Biology subjects

Brands, M.

Publications and source records attributed to Brands, M..

5 recordsLinked to original sources

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↗

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↗

bioRxiv2020

Palmitvaccenic acid (Δ11-cis-hexadecenoic acid) is synthesized by an OLE1-like desaturase in the arbuscular mycorrhiza fungus Rhizophagus irregularis

Arbuscular mycorrhiza (AM) fungi deliver mineral nutrients to the plant host in exchange for reduced carbon in the form of sugars and lipids. Colonization with AM fungi upregulates a specific host lipid synthesis pathway resulting in the production of fatty acids. The fungus Rhizophagus irregularis accumulates predominantly palmitic acid (16:0) and the unusual palmitvaccenic acid (16:1{Delta}11cis). Here, we present the isolation and characterization of RiOLE1-LIKE, the desaturase involved in palmitvaccenic acid synthesis, by heterologous expression in yeast and plants. Results are in line with the scenario that RiOLE1-LIKE encodes an acyl-CoA desaturase with substrate specificity for C15-C18 acyl groups, in particular C16. Phylogenetic analysis of RiOLE1-LIKE related sequences revealed that this gene is conserved in AM fungi from the Glomales and Diversisporales, but is absent from non-symbiotic Mortierellaceae and Mucoromycotina fungi, suggesting that 16:1{Delta}11cis provides a specific function during AM colonization.

plant biology↗

bioRxiv2017

Lipid transfer from plants to arbuscular mycorrhiza fungi

Arbuscular mycorrhiza (AM) symbioses contribute to global carbon cycles as plant hosts divert up to 20% of photosynthate to the obligate biotrophic fungi. Previous studies suggested carbohydrates as the only form of carbon transferred to the fungi. However, de novo fatty acid (FA) synthesis has not been observed in AM fungi in absence of the plant. In a forward genetic approach, we identified two Lotus japonicus mutants defective in AM-specific paralogs of lipid biosynthesis genes (KASI and GPAT6). These mutants perturb fungal development and accumulation of emblematic fungal 16:1{omega}5 FAs. Using isotopolog profiling we demonstrate that 13C patterns of fungal FAs recapitulate those of wild-type hosts, indicating cross-kingdom lipid transfer from plants to fungi. This transfer of labelled FAs was not observed for the AM-specific lipid biosynthesis mutants. Thus, growth and development of beneficial AM fungi is not only fueled by sugars but depends on lipid transfer from plant hosts.

plant biology↗