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Abstract Designing catalysts with well-defined, identical sites that achieve site-specific selectivity, and activity remains a significant challenge. In this work, we introduce a design principle of topological-single-atom catalysts (T-SACs) guided by density functional theory (DFT) and Ab initio molecular dynamics (AIMD) calculations, where metal single atoms are arranged in asymmetric configurations that electronic shield topologically misorients d orbitals, minimizing unwanted interactions between reactants and the support surface. Mn1/CeO2 catalysts, synthesized via a charge-transfer-driven approach, demonstrate superior catalytic activity and selectivity for NO x removal. A life-cycle assessment (LCA) reveals that Mn1/CeO2 significantly reduces environmental impact compared to traditional V-W-Ti catalysts. Through in-situ spectroscopic characterizations combined with DFT calculations, we elucidate detailed reaction mechanisms. This study establishes T-SACs as a promising class of catalysts, offering a systematic framework to address catalytic challenges by defining site characteristics. The concept highlights their potential for advancing selective catalytic processes and promoting sustainable technologies.

For the project of pipe jacking in cohesionless soil, it is key to determine the vertical load on jacked pipe so as to predict the jacking force accurately. In this paper, a new parabolic soil arching model was proposed to calculate the vertical load on jacked pipe. This proposed analytical model was composed of parabolic soil arching zone, parabola-typed collapse zone and friction arch zone. Combined with existing literature, the key parameters (i.e., height of parabolic soil arching, horizontal pressure coefficient and width and height of friction arch) were determined. In addition, considering that the trajectory of major stress is parabola, the formula of horizontal pressure coefficient was deduced in the friction arch. The parabolic soil arching zone is assumed as a three-hinged arch with reasonable arch axis, and the formula of load transfer was derived considering the transition effect of parabolic soil arching. The results of experiment, theoretical models and numerical model were adopted to verify the proposed analytical model. Finally, the influence of the key parameters on the vertical load on jacked pipe were also discussed in detail. This work provides a meaningful reference for evaluating the vertical load on jacked pipe for design of pipe jacking.

Plant cell walls are largely composed of polysaccharide polymers, including cellulose, hemicelluloses (xyloglucan, xylan, mannan, and mixed-linkage β-1,3/1,4-glucan), and pectins. Among these cell wall polysaccharides, xyloglucan, xylan, mannan, and pectins are often O-acetylated, and polysaccharide O-acetylation plays important roles in cell wall assembly and disease resistance. Genetic and biochemical analyses have implicated the involvement of three groups of proteins in plant cell wall polysaccharide O-acetylation: trichome birefringence-like (TBL)/domain of unknown function 231 (DUF231), reduced wall acetylation (RWA), and altered xyloglucan 9 (AXY9). Although the exact roles of RWAs and AXY9 are yet to be identified, members of the TBL/DUF231 family have been found to be O-acetyltransferases responsible for the O-acetylation of xyloglucan, xylan, mannan, and pectins. Here, we provide a comprehensive overview of the occurrence of O-acetylated cell wall polysaccharides, the biochemical properties, structural features, and evolution of cell wall polysaccharide O-acetyltransferases, and the potential biotechnological applications of manipulations of cell wall polysaccharide acetylation. Further in-depth studies of the biochemical mechanisms of cell wall polysaccharide O-acetylation will not only enrich our understanding of cell wall biology, but also have important implications in engineering plants with increased disease resistance and reduced recalcitrance for biofuel production.

MOF-74 (metal–organic framework) is utilized as a filler in mixed-matrix membranes (MMMs) to improve gas selectivity due to its unique one-dimensional hexagonal channels and high-density open metal sites (OMSs), which exhibit a strong affinity for CO2 molecules. Reducing the agglomeration of nanoparticles and improving the compatibility with the matrix can effectively avoid the existence of non-selective voids to improve the gas separation efficiency. We propose a novel, layer-by-layer modification strategy for MOF-74 with graphene oxide. Two-dimensional graphene oxide nanosheets as a supporting skeleton creatively improve the dispersion uniformity of MOFs in MMMs, enhance their interfacial compatibility, and thus optimize the selective gas permeability. Additionally, they extended the gas diffusion paths, thereby augmenting the dissolution selectivity. Compared with doping with a single component, the use of a GO skeleton to disperse MOF-74 into Pebax®1657 (Polyether Block Amide) achieved a significant improvement in terms of the gas separation effect. The CO2/N2 selectivity of Pebax®1657-MOF-74 (Ni)@GO membrane with a filler concentration of 10 wt% was 76.96, 197.2% higher than the pristine commercial membrane Pebax®1657. Our results highlight an effective way to improve the selective gas separation performance of MMMs by functionalizing the MOF supported by layered GO. As an efficient strategy for developing porous MOF-based gas separation membranes, this method holds particular promise for manufacturing advanced carbon dioxide separation membranes and also concentrates on improving CO2 capture with new membrane technologies, a key step in reducing greenhouse gas emissions through carbon capture and storage.

Amine-functionalized metal-organic framework (MOF) material is a promising CO2 captor in the post-combustion capture process owing to its large CO2 working capacity as well as high CO2 selectivity and easy regeneration. In this study, an ethylenediamine (ED)-decorated Al-based MOFs (named ED@MOF-520) with a high specific area and permanent porosity are prepared and evaluated to study the adsorption and separation of CO2 from N2. The results show that ED@MOF-520 adsorbent displays a superior CO2 capture performance with a CO2/N2 separation factor of 50 at 273 K, 185% times increase in the CO2/N2 separation efficiency in comparison with blank MOF-520. Furthermore, ED@MOF-520 exhibits a moderate-strength interaction with 29 kJ mol−1 adsorption heat for CO2 uptake, which not only meets the requirement of CO2 adsorption but also has good cycle stability. This work provides a promising adsorbent with a high CO2/N2 separation factor to deal with carbon peak and carbon neutrality.

