Putative rhamnogalacturonan-II glycosyltransferase identified through callus gene editing bypasses embryo lethality.

Rhamnogalacturonan II (RG-II) is a structurally complex and conserved domain of the pectin present in the primary cell walls of vascular plants. Borate crosslinking of RG-II is required for plants to grow and develop normally. Mutations that alter RG-II structure also affect crosslinking and are lethal or severely impair growth. Thus, few genes involved in RG-II synthesis have been identified. Here we developed a method to generate viable loss-of-function Arabidopsis (Arabidopsis thaliana) mutants in callus tissue via CRISPR/Cas9-mediated gene editing. We combined this with a candidate gene approach to characterize the male gametophyte defective 2 (MPG2) gene that encodes a putative family GT29 glycosyltransferase. Plants homozygous for this mutation do not survive. We showed that in the callus mutant cell walls, RG-II does not crosslink normally because it lacks 3-deoxy-D-manno-octulosonic acid (Kdo) and thus cannot form the α-L-Rhap-(1→5)-α-D-kdop-(1→ sidechain. We suggest that MGP2 encodes an inverting RG-II CMP-ß-Kdo transferase (RCKT1). Our discovery provides further insight into the role of sidechains in RG-II dimerization. Our method also provides a viable strategy for further identifying proteins involved in the biosynthesis of RG-II.

Pectic-AGP is a major form of Arabidopsis AGPs.

As a key component in cell walls of numerous organisms ranging from green algae to higher plants, AGPs play principal roles in many biological processes such as cell-cell adhesion and regulating Ca2+ signaling pathway as a Ca2+-capacitor. Consistently, AGP structures vary from species to species and from tissue to tissue. To understand the functions of AGPs, it is vital to know their structural differences relative to their location in the plant. Thus, AGPs were purified from different Arabidopsis tissues. Analyses of these AGPs demonstrated that the AGPs comprised covalently linked pectin and AGP, referred to as pectic-AGPs. Importantly, these pectic-AGPs were glycosylated with a remarkable variety of polysaccharides including homogalacturonan, rhamnogalacturonan-I, and type II arabinogalactan at different ratios and lengths. This result not only suggests that pectic-AGP is a major form of Arabidopsis AGPs, but also supports AGPs serve as crosslinkers covalently connecting pectins with structures tailored for tissue-specific functions.

Engineering custom morpho- and chemotypes of Populus for sustainable production of biofuels, bioproducts, and biomaterials.

Humans have been modifying plant traits for thousands of years, first through selection (i.e., domestication) then modern breeding, and in the last 30 years, through biotechnology. These modifications have resulted in increased yield, more efficient agronomic practices, and enhanced quality traits. Precision knowledge of gene regulation and function through high-resolution single-cell omics technologies, coupled with the ability to engineer plant genomes at the DNA sequence, chromatin accessibility, and gene expression levels, can enable engineering of complex and complementary traits at the biosystem level. Populus spp., the primary genetic model system for woody perennials, are among the fastest growing trees in temperate zones and are important for both carbon sequestration and global carbon cycling. Ample genomic and transcriptomic resources for poplar are available including emerging single-cell omics datasets. To expand use of poplar outside of valorization of woody biomass, chassis with novel morphotypes in which stem branching and tree height are modified can be fabricated thereby leading to trees with altered leaf to wood ratios. These morphotypes can then be engineered into customized chemotypes that produce high value biofuels, bioproducts, and biomaterials not only in specific organs but also in a cell-type-specific manner. For example, the recent discovery of triterpene production in poplar leaf trichomes can be exploited using cell-type specific regulatory sequences to synthesize high value terpenes such as the jet fuel precursor bisabolene specifically in the trichomes. By spatially and temporally controlling expression, not only can pools of abundant precursors be exploited but engineered molecules can be sequestered in discrete cell structures in the leaf. The structural diversity of the hemicellulose xylan is a barrier to fully utilizing lignocellulose in biomaterial production and by leveraging cell-type-specific omics data, cell wall composition can be modified in a tailored and targeted specific manner to generate poplar wood with novel chemical features that are amenable for processing or advanced manufacturing. Precision engineering poplar as a multi-purpose sustainable feedstock highlights how genome engineering can be used to re-imagine a crop species.

Acetylation in Ionic Liquids Dramatically Increases Yield in the Glycosyl Composition and Linkage Analysis of Insoluble and Acidic Polysaccharides.

