Biology subjects

Pauly, M.

Publications and source records attributed to Pauly, M..

At least 19 recordsLinked to original sources

bioRxiv2026

Yeast surface display reveals structure-dependent β-glucan association with the plant immune receptor AtIGP1

Cell wall-derived oligosaccharides can function as immune-active signals in plants and trigger pattern-triggered immunity (PTI) through pattern recognition receptors (PRRs). In Arabidopsis thaliana, the leucine-rich repeat malectin (LRR-MAL) receptor kinase IGP1 (impaired in glycan perception 1) contributes to immune responses induced by cellulose- and mixed-linkage {beta}-1,3/1,4-glucan (MLG)-derived oligosaccharides, although whether MLG-derived oligosaccharides are directly recognized by AtIGP1 needs further clarification. We established a Saccharomyces cerevisiae surface-display system in which the AtIGP1 extracellular domain (ECD) is presented at the yeast cell surface, allowing oligosaccharide recognition to be examined separately from downstream plant signaling and without receptor purification. Previously, cellulose-derived oligosaccharides have been shown to elicit plant defense responses via AtIGP1. Here, surface-displayed AtIGP1 retained the ability to recognize fluorescently labeled cellotriose (CEL3) and cellopentaose (CEL5) ligands, supporting functional presentation of the receptor for investigating glycan recognition in a heterologous context. Using this platform, we investigated the association of AtIGP1 with fluorescently labeled MLG-derived oligosaccharides differing in degree of polymerization (DP) and glycosidic linkage arrangement. This analysis revealed a specific, competitively displaceable association with MLG DP2 (G3G; laminaribiose), whereas the DP3 (G4G3G) and DP4 (G4G4G3G) structures tested showed no detectable association. To test whether this association is relevant in planta, we treated A. thaliana seedlings with unlabeled MLG DP2, which induced a cytosolic Ca2+ response, an early readout of immune activation. This response was markedly reduced in the igp1-3 mutant. Together, these results identify laminaribiose as an additional candidate ligand of AtIGP1. The established yeast surface-display platform thus provides an approach for testing candidate oligosaccharides for association with the extracellular domains of plant PRRs.

synthetic biology↗

bioRxiv2026

Genome-wide association study in a maize diversity panel dissects the genetic basis of lignocellulosic recalcitrance

Lignocellulosic biomass is an abundant, renewable resource for the production of biorenewable products. Its efficient utilization is largely hindered by the inherent recalcitrance of lignocellulose to degradation. Natural genetic variation in biomass saccharification efficiency and lignocellulose components across diverse maize germplasm provides a powerful resource to dissect the genetic basis of lignocellulosic recalcitrance. Here, we performed high-throughput profiling of lignocellulosic components and saccharification efficiency in mature stalks across a diverse panel of 239 field grown maize inbred lines, and identified extensive natural variation in biomass properties. Saccharification efficiency was strongly positively associated with matrix glucose content, moderately positively associated with the arabinose-to-xylose (Ara:Xyl) molar ratio and crystalline cellulose content, whereas saccharification efficiency was strongly negatively associated with xylose and lignin content. Genome-wide association studies (GWAS) were conducted to identify single nucleotide polymorphisms (SNPs) associated with saccharification efficiency and lignocellulosic components. Numerous significant single nucleotide polymorphisms (SNPs) were identified, defining 79 quantitative trait loci (QTLs) across all 10 maize chromosomes. The presence of pleiotropic SNPs and the extensive co-localization of QTLs for multiple traits highlight the complex genetic architecture and shared genetic basis of maize biomass properties. Our study reveals substantial natural variation in maize biomass digestibility and identifies multiple novel genetic loci underlying variation in saccharification efficiency and lignocellulose components.

plant biology↗

bioRxiv2026

ZmPMI3 phosphomannose isomerase kinetics is associated with natural variation of watersoluble carbohydrate content in mature maize stem