Amine-functionalized metal-organic frameworks (MOFs) are a promising strategy for the high-efficiency capture and separation of CO2. In this work, by tuning the ratio of 1,3,5-benzenetricarboxylic acid (H3BTC) to 5-aminoisophthalic acid (5-NH2-H2IPA), we designed and synthesized a series of amine-functionalized highly stable Ti-based MOFs (named MIP-207-NH2-n, in which n represents 15%, 25%, 50%, 60%, and 100%). The structural analysis shows that the original framework of MIP-207 in the MIP-207-NH2-n (n = 15%, 25%, and 50%) MOFs remains intact when the mole ratio of ligand H3BTC to 5-NH2-H2IPA is less than 1 to 1 in the resulting MOFs. By the introduction of amino groups, MIP-207-NH2-25% demonstrates outstanding CO2 capture performance up to 3.96 and 2.91 mmol g−1, 20.7% and 43.3% higher than those of unmodified MIP-207 at 0 and 25 °C, respectively. Furthermore, the breakthrough experiment indicates that the dynamic CO2 adsorption capacity and CO2/N2 separation factors of MIP-207-NH2-25% are increased by about 25% and 15%, respectively. This work provides an additional strategy to construct amine-functionalized MOFs with the maintenance of the original MOF structure and high performance of CO2 capture and separation.

Wood represents the most abundant biomass produced by plants and one of its major components is acetyl xylan. Acetylation in xylan can occur at O-2 or O-3 of a xylosyl residue, at both O-2 and O-3 of a xylosyl residue, and at O-3 of a xylosyl residue substituted at O-2 with glucuronic acid. Acetyltransferases responsible for the regiospecific acetylation of xylan in tree species have not yet been characterized. Here we report the biochemical characterization of twelve Populus trichocarpa DUF231-containing proteins, named PtrXOATs, for their roles in the regiospecific acetylation of xylan. The PtrXOAT genes were found to be differentially expressed in Populus organs and among them, PtrXOAT1, PtrXOAT2, PtrXOAT9 and PtrXOAT10 exhibited the highest level of expression in stems undergoing wood formation. Activity assays of recombinant proteins demonstrated that all twelve PtrXOAT proteins were able to transfer acetyl groups from acetyl CoA onto a xylohexaose acceptor with PtrXOAT1, PtrXOAT2, PtrXOAT3, PtrXOAT11 and PtrXOAT12 having the highest activity. Structural analysis of the PtrXOAT-catalyzed reaction products using 1H NMR spectroscopy revealed that PtrXOAT1, PtrXAOT2 and PtrXOAT3 mediated 2-O- and 3-O-monoacetylation and 2,3-di-O-acetylation of xylosyl residues and PtrXOAT11 and PtrXOAT12 only catalyzed 2-O- and 3-O-monoacetylation of xylosyl residues. Of the twelve PtrXOATs, only PtrXOAT9 and PtrXOAT10 were capable of transferring acetyl groups onto the O-3 position of 2-O-glucuronic acid-substituted xylosyl residues. Furthermore, when expressed in the Arabidopsis eskimo1 mutant, PtrXOAT1, PtrXAOT2 and PtrXOAT3 were able to rescue the defects in xylan acetylation. Together, these results demonstrate that the twelve PtrXOATs are acetyltransferases with different roles in xylan acetylation in P. trichocarpa.

Xylan is a major acetylated polymer in plant lignocellulosic biomass and it can be mono- and di-acetylated at O-2 and O-3 as well as mono-acetylated at O-3 of xylosyl residues that is substituted with glucuronic acid (GlcA) at O-2. Based on the finding that ESK1, an Arabidopsis thaliana DUF231 protein, specifically mediates xylan 2-O- and 3-O-monoacetylation, we previously proposed that different acetyltransferase activities are required for regiospecific acetyl substitutions of xylan. Here, we demonstrate the functional roles of TBL32 and TBL33, two ESK1 close homologs, in acetyl substitutions of xylan. Simultaneous mutations of TBL32 and TBL33 resulted in a significant reduction in xylan acetyl content and endoxylanase digestion of the mutant xylan released GlcA-substituted xylooligomers without acetyl groups. Structural analysis of xylan revealed that the tbl32 tbl33 mutant had a nearly complete loss of 3-O-acetylated, 2-O-GlcA-substituted xylosyl residues. A reduction in 3-O-monoacetylated and 2,3-di-O-acetylated xylosyl residues was also observed. Simultaneous mutations of TBL32, TBL33 and ESK1 resulted in a severe reduction in xylan acetyl level down to 15% of that of the wild type, and concomitantly, severely collapsed vessels and stunted plant growth. In particular, the S2 layer of secondary walls in xylem vessels of tbl33 esk1 and tbl32 tbl33 esk1 exhibited an altered structure, indicating abnormal assembly of secondary wall polymers. These results demonstrate that TBL32 and TBL33 play an important role in xylan acetylation and normal deposition of secondary walls.

Switchgrass is a promising biofuel feedstock due to its high biomass production and low agronomic input requirements. Because the bulk of switchgrass biomass used for biofuel production is lignocellulosic secondary walls, studies on secondary wall biosynthesis and its transcriptional regulation are imperative for designing strategies for genetic improvement of biomass production in switchgrass. Here, we report the identification and functional characterization of a group of switchgrass transcription factors, including several NACs (PvSWNs) and a MYB (PvMYB46A), for their involvement in regulating secondary wall biosynthesis. PvSWNs and PvMYB46A were found to be highly expressed in stems and their expression was closely associated with sclerenchyma cells. Overexpression of PvSWNs and PvMYB46A in Arabidopsis was shown to result in activation of the biosynthetic genes for cellulose, xylan and lignin and ectopic deposition of secondary walls in normally parenchymatous cells. Transactivation and complementation studies demonstrated that PvSWNs were able to activate the SNBE-driven GUS reporter gene and effectively rescue the secondary wall defects in the Arabidopsis snd1 nst1 double mutant, indicating that they are functional orthologs of Arabidopsis SWNs. Furthermore, we showed that PvMYB46A could activate the SMRE-driven GUS reporter gene and complement the Arabidopsis myb46 myb83 double mutant, suggesting that it is a functional ortholog of Arabidopsis MYB46/MYB83. Together, these results indicate that PvSWNs and PvMYB46A are transcriptional switches involved in regulating secondary wall biosynthesis, which provides molecular tools for genetic manipulation of biomass production in switchgrass.

