‐genome sequencing, and was further mapped between 0 and 1.178149 Mb by using the backcross 1 (BC1) population. Finally, the locus was fine‐mapped within 535.974‐ and 552.027‐kb intervals by using 151 F2 individuals and 75 individuals from a BC1 self‐pollinated (BC1S1) population, respectively. Pp3G013600, encoding a GST that is known to transport anthocyanin, was identified within the mapping interval. The analysis of genome sequence data showed Pp3G013600 in white flowers has a 2‐bp insertion or a 5‐bp deletion in the third exon. These variants likely render the GST non‐functional because of early stop codons that reduce the protein length from 215 amino acids to 167 and 175 amino acids, respectively. Genetic markers based on these variants validated a complete correlation between the GST loss‐of‐function alleles and white flower in 128 peach accessions. This correlation was further confirmed by silencing of Pp3G013600 using virus‐induced gene silencing technology, which reduced anthocyanin accumulation in peach fruit. The new knowledge from this study is useful for designing peach breeding programs to generate cultivars with white flower and fruit skin.
Significance Statement
Integrating omics data, the locus controlling flower and fruit skin color in peach (Prunus persica) was fine‐mapped. Using resequencing data, two alleles with a 2‐bp insertion or a 5‐bp deletion were identified in the third exon of Pp3G013600 in the white‐flowered type, which rendered its encoded protein (glutathione S‐transferase) non‐functional. Virus‐induced gene silencing analysis and the InDel marker‐linked phenotype in 128 accessions supported our results. The new knowledge is useful for designing peach breeding programs to generate cultivars with anthocyanin deficiency in flower and fruit skin.
Genome structural variations (SVs) have been associated with key traits in a wide range of agronomically important species; however, SV profiles of peach and their functional impacts remain largely ...unexplored.
Here, we present an integrated map of 202,273 SVs from 336 peach genomes. A substantial number of SVs have been selected during peach domestication and improvement, which together affect 2268 genes. Genome-wide association studies of 26 agronomic traits using these SVs identify a number of candidate causal variants. A 9-bp insertion in Prupe.4G186800, which encodes a NAC transcription factor, is shown to be associated with early fruit maturity, and a 487-bp deletion in the promoter of PpMYB10.1 is associated with flesh color around the stone. In addition, a 1.67 Mb inversion is highly associated with fruit shape, and a gene adjacent to the inversion breakpoint, PpOFP1, regulates flat shape formation.
The integrated peach SV map and the identified candidate genes and variants represent valuable resources for future genomic research and breeding in peach.
To meet the huge market demand for carbon fibers (CFs), great efforts have been focused on developing low-cost and sustainable CFs with comparable properties. Lignin, a polyaromatic heteropolymer in ...nature, is considered a promising precursor suitable for CFs fabrication due to its abundant, renewable, low-cost, high-carbon, thermostable, and thermoplastic characteristics. Although research on lignin-based carbon fibers (LCFs) has achieved impressive results, their mechanical properties are still inferior to those of commercialized CFs. In this review, the structural characteristics of the lignin polymers from different plant sources and isolation methods are introduced. The key factors affecting LCFs performances and the effective strategies aiming to improve the properties of LCFs are also summarized in detail, revealing the influences of structural features of lignin on the performances of LCFs. In particular, recent advances in precursors, spinning techniques, stabilization, carbonization, graphitization, and activization of LCFs since 2017 are systematically reviewed. Furthermore, to expand the new applications of LCFs, a comprehensive overview of LCFs applications in diverse fields (electrochemical energy storage, adsorption, catalysis, and other emerging fields) is provided. Finally, the current challenges and opportunities for the future development of LCFs are proposed.
The precursor formulations, fabrications, properties, and various applications of lignin-based carbon fibers (LCFs) since 2017 are reviewed.