Mature maize stems accumulate substantial amounts of water-soluble carbohydrates (WSC) providing an accessible carbon pool for industrial bioconversion. However, the genetic factors controlling WSC reserves under field conditions remain poorly resolved. In this study, we quantified total WSC including glucose, fructose, sucrose contents in the internode below the first ear of a genetically diverse maize panel at physiological maturity and associated trait variation with genome-wide SNP data. The panel displayed extensive variation in stem WSCs content, with values ranging up to 50.4 % of dry weight. Genome-wide association mapping identified 20 quantitative trait loci associated with individual sugars or total WSC content. One fructose associated region contained two adjacent gene annotations predicted to encode fragments of a phosphomannose isomerase. Sequence comparison, cDNA amplification and protein structure prediction supported a unified gene model, here designated as ZmPMI3. Biochemical characterization showed ZmPMI3 catalyzes the reversible conversion between mannose-6-phosphate and fructose-6-phosphate, a central reaction in carbohydrate metabolism. Natural protein haplotypes with distinct kinetic properties were identified correlating with significant differences in stem WSC content. Together, these findings identify ZmPMI3 as a candidate contributor to natural variation in maize stem carbohydrate reserves, potentially through altered hexose-phosphate partitioning.

plant biology↗

bioRxiv2026

Characterization of a fungal mixed-linkage glucan synthase

Mixed-linkage (1,3;1,4)-{beta}-glucan (MLG) is a cell wall polysaccharide found in fungi, bacteria, and plants, yet the enzymatic machinery and structural determinants governing fungal MLG biosynthesis remain poorly understood. In Aspergillus fumigatus, TFT1 (AfTFT1) has previously been implicated in MLG biosynthesis, but its direct biochemical activity remained unresolved. The structural characterization of A. fumigatus wall MLG revealed a distinct polymer profile. Heterologous expression of AfTFT1 in Komagataella phaffii enabled MLG production, generating an oligosaccharide profile that closely matched that of the native fungal polymer and demonstrating that AfTFT1 functions as an MLG synthase. Phylogenetic analysis placed AfTFT1 within a distinct glycosyltransferase family 2 (GT2) fungal lineage containing related candidate MLG synthases across diverse filamentous Ascomycota and separate from the major plant and bacterial synthase lineages. Structure-guided mutagenesis showed that individual substitutions within the transmembrane pore and switch motif altered the lichenase-derived oligosaccharide profile while retaining detectable MLG production, whereas replacement of the entire switch motif with the corresponding HvCSLF6 sequence resulted in no detectable MLG production. Together, these findings establish AfTFT1 as a fungal MLG synthase and identify the switch motif and adjacent transmembrane region as important determinants of MLG synthase function and product fine structure, providing insight into the structural and evolutionary diversification of MLG biosynthesis.

synthetic biology↗

bioRxiv2026

MYC2 mediated regulation of xylan substitution patterns

O-Acetylation is the most abundant xylan decoration in eudicot plants and plays a critical role in determining xylan conformation and its interactions with cellulose and lignin, thereby contributing to secondary cell wall (SCW) integrity. In Arabidopsis, loss of the xylan O-acetyltransferase TBL29/ESK1 causes collapsed xylem and growth defects that can be suppressed by mutations in strigolactone (SL) biosynthesis genes such as MAX3. However, the molecular basis of this suppression remains unknown. Hypoacetylated xylan in tbl29 has a higher frequency of methyl glucuronic acid (MeGlcA) substituents, while the ratio of GlcA/MeGlcA is recovered in tbl29 max3. Furthermore, gene expression analyses reveal that the three xylan glucuronoxylan methyltransferases (GXM1/2/3) involved in xylan MeGlcA modification are upregulated in tbl29 SCWs but downregulated in tbl29 max3. Genetic analysis shows that the transcription factor MYC2 is required for max3-mediated suppression: the loss of MYC2 in tbl29 max3 prevents growth recovery and reverts GXM genes expression and xylan MeGlcA substitution levels. We propose a model where SL deficiency enhances MYC2 transcription, which in turn represses GXMs, thereby fine-tuning xylan methylation and re-establishing the MeGlcA/GlcA substitution balance under conditions of reduced O-acetylation. Our findings identify a MYC2-dependent regulatory module linking SL signalling to xylan methylation and reveal a genetically encoded compensatory mechanism that mitigates the consequences of defective xylan O-acetylation. More broadly, this work demonstrates that plants can preserve SCW function through adaptive remodelling of polysaccharide substitution patterns, highlighting an unexpected plasticity in SCW biosynthesis. Significance StatementSecondary cell wall integrity depends on the coordinated modification of xylan. We show that defects caused by reduced xylan O-acetylation can be alleviated through a strigolactone- and MYC2-dependent pathway that alters xylan methylglucuronidation. Rather than restoring the original wall composition, this mechanism appears to compensate for the loss of O-acetyl groups by remodelling polysaccharide substitution patterns to maintain cell wall function, revealing a new layer of plasticity in secondary wall biosynthesis.