Glycosyl composition and linkage analyses are important first steps toward understanding the structural diversity and biological importance of polysaccharides. Failure to fully solubilize samples prior to analysis results in the generation of incomplete and poor-quality composition and linkage data by gas chromatography-mass spectrometry (GC-MS). Acidic polysaccharides also do not give accurate linkage results, because they are poorly soluble in DMSO and tend to undergo ß-elimination during permethylation. Ionic liquids can solubilize polysaccharides, improving their derivatization and extraction for analysis. We show that water-insoluble polysaccharides become much more amenable to chemical analysis by first acetylating them in an ionic liquid. Once acetylated, these polysaccharides, having been deprived of their intermolecular hydrogen bonds, are hydrolyzed more readily for glycosyl composition analysis or methylated more efficiently for glycosyl linkage analysis. Acetylation in an ionic liquid greatly improves composition analysis of insoluble polysaccharides when compared to analysis without acetylation, enabling complete composition determination of normally recalcitrant polysaccharides. We also present a protocol for uronic acid linkage analysis that incorporates this preacetylation step. This protocol produces partially methylated alditol acetate derivatives in high yield with minimal ß-elimination and gives sensitive linkage results for acidic polysaccharides that more accurately reflect the structures being analyzed. We use important plant polysaccharides to show that the preacetylation step leads to superior results compared to traditional methodologies.

The Plasminogen-Apple-Nematode (PAN) domain suppresses JA/ET defense pathways in plants.

Suppression of immune response is a phenomenon that enables biological processes such as gamete fertilization, cell growth, cell proliferation, endophyte recruitment, parasitism, and pathogenesis. Here, we show for the first time that the Plasminogen-Apple-Nematode (PAN) domain present in G-type lectin receptor-like kinases is essential for immunosuppression in plants. Defense pathways involving jasmonic acid and ethylene are critical for plant immunity against microbes, necrotrophic pathogens, parasites, and insects. Using two Salix purpurea G-type lectin receptor kinases, we demonstrated that intact PAN domains suppress jasmonic acid and ethylene signaling in Arabidopsis and tobacco. Variants of the same receptors with mutated residues in this domain could trigger induction of both defense pathways. Assessment of signaling processes revealed significant differences between receptors with intact and mutated PAN domain in MAPK phosphorylation, global transcriptional reprogramming, induction of downstream signaling components, hormone biosynthesis and resistance to Botrytis cinerea . Further, we demonstrated that the domain is required for oligomerization, ubiquitination, and proteolytic degradation of these receptors. These processes were completely disrupted when conserved residues in the domain were mutated. Additionally, we have tested the hypothesis in recently characterized Arabidopsis mutant which has predicted PAN domain and negatively regulates plant immunity against root nematodes. ern1.1 mutant complemented with mutated PAN shows triggered immune response with elevated WRKY33 expression, hyperphosphorylation of MAPK and resistant to necrotrophic fungus Botrytis cinerea . Collectively, our results suggest that ubiquitination and proteolytic degradation mediated by the PAN domain plays a role in receptor turn-over to suppress jasmonic acid and ethylene defense signaling in plants.

Overexpression of REDUCED WALL ACETYLATION C increases xylan acetylation and biomass recalcitrance in Populus.

Plant lignocellulosic biomass, i.e. secondary cell walls of plants, is a vital alternative source for bioenergy. However, the acetylation of xylan in secondary cell walls impedes the conversion of biomass to biofuels. Previous studies have shown that REDUCED WALL ACETYLATION (RWA) proteins are directly involved in the acetylation of xylan but the regulatory mechanism of RWAs is not fully understood. In this study, we demonstrate that overexpression of a Populus trichocarpa PtRWA-C gene increases the level of xylan acetylation and increases the lignin content and S/G ratio, ultimately yielding poplar woody biomass with reduced saccharification efficiency. Furthermore, through gene coexpression network and expression quantitative trait loci (eQTL) analysis, we found that PtRWA-C was regulated not only by the secondary cell wall hierarchical regulatory network but also by an AP2 family transcription factor HARDY (HRD). Specifically, HRD activates PtRWA-C expression by directly binding to the PtRWA-C promoter, which is also the cis-eQTL for PtRWA-C. Taken together, our findings provide insights into the functional roles of PtRWA-C in xylan acetylation and consequently saccharification and shed light on synthetic biology approaches to manipulate this gene and alter cell wall properties. These findings have substantial implications for genetic engineering of woody species, which could be used as a sustainable source of biofuels, valuable biochemicals, and biomaterials.