Foxp3-expressing CD4
CD25
regulatory T cells (Tregs) constitutively and highly express the immune checkpoint receptor cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4), whose Treg-specific ...deficiency causes severe systemic autoimmunity. As a key mechanism of Treg-mediated suppression, Treg-expressed CTLA-4 down-regulates the expression of CD80/CD86 costimulatory molecules on antigen-presenting cells (APCs). Here, we show that Treg-expressed CTLA-4 facilitated Treg-APC conjugation and immune synapse formation. The immune synapses thus formed provided a stable platform whereby Tregs were able to deplete CD80/CD86 molecules on APCs by extracting them via CTLA-4-dependent trogocytosis. The depletion occurred even with Tregs solely expressing a mutant CTLA-4 form lacking the cytoplasmic portion required for its endocytosis. The CTLA-4-dependent trogocytosis of CD80/CD86 also accelerated in vitro and in vivo passive transfer of other membrane proteins and lipid molecules from APCs to Tregs without their significant reduction on the APC surface. Furthermore, CD80 down-regulation or blockade by Treg-expressed membrane CTLA-4 or soluble CTLA-4-immunoglobulin (CTLA-4-Ig), respectively, disrupted cis-CD80/programmed death ligand-1 (PD-L1) heterodimers and increased free PD-L1 on dendritic cells (DCs), expanding a phenotypically distinct population of CD80
free PD-L1
DCs. Thus, Tregs are able to inhibit the T cell stimulatory activity of APCs by reducing their CD80/CD86 expression via CTLA-4-dependent trogocytosis. This CD80/CD86 reduction on APCs is able to exert dual suppressive effects on T cell immune responses by limiting CD80/CD86 costimulation to naïve T cells and by increasing free PD-L1 available for the inhibition of programmed death-1 (PD-1)-expressing effector T cells. Blockade of CTLA-4 and PD-1/PD-L1 in combination may therefore synergistically hinder Treg-mediated immune suppression, thereby effectively enhancing immune responses, including tumor immunity.
Unveiling the fundamental chemistry of lignin under ionic liquid (IL) pretreatment will facilitate the understanding of biomass recalcitrance involved in pretreatment processes. To examine in greater ...detail the chemical transformations of lignin under different IL pretreatment conditions without competing reactions from plant polysaccharides, the IL pretreatment of the isolated poplar alkaline lignin (hardwood lignin) under varying IL pretreatment conditions (i.e., 110-170 degree C, 1-16 hours) was performed in an appropriate manner. The structural transformations of the lignin have been investigated by elemental analysis, 2D-HSQC spectra, quantitative super(13)C-NMR spectra, super(31)P NMR, and GPC analysis. Results revealed that a decrease of aliphatic OH and an increase in phenolic hydroxyl groups occurred in lignin as the pretreatment proceeded. The increased phenolic OH was mainly as a result of cleavage of beta -O-4' linkages, while the reduced aliphatic OH is probably attributed to the dehydration reaction. The cleavage of beta -O-4' linkages, degradation of beta - beta ' and beta -5' linkages obviously happened at high temperatures and resulted in the decrease of molecular weights. In addition, IL pretreatment selectively degraded the G-type lignin fractions and the condensation reaction took place more easily at S units than G units. Moreover, the demethoxylation preferentially occurred in G units, especially at higher temperatures. It is believed that investigating the fundamental chemistry of lignin during IL pretreatments would be beneficial to optimize and control the pretreatment process.
The demand for efficient utilization of biomass induces a detailed analysis of the fundamental chemical structures of biomass, especially the complex structures of lignin polymers, which have long ...been recognized for their negative impact on biorefinery. Traditionally, it has been attempted to reveal the complicated and heterogeneous structure of lignin by a series of chemical analyses, such as thioacidolysis (TA), nitrobenzene oxidation (NBO), and derivatization followed by reductive cleavage (DFRC). Recent advances in nuclear magnetic resonance (NMR) technology undoubtedly have made solution-state NMR become the most widely used technique in structural characterization of lignin due to its versatility in illustrating structural features and structural transformations of lignin polymers. As one of the most promising diagnostic tools, NMR provides unambiguous evidence for specific structures as well as quantitative structural information. The recent advances in two-dimensional solution-state NMR techniques for structural analysis of lignin in isolated and whole cell wall states (
), as well as their applications are reviewed.
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