Biology subjects

Dupree, P.

Publications and source records attributed to Dupree, P..

At least 19 recordsLinked to original sources

bioRxiv2026

Preserving Native Cellulose-Xylan Architecture Enables Structure-Property Control in Holocellulose Nanofibrils and High-Performance Sustainable Materials

The hierarchical organization of cellulose microfibrils and their intimate interactions with hemicelluloses such as xylan underpin the exceptional mechanical performance of plant cell walls. However, translating these biological design principles into sustainable nanocellulosic materials remains limited by conventional cellulose nanofibril production routes, which rely on harsh chemical treatments that disrupt the native cellulose-hemicellulose architecture. Here, we present an optimized isolation strategy for holocellulose nanofibrils (hCNFs) that preserves native cellulose structure, xylan substitution and conformation, and cellulose-xylan interactions. Using wild-type Arabidopsis thaliana, a xylan glucuronidation-deficient gux1/2 mutant, and Brassica napus straw as model systems, we systematically elucidate how xylan content and substitution pattern govern nanofibril isolation, interfacial interactions, and macroscopic properties. Two-dimensional 13C magic-angle spinning NMR demonstrates retention of native cellulose glucosyl environments, the presence of two-fold and three-fold helical xylan conformations, and cellulose-associated two-fold helical xylan. Cryogenic transmission electron microscopy reveals fibril widths of [~]3 nm, consistent with elementary cellulose I{beta} microfibrils. We show that xylan glucuronidation regulates colloidal stability, hydration behavior, and interfibrillar cohesion, whereas xylan content controls nanofibrillation efficiency. These multiscale structural features translate directly into moisture sorption, thermal behavior, and mechanical performance. Notably, Brassica napus hCNF films exhibit exceptional strength and extensibility, surpassing many chemically modified CNF systems. This work demonstrates that preserving the native cellulose-hemicellulose architecture enables high-performance, sustainable nanocellulosic materials without chemical reconstruction.

biochemistry↗

bioRxiv2026

Unsupervised protein language models learn patterns of enzyme function

While enormous amounts of sequence information have become available, assignment of sequence to a particular enzymatic function has remained elusive. Here we describe a framework that drives a general protein language model to find a target reaction without specific training, using an initial bridgehead protein. At the heart of this framework is PLM-clust, an algorithm that employs k-means on top of protein language model embeddings to convert sequence space into functional reservoirs of latent space, and samples from these clusters based on accelerated zero-shot scoring. We demonstrate PLM-clust in a recursive discovery process (with enzyme hit rates quickly rising to >90%), segmenting isofunctional reservoirs and exploring them in greater detail. This approach - exemplified for glycosyl hydrolases (a xylanase, >100-fold activity increase) and for imine reductases (IREDs, >100-fold increase in catalytic promiscuity profiles) - reliably brings about novel enzymes that are proficient at the catalytic task at hand, reaching deeply into sequence space with a majority of residues exchanged.

synthetic biology↗

bioRxiv2026

AGP-Ca2+ binding is essential for pollen development and pollen tube growth in Arabidopsis thaliana

Arabinogalactan-proteins (AGPs) are highly glycosylated cell wall proteins essential for plant reproduction, although their mode of action remains unclear. AGPs have been proposed to bind and store calcium (Ca2+) in the apoplast via glucuronic acid (GlcA) residues added by glucuronosyltransferases (GLCATs), potentially acting as Ca2+ capacitors. Here we report that Ca2+ binding by AGPs is required for successful double fertilisation in Arabidopsis. Analysis of glcat14a glcat14b glcat14d triple mutants revealed reduced seed set due to the abortion of pollen grains, which lacked cytoplasmic content and an intine layer, as confirmed by the absence of cellulose, resembling the phenotype of AGP-deficient mutants. When grown under Ca2+-deficient conditions, GLCAT mutants showed exacerbated and conditional reproductive defects that were attenuated under standard Ca2+ conditions. Our findings establish a functional requirement for GlcA-mediated Ca2+ binding by AGPs and support their role as apoplastic Ca2+ stores essential for male fertility and reproductive success in plants.

plant biology↗

bioRxiv2025

The Carbohydrate Binding Module of TrCel7A Aids in Navigating the Complexity of Plant Cell Walls

Efficient enzymatic deconstruction of plant cell walls is critical for utilization of lignocellulose biomass. Key enzymes in this process are cellobiohydrolases, a class of cellulases that processively degrade crystalline cellulose. Many cellobiohydrolases possess a carbohydrate-binding module (CBM), yet the importance of CBMs in substrate interaction remains unclear. Here, we use single-molecule fluorescence microscopy to investigate how CBM1 of Trichoderma reesei Cel7A influences enzyme binding and motility on cellulose substrates of varying complexity. We compare wild-type Cel7A with a truncated variant lacking CBM1 (Cel7A{Delta}CBM) on bacterial cellulose (BC), phosphoric acid swollen cellulose (PASC), delignified milkweed cellulose (MWC), and holocellulose nanofibrils (hCNF). While both variants showed similar steady-state binding densities on BC and PASC, Cel7A{Delta}CBM exhibited reduced binding on MWC and hCNF, with the greatest reduction on the hemicellulose-rich hCNF. Alkali removal of hemicellulose partially restored Cel7A{Delta}CBM binding, suggesting a role for CBM1 in substrate navigation and productive binding sites recognition. Kinetic analyses revealed that CBM1 enables a rapid binding mode absent in the truncated variant. Comparisons with isolated CBM3 further showed that CBMs are capable of fast substrate association. These findings demonstrate that CBMs enhance cellulase-substrate interactions by accelerating binding, enabling navigation of the complex environment of plant cell walls. Our results emphasize the importance of CBMs in natural cellobiohydrolase function and highlight their value in the design of improved cellulases for industrial biomass conversion.

biochemistry↗

bioRxiv2025

GT61 β-1,2-xylosyltransferases define a conserved xylan modification in gymnosperm and Arabidopsis primary cell walls

Plant primary and secondary cell walls differ in molecular composition, structure, and mechanical properties. While secondary wall xylan has been extensively characterised, the structure of xylan in primary walls remains less well understood, particularly in gymnosperms. Here, we identify a previously uncharacterised {beta}-1,2-linked xylosyl side chain in conifer and Arabidopsis thaliana xylan. Using enzymatic fingerprinting, NMR, and mass spectrometry, we show that this structure is positioned two xylose residues away from glucuronic acid substitutions, forming an evenly patterned substituted xylan. This spacing pattern is consistent with xylan-cellulose interaction, suggesting a structural role in primary wall architecture. This modification, found in primary wall-rich tissues of diverse conifer species, including needles and pro-embryogenic mass (PEM), is also present in Arabidopsis callus. We demonstrate that conifer Group III GT61 glycosyltransferases introduce this modification with consistent positional specificity. In Arabidopsis, three closely related GT61 enzymes act redundantly to generate the same structure, and their combined loss results in its complete absence. These findings uncover a conserved primary wall xylan modification in seed plants and define the GT61 enzymes responsible for its biosynthesis, opening new avenues to explore how xylan structure contributes to primary wall function. Significance StatementXylan structure is well characterised in secondary walls, but its primary wall counterpart remains poorly understood. We identified a conserved {beta}-1,2-xylosyl modification on xylan in the primary walls of conifers and Arabidopsis. This side chain is positioned at a defined position from a glucuronic acid substitution and is introduced by GT61 glycosyltransferases that cluster in one phylogenetic subclade. Our findings revealed a previously unrecognised xylan structural pattern and the biosynthetic enzymes responsible for its addition. This work expands the current understanding of primary wall architecture across seed plants.

plant biology↗

bioRxiv2025

Atypical endo-β-1,4-mannannases are necessary for normal glucomannan synthesis in Arabidopsis

The molecular mechanisms underlying the synthesis of large cell wall polysaccharides in plant cells are not fully understood. Here we report that two atypical endo-{beta}-1,4-mannanases (MANs), which are not secreted and do not degrade glucomannan in the cell wall, play a novel role in glucomannan synthesis. Among the six MANs in Arabidopsis, AtMAN2 and AtMAN5 contain a transmembrane domain at their N-terminal region instead of a signal peptide. Subcellular localization using MAN protein fused with fluorescent protein demonstrated that AtMAN2 localizes to the endomembrane system including the Golgi apparatus in xylem and interfascicular fiber cells. We found that an Arabidopsis man2 man5 double mutant lost 65% of glucomannan in the cell walls of the inflorescence stem. Immunostaining and immunoelectron microscopic observation also revealed that the man2 man5 double mutant lost glucomannan in the cell walls to about the same extent as the csla2 csla9 double mutant, which lacks major glucomannan synthases. Gene complementation experiments showed that the enzymatic activities of AtMAN2 and AtMAN5 are important for the function in synthesis of glucomannan for the cell wall. Arabidopsis possesses another atypical MAN, AtMAN6, with an HDEL retention signal at its C-terminus. However, mutation of AtMAN6 did not affect glucomannan content in the cell walls, suggesting distinct functions for these MANs. This study has identified AtMAN2 and AtMAN5 as novel factors necessary for the normal glucomannan synthesis in Arabidopsis, along with GDP-mannose generating enzymes and CslAs, and suggests that the glucomannan hydrolysis by these MANs contributes to the maintenance of glucomannan synthesis.

plant biology↗

bioRxiv2024

Hydrothermal pretreatment renders peat susceptible to enzymatic saccharification

Sphagnum peat bogs store a large fraction of biologically-bound carbon, due to a steady accumulation of plant material over millennia. The resistance of Sphagnum biomass to decay is poorly understood but of high importance for preservation efforts and climate models. It is shown that peat cellulose and other glucose-rich polysaccharides are readily degradable by a commercial enzyme cocktail designed for the industrial saccharification of lignocellulose of vascular plants. However, prior hydrothermal pretreatment of peat was required for the enzymes to gain access to the polysaccharides. The pretreatment itself released monosaccharides and glucose-containing soluble oligosaccharides. The monosaccharide profile released from hydrothermal pretreatment was consistent with the expected hemicellulose content of Sphagnum and was clearly different from that seen for pretreated tissue from vascular plants, such as pretreated wheat straw. Cellulose retained in the insoluble part of peat was cleaved at a similar or higher rate compared to cellulose from vascular plant tissues. Confocal laser scanning microscopy showed that the hydrothermal pretreatment disrupted the cells and relocated lignin-like compounds. Peat contains a high concentration of iron, which likely explains the pronounced acidification observed for the pretreated peat slurry at ambient conditions during saccharification assays. The acidification is due to abiotic oxidative reactions that also inactivate the enzymes. Adding catalase to the reactions alleviated enzyme inactivation and essentially stopped acidification during saccharification. This study confirms the importance of considering those abiotic oxidative reactions that take place in drained peat material.

plant biology↗

bioRxiv2024

Glucomannan engineering highlights the role of galactosyl modification in fine-tuning cellulose-glucomannan interaction in Arabidopsis cell walls

Widely found in most plant lineages, {beta}-mannans are structurally diverse polysaccharides that can bind to cellulose fibrils to form the complex polysaccharide architecture of the cell wall. Glucomannan backbones acquire variable patterns of galactosyl substitutions, depending on plant developmental stage and species. How the changes in polysaccharide structure influence its cell wall solubility or promote appropriate interaction with cellulose fibrils is poorly understood. Here, we show that fine-tuning of galactosyl modification on glucomannans is achieved by the differing acceptor recognition of mannan -galactosyltransferases (MAGTs). Biochemical analysis and 13C solid-state nuclear magnetic resonance spectroscopy of Arabidopsis with cell wall glucomannan engineered by MAGTs revealed that the degree of galactosylation strongly affects the interaction with cellulose. The findings indicate that plants tailor galactosyl modification on glucomannans for constructing an appropriate cell wall architecture, paving the way to convert properties of lignocellulosic biomass for better use.

bioengineering↗

bioRxiv2024

New insights into the structure of cellulose in plant cell walls

The structure of plant cellulose microfibrils remains elusive, despite the abundance of cellulose and its utility in industry. Using 2D solid-state NMR of 13C labelled never-dried plants, six major glucose environments are resolved which are common to the cellulose of softwood, hardwood and grasses. These environments are maintained in isolated holo-cellulose nanofibrils, allowing more detailed microfibril characterisation. We show there are only two glucose environments that reside within the microfibril interior. These have the same NMR 13C chemical shifts as tunicate cellulose I{beta} centre and origin chains, with no cellulose I being detected. The third major glucose site with a carbon 4 chemical shift near 89 ppm, previously assigned to the crystalline microfibril interior, is now shown to be one of four surface glucose environments. The NMR peak widths of all four surface glucose environments are similar to those of the core indicating that their glucose local order is comparable; there is no significant amorphous cellulose in the microfibrils. Consequently, the ratio of the carbon 4 peaks at [~]89 and [~]84 ppm, which has often provided a sample cellulose crystallinity index, is not a meaningful measure of crystallinity or the interior to surface ratio. The revised ratio for poplar wood microfibrils is estimated to be 1:2, which is consistent with a cellulose I{beta} 18-chain microfibril having 6 core and 12 surface chains, although other microfibril sizes are possible. These advances change substantially both the interpretation of solid-state NMR studies of cellulose and the understanding of cellulose microfibril structure and crystallinity.

biochemistry↗

bioRxiv2024

Convergent Acquisition of Glucomannan β-galactosyltransferases in Asterids and Rosids

{beta}-Galactoglucomannan ({beta}-GGM) is a primary cell wall polysaccharide in rosids and asterids. The {beta}-GGM polymer has a backbone of repeating glucose and mannose, usually with mono- or di-galactosyl sidechains on the mannosyl residues. CELLULOSE SYNTHASE-LIKE 2 (CSLA2), MANNAN -GALACTOSYLTRANSFERASE (MAGT), and MANNAN {beta}-GALACTOSYLTRANSFERASE (MBGT) are required for {beta}-GGM synthesis in Arabidopsis thaliana. The single MBGT identified so far, AtMBGT1, lies in glycosyltransferase family 47A subclade VII, and was identified in Arabidopsis. However, despite the presence of {beta}-GGM, an orthologous gene is absent in tomato (Solanum lycopersicum), a model asterid. In this study, we screened candidate MBGT genes from the tomato genome, functionally tested the activities of encoded proteins, and identified the tomato MBGT (SlMBGT1) in GT47A-III. Interestingly therefore, AtMBGT1 and SlMBGT1 are located in different GT47A subclades. Further, phylogenetic and glucomannan structural analysis from different species raised the possibility that various asterids possess conserved MBGTs in GT47A-III, indicating that MBGT activity has been acquired convergently among asterids and rosids. Although functional convergence was observed, the acquired amino acid substitutions among the two MBGT groups were not shared, suggesting different evolutionary pathways to achieve the same biochemical outcome. The present study highlights the promiscuous emergence of donor and acceptor preference in GT47A enzymes, and suggests an adaptive advantage for eudicots to acquire {beta}-GGM {beta}-galactosylation.

plant biology↗

bioRxiv2024

XAPT and XLPT enzymes modify the glucuronic acid side chains of tissue-specific xylans in Arabidopsis and Eucalyptus

* Polysaccharide structural complexity not only influences cell wall strength and extensibility, but also hinders pathogenic and biotechnological attempts to saccharify the wall. In certain species and tissues, glucuronic acid side chains on xylan exhibit arabinopyranose or galactose decorations whose genetic and evolutionary basis is completely unknown, impeding efforts to understand their function and engineer wall digestibility. * Genetics and polysaccharide profiling were used to identify the responsible loci in Arabidopsis and Eucalyptus from proposed candidates, while phylogenies uncovered a shared evolutionary origin. GH30-family endo-glucuronoxylanase activities were analysed by electrophoresis and their differing specificities were rationalised by phylogeny and structural analysis. * The newly identified xylan arabinopyranosyltransferases comprise an overlooked subfamily in the GT47-A family of Golgi glycosyltransferases, previously assumed to comprise mainly xyloglucan galactosyltransferases, highlighting an unanticipated adaptation of both donor and acceptor specificities. Further neofunctionalisation has produced a Myrtaceae-specific xylan galactosyltransferase. Simultaneously, GH30 endo-glucuronoxylanases have convergently adapted to overcome these decorations, suggesting a role for these structures in defence. The differential expression of glucuronoxylan-modifying genes across Eucalyptus tissues, however, hints at further functions. * Our results demonstrate the rapid adaptability of biosynthetic and degradative carbohydrate-active enzyme activities, providing insight into a plant-pathogen arms race and facilitating plant cell wall biotechnological utilisation.

plant biology↗

bioRxiv2023

Sub-single-turnover quantification of enzyme catalysis at ultrahigh throughput via a versatile NAD(P)H coupled assay in microdroplets

Enzyme engineering and discovery are crucial for a future sustainable bioeconomy. Harvesting new biocatalysts from large libraries through directed evolution or functional metagenomics requires accessible, rapid assays. Ultra-high throughput screening formats often require optical readouts, leading to the use of model substrates that may misreport target activity and necessitate bespoke synthesis. This is a particular challenge when screening glycosyl hydrolases, which leverage molecular recognition beyond the target glycosidic bond, so that complex chemical synthesis would have to be deployed to build a fluoro- or chromogenic substrate. In contrast, coupled assays represent a modular plug-and-play system: any enzyme- substrate pairing can be investigated, provided the reaction can produce a common intermediate which links the catalytic reaction to a detection cascade readout. Here, we establish a detection cascade producing a fluorescent readout in response to NAD(P)H via glutathione reductase and a subsequent thiol-mediated uncaging reaction, with a low nanomolar detection limit in plates. Further scaling down to microfluidic droplet screening is possible: the fluorophore is leakage- free and we report a three orders of magnitude improved sensitivity compared to absorbance- based systems, so that less than one turnover per enzyme molecule expressed from a single cell is detectable. Our approach enables the use of non-fluorogenic substrates in droplet-based enrichments, with applicability in screening for glycosyl hydrolases and imine reductases (IREDs). To demonstrate the assays readiness for combinatorial experiments, one round of directed evolution was performed to select a glycosidase processing a natural substrate, beechwood xylan, with improved kinetic parameters from a pool of >106 mutagenized sequences.

biochemistry↗

bioRxiv2023

Altering the substitution and crosslinking of glucuronoarabinoxylans affects cell wall porosity and assembly in Brachypodium distachyon.

O_LIThe Poaceae family of plants provides cereal crops that are critical for human and animal nutrition and also they are an important source of biomass. Interacting plant cell wall components give rise to recalcitrance to digestion, thus understanding the wall molecular architecture is important to improve biomass properties. Xylan is the main hemicellulose in grass cell walls. Recently, we reported structural variation in grass xylans, suggesting functional specialisation and distinct interactions with cellulose and lignin. Here, we investigated the functions of these xylans by perturbing the biosynthesis of specific xylan types. C_LIO_LIWe generated CRISPR/Cas9 knockout mutants in Brachypodium distachyon XAX1 and GUX2 genes involved in xylan biosynthesis. Using carbohydrate gel electrophoresis we identified biochemical changes in different xylan types. Saccharification, cryo-SEM, subcritical water extraction and ssNMR were used to study wall architecture. C_LIO_LIBdXAX1A and BdGUX2 enzymes modify different types of grass xylan. Brachypodium mutant walls are more porous, suggesting the xylan substitutions directed by both BdXAX1A andGUX2 enzymes influence xylan-xylan and/or xylan-lignin interactions. C_LIO_LISince xylan substitutions influence wall architecture and digestibility, our findings open new avenues to improve cereals for food and to use grass biomass for feed and the production of bioenergy and biomaterials. C_LI

biochemistry↗

bioRxiv2023

Differing structures of galactoglucomannan in eudicots and non-eudicot angiosperms

The structures of cell wall mannan hemicelluloses have changed during plant evolution. Recently, a new structure called {beta}-galactoglucomannan ({beta}-GGM) was discovered in eudicot plants. This galactoglucomannan has {beta}-(1,2)-Gal--(1,6)-Gal disaccharide branches on some mannosyl residues of the strictly alternating Glc-Man backbone. Studies in Arabidopsis revealed {beta}-GGM is related in structure, biosynthesis and function to xyloglucan. However, when and how plants acquired {beta}-GGM remains elusive. Here, we studied mannan structures in many sister groups of eudicots. All glucomannan structures were distinct from {beta}-GGM. In addition, we searched for candidate mannan {beta}-galactosyltransferases (MBGT) in non-eudicot angiosperms. Candidate AtMBGT1 orthologues from rice and Amborella did not show MBGT activity in vivo. However, the AtMBGT1 orthologue from rice showed MUR3-like xyloglucan galactosyltransferase activity in complementation analysis using Arabidopsis. Further, reverse genetic analysis revealed that the enzyme contributes to proper root growth in rice. Together, gene duplication and diversification of GT47A-VII in eudicot evolution may have been involved in the acquisition of mannan {beta}-galactosyltransferase activity. Our results indicate that {beta}-GGM is likely to be a eudicot-specific mannan.

biochemistry↗

bioRxiv2023

The biosynthesis, degradation, and function of cell wall β-xylosylated xyloglucan mirrors that of arabinoxyloglucan

O_LIXyloglucan is an abundant polysaccharide in many primary cell walls and in the human diet. Decoration of its -xylosyl side chains with further sugars is critical for plant growth, even though the sugars themselves vary considerably between species. Plants in the Ericales order--prevalent in human diets--exhibit {beta}1,2-linked xylosyl decorations. The biosynthetic enzymes responsible for adding these xylosyl decorations, as well as the hydrolases that remove them in the human gut, are unidentified. C_LIO_LIGT47 xyloglucan glycosyltransferase candidates were expressed in Arabidopsis and endo-xyloglucanase products from transgenic wall material were analysed by electrophoresis, mass spectrometry, and NMR. The activities of gut bacterial hydrolases BoGH43A and BoGH43B on synthetic glycosides and xyloglucan oligosaccharides were measured by colorimetry and electrophoresis. C_LIO_LICcXBT1 is a xyloglucan {beta}-xylosyltransferase from coffee that can modify Arabidopsis xyloglucan and restore the growth of galactosyltransferase mutants. Related VmXST1 is a weakly active xyloglucan -arabinofuranosyltransferase from cranberry. BoGH43A hydrolyses both -arabinofuranosylated and {beta}-xylosylated oligosaccharides. C_LIO_LICcXBT1s presence in coffee and BoGH43As promiscuity suggest that {beta}-xylosylated xyloglucan is not only more widespread than thought, but might also nourish beneficial gut bacteria. The evolutionary instability of transferase specificity and lack of hydrolase specificity hint that, to enzymes, xylosides and arabinofuranosides are closely resemblant. C_LI

biochemistry↗

bioRxiv2022

Eudicot primary cell wall glucomannan is related in synthesis, structure and function to xyloglucan

The functional differences between plant cell wall hemicelluloses such as glucomannan, xylan and xyloglucan (XyG) remain unclear. These polysaccharides influence assembly and properties of the wall, perhaps by interacting with cellulose to affect the deposition and bundling of the fibrils. As the most abundant hemicellulose, XyG is considered important in eudicot primary cell walls (PCWs), but plants devoid of XyG show relatively mild phenotypes. We report here that a patterned {beta}-galactoglucomannan ({beta}-GGM) is widespread in PCW of eudicots and shows remarkable similarities to XyG. The sugar linkages forming the backbone and side chains of {beta}-GGM are analogous to those that make up XyG, and moreover, these linkages are formed by glycosyltransferases from the same CAZy families. Solid-state NMR indicated that {beta}-GGM shows low mobility in the cell wall, consistent with interaction with cellulose. Although Arabidopsis {beta}-GGM synthesis mutants show no obvious growth defects, genetic crosses between {beta}-GGM and XyG mutants produce exacerbated phenotypes compared to XyG mutants. These findings demonstrate a related role of these two similar but distinct classes of hemicelluloses in PCWs. This work will provide new avenues to study the roles of both {beta}-GGM and XyG in PCWs. One sentence summaryPatterned {beta}-GGM resembles xyloglucan in structure, biosynthesis and function.

plant biology↗

bioRxiv2022

Functional metagenomic screening in microfluidic droplets identifies a β-glucuronidase in an unprecedented sequence neighbourhood

The abundance of recorded protein sequence data stands in contrast to the small number of experimentally verified functional annotation. Here we screened a million-membered metagenomic library at ultrahigh throughput in microfluidic droplets for {beta}-glucuronidase activity. We identified SN243, a genuine {beta}-glucuronidase with little homology to previously studied enzymes of this type, as a glycoside hydrolase (GH) 3 family member. This GH family had no recorded evidence of {beta}-glucuronidases at the outset of this study, showing that a functional metagenomic approach can shed light on assignments that are currently unpredictable by bioinformatics. Kinetic analyses of SN243 characterised it as a promiscuous catalyst and structural analysis suggests regions of divergence from homologous GH3 members creating a wide-open active site. With a screening throughput of >107 library members per day, picolitre volume microfluidic droplets enable functional assignments that complement current enzyme database dictionaries and provide bridgeheads for the annotation of unexplored sequence space.

biochemistry↗

bioRxiv2021

Discovery of putative Golgi S-Adenosyl methionine transporters reveals the importance of plant cell wall polysaccharide methylation

Polysaccharide methylation, especially that of pectin, is a common and important feature of land plant cell walls. Polysaccharide methylation takes place in the Golgi apparatus and therefore relies on the import of S-adenosyl methionine (SAM) from the cytosol into the Golgi. However, to date, no Golgi SAM transporter has been identified in plants. In this work, we studied major facilitator superfamily members in Arabidopsis that we identified as putative Golgi SAM transporters (GoSAMTs). Knock-out of the two most highly expressed GoSAMTs led to a strong reduction in Golgi-synthesised polysaccharide methylation. Furthermore, solid-state NMR experiments revealed that reduced methylation changed cell wall polysaccharide conformations, interactions and mobilities. Notably, the NMR revealed the existence of pectin egg-box structures in intact cell walls, and showed that their formation is enhanced by reduced methyl-esterification. These changes in wall architecture were linked to substantial growth and developmental phenotypes. In particular, anisotropic growth was strongly impaired in the double mutant. The identification of putative transporters that import SAM into the Golgi lumen in plants provides new insights into the paramount importance of polysaccharide methylation for plant cell wall structure and function.

plant biology↗