developmental biology↗

bioRxiv2026

A chromosome-scale super-pangenome of the lichen genus Peltigera reveals genome architecture and expanded interaction repertoires shared across pathogenic and mutualistic fungi

Fungi engage in associations with other organisms across a continuum from pathogenic to mutualistic lifestyles. Hence, they require a compendium of molecular capacities, including partner recognition, extracellular signaling, nutrient exchange, immune modulation, and control of microbial competitors. In filamentous pathogens such traits are frequently associated with compartmentalized genomes, including rapidly evolving secreted proteins known as effectors and expanded receptor families, but it remains unclear whether similar genomic principles shape mutualistic fungal symbioses. Here, we generated a chromosome-scale super-pangenome for the lichen-forming genus Peltigera, comprising 41 mycobiont assemblies representing eleven species, together with genomes of associated Nostoc and, in tripartite species, Coccomyxa photobionts. The mycobiont genomes revealed extensive variation in genome size, transposable element content, biosynthetic gene clusters, and lineage-specific gene content, with pronounced expansions in tripartite species. Across Peltigera, secreted protein encoding genes were preferentially located in TE-rich regions. We further identified Starship-like transposon elements, expanded antimicrobial protein repertoires, and a large, previously underestimated repertoire of fungal GPCRs dominated by Pth11-like receptors. Layer-specific transcriptomics of a P. rufescens thallus showed differential expression of several interaction-associated gene families, e.g. lectins, antimicrobial proteins and Pth11-like GPCRs. These data indicate that pathogenic and mutualistic fungi might exhibit shared genomic principles, including genome compartmentalization, mobile-element-associated diversification, and the expansion of molecular repertoires involved in recognition, extracellular control and signaling.

genomics↗

bioRxiv2026

Systematic evaluation of Cyanidioschyzon merolae across photobioreactor systems: Linking reactor design to biomass production and biochemical composition

Extremophilic red microalgae are promising platforms for sustainable biotechnology, combining robust growth under selective thermoacidophilic conditions with production of thermostable phycobiliproteins and carbon-rich biomass. However, reactor-dependent effects on growth, product formation and biomass composition remain insufficiently resolved. Here, we systematically evaluated the extremophilic red microalga Cyanidioschyzon merolae across cultivation scales and reactor formats and benchmarked its performance against the well-established Galdieria javensis and Limnospira platensis. In small-scale multi-cultivator photobioreactors and microfluidic growth chambers, C. merolae showed superior growth, reaching a maximum growth rate of 0.034 {+/-} 0.001 h-1 and 8.3 {+/-} 0.3 g l-1 cell dry weight. Microfluidic cultivation enabled growth analysis at single-cell resolution and matched growth rates obtained in photobioreactors. To identify scalable production strategies, C. merolae was further cultivated in a flat-panel photobioreactor and a custom-designed internally illuminated photobioreactor. The custom-designed photobioreactor delivered the highest biomass concentration and productivity, yielding 11.5 {+/-} 0.6 g l-1 cell dry weight and 1.07 {+/-} 0.06 g l-1 d-1, and comparable yields with regard to R-phycocyanin and R-allophycocyanin. Biomass analysis revealed substantial carbon and nitrogen contents, starch accumulation up to > 20 % of cell dry weight, and fatty acids dominated by palmitic, linoleic and oleic acids. Despite its reduced cell wall fraction, C. merolae contained structurally diverse, cultivation-dependent polysaccharides. These results establish C. merolae as a versatile chassis for thermostable pigment production and renewable feedstock generation, highlighting photobioreactor design as a key determinant of productivity and biomass quality.

microbiology↗

bioRxiv2026

REVOLUTA regulates cell fate and wall patterning in the fruit endocarp

Explosive seed dispersal distinguishes Cardamine species from Arabidopsis and depends on polarized secondary cell wall (SCW) deposition in fruit endocarp b (endb) cells. How this SCW pattern is specified and environmentally modulated remains unclear. The polyploid Cardamine chenopodiifolia produces explosive aerial fruit and non-explosive subterranean fruit, creating a tractable system to address this problem. We show light triggers underground fruit to explode by reprogramming endb SCW patterning from uniform to polar. We identify the HD-ZIPIII transcription factor REVOLUTA as a central regulator of endb cell fate, SCW formation, and organ polarity in Arabidopsis and Cardamine hirsuta. In C. hirsuta, duplicated REVOLUTA paralogs are required for endb SCW deposition, while other HD-ZIPIII genes contribute redundantly to cell fate and organ polarity. REVOLUTA over-expression converts polar endb SCWs to uniform, producing non-explosive fruit. Together, these findings reveal a tunable developmental module underlying evolutionary transitions between explosive and non-explosive seed dispersal strategies.

plant biology↗

bioRxiv2026

The transcription factor SiROCX controls a monocot-specific CAZyme program for host cell wall remodeling during symbiotic root colonization

Intracellular accommodation of beneficial fungi requires controlled remodeling of host cell walls while avoiding activation of plant immune responses. During colonization of monocot roots, the endophytic fungus Serendipita indica induces a suite of carbohydrate-active enzymes (CAZymes) targeting xylan and cellulose. Weighted gene co-expression network analysis identified the basidiomycete-specific transcription factor SiROCX as a key regulator of this monocot-adapted program. DNA affinity purification sequencing (DAP-seq) defined the SiROCX binding motif and revealed a CAZyme-enriched target regulon. Inducible SiROCX overexpression selectively activated motif-containing CAZyme genes and markedly enhanced xylanase and cellulase activities on xylan and native barley root cell walls. Premature activation of this program triggered expression of a plant immune marker despite comparable fungal biomass, indicating that precise temporal control of CAZyme deployment is required to maintain symbiotic compatibility. Together, these findings identify SiROCX as a central regulator of a monocot-adapted cell wall-degrading secretome and reveal a basidiomycete-specific regulatory module that coordinates host cell wall remodeling with immune-compatible symbiotic colonization. SignificanceBeneficial fungi colonize living plant cells, requiring host cell wall remodeling while avoiding immune activation. However, the key transcriptional regulators coordinating this process in basidiomycetes during symbiotic root colonization remain unknown. We identify SiROCX, a conserved basidiomycete-specific transcription factor, as a master activator of a monocot-adapted xylan/cellulose degradation program in the root endophyte Serendipita indica. By integrating in planta co-expression networks, DAP-seq, secretome proteomics, and enzymatic assays, we show that SiROCX overexpression markedly enhances secretion and activity of xylan- and cellulose-degrading enzymes, boosting sugar release from monocot cell walls. These findings reveal a basidiomycete-specific regulatory module for immune-compatible host cell wall remodeling, providing a framework to engineer fungal CAZyme programs for crop symbiosis and biomass conversion.

microbiology↗

bioRxiv2026

CESA7 and microtubules pattern complex secondary cell walls in explosive fruit

Secondary cell walls (SCW) constitute the most abundant form of renewable plant biomass and are major sinks for atmospheric carbon. Their highly ordered patterns underpin specialized cell functions. In Cardamine hirsuta, the geometry of a polarly localized SCW in fruit endocarp b (endb) cells determines the mechanics of explosive seed dispersal. Yet, the genetic control of SCW synthesis and patterning in these specialized cells remains poorly understood. Here we show that CELLULOSE SYNTHASE 7 (CESA7) is required to synthesize SCW cellulose in endb cells. While lignin and xylan deposition occurs independently of cellulose patterning in cesa7 endb SCWs, the final geometry and layered organization of wild-type endb SCWs depend on CESA7. Cellulose serves as a scaffold for the organized assembly of SCW polymers, thereby maintaining the precise SCW patterns observed in endb cells of fruits and metaxylem cells in roots. Cortical microtubules guide the patterned deposition of cellulose, lignin and xylan in endb cells, creating SCW-depleted domains along cell edges that produce the specific hinged SCW geometry. Disrupting microtubules abolished this pattern and prevented explosive coiling of the fruit valves. Our findings show that microtubules and CESA7 shape the form and function of endb SCWs in exploding seed pods.

plant biology↗

bioRxiv2025

Genetic factors driving multi-host infection in a core member of the root mycobiota

Core members of the fungal root microbiota include pathogens capable of colonizing multiple hosts, yet the underlying genetic determinants remain unknown. We report that Plectosphaerella cucumerina is a core member of the Arabidopsis thaliana root microbiota displaying high pathogenic potential and multi-host colonization capabilities. Establishment of a Plectosphaerella reference culture collection, followed by whole-genome sequencing of 72 strains reveals subtle phenotypic and genotypic variation that associate with fungal phylogeny, but not host plant identity. Transcriptome profiling of a model P. cucumerina isolate in roots of multiple hosts identifies core and host-specific fungal processes linked to carbon catabolism and root cell wall deconstruction of the hosts. A fungal gene encoding a candidate {beta}-1,3-glucanase (GH64) was identified as a key genetic factor driving infection and disease in plants that diverged 110 million years ago. The gene is enriched in plant-colonizing fungi and consistently functions as a disease determinant in the root pathogen Colletotrichum incanum. We conclude that diverse and tunable fungal repertoires of carbohydrate-active enzymes act as disease determinants and drive multi-host compatibility belowground.

microbiology↗

bioRxiv2025

Extracellular Polymeric Substances Drive Curvibacter Host Adaptation and Co-Speciation with Hydra

The interactions between hosts and their microbial symbionts play a crucial role in shaping biological diversity and ecosystem function. Bacteria can adapt to specific host environments over evolutionary timescales, leading to co-speciation and the formation of specialized host-microbe relationships. Understanding the molecular mechanisms underlying these adaptations provides key insights into the evolution of symbiosis and the stability of microbial communities. This study investigates the co-speciation and molecular adaptations of Curvibacter to its host Hydra, a well-established model for the study of host-microbe interactions. We provide strong evidence of co-speciation, as demonstrated by phylogenetic congruence between different Hydra species and their corresponding Curvibacter symbionts, along with preferential recolonization of germ-free Hydra by their native Curvibacter strains. Comparative genomic analyses reveal that host-associated Curvibacter strains exhibit distinct metabolic and biosynthetic adaptations compared to their free-living relatives. Specifically, the enrichment of proteins involved in sugar metabolism and transport, as well as the selective purification of proteins linked to macromolecule biosynthesis, highlights the specialization of Curvibacter symbionts within the Hydra glycocalyx. Functional experiments identify a symbiont-specific extracellular polymeric substances (EPS) operon as key factor for microbial adhesion and host colonization, underscoring its role in facilitating symbiont specificity and stability. These findings provide insights into the molecular mechanisms driving host-microbe co-evolution and highlight the evolutionary forces shaping microbial specialization within host-symbiont relationships. Significant StatementThe vast majority of animal and plant species are associated with microbial organisms that offer a wide range of benefits for development, physiology, and health. Understanding the evolutionary forces that shape these symbiotic interactions is crucial for elucidating the mechanisms through which organisms mitigate environmental stress and enhance their resilience, particularly in response to rapidly changing environmental conditions. Using advanced bioinformatic, bioanalytical, and genetic approaches, this study demonstrates that Curvibacter symbionts have evolved specific extracellular polymeric substances to enhance their ability to form a specific symbiosis with Hydra.

microbiology↗

bioRxiv2025

Surveillance on California dairy farms reveals multiple sources of H5N1 transmission

Transmission routes of highly pathogenic H5N1 between cows or to humans remain unclear due to limited data from affected dairy farms. We performed air, farm wastewater, and milk sampling on 14 H5N1 positive dairy farms across two different California regions. Infectious virus was detected in the air in milking parlors and in wastewater streams, while viral RNA was found in exhaled breath of cows. Sequence analysis of infectious H5N1 virus from air and wastewater samples on one farm revealed viral variants relevant for potential human susceptibility. Longitudinal analysis of milk from the individual quarters of cows revealed a high prevalence of subclinical H5N1 positive cows. Additionally, a heterogeneous distribution of infected quarters that maintained a consistent pattern over time was observed, inconsistent with shared milking equipment serving as the sole transmission mode. The presence of subclinically infected cows was further supported by detection of antibodies in the milk of animals that exhibited no clinical signs during the H5N1 outbreak on one farm. Our data highlight additional sources and potential modes of H5N1 transmission on dairy farms.

microbiology↗

bioRxiv2025

Host-adapted enzymatic deconstruction of acetylated xylan enables mutualistic colonization of monocot roots

Intracellular accommodation of mutualistic fungi in plant roots depends on selective remodeling of host cell walls while minimizing activation of plant immune responses. In this study, we identify a host-adapted enzymatic module in the root endophyte Serendipita indica that targets acetylated xylan, a major structural component of monocot cell walls. The glycoside hydrolase SiGH11 cleaves the xylan backbone and releases O-acetylated oligosaccharides, which are subsequently deacetylated by the XynE-like esterase SiAXE. These enzymes are co-expressed within a monocot-specific transcriptional program that is enriched in carbohydrate-active enzymes and sugar transporters. Their combined activity enhances enzymatic degradation and facilitates downstream hydrolysis by exo-xylanases, which reduces the production of apoplastic reactive oxygen species triggered by damage-associated molecular patterns. Functional analysis shows that overexpression of SiAXE promotes early root colonization, while deletion of the gene compromises fungal proliferation during later stages. These findings define a coordinated and immune-compatible strategy for host cell wall deconstruction that enables fungal adaptation and endophytic colonization of monocot roots. In BriefSerendipita indica utilizes a transcriptionally coordinated xylanase and esterase module to degrade acetylated xylan in monocot roots. This enzyme cooperation enhances substrate breakdown, suppresses immune responses, and enables endophytic colonization, illustrating how mutualistic fungi adapt saprotrophic enzymes for host-specific intracellular accommodation. HighlightsO_LIMutualistic fungal endophyte repurposes saprotrophic enzymes to enable monocot-specific intracellular root colonization C_LIO_LICoordinated xylanase and esterase activity remodels host cell walls and dampens immune responses C_LIO_LIExpression of cell wall degrading enzymes is regulated by host species and colonization stage C_LIO_LIResults reveal fungal adaptation to monocot roots along the saprotrophy to symbiosis transition C_LI

plant biology↗

bioRxiv2023

A GH81-type β-glucan-binding protein facilitates colonization by mutualistic fungi in barley

Cell walls are important interfaces of plant-fungal interactions. Host cell walls act as robust physical and chemical barriers against fungal invaders, making them an essential line of defense. Upon fungal colonization, plants deposit phenolics and callose at the sites of fungal penetration to reinforce their walls and prevent further fungal progression. Alterations in the composition of plant cell walls significantly impact host susceptibility. Furthermore, plants and fungi secrete glycan hydrolases acting on each others cell walls. These enzymes release a wide range of sugar oligomers into the apoplast, some of which trigger the activation of host immunity via host surface receptors. Recent characterization of cell walls from plant-colonizing fungi have emphasized the abundance of {beta}-glucans in different cell wall layers, which makes them suitable targets for recognition. To characterize host components involved in immunity against fungi, we performed a protein pull-down with the biotinylated {beta}-glucan laminarin. Thereby, we identified a glycoside hydrolase family 81-type glucan-binding protein (GBP) as the major {beta}-glucan interactor. Mutation of GBP1 and its only paralogue GBP2 in barley led to decreased colonization by the beneficial root endophytes Serendipita indica and S. vermifera, as well as the arbuscular mycorrhizal fungus Rhizophagus irregularis. The reduction of symbiotic colonization was accompanied by enhanced responses at the host cell wall. Moreover, GBP mutation in barley also increased resistance to fungal infections in roots and leaves by the hemibiotrophic pathogen Bipolaris sorokiniana and the obligate biotrophic pathogen Blumeria graminis f. sp. hordei, respectively. These results indicate that GBP1 is involved in the establishment of symbiotic associations with beneficial fungi, a role that has potentially been appropriated by barley-adapted pathogens. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=134 SRC="FIGDIR/small/536646v1_figu1.gif" ALT="Figure 1"> View larger version (39K): org.highwire.dtl.DTLVardef@c47957org.highwire.dtl.DTLVardef@fa6727org.highwire.dtl.DTLVardef@18a54d2org.highwire.dtl.DTLVardef@c6b103_HPS_FORMAT_FIGEXP M_FIG C_FIG In BriefGBP1, a family 81 glycoside hydrolase, is an important {beta}-glucan interactor in barley. Mutation of GBP1 and its sole paralogue GBP2 leads to reduced colonization by beneficial root endophytes, AM fungi and pathogens, accompanied by enhanced responses at the plant cell wall. This indicates that GBP1 and {beta}-glucans are compatibility factors involved in the establishment of symbiotic associations with beneficial fungi, a role possibly hijacked by pathogens.

plant biology↗

bioRxiv2022

Interplay of EXO70 and MLO proteins modulates trichome cell wall composition and powdery mildew susceptibility

EXO70 proteins are essential constituents of the octameric exocyst complex implicated in vesicle tethering during exocytosis, while MLO proteins are plant-specific calcium channels of which some isoforms play a key role during fungal powdery mildew pathogenesis. We here detected by a variety of histochemical staining procedures an unexpected phenotypic overlap of A. thaliana exo70H4 and mlo2 mlo6 mlo12 triple mutant plants regarding the biogenesis of leaf trichome secondary cell walls. Biochemical and Fourier transform infrared spectroscopic analyses of isolated trichomes corroborated deficiencies in the composition of trichome cell walls in exo70H4 and mlo2 mlo6 mlo12 mutants. Transgenic lines expressing fluorophore- tagged EXO70H4 and MLO variants exhibited extensive co-localization of these proteins at the trichome plasma membrane and cell wall. Furthermore, mCherry- EXO70H4 mislocalized in trichomes of the mlo triple mutant and, vice versa, MLO6- GFP exhibited aberrant subcellular localization in trichomes of the exo70H4 mutant. Transgenic expression of GFP-marked PMR4 callose synthase, a previously identified cargo of EXO70H4 dependent exocytosis, revealed reduced cell wall delivery of GFP- PMR4 in mlo triple mutant plants. In vivo protein-protein interaction assays uncovered isoform-preferential physical interaction between EXO70 and MLO proteins. Finally, exo70H4 and mlo mutants, when combined, showed synergistically enhanced resistance to powdery mildew attack. Taken together, our data point to an isoform- specific interplay of EXO70 and MLO proteins in the modulation of trichome cell wall biogenesis and powdery mildew susceptibility, possibly by (co-)regulating focal secretion of cell wall-related cargo.

plant biology↗

bioRxiv2022

A conserved enzyme of smut fungi facilitates cell-to-cell movement in the plant bundle sheath

The smut fungi are one of the largest groups of fungal plant pathogens, causing disease in all cereal crops. They directly penetrate their hosts and establish a biotrophic interaction. During colonization of the plant, smut fungi secrete a wide range of effector proteins, which suppress plant immunity and modulate cellular functions as well as development of the host, thereby determining the pathogens life-style and virulence potential. The conserved effector Erc1 (enzyme required for cell-to-cell movement) contributes to virulence of the corn smut Ustilago maydis in maize leaves, but not on the tassel. Erc1 binds to host cell wall components and has a 1,3-{beta}-glucanase activity, which is required to attenuate {beta}-glucan-induced defense responses in host leaves. Confocal microscopy revealed that Erc1 has a cell type-specific virulence function, being necessary for fungal cell-to-cell movement in the plant bundle sheath. This cell type-specific virulence function of Erc1 is fully conserved in the barley pathogen Ustilago hordei, which has a functionally conserved Erc1 orthologue. Thus, Erc1 is an enzymatically active core virulence factor with a cell type-specific virulence function in different hosts, which is important for cell-to-cell movement during host colonization of pathogenic smut fungi.

plant biology↗

bioRxiv2022

Explosive seed dispersal depends on SPL7 to ensure sufficient copper for localized lignin deposition via laccases

Exploding seed pods evolved in the Arabidopsis relative, Cardamine hirsuta, via morphomechanical innovations that allow the storage and rapid release of elastic energy. Asymmetric lignin deposition within endocarpb cell walls is one such innovation that is required for explosive seed dispersal and evolved in association with the trait. However, the genetic control of this novel lignin pattern is unknown. Here, we identify three lignin-polymerizing laccases, LAC4, 11 and 17, that precisely co-localize with, and are redundantly required for, asymmetric lignification of endocarpb cells. By screening for C. hirsuta mutants with less lignified fruit valves, we found that loss of function of the transcription factor gene SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 7 (SPL7) caused a reduction in endocarpb cell wall lignification and a consequent reduction in seed dispersal range. SPL7 is a conserved regulator of copper homeostasis and is both necessary and sufficient for copper to accumulate in the fruit. Laccases are copper-requiring enzymes. We discovered that laccase activity in endocarpb cell walls depends on the SPL7 pathway to acclimate to copper deficiency and provide sufficient copper for lignin polymerization. Hence, SPL7 links mineral nutrition to efficient dispersal of the next generation.

plant biology↗