A single amino acid change led to structural and functional differentiation of PvHd1 to control flowering in switchgrass.

Switchgrass, a forage and bioenergy crop, occurs as two main ecotypes with different but overlapping ranges of adaptation. The two ecotypes differ in a range of characteristics, including flowering time. Flowering time determines the duration of vegetative development and therefore biomass accumulation, a key trait in bioenergy crops. No causal variants for flowering time differences between switchgrass ecotypes have, as yet, been identified. In this study, we mapped a robust flowering time quantitative trait locus (QTL) on chromosome 4K in a biparental F2 population and characterized the flowering-associated transcription factor gene PvHd1, an ortholog of CONSTANS in Arabidopsis and Heading date 1 in rice, as the underlying causal gene. Protein modeling predicted that a serine to glycine substitution at position 35 (p.S35G) in B-Box domain 1 greatly altered the global structure of the PvHd1 protein. The predicted variation in protein compactness was supported in vitro by a 4 °C shift in denaturation temperature. Overexpressing the PvHd1-p.35S allele in a late-flowering CONSTANS-null Arabidopsis mutant rescued earlier flowering, whereas PvHd1-p.35G had a reduced ability to promote flowering, demonstrating that the structural variation led to functional divergence. Our findings provide us with a tool to manipulate the timing of floral transition in switchgrass cultivars and, potentially, expand their cultivation range.

Glycosyltransferase family 47 (GT47) proteins in plants and animals.

Glycosyltransferases (GTs) are carbohydrate-active enzymes that are encoded by the genomes of organisms spanning all domains of life. GTs catalyze glycosidic bond formation, transferring a sugar monomer from an activated donor to an acceptor substrate, often another saccharide. GTs from family 47 (GT47, PF03016) are involved in the synthesis of complex glycoproteins in mammals and insects and play a major role in the synthesis of almost every class of polysaccharide in plants, with the exception of cellulose, callose, and mixed linkage ß-1,3/1,4-glucan. GT47 enzymes adopt a GT-B fold and catalyze the formation of glycosidic bonds through an inverting mechanism. Unlike animal genomes, which encode few GT47 enzymes, plant genomes contain 30 or more diverse GT47 coding sequences. Our current knowledge of the GT47 family across plant species brings us an interesting view, showcasing how members exhibit a great diversity in both donor and acceptor substrate specificity, even for members that are classified in the same phylogenetic clade. Thus, we discuss how plant GT47 family members represent a great case to study the relationship between substrate specificity, protein structure, and protein evolution. Most of the plant GT47 enzymes that are identified to date are involved in biosynthesis of plant cell wall polysaccharides, including xyloglucan, xylan, mannan, and pectins. This indicates unique and crucial roles of plant GT47 enzymes in cell wall formation. The aim of this review is to summarize findings about GT47 enzymes and highlight new challenges and approaches on the horizon to study this family.

Structural and biochemical insight into a modular ß-1,4-galactan synthase in plants.

Rhamnogalacturonan I (RGI) is a structurally complex pectic polysaccharide with a backbone of alternating rhamnose and galacturonic acid residues substituted with arabinan and galactan side chains. Galactan synthase 1 (GalS1) transfers galactose and arabinose to either extend or cap the ß-1,4-galactan side chains of RGI, respectively. Here we report the structure of GalS1 from Populus trichocarpa, showing a modular protein consisting of an N-terminal domain that represents the founding member of a new family of carbohydrate-binding module, CBM95, and a C-terminal glycosyltransferase family 92 (GT92) catalytic domain that adopts a GT-A fold. GalS1 exists as a dimer in vitro, with stem domains interacting across the chains in a 'handshake' orientation that is essential for maintaining stability and activity. In addition to understanding the enzymatic mechanism of GalS1, we gained insight into the donor and acceptor substrate binding sites using deep evolutionary analysis, molecular simulations and biochemical studies. Combining all the results, a mechanism for GalS1 catalysis and a new model for pectic galactan side-chain addition are proposed.

Insights into pectin O-acetylation in the plant cell wall: structure, synthesis, and modification.