One of the most prominent features of xylem conducting cells is the deposition of secondary walls. In Arabidopsis, secondary wall biosynthesis in the xylem conducting cells, vessels, has been shown to be regulated by two VASCULAR-RELATED NAC-DOMAIN (VND) genes, VND6 and VND7. In this report, we have investigated the roles of five additional Arabidopsis VND genes, VND1 to VND5, in regulating secondary wall biosynthesis in vessels. The VND1 to VND5 genes were shown to be specifically expressed in vessels but not in interfascicular fibers in stems. The expression of VND4 and VND5 was also seen specifically in vessels in the secondary xylem of the root-hypocotyl region. When overexpressed, VND1 to VND5 were able to activate the expression of secondary wall-associated transcription factors and genes involved in secondary wall biosynthesis and programmed cell death. As a result, many normally parenchymatous cells in leaves and stems acquired thickened secondary walls in the VND1 to VND5 overexpressors. In contrast, dominant repression of VND3 function resulted in reduced secondary wall thickening in vessels and a collapsed vessel phenotype. In addition, VND1 to VND5 were shown to be capable of rescuing the secondary wall defects in the fibers of the snd1 nst1 double mutant when expressed under the SND1 promoter. Furthermore, transactivation analysis revealed that VND1 to VND5 could activate expression of the GUS reporter gene driven by the secondary wall NAC binding element (SNBE). Together, these results demonstrate that VND1 to VND5 possess functions similar to that of the SND1 secondary wall NAC and are transcriptional regulators of secondary wall biosynthesis in vessels.

Wood is one of the promising bioenergy feedstocks for lignocellulosic biofuel production. Understanding how wood components are synthesized will help us design strategies for better utilization of wood for biofuel production. One of the major wood components is xylan, in which about 10% of xylosyl residues are substituted with glucuronic acid (GlcA) side chains. All the GlcA side chains of xylan in wood of Populus trichocarpa are methylated, which is different from Arabidopsis xylan in which about 60% of GlcA side chains are methylated. Genes responsible for methylation of GlcA side chains in Populus xylan have not been identified. Here, we report genetic and biochemical analyses of four DUF579 domain-containing proteins, PtrGXM1, PtrGXM2, PtrGXM3 and PtrGXM4, from Populus trichocarpa and their roles in GlcA methylation in xylan. The PtrGXM genes were found to be highly expressed in wood-forming cells and their encoded proteins were shown to be localized in the Golgi. When overexpressed in the Arabidopsis gxm1/2/3 triple mutant, PtrGXMs were able to partially complement the mutant phenotypes including defects in glucuronoxylan methyltransferase activity and GlcA methylation in xylan, indicating that PtrGXMs most likely function as glucuronoxylan methyltransferases. Direct evidence was provided by enzymatic analysis of recombinant PtrGXM proteins showing that they possessed a methyltransferase activity capable of transferring the methyl group onto GlcA-substituted xylooligomers. Kinetic analysis showed that PtrGXMs exhibited differential affinities toward the GlcA-substituted xylooligomer acceptor with PtrGXM3 and PtrGXM4 having 10 times higher K m values than PtrGXM1 and PtrGXM2. Together, these findings indicate that PtrGXMs are methyltransferases mediating GlcA methylation in Populus xylan during wood formation.

Wood is mainly composed of secondary walls, which constitute the most abundant stored carbon produced by vascular plants. Understanding the molecular mechanisms controlling secondary wall deposition during wood formation is not only an important issue in plant biology but also critical for providing molecular tools to custom-design wood composition suited for diverse end uses. Past molecular and genetic studies have revealed a transcriptional network encompassing a group of wood-associated NAC and MYB transcription factors that are involved in the regulation of the secondary wall biosynthetic program during wood formation in poplar trees. Here, we report the functional characterization of poplar orthologs of MYB46 and MYB83 that are known to be master switches of secondary wall biosynthesis in Arabidopsis. In addition to the two previously-described PtrMYB3 and PtrMYB20, two other MYBs, PtrMYB2 and PtrMYB21, were shown to be MYB46/MYB83 orthologs by complementation and overexpression studies in Arabidopsis. The functional roles of these PtrMYBs in regulating secondary wall biosynthesis were further demonstrated in transgenic poplar plants showing an ectopic deposition of secondary walls in PtrMYB overexpressors and a reduction of secondary wall thickening in their dominant repressors. Furthermore, PtrMYB2/3/20/21 together with two other tree MYBs, the Eucalyptus EgMYB2 and the pine PtMYB4, were shown to differentially bind to and activate the eight variants of the 7-bp SMRE consensus sequence, composed of ACC(A/T)A(A/C)(T/C). Together, our results indicate that the tree MYBs, PtrMYB2/3/20/21, EgMYB2 and PtMYB4, are master transcriptional switches that activate the SMRE sites in the promoters of target genes and thereby regulate secondary wall biosynthesis during wood formation.

The article presents the synthesis of a novel porous metal-organic replica of [alpha]-Pb[O.sub.2]. The compound is shown to be extremely beneficial for the capturing of a nerve agent surrogate.

