Biology subjects

Kohler, A.

Publications and source records attributed to Kohler, A..

18 recordsLinked to original sources

bioRxiv2026

Spatially resolved transcriptomics of poplar reveals tissue organization across shoot-associated organs

Poplar (Populus spp.) is a model for tree biology and a platform for engineering woody biomass, biofuels, biomaterials, and bioproducts. Many relevant traits depend on tissue position, developmental stage, and cell type, yet these spatial relationships are difficult to recover from bulk or single-cell transcriptomes. Here, we generated a spatial transcriptome atlas of Populus tremula x P. alba INRA 717-1B4 across the shoot apex, axillary bud, stem, and petiole. After quality control, the atlas retained 29,687 spatial spots from 45 tissue sections and detected 58,748 genes. Histology-guided clustering and marker analysis resolved meristematic, epidermal, cortical, vascular, and organ-specific domains. Cross-organ comparisons assessed whether published markers retained tissue-associated expression across different anatomical contexts and developmental stages, while de novo analysis identified additional domain-enriched candidates. As case studies of the utility of the atlas, we examined the emergence of trichome-associated programs in the shoot apex and adaxial - abaxial expression differences in petioles. A trichome identity score based on poplar markers from the single-cell shoot atlas peaked along the inferred meristem-to-primordium trajectory, revealing spatially localized expression of trichome-associated programs during early leaf development. Petiole expression differences were concentrated in the epidermis and cortex and involved polarity-associated, auxin-responsive, and cell-wall-remodeling genes, with distinct expression profiles across leaf positions. Together, these data provide a spatial reference for investigating tissue differentiation and developmental patterning in a transformable poplar genotype.

plant biology↗

bioRxiv2026

Retrograde signalling mediates cellular adaptation to mitochondrial DNA copy number alterations

Eukaryotic cells maintain multiple copies of the mitochondrial genome, which is essential for cellular metabolism. Accordingly, alterations in the mitochondrial DNA (mtDNA) copy number are associated with severe human diseases and ageing. However, the mechanisms through which cells regulate mtDNA copy number and the cellular consequences of altered copy number remain poorly understood. Here, using budding yeast as a model, we show that mtDNA copy number is determined by the amount of three limiting factors, Mip1, Abf2, and Rim1. By synthetically tuning the concentrations of only these three proteins, we can modulate mtDNA dosage inside the cell. This revealed that cells are surprisingly robust to mtDNA copy number alterations, with increased copy numbers even accelerating cell growth. Our findings suggest that this robustness is due to protein dosage compensation and independent regulation of mitochondrial morphology. Mechanistically, we identified a critical role of the retrograde signalling pathway for this adaptation. We show that signalling from mitochondria to the nucleus is upregulated in cells with higher mtDNA copy number, and disruption of this regulation diminishes their faster growth. Taken together, our work reveals regulatory principles that enable cells to adapt to mtDNA copy number alterations.

cell biology↗

bioRxiv2025

Machine-Learning-Guided Video Analysis Identifies Sound-Evoked Pain Behaviors from Facial Grimace and Body Cues in Mice