O-Acetyl esterification is an important structural and functional feature of pectins present in the cell walls of all land plants. The amount and positions of pectin acetyl substituents varies across plant tissues and stages of development. Plant growth and response to biotic and abiotic stress are known to be significantly influenced by pectin O-acetylation. Gel formation is a key characteristic of pectins, and many studies have shown that gel formation is dependent upon the degree of acetylation. Previous studies have indicated that members of the TRICHOME BIREFRINGENCE-LIKE (TBL) family may play a role in the O-acetylation of pectin, however, biochemical evidence for acceptor specific pectin acetyltransferase activity remains to be confirmed and the exact mechanism(s) for catalysis must be determined. Pectin acetylesterases (PAEs) affect pectin acetylation as they hydrolyze acetylester bonds and have a role in the amount and distribution of O-acetylation. Several mutant studies suggest the critical role of pectin O-acetylation; however, additional research is required to fully understand this. This review aims to discuss the importance, role, and putative mechanism of pectin O-acetylation.

Chemo-Enzymatic Synthesis of Long-Chain Oligosaccharides for Studying Xylan-Modifying Enzymes.

Plant research is hampered in several aspects by a lack of pure oligosaccharide samples that closely represent structural features of cell wall glycans. An alternative to purely chemical synthesis to access these oligosaccharides is chemo-enzymatic synthesis using glycosynthases. These enzymes enable the ligation of oligosaccharide donors, when activated for example as α-glycosyl fluorides, with suitable acceptor oligosaccharides. Herein, the synthesis of xylan oligosaccharides up to dodecasaccharides is reported, with glycosynthase-mediated coupling reactions as key steps. The xylo-oligosaccharide donors were protected at the non-reducing end with a 4-O-tetrahydropyranyl (THP) group to prevent polymerization. Installation of an unnatural 3-O-methylether substituent at the reducing end xylose of the oligosaccharides ensured good water solubility. Biochemical assays demonstrated enzymatic activity for the xylan acetyltransferase XOAT1 from Arabidopsis thaliana, xylan arabinofuranosyl-transferase XAT3 enzymes from rice and switchgrass, and the xylan glucuronosyltransferase GUX3 from Arabidopsis thaliana. In case of the glucuronosyltransferase GUX3, MALDI-MS/MS analysis of the reaction product suggested that a single glucuronosyl substituent was installed primarily at the central xylose residues of the dodecasaccharide acceptor, demonstrating the value of long-chain acceptors for assaying biosynthetic glycosyltransferases.

An update on xylan structure, biosynthesis, and potential commercial applications.

•Xylan is an abundant carbohydrate component of plant cell walls that is vital for proper cell wall structure and vascular tissue development.•Xylan structure is known to vary between different tissues and species.•The role of xylan in the plant cell wall is to interact with cellulose, lignin, and hemicelluloses.•Xylan synthesis is directed by several types of Golgi-localized enzymes.•Xylan is being explored as an eco-friendly resource for diverse commercial applications.

Most of the rhamnogalacturonan-I from cultured Arabidopsis cell walls is covalently linked to arabinogalactan-protein.

To characterize a purified rhamnogalacturonan-I (RG-I) containing both RG-I and arabinogalactan-protein (AGP) types of glycosyl residues, an AGP-specific ß-1,3-galactanase that can cleave the AG backbone and release the AG sidechain was applied to this material. Carbohydrate analysis and NMR spectroscopy verified that the galactanase-released carbohydrate consists of RG-I covalently attached to the AG sidechain, proving a covalent linkage between RG-I and AGP. Size exclusion chromatography-multiangle light scattering-refractive index detection revealed that the galactanase-released RG-I has an average molecular weight of 41.6 kDa, which, together with the percentage of pectic sugars suggests an RG-I-AGP comprising one AGP covalently linked to two RG-I glycans. Carbohydrate analysis and NMR results of the RG-I-AGP, the galactanase-released glycans, and the RG lyase-released glycans demonstrated that the attached RG-I glycans are decorated with α-1,5-arabinan, ß-1,4-galactan, xylose, and 4-O-Me-xylose sidechains. Our measurement suggests that the covalently linked RG-I-AGP is the major component of the traditionally prepared RG-I.

Enzymatic Synthesis of Xylan Microparticles with Tunable Morphologies.

Xylans are a diverse family of hemicellulosic polysaccharides found in abundance within the cell walls of nearly all flowering plants. Unfortunately, naturally occurring xylans are highly heterogeneous, limiting studies of their synthesis and structure-function relationships. Here, we demonstrate that xylan synthase 1 from the charophyte alga Klebsormidium flaccidum is a powerful biocatalytic tool for the bottom-up synthesis of pure ß-1,4 xylan polymers that self-assemble into microparticles in vitro. Using uridine diphosphate-xylose (UDP-xylose) and defined saccharide primers as substrates, we demonstrate that the shape, composition, and properties of the self-assembling xylan microparticles could be readily controlled via the fine structure of the xylan oligosaccharide primer used to initiate polymer elongation. Furthermore, we highlight two approaches for bottom-up and surface functionalization of xylan microparticles with chemical probes and explore the susceptibility of xylan microparticles to enzymatic hydrolysis. Together, these results provide a useful platform for structural and functional studies of xylans to investigate cell wall biosynthesis and polymer-polymer interactions and suggest possible routes to new biobased materials with favorable properties for biomedical and renewable applications.

Insights into the xylan degradation system of Cellulomonas sp. B6: biochemical characterization of rCsXyn10A and rCsAbf62A.

Valorization of the hemicellulose fraction of plant biomass is crucial for the sustainability of lignocellulosic biorefineries. The Cellulomonas genus comprises Gram-positive Actinobacteria that degrade cellulose and other polysaccharides by secreting a complex array of enzymes. In this work, we studied the specificity and synergy of two enzymes, CsXyn10A and CsAbf62A, which were identified as highly abundant in the extracellular proteome of Cellulomonas sp. B6 when grown on wheat bran. To explore their potential for bioprocessing, the recombinant enzymes were expressed and their activities were thoroughly characterized. rCsXyn10A is a GH10 endo-xylanase (EC 3.2.1.8), active across a broad pH range (5 to 9), at temperatures up to 55 °C. rCsAbf62A is an α-L-arabinofuranosidase (ABF) (EC 3.2.1.55) that specifically removes α-1,2 and α-1,3-L-arabinosyl substituents from arabino-xylo-oligosaccharides (AXOS), xylan, and arabinan backbones, but it cannot act on double-substituted residues. It also has activity on pNPA. No differences were observed regarding activity when CsAbf62A was expressed with its appended CBM13 module or only the catalytic domain. The amount of xylobiose released from either wheat arabinoxylan or arabino-xylo-oligosaccharides increased significantly when rCsXyn10A was supplemented with rCsAbf62A, indicating that the removal of arabinosyl residues by rCsAbf62A improved rCsXyn10A accessibility to ß-1,4-xylose linkages, but no synergism was observed in the deconstruction of wheat bran. These results contribute to designing tailor-made, substrate-specific, enzymatic cocktails for xylan valorization. KEY POINTS: • rCsAbf62A removes α-1,2 and α-1,3-L-arabinosyl substituents from arabino-xylo-oligosaccharides, xylan, and arabinan backbones. • The appended CBM13 of rCsAbf62A did not affect the specific activity of the enzyme. • Supplementation of rCsXyn10A with rCsAbf62A improves the degradation of AXOS and xylan.

Accelerating Biological Insight for Understudied Genes.

The rapid expansion of genome sequence data is increasing the discovery of protein-coding genes across all domains of life. Annotating these genes with reliable functional information is necessary to understand evolution, to define the full biochemical space accessed by nature, and to identify target genes for biotechnology improvements. The majority of proteins are annotated based on sequence conservation with no specific biological, biochemical, genetic, or cellular function identified. Recent technical advances throughout the biological sciences enable experimental research on these understudied protein-coding genes in a broader collection of species. However, scientists have incentives and biases to continue focusing on well documented genes within their preferred model organism. This perspective suggests a research model that seeks to break historic silos of research bias by enabling interdisciplinary teams to accelerate biological functional annotation. We propose an initiative to develop coordinated projects of collaborating evolutionary biologists, cell biologists, geneticists, and biochemists that will focus on subsets of target genes in multiple model organisms. Concurrent analysis in multiple organisms takes advantage of evolutionary divergence and selection, which causes individual species to be better suited as experimental models for specific genes. Most importantly, multisystem approaches would encourage transdisciplinary critical thinking and hypothesis testing that is inherently slow in current biological research.

Rational enzyme design for controlled functionalization of acetylated xylan for cell-free polymer biosynthesis.

Xylan O-acetyltransferase 1 (XOAT1) is involved in O-acetylating the backbone of hemicellulose xylan. Recent structural analysis of XOAT1 showed two unequal lobes forming a cleft that is predicted to accommodate and position xylan acceptors into proximity with the catalytic triad. Here, we used docking and molecular dynamics simulations to investigate the optimal orientation of xylan in the binding cleft of XOAT1 and identify putative key residues (Gln445 and Arg444 on Minor lobe & Asn312, Met311 and Asp403 on Major lobe) involved in substrate interactions. Site-directed mutagenesis coupled with biochemical analyses revealed the major lobe of XOAT1 is important for xylan binding. Mutation of single key residues yielded XOAT1 variants with various enzymatic efficiencies that are applicable to one-pot synthesis of xylan polymers with different degrees of O-acetylation. Taken together, our results demonstrate the effectiveness of computational modeling in guiding enzyme engineering aimed at modulating xylan and redesigning plant cell walls.

Protocols for isolating and characterizing polysaccharides from plant cell walls: a case study using rhamnogalacturonan-II.

BACKGROUND: In plants, a large diversity of polysaccharides comprise the cell wall. Each major type of plant cell wall polysaccharide, including cellulose, hemicellulose, and pectin, has distinct structures and functions that contribute to wall mechanics and influence plant morphogenesis. In recent years, pectin valorization has attracted much attention due to its expanding roles in biomass deconstruction, food and material science, and environmental remediation. However, pectin utilization has been limited by our incomplete knowledge of its structure. Herein, we present a workflow of principles relevant for the characterization of polysaccharide primary structure using nature's most complex polysaccharide, rhamnogalacturonan-II (RG-II), as a model. RESULTS: We outline how to isolate RG-II from celery and duckweed cell walls and from red wine using chemical or enzymatic treatments coupled with size-exclusion chromatography. From there, we applied mass spectrometry (MS)-based techniques to determine the glycosyl residue and linkage compositions of the intact RG-II and derived oligosaccharides including special considerations for labile monosaccharides. In doing so, we demonstrated that in the duckweed Wolffiella repanda the arabinopyranosyl (Arap) residue of side chain B is substituted at O-2 with rhamnose. We used electrospray-MS techniques to identify non-glycosyl modifications including methyl-ethers, methyl-esters, and acetyl-esters on RG-II-derived oligosaccharides. We then showed the utility of proton nuclear magnetic resonance spectroscopy (1H-NMR) to investigate the structure of intact RG-II and to complement the RG-II dimerization studies performed using size-exclusion chromatography. CONCLUSIONS: The complexity of pectic polysaccharide structures has hampered efforts aimed at their valorization. In this work, we used RG-II as a model to demonstrate the steps necessary to isolate and characterize polysaccharides using chromatographic, MS, and NMR techniques. The principles can be applied to the characterization of other saccharide structures and will help inform researchers on how saccharide structure relates to functional properties in the future.

AtFUT4 and AtFUT6 Are Arabinofuranose-Specific Fucosyltransferases.

The bulk of plant biomass is comprised of plant cell walls, which are complex polymeric networks, composed of diverse polysaccharides, proteins, polyphenolics, and hydroxyproline-rich glycoproteins (HRGPs). Glycosyltransferases (GTs) work together to synthesize the saccharide components of the plant cell wall. The Arabidopsis thaliana fucosyltransferases (FUTs), AtFUT4, and AtFUT6, are members of the plant-specific GT family 37 (GT37). AtFUT4 and AtFUT6 transfer fucose (Fuc) onto arabinose (Ara) residues of arabinogalactan (AG) proteins (AGPs) and have been postulated to be non-redundant AGP-specific FUTs. AtFUT4 and AtFUT6 were recombinantly expressed in mammalian HEK293 cells and purified for biochemical analysis. We report an updated understanding on the specificities of AtFUT4 and AtFUT6 that are involved in the synthesis of wall localized AGPs. Our findings suggest that they are selective enzymes that can utilize various arabinogalactan (AG)-like and non-AG-like oligosaccharide acceptors, and only require a free, terminal arabinofuranose. We also report with GUS promoter-reporter gene studies that AtFUT4 and AtFUT6 gene expression is sub-localized in different parts of developing A. thaliana roots.