Xylan is a major hemicellulose in the secondary walls of vessels and fibers, and its acetylation is essential for normal secondary wall assembly and properties. The acetylation of xylan can occur at multiple positions of its backbone xylosyl residues, including 2-O-monoacetylation, 3-O-monoacetylation, 2,3-di-O-acetylation and 3-O-acetylation of 2-Oglucuronic acid (GlcA)-substituted xylosyl residues, but the biochemical mechanism controlling the regiospecific acetylation of xylan is largely unknown. Here, we present biochemical characterization of a group of Arabidopsis thaliana DUF231-containing proteins, namely TBL28, ESK1/TBL29, TBL30, TBL3, TBL31, TBL32, TBL33, TBL34 and TBL35, for their roles in catalyzing the regiospecific acetylation of xylan. Acetyltransferase activity assay of recombinant proteins demonstrated that all of these proteins possessed xylan acetyltransferase activities catalyzing the transfer of acetyl groups from acetyl-CoA onto xylooligomer acceptors albeit with differential specificities. Structural analysis of their reaction products revealed that TBL28, ESK1, TBL3, TBL31 and TBL34 catalyzed xylan 2-O- and 3-O-monoacetylation and 2,3-di-Oacetylation with differential positional preference, TBL30 carried out 2-O- and 3-O-monoacetylation, TBL35 catalyzed 2,3-di-O-acetylation, and TBL32 and TBL33 mediated 3-Oacetylation of 2-O-GlcA-substituted xylosyl residues. Furthermore, mutations of the conserved GDS and DXXH motifs in ESK1 were found to result in a complete loss of its acetyltransferase activity. Together, these results establish that these nine DUF231-containing proteins are xylan acetyltransferases mediating the regiospecific acetylation of xylan and that the conserved GDS and DXXH motifs are critical for their acetyltransferase activity. [ABSTRACT FROM AUTHOR]

Xylan and xyloglucan are the twomajor cell wall hemicelluloses in plants, and their biosynthesis requires a steady supply of the sugar donor, UDP-xylose. UDP-xylose is synthesized through conversion of UDP-glucuronic acid (UDP-GlcA) by the activities of UDP-xylose synthase (UXS). There exist six UXS genes in the Arabidopsis thaliana genome; three of them (UXS1, UXS2 and UXS4) encode Golgi-localized enzymes and the other three (UXS3, UXS5 and UXS6) encode cytosol-localized enzymes. In this report, we investigated the contributions of these UXS genes in supplying UDP-xylose for the biosynthesis of xylan and xyloglucan. Expression analyses revealed that the six UXS genes exhibited distinct and overlapping expression patterns in different cell types of stems, root-hypocotyls and young seedlings, and that the relative enzymatic activity of UXS in the cytosol was 17 times higher than that in the Golgi. Among the six UXS genes, UXS3, UXS5 and UXS6 showed the highest expression in stems and were expressed predominantly in xylem cells and interfascicular fibers. Their predominant expression in secondary wall-forming cells was consistent with the finding that the expression of UXS3, UXS5 and UXS6 was directly activated by the secondary wall NAC master switches. Although simultaneous mutations of UXS1, UXS2 and UXS4 did not cause any apparent effects on plant growth and xylan biosynthesis, simultaneous down-regulation/mutations of UXS3, UXS5 and UXS6 led to a drastic reduction in secondary wall thickening, a severe deformation of xylem vessels, a significant decrease in xylan content without an apparent reduction in its chain length and an absence of GlcA side chains in xylan, which are reminiscent of the phenotypes of some known xylan-deficient mutants. Moreover, Immunolocalization with two xyloglucan monoclonal antibodies, LM15 and LM25, revealed a significant reduction in the amount of xylogulcan in the primary walls. These results demonstrate that the cytosol-localized UXS3, UXS5 and UXS6 play a predominant role in the supply of UDP-xylose for the biosynthesis of xylan and xyloglucan. [ABSTRACT FROM AUTHOR]

Xylan is a major cross-linking hemicellulose in secondary walls of vascular tissues, and the recruitment of xylan as a secondary wall component was suggested to be a pivotal event for the evolution of vascular tissues. To decipher the evolution of xylan structure and xylan biosynthetic genes, we analyzed xylan substitution patterns and characterized genes mediating methylation of glucuronic acid (GlcA) side chains in xylan of the model seedless vascular plant, Selaginella moellendorffii, and investigated GT43 genes from S. moellendorffii and the model non-vascular plant, Physcomitrella patens, for their roles in xylan biosynthesis. Using nuclear magentic resonance spectroscopy, we have demonstrated that S. moellendorffii xylan consists of β-1,4- linked xylosyl residues subsituted solely with methylated GlcA residues and that xylans from both S. moellendorffii and P. patens are acetylated at O-2 and O-3. To investigate genes responsible for GlcA methylation of xylan, we identified two DUF579 genes in the S. moellendorffii genome and showed that one of them, SmGXM, encodes a glucuronoxylan methyltransferase capable of adding the methyl group onto the GlcA side chain of xylooligomers. Furthermore, we revealed that the two GT43 genes in S. moellendorffii, SmGT43A and SmGT43B, are functional orthologs of the Arabidopsis xylan backbone biosynthetic genes IRX9 and IRX14, respectively, indicating the evolutionary conservation of the involvement of two functionally non-redundant groups of GT43 genes in xylan backbone biosynthesis between seedless and seed vascular plants. Among the five GT43 genes in P. patens, PpGT43A was found to be a functional ortholog of Arabidopsis IRX9, suggesting that the recruitment of GT43 genes in xylan backbone biosynthesis occurred when non-vascular plants appeared on land. [ABSTRACT FROM AUTHOR]

Xylan, a major constituent of secondary cell walls, is made of a linear chain of β-1,4-linked xylosyl residues that are often substituted with glucuronic acid/methylglucuronic acid side chains and acetylated at O-2 and O-3. Previous studies have shown that ESK1, an Arabidopsis DUF231 protein, is an acetyltransferase catalyzing 2-O- and 3-O-monoacetylation of xylan. However, the esk1 mutation only causes a partial loss of xylan 2-O- and 3-O-monoacetylation, suggesting that additional xylan acetyltransferase activities are involved. In this report, we demonstrated the essential roles of two other Arabidopsis DUF231 genes, TBL3 and TBL31, in xylan acetylation. The expression of both TBL3 and TBL31 was shown to be induced by overexpression of the secondary wall master transcriptional regulator SND1 (secondary wall-associated NAC domain protein1) and down-regulated by simultaneous mutations of SND1 and its paralog NST1, indicating their involvement in secondary wall biosynthesis. β- Glucurondase (GUS) reporter gene analysis showed that TBL3 and TBL31 were specifically expressed in the xylem and interfascicular fibers in stems and the secondary xylem in root hypocotyls. Expression of fluorescent protein- tagged TBL3 and TBL31 in protoplasts revealed their localization in the Golgi, where xylan biosynthesis occurs. Although mutation of either TBL3 or TBL31 alone did not cause any apparent alterations in cell wall composition, their simultaneous mutations were found to result in a reduction in xylan acetylation. Further structural analysis demonstrated that the tbl3 tbl31 double mutant had a specific reduction in 3-O-acetylation of xylan. In addition, the tbl3 tbl31 esk1 triple mutant displayed a much more drastic decrease in 3-O-acetylation of xylan, indicating their functional redundancy in xylan 3-O-acetylation. These findings indicate that TBL3 and TBL31 are secondary wall-associated DUF231 genes specifically involved in xylan 3-O-acetylation. [ABSTRACT FROM AUTHOR]

Wood (also termed secondary xylem) is the most abundant biomass produced by plants, and is one of the most important sinks for atmospheric carbon dioxide. The development of wood begins with the differentiation of the lateral meristem, vascular cambium, into secondary xylem mother cells followed by cell expansion, secondary wall deposition, programmed cell death, and finally heartwood formation. Significant progress has been made in the past decade in uncovering the molecular players involved in various developmental stages of wood formation in tree species. Hormonal signalling has been shown to play critical roles in vascular cambium cell proliferation and a peptide-receptor-transcription factor regulatory mechanism similar to that controlling the activity of apical meristems is proposed to be involved in the maintenance of vascular cambium activity. It has been demonstrated that the differentiation of vascular cambium into xylem mother cells is regulated by plant hormones and HD-ZIP III transcription factors, and the coordinated activation of secondary wall biosynthesis genes during wood formation is mediated by a transcription network encompassing secondary wall NAC and MYB master switches and their downstream transcription factors. Most genes encoding the biosynthesis enzymes for wood components (cellulose, xylan, glucomannan, and lignin) have been identified in poplar and a number of them have been functionally characterized. With the availability of genome sequences of tree species from both gymnosperms and angiosperms, and the identification of a suite of wood-associated genes, it is expected that our understanding of the molecular control of wood formation in trees will be greatly accelerated. [ABSTRACT FROM AUTHOR]

A novel metal-organic replica of α-PbO2 exhibits high capacity for capture of nerve agent surrogate. [ABSTRACT FROM AUTHOR]

We report the genome-wide analysis of direct target genes of SND1 and VND7, two Arabidopsis thaliana NAC domain transcription factors that are master regulators of secondary wall biosynthesis in fibers and vessels, respectively. Systematic mapping of the SND1 binding sequence using electrophoretic mobility shift assay and transactivation analysis demonstrated that SND1 together with other secondary wall NACs (SWNs), including VND6, VND7, NST1, and NST2, bind to an imperfect palindromic 19-bp consensus sequence designated as secondary wall NAC binding element (SNBE), (T/A)NN(C/T) (T/C/G)TNNNNNNNA(A/C)GN(A/C/T) (A/T), in the promoters of their direct targets. Genome-wide analysis of direct targets of SND1 and VND7 revealed that they directly activate the expression of not only downstream transcription factors, but also a number of non-transcription factor genes involved in secondary wall biosynthesis, cell wall modification, and programmed cell death, the promoters of which all contain multiple SNBE sites. SND1 and VND7 directly regulate the expression of a set of common targets but each of them also preferentially induces a distinct set of direct targets, which is likely attributed to their differential activation strength toward SNBE sites. Complementation study showed that the SWNs were able to rescue the secondary wall defect in the snd1 nst1 mutant, indicating that they are functionally interchangeable. Together, our results provide important insight into the complex transcriptional program and the evolutionary mechanism underlying secondary wall biosynthesis, cell wall modification, and programmed cell death in secondary wall-containing cell types. [ABSTRACT FROM PUBLISHER]

There exist four members of family GT43 glycosyltransferases in the Arabidopsis (Arabidopsis thaliana) genome, and mutations of two of them, IRX9 and IRX14, have previously been shown to cause a defect in glucuronoxylan (GX) biosynthesis. However, it is currently unknown whether IRX9 and IRX14 perform the same biochemical function and whether the other two GT43 members are also involved in GX biosynthesis. In this report, we performed comprehensive genetic analysis of the functional roles of the four Arabidopsis GT43 members m GX biosynthesis. The I9H (IRX9 homolog) and I14H (IRX14 homolog) genes were shown to be specifically expressed in cells undergoing secondary wall thickening, and their encoded proteins were targeted to the Golgi, where GX is synthesized. Overexpression of I9H but not IRX14 or I14H rescued the GX defects conferred by the irx9 mutation, whereas overexpression of I14H but not IRX9 or I9H complemented the GX defects caused by the irx14 mutation. Double mutant analyses revealed that I9H functioned redundantly with IRX9 and that I14H was redundant with IRX14 in their functions. In addition, double mutations of IRX9 and IRX14 were shown to cause a loss of secondary wall thickening in fibers and a much more severe reduction in GX amount than their single mutants. Together, these results provide genetic evidence demonstrating that all four Arabidopsis GT43 members are involved in GX biosynthesis and suggest that they form two functionally nonredundant groups essential for the normal elongation of GX backbone. [ABSTRACT FROM AUTHOR]

Wood is the most abundant biomass produced by land plants. Dissection of the molecular mechanisms underlying the transcriptional regulation of wood formation is a fundamental issue in plant biology and has important implications in tree biotechnology. Although a number of transcription factors in tree species have been shown to be associated with wood formation and some of them are implicated in lignin biosynthesis, none of them have been demonstrated to be key regulators of the biosynthesis of all three major components of wood. In this report, we have identified a group of NAC domain transcription factors, PtrWNDs, that are preferentially expressed in developing wood of poplar (Populus trichocarpa). Expression of PtrWNDs in the Arabidopsis (Arabidopsis thaliana) snd1 nst1 double mutant effectively complemented the secondary wall defects in fibers, indicating that PtrWNDs are capable of activating the entire secondary wall biosynthetic program. Overexpression of PtrWND2B and PtrWND6B in Arabidopsis induced the expression of secondary wall-associated transcription factors and secondary wall biosynthetic genes and, concomitantly, the ectopic deposition of cellulose, xylan, and ligniri. Furthermore, PtrWND2B and PtrWND6B were able to activate the promoter activities of a number of poplar wood-associated transcription factors and wood biosynthetic genes. Together, these results demonstrate that PtrWNDs are functional orthologs of SND1 and suggest that PtrWNDs together with their downstream transcription factors form a transcriptional network involved in the regulation of wood formation in poplar. [ABSTRACT FROM AUTHOR]

In atherosclerosis and Alzheimer's disease, deposition of the altered self components oxidized low-density lipoprotein (LDL) and amyloid-β triggers a protracted sterile inflammatory response. Although chronic stimulation of the innate immune system is believed to underlie the pathology of these diseases, the molecular mechanisms of activation remain unclear. Here we show that oxidized LDL and amyloid-β trigger inflammatory signaling through a heterodimer of Toll-like receptors 4 and 6. Assembly of this newly identified heterodimer is regulated by signals from the scavenger receptor CD36, a common receptor for these disparate ligands. Our results identify CD36-TLR4-TLR6 activation as a common molecular mechanism by which atherogenic lipids and amyloid-β stimulate sterile inflammation and suggest a new model of TLR heterodimerization triggered by coreceptor signaling events. [ABSTRACT FROM AUTHOR]

It has previously been shown that SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) is a key transcription factor regulating secondary cell wall formation, including the biosynthesis of cellulose, xylan, and lignin. In this study, we show that two closely related SND1-regulated MYB transcription factors, MYB58 and MYB63, are transcriptional regulators specifically activating lignin biosynthetic genes during secondary wall formation in Arabidopsis thaliana. MYB58 and MYB63 are phylogenetically distinct from previously characterized MYBs shown to be associated with secondary wall formation or phenylpropanoid metabolism. Expression studies showed that MYB58 and MYB63 are specifically expressed in fibers and vessels undergoing secondary wall thickening. Dominant repression of their functions led to a reduction in secondary wall thickening and lignin content. Overexpression of MYB58 and MYB63 resulted in specific activation of lignin biosynthetic genes and concomitant ectopic deposition of lignin in cells that are normally unlignified. MYB58 was able to activate directly the expression of lignin biosynthetic genes and a secondary wall-associated laccase (LAC4) gene. Furthermore, the expression of MYB58 and MYB63 was shown to be regulated by the SND1 close homologs NST1, NST2, VND6, and VND7 and their downstream target MYB46. Together, our results indicate that MYB58 and MYB63 are specific transcriptional activators of lignin biosynthesis in the SND1-mediated transcriptional network regulating secondary wall formation. [ABSTRACT FROM AUTHOR]

SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1) is a master transcriptional switch activating the developmental program of secondary wall biosynthesis. Here, we demonstrate that a battery of SND1-regulated transcription factors is required for normal secondary wall biosynthesis in Arabidopsis thaliana. The expression of 11 SND1-regulated transcription factors, namely, SND2, SND3, MYB103, MYB85, MYB52, MYB54, MYB69, MYB42, MYB43, MYB20, and KNAT7 (a Knotted1-like homeodomain protein), was developmentally associated with cells undergoing secondary wall thickening. Of these, dominant repression of SND2, SND3, MYB103, MYB85, MYB52, MYB54, and KNAT7 significantly reduced secondary wall thickening in fiber cells. Overexpression of SND2, SND3, and MYB103 increased secondary wall thickening in fibers, and overexpression of MYB85 led to ectopic deposition of lignin in epidermal and cortical cells in stems. Furthermore, SND2, SND3, MYB103, MYB85, MYB52, and MYB54 were able to induce secondary wall biosynthetic genes. Direct target analysis using the estrogen-inducible system revealed that MYB46, SND3, MYB103, and KNAT7 were direct targets of SND1 and also of its close homologs, NST1, NST2, and vessel-specific VND6 and VND7. Together, these results demonstrate that a transcriptional network consisting of SND1 and its downstream targets is involved in regulating secondary wall biosynthesis in fibers and that NST1, NST2, VND6, and VND7 are functional homologs of SND1 that regulate the same downstream targets in different cell types. [ABSTRACT FROM AUTHOR]

We demonstrate that the Arabidopsis thaliana MYB46 transcription factor is a direct target of SECONDARY WALL-ASSOCIATED NAC DOMAIN PROTEIN1 (SND1), which is a key transcriptional activator regulating the developmental program of secondary wall biosynthesis. The MYB46 gene is expressed predominantly in fibers and vessels in stems, and its encoded protein is targeted to the nucleus and can activate transcription. MYB46 gene expression was shown to be regulated by SND1, and transactivation analysis demonstrated that SND1 as well as its close homologs were able to activate the MYB46 promoter. Electrophoretic mobility shift assays and chromatin immunoprecipitation experiments revealed that SND1 binds to the MYB46 promoter. Dominant repression of MYB46 caused a drastic reduction in the secondary wall thickening of fibers and vessels. Overexpression of MYB46 resulted in an activation of the biosynthetic pathways of cellulose, xylan, and lignin and concomitantly led to ectopic deposition of secondary walls in cells that are normally nonsclerenchymatous. In addition, the expression of two secondary wall-associated transcription factors, MYB85 and KNAT7, was highly upregulated by MYB46 overexpression. These results demonstrate that MYB46 is a direct target of SND1 and is another key player in the transcriptional network involved in the regulation of secondary wall biosynthesis in Arabidopsis. [ABSTRACT FROM AUTHOR]

Secondary walls in fibers and tracheary elements constitute the most abundant biomass produced by plants. Although a number of genes involved in the biosynthesis of secondary wall components have been characterized, little is known about the molecular mechanisms underlying the coordinated expression of these genes. Here, we demonstrate that the Arabidopsis thaliana NAC (for NAM, ATAF1/2, and CUC2) domain transcription factor, SND1 (for secondary wall-associated NAC domain protein), is a key transcriptional switch regulating secondary wall synthesis in fibers. We show that SND1 is expressed specifically in interfascicular fibers and xylary fibers in stems and that dominant repression of SND1 causes a drastic reduction in the secondary wall thickening of fibers. Ectopic overexpression of SND1 results in activation of the expression of secondary wall biosynthetic genes, leading to massive deposition of secondary walls in cells that are normally nonsclerenchymatous. In addition, we have found that SND1 upregulates the expression of several transcription factors that are highly expressed in fibers during secondary wall synthesis. Together, our results reveal that SND1 is a key transcriptional activator involved in secondary wall biosynthesis in fibers. [ABSTRACT FROM AUTHOR]

Xylan is the major hemicellulose in dicot wood. Unraveling genes involved in the biosynthesis of xylan will be of importance in understanding the process of wood formation. In this report, we investigated the possible role of poplar GT47C, a glycosyltransferase belonging to family GT47, in the biosynthesis of xylan. PoGT47C from the hybrid poplar Populus alba × tremula exhibits 84% sequence similarity to Fragile fiber8 (FRA8), which is involved in the biosynthesis of glucuronoxylan in Arabidopsis. Phylogenetic analysis of glycosyltransferase family GT47 in the Populus trichocarpa genome revealed that GT47C is the only close homolog of FRA8. In situ hybridization showed that the PoGT47C gene was expressed in developing primary xylem, secondary xylem and phloem fibers of stems, and in developing secondary xylem of roots. Sequence analysis suggests that PoGT47C is a type II membrane protein, and study of the subcellular localization demonstrated that fluorescent protein-tagged PoGT47C was located in the Golgi. Immunolocalization with a xylan monoclonal antibody LM10 revealed a nearly complete loss of xylan signals in the secondary walls of fibers and vessels in the Arabidopsis fra8 mutant. Expression of PoGT47C in the fra8 mutant restored the secondary wall thickness and xylan content to the wild-type level. Together, these results suggest that PoGT47C is functionally conserved with FRA8 and it is probably involved in xylan synthesis during wood formation. [ABSTRACT FROM AUTHOR]

Type II inositol polyphosphate 5-phosphatases (5PTases) in animals and yeast have been known to be important for regulating inositol and phospholipid signaling by hydrolyzing phosphate from both inositol polyphosphates and phosphoinositides. However, the molecular and biochemical properties of type II 5PTases in plants have not yet been studied. In this report, we show that three Arabidopsis genes, At5PTase12, At5PTase13 and At5PTase14, encode proteins with a 5PTase domain and a WD-repeat domain, a novel combination present only in plant 5PTases. We demonstrate that these genes are differentially expressed in Arabidopsis organs and At5PTase13 is induced in response to ABA and wounding treatments. Our biochemical studies reveal that although both At5PTase12 and At5PTase13 exhibit phosphatase activity toward only Ins(1,4,5)P3, At5PTase14 hydrolyzes phosphate from PI(4,5)P2, PI(3,4,5)P3 and Ins(1,4,5)P3 with the highest substrate affinity toward PI(4,5)P2. All three At5PTases require Mg2+ for their phosphatase activities. Our molecular and biochemical characterization of three WD-repeat-domain-containing At5PTases provides a foundation for further elucidation of their cellular functions in Arabidopsis. [ABSTRACT FROM AUTHOR]

In Arabidopsis stems, the vascular bundles in the stele are arranged in a ring-like pattern and the vascular tissues in each bundle are organized in a collateral pattern. We have shown previously that the semidominant amphivasal vascular bundle 1 (avb1) mutation transforms the collateral vascular bundles into amphivasal bundles and disrupts the ring-like arrangement of vascular bundles in the stele. In this study, we show that the avb1 mutation occurred in the putative microRNA 165 target sequence in the IFL1/REV gene and caused an amino acid substitution in the putative sterol/lipid-binding START domain. We present direct evidence that the wild-type IFL1/REV mRNA was cleaved within the microRNA 165 target sequence and the avb1 mutation resulted in an inhibition of cleavage and a higher level accumulation of full-length mRNA, suggesting a role of microRNA 165 in the regulation of IFL1/REV gene expression. In addition to an alteration in vascular patterning, the avb1 mutation also caused dramatic changes in fiber cell wall thickening and organ polarity, including aberrant formation and proliferation of cauline leaves and branches, production of trumpet-shaped leaves with reversed adaxial-abaxial identity, ectopic growth of carpel-like structures on the outer surface of carpels, and fasciation of inflorescence. Ectopic overexpression of the avb1 mutant cDNA not only phenocopied most of the avb1 mutant phenotypes but also led to additional novel phenotypes such as formation of leaves with extremely narrow blades and ectopic production of branches in the axil of siliques. Taken together, these results suggest that the avb1 gain-of-function mutation of the IFL1/REV gene alters the positional information that determines vascular patterning and organ polarity. [ABSTRACT FROM PUBLISHER]

The Arabidopsis thaliana (L.) Heynh. ROOT HAIR DEFECTIVE3 ( RHD3) gene has previously been shown to be essential for normal cell expansion [H. Wang et al. (1997) Genes Dev 11:799?811]. In this report, we demonstrated that mutation of the RHD3 gene in the Arabidopsis fragile fiber 4 ( fra4) mutant caused a dramatic reduction in the wall thickness of fibers, vessels, and pith cells in the inflorescence stems and, concomitantly, a decrease in the mechanical strength of stems. The reduced wall thickness in the fra4 mutant was accompanied by an alteration in cell wall composition. Consistent with the defective fiber and vessel wall phenotypes, the RHD3 gene exhibited a strong expression in developing fiber and xylem cells. We showed that the Arabidopsis genome contains two additional RHD3-like genes, one of which was expressed specifically in flowers. In addition, we found that mutation of the RHD3 gene caused an alteration in the organization of the actin cytoskeleton but no effects on cortical microtubules. Our findings suggest an essential role of RHD3 in cell wall biosynthesis and actin organization, both of which are known to be important for cell expansion. [ABSTRACT FROM AUTHOR]

Examines the elucidation of the cellular functions of SAC domain-containing proteins in Arabidopsis. Factors affecting diverse cellular functions; Regulation of the levels of various phosphoinositides in the phosphoinositide phosphatase activities; Modulation of vesicle trafficking.

Xylan is the second most abundant polysaccharide in dicot wood. Unraveling the biosynthetic pathway of xylan is important not only for our understanding of the process of wood formation but also for our rational engineering of wood for biofuel production. Although several glycosyltransferases are implicated in glucuronoxylan (GX) biosynthesis in Arabidopsis, whether their close orthologs in woody tree species are essential for GX biosynthesis during wood formation has not been investigated. In fact, no studies have been reported to evaluate the effects of alterations in secondary wall-associated glycosyltransferases on wood formation in tree species. In this report, we demonstrate that PoGT47C, a poplar glycosyltransferase belonging to family GT47, is essential for the normal biosynthesis of GX and the normal secondary wall thickening in the wood of the hybrid poplar Populus alba × tremula. RNA interference (RNAi) inhibition of PoGT47C resulted in a drastic reduction in the thickness of secondary walls, a deformation of vessels and a decreased amount of GX in poplar wood. Structural analysis of GX using nuclear magnetic resonance (NMR) spectroscopy demonstrated that the reducing end of GX from poplar wood contains the tetrasaccharide sequence, β-d-Xylp-(1→3)-α-l-Rhap-(1→2)-α-d-GalpA-(1→4)-d-Xylp, and that its abundance was significantly decreased in the GX from the wood of the GT47C-RNAi lines. The transgenic wood was found to yield more glucose by cellulase digestion than the wild-type wood, indicating that the GX reduction in wood reduces the recalcitrance of wood to cellulase digestion. Together, these results provide direct evidence demonstrating that the PoGT47C glycosyltransferase is essential for normal GX biosynthesis in poplar wood and that GX modification could improve the digestibility of wood cellulose by cellulase. [ABSTRACT FROM AUTHOR]

The FRAGILE FIBER8 (FRA8) gene was previously shown to be required for the biosynthesis of the reducing end tetrasaccharide sequence of glucuronoxylan (GX) in Arabidopsis thaliana. Here, we demonstrate that F8H, a close homolog of FRA8, is a functional paralog of FRA8 involved in GX biosynthesis. The F8H gene is preferentially expressed in xylem cells, in which the secondary walls contain an abundant amount of GX, and the F8H protein is targeted to the Golgi where GX is synthesized. Overexpression of F8H in the fra8 mutant completely complemented the fra8 mutant phenotypes including the secondary wall thickness of fibers and vessels, vessel morphology, GX content and the abundance of the reducing end tetrasaccharide sequence of GX, indicating that F8H shares the same biochemical function as FRA8. Although the f8h mutant alone did not show any detectable cell wall defects, the f8h/fra8 double mutant exhibits an additional reduction in cell wall xylose level, a more severe deformation of vessels and an extreme retardation in plant growth compared with the fra8 mutant. Together, our findings suggest that F8H and FRA8 are functional paralogs and that they function redundantly in GX biosynthesis during secondary wall formation in the xylem. [ABSTRACT FROM AUTHOR]

Xylan, cellulose and lignin are the three major components of secondary walls in wood, and elucidation of the biosynthetic pathway of xylan is of importance for potential modification of secondary wall composition to produce wood with improved properties. So far, three Arabidopsis glycosyltransferases, FRAGILE FIBER8, IRREGULAR XYLEM8 and IRREGULAR XYLEM9, have been implicated in glucuronoxylan (GX) biosynthesis. In this study, we demonstrate that PARVUS, which is a member of family GT8, is required for the biosynthesis of the tetrasaccharide primer sequence, β-d-Xyl-(1 → 3)-α-l-Rha-(1 → 2)-α-d-GalA-(1 → 4)-d-Xyl, located at the reducing end of GX. The PARVUS gene is expressed during secondary wall biosynthesis in fibers and vessels, and its encoded protein is predominantly localized in the endoplasmic reticulum. Mutation of the PARVUS gene leads to a drastic reduction in secondary wall thickening and GX content. Structural analysis of GX using 1H-nuclear magnetic resonance (NMR) spectroscopy revealed that the parvus mutation causes a loss of the tetrasaccharide primer sequence at the reducing end of GX and an absence of glucuronic acid side chains in GX. Activity assay showed that the xylan xylosyltransferase and glucuronyltransferase activities were not affected in the parvus mutant. Together, these findings implicate a possible role for PARVUS in the initiation of biosynthesis of the GX tetrasaccharide primer sequence and provide novel insights into the mechanisms of GX biosynthesis. [ABSTRACT FROM AUTHOR]