Humans can experience sound-evoked pain, either from extremely loud sounds or in cases of pain hyperacusis from typically tolerable sounds. However, the mechanisms underlying sound-evoked pain remain poorly understood. Developing behavioral methods to measure sound-evoked pain in animal models is critical for elucidating these mechanisms. Here, a machine learning-based approach was developed to measure sound-evoked pain in freely moving mice by analyzing facial grimace and body position from video recordings during sound exposure. Facial grimace, a commonly used method to detect pain in mice, and body position, which can be used to measure postural and movement changes that also indicate pain, were both quantified using a deep neural network model trained to extract established facial and body features from video recorded by a single camera. To validate the models capability to detect pain, a known painful state, migraine induced by the injection of the neuropeptide calcitonin gene-related peptide (CGRP), was used. Using this machine learning-based approach, the ability to quantify a pain response from CGRP-induced migraine, distinct from baseline behavior, was demonstrated, resulting in a defined pain threshold. Sound exposures at high intensities elicited significant changes in facial grimace and body position, in comparison, surpassing the pain threshold calculated from CGRP-induced migraine. These behavioral changes were absent in Tmie-knockout mice, which lack functional sound transduction in the cochlea. This automated, high-throughput framework enables objective and sensitive analysis of pain providing a foundation for future studies investigating the peripheral and central mechanisms of sound-evoked pain. SignificanceThis study introduces a quantitative framework for assessing pain using a single-camera setup and machine learning guided analysis to capture and analyze mouse behavior. By integrating two established pain metrics, facial grimace and attenuated movement, this method enables precise, non-invasive quantification of pain-related behaviors. The approach was validated with a well-characterized pain model, migraine, induced by injection of the neuropeptide CGRP, demonstrating the ability to quantify a pain response distinct from baseline behavior. By applying this framework to sound-evoked pain, the data revealed that exposure to intense sound triggers significant pain behavioral responses. These novel findings provide insights into the behavioral manifestations and neural underpinnings of sound-evoked pain, offering a robust tool for studying the mechanisms of pain perception.

animal behavior and cognition↗

bioRxiv2025

Prevalence of water and nutrient availability in structuring fungal communities of healthy and decaying beech trees in forests

Background and aimsIn forest ecosystems, trees interact with a broad range of soil microorganisms, such as ectomycorrhizal fungi, improving nutrition and water uptake and mitigating biotic and abiotic stress. In the context of the predicted more frequent and more severe droughts, it is critical to characterise how trees and their associated fungal partners respond to water shortage to improve future forest management. MethodsWe investigated the importance of diverse environmental predictors (e.g., edaphic, climatic, topographic) on the fungal communities associated with the root systems of decaying and healthy beech trees in natural beech forests. In parallel, we identified specific fungal taxa linked with their host vitality and water stress gradient. ResultsWe observed that soil water shortage had a greater effect on the structuring of fungal communities than beech vitality or other environmental factors. We identified a core group of fungi that remained unaffected by water availability among all study sites, while other fungal species were more abundant in sampling sites more prone to water shortage. Finally, we showed that the abundance of ectomycorrhizal fungi was significantly associated with healthy beech root systems, while saprotrophic fungi prevailed in the roots of trees exhibiting severe decay. ConclusionsOverall, our study highlights the major role of drought in structuring fungal communities associated with beech root systems and pinpoints the key fungal taxonomic groups found in healthy beech trees.

ecology↗

bioRxiv2025

Poplar CLE peptides stimulating ectomycorrhizal symbiosis uncovered by genome-wide identification of ectomycorrhizal-responsive small secreted peptides

Plants small secreted peptides (SSPs) regulate root development, immunity and symbiotic relationships in herbaceous plants. These processes are equally important for establishing functional ectomycorrhizal associations in trees. While fungal SSPs involved in ectomycorrhizal establishment have been identified, the role of plant SSPs remains largely unexplored. Although thousands of SSPs were predicted in plant genomes, their small size and high sequence divergence hinder their accurate automated annotations. To address this issue, we combined de novo gene prediction with family-specific motif search to identify 1,053 SSPs from 21 symbiosis-related families in the genomes of two ectomycorrhizal tree species: Populus trichocarpa and Quercus robur. Nearly half of these SSPs are transcriptionally regulated during ectomycorrhizal symbiosis with various fungal partners. Functional assays of selected Populus CLE peptides, a SSP family known to repress arbuscular mycorrhizal and rhizobial symbioses, revealed that five enhanced ectomycorrhizal roots formation. Unlike CLEs involved in the autoregulation of arbuscular mycorrhizal and rhizobial symbioses, these peptides belonged to clades associated with meristem activity. Their activity did not increase lateral root number but inhibited adventitious root growth, suggesting their role in promoting ectomycorrhizal root organogenesis. These findings demonstrate that CLE peptides promote, rather than repress, ectomycorrhizal symbiosis. This functional divergence from their roles in other symbioses suggests that poplar co-opted a distinct set of SSPs to support ectomycorrhizal development. Our results expand the understanding of host tree contributions to ectomycorrhizal development and identify a set of candidate SSPs for future functional studies, thereby highlighting a new layer of regulation in tree-fungal mutualism.

plant biology↗

bioRxiv2025

Comparative transcriptomics uncovers plant and fungal genetic determinants of mycorrhizal compatibility

Ectomycorrhizal symbiosis supports tree growth and is crucial for nutrient cycling and temperate and boreal ecosystems functioning. The establishment of functional ECM first requires the association of compatible partners. However, host and fungal genetic determinants governing mycorrhizal compatibility are unknown. To identify such factors in poplar and its fungal associates, we mined existing and de-novo tree and fungal transcriptional datasets. We identified core plant regulons enabling ECM symbiosis at early and mature stages of the interaction. These regulons can be divided into general fungal-sensing and ECM-specific components. We highlight the importance of fungal modulation of plant JA-related defences and the regulation of secretory pathways for ECM compatibility, including upregulation of key fungal small secreted proteins, the downregulation of plant secreted peroxidases and the downregulation of plant cell-wall remodelling proteins concomitantly with the upregulation of fungal glycosyl hydrolases acting on pectin. Not only gene-regulation, but also its temporal scale and dynamics seems to play a crucial role for mycorrhizal compatibility. The expression profile of the host Common Symbiosis Pathway was also studied, revealing constitutive levels of expression of a part of the pathway and moderate upregulation in compatible ECM interactions. Overall, these results underscore the importance of novel biological functions during the establishment of ECM symbiosis, help us gain insights into the molecular events determining mycorrhiza compatibility and serve as a data-rich transcriptomic resource to open new research questions in the field. Significance statementEctomycorrhizal symbiosis is essential for forest ecosystems, but the genetic determinants of host and fungal compatibility remain underexplored. Employing comparative transcriptomics, we identified plant general and ECM-specific gene regulons, outlining the expression profile of Common Symbiosis Pathway genes in multiple ECM interactions and highlighting fungal and plant genes associated to interkingdom crosstalk and cell wall remodelling. These findings help us gain insights into the molecular events determining mycorrhiza compatibility.

plant biology↗

bioRxiv2024

Hypoxia impedes differentiation of cranial neural crest cells into derivatives relevant for craniofacial development

Orofacial clefts are the second-most prevalent congenital malformation. Risk factors are multifactorial and include genetic components but also environmental factors. One environmental factor is hypoxia during pregnancy, caused for instance by tobacco smoking, medication or living at high altitudes. Knowledge about the molecular link between hypoxia and orofacial clefts is at large. We here show that hypoxia has only modest effects on proliferating cranial neural crest cells, but dramatically influences their differentiation potential. We detected massive perturbations in their differentiation to chondrocytes, osteoblasts and smooth muscle cells. The transcriptional induction of the majority of regulated genes during each of these processes was grossly impaired by hypoxic conditions, as evidenced by genome-wide transcriptomic analyses. Bioinformatic analyses pointed to cytoskeletal organization and amino acid metabolism as two main processes compromised during all three differentiation pathways, and several orofacial cleft risk genes were among the genes with impaired induction during hypoxia. Our analyses reveal a drastic influence of hypoxia on the differentiation potential of cranial neural crest cells as a possible source for the occurrence of orofacial clefts.

genomics↗

bioRxiv2024

Discovery of a synthetic small molecule targeting the central regulator of Salmonella pathogenicity

The enteric pathogen Salmonella enterica serovar Typhimurium relies on the activity of effector proteins to invade, replicate, and disseminate into host epithelial cells and other tissues, thereby causing disease. Secretion and injection of effector proteins into host cells is mediated by dedicated secretion systems, which hence represent major virulence determinants. Here, we report the identification of a synthetic small molecule with drug-like properties, C26, which suppresses the secretion of effector proteins, and consequently hinders bacterial invasion of eukaryotic cells. C26 binds to and inhibits HilD, the transcriptional regulator of the major secretion systems. While sharing the same binding pocket as the previously described long-chain fatty acid ligands, C26 inhibits HilD with a unique binding mode and a distinct mechanism. We provide evidence for target engagement within infected eukaryotic cells and present analogs with improved potency and suitability as scaffolds to develop anti-virulence agents against Salmonella infections in humans and animals.

microbiology↗

bioRxiv2022

The establishment of Populus x Laccaria bicolor ectomycorrhiza requires the inactivation of MYC2 coordinated defense response with a key role for root terpene synthases

The jasmonic acid (JA) signaling pathway plays an important role in the establishment of the ectomycorrhizal symbiosis (ECM) between Laccaria bicolor and poplar. We previously showed that the L. bicolor effector MiSSP7 induces the stabilization of the poplar JAZ6, a JA co-repressor protein that binds to Populus MYC2.1 and MYC2.2, orthologs of the Arabidopsis MYC2 transcription factor (TF), blocking their activity. Here we showed that both TFs play a central role in root colonization by L. bicolor mycelium, since their overexpression decreased the formation of the Hartig net, the hyphal network involved in symbiotic nutrient exchanges. By combining RNA sequencing and DNA Affinity Purification sequencing (DAP-seq) analysis, we identified a core set of JA-responsive genes directly activated by poplar MYC2.1 and MYC2.2, that need to be bypassed by the fungi to colonize root apoplastic spaces. These genes encode for other TFs, receptor-like kinases and many defense-related proteins, including terpene synthases (TPS). Monoterpenes produced by some of these TPS impact L. bicolor growth and ECM formation, suggesting a role for poplar root monoterpenes as negative regulators of in planta fungal growth and ECM symbiosis. Significance statementThe ectomycorrhizal symbiosis is a predominant mutualistic plant-fungus interaction occurring in forests, sustaining tree health. Ectomycorrhizal fungi colonize the root intercellularly establishing the symbiotic interface required for bidirectional nutrients exchanges, the Hartig net. During root colonization, the fungus L. bicolor produces the effector protein MiSSP7 that binds to the jasmonate co-receptor PtJAZ6, maintaining the repression of MYC2-targeted genes. Here we showed that defensive genes are major targets of MYC2, suggesting that their strict control is required to allow fungal colonization, with special emphasis on the host root monoterpene synthesis. Future research will focus on how root terpene defenses mediate belowground mutualistic interactions and how they can be manipulated to engineer plants with enhanced disease resistance but stable mutualistic interactions.

plant biology↗

bioRxiv2021

The ectomycorrhizal basidiomycete Laccaria bicolor releases a GH28 polygalacturonase that plays a key role in symbiosis establishment

O_LIIn ectomycorrhiza, root penetration and colonization of the intercellular space by symbiotic hyphae is thought to rely on the mechanical force that results from hyphal tip growth, enhanced by the activity of secreted cell-wall-degrading enzymes. C_LIO_LIHere, we characterize the biochemical properties of the symbiosis-induced polygalacturonase LbGH28A from the ectomycorrhizal fungus Laccaria bicolor. The transcriptional regulation of LbGH28A was measured by qPCR. The biological relevance of LbGH28A was confirmed by generating RNAi-silenced LbGH28A mutants. We localized the LbGH28A protein by immunofluorescence confocal and immunogold cytochemical microscopy in poplar ectomycorrhizal roots. C_LIO_LIqPCR confirmed the induced expression of LbGH28A during ectomycorrhiza formation. L. bicolor RNAi mutants have a lower ability to establish ectomycorrhiza confirming the key role of this enzyme in symbiosis. The purified recombinant LbGH28A has its highest activity towards pectin and polygalacturonic acid. In situ localization of LbGH28A indicates that this endopolygalacturonase is located in both fungal and plant cell walls at the symbiotic hyphal front. C_LIO_LIThe present findings suggest that the symbiosis-induced pectinase LbGH28A is involved in the Hartig net formation and is an important determinant for successful symbiotic colonization. C_LI

plant biology↗

bioRxiv2021

Molecular basis of differential adventitious rooting competence in poplar genotypes

O_LIRecalcitrant adventitious root (AR) development is a major hurdle in propagating commercially important woody plants. Although significant progress has been made to identify genes involved in subsequent steps of AR development, the molecular basis of differences in apparent recalcitrance to form AR between easy-to-root and difficult-to-root genotypes remains unknown. C_LIO_LITo address this, we generated cambium tissue-specific transcriptomic data from stem cuttings of hybrid aspen, T89 (difficult-to-root) and hybrid poplar OP42 (easy-to-root) and used transgenic approaches to verify the role of several transcription factors (TF) in the control of adventitious rooting. C_LIO_LIIncreased peroxidase activity is positively correlated with better rooting. We found differentially expressed genes encoding Reactive Oxygen Species (ROS) scavenging proteins to be enriched in OP42 compared to T89. A higher number of differentially expressed TF in OP42 compared to T89 cambium cells was revealed by a more intense transcriptional reprograming in the former. PtMYC2, a potential negative regulator, was less expressed in OP42 compared to T89. Using transgenic approaches, we have demonstrated that PttARF17.1 and PttMYC2.1 negatively regulate adventitious rooting. C_LIO_LIOur results provide insights into the molecular basis of genotypic differences in AR and implicate differential expression of the master regulator MYC2 as a critical player in this process. C_LI

plant biology↗

bioRxiv2021

Evolutionary innovations through gain and loss of genes in the ectomycorrhizal Boletales

O_LIIn this study, we aim to identify genomic traits of the transitions to the ectomycorrhizal ecology within the Boletales, one of the most diverse lineages of symbiotrophic fungi. C_LIO_LIWe sequenced the genomes and compared the gene repertoires of symbiotrophic Boletales species to their saprotrophic brown-rot relatives. We also reconstructed gene duplication/loss histories along a time-calibrated phylogeny. C_LIO_LIWe showed that the rate of gene duplication is constant along the backbone of Boletales phylogeny with large loss events in lineages leading to several families. The rate of gene family expansion sharply increased in the late Miocene and mostly took place in Boletaceae. C_LIO_LIMost of the ectomycorrhizal Boletales are characterized by a large genome size due to transposable element (TE) expansions and a reduction in the diversity of plant cell wall degrading enzymes (PCWDEs) compared to their brown-rot relatives. However, several species in the Boletaceae, Paxillaceae and Boletinellaceae have kept a substantial set of endoglucanases and LPMOs acting on cellulose/hemicellulose and fungal polysaccharides suggesting that they may partly decompose organic matter by a combined activity of oxidative and hydrolytic enzymes. C_LIO_LIThe present study provides novel insights on our understanding of the mechanisms that influence the evolutionary diversification of boletes and symbiosis evolution. C_LI

genomics↗

bioRxiv2021

Cryptic genetic structure and copy-number variation in the ubiquitous forest symbiotic fungus Cenococcum geophilum

Ectomycorrhizal (ECM) fungi associated with plants constitute one of the most successful symbiotic interactions in forest ecosystems. ECM support trophic exchanges with host plants and are important factors for the survival and stress resilience of trees. However, ECM clades often harbour morpho-species and cryptic lineages, with weak morphological differentiation. How this relates to intraspecific genome variability and ecological functioning is poorly known. Here, we analysed 16 European isolates of the ascomycete Cenococcum geophilum, an extremely ubiquitous forest symbiotic fungus with no known sexual or asexual spore forming structures but with a massively enlarged genome. We carried out whole-genome sequencing to identify single-nucleotide polymorphisms. We found no geographic structure at the European scale but divergent lineages within sampling sites. Evidence for recombination was restricted to specific cryptic lineages. Lineage differentiation was supported by extensive copy-number variation. Finally, we confirmed heterothallism with a single MAT1 idiomorph per genome. Synteny analyses of the MAT1 locus revealed substantial rearrangements and a pseudogene of the opposite MAT1 idiomorph. Our study provides the first evidence for substantial genome-wide structural variation, lineage-specific recombination and low continent-wide genetic differentiation in C. geophilum. Our study provides a foundation for targeted analyses of intra-specific functional variation in this major symbiosis. Originality-Significance StatementWe provide the first report on the genetic structure and copy-number variation of the globally ubiquitous and key forest symbiotic fungus Cenococcum geophilum using whole-genome sequencing data. We found divergent lineages within sampling sites, while closely related lineages appear over large geographic distances on a continental scale. Even though no sexual spore forming structures have been reported to date, we provide evidence of recombination in a specific lineage suggesting mating activity. Our findings help explain the high genetic diversity occurring within populations and their resilience to changing and adverse environmental conditions. Furthermore, we identify a single MAT1 idiomorph per genome, confirming heterothallism, and discover that major genomic rearrangements are found in their flanking regions based on chromosomal synteny analysis. Intriguingly, a pseudogene of the opposite functional idiomorph has been characterised in each genome, suggesting a common homothallic ancestor to the species. As Cenococcum geophilum is a pivotal mycorrhizal associate of a broad range of trees and shrubs providing nutrition and water supply to their hosts, we highlight and discuss the potential role of the large genome-wide structural variations in environmental selection.

genomics↗

bioRxiv2021

A comprehensive collection of transcriptome data to support life cycle analysis of the poplar rust fungus Melampsora larici-populina

Melampsora larici-populina is an obligate biotrophic plant pathogen responsible for the poplar rust disease. This fungus belongs to the taxonomical order Pucciniales and exhibits a complex heteroecious and macrocyclic life cycle, i.e. it has the capacity to infect two unrelated host plants, larch and poplar, and to form five distinct spore types through the year. The M. larici-populina genome has been sequenced and annotated in 2011 and since, different transcriptomic analyses were conducted at different stages with oligoarrays and later on with RNA-Seq covering most of its life cycle. Here, we collected published transcriptome data for the poplar rust fungus, transposed them for the version 2 of the genome now available at the Joint Genome Institute Mycocosm website and performed normalization of different oligoarray datasets on one hand, and of RNA-Seq on the other hand. We report a comprehensive normalized dataset for this fungus, made available for the community, which allows life cycle transcriptomics analysis.

microbiology↗

bioRxiv2021

Genetic determinants of endophytism in the Arabidopsis root mycobiome

Roots of Arabidopsis thaliana do not engage in symbiotic associations with mycorrhizal fungi but host taxonomically diverse fungal communities that influence health and disease states. We sequenced the genomes of 41 fungal isolates representative of the A. thaliana root mycobiota for comparative analysis with 79 other plant-associated fungi. We report that root mycobiota members evolved from ancestors with diverse lifestyles and retained large repertoires of plant cell wall-degrading enzymes (PCWDEs) and effector-like small secreted proteins. We identified a set of 84 gene families predicting best endophytism, including families encoding PCWDEs acting on xylan (GH10) and cellulose (AA9). These genes also belong to a core transcriptional response induced by phylogenetically-distant mycobiota members in A. thaliana roots. Recolonization experiments with individual fungi indicated that strains with detrimental effects in mono-association with the host not only colonize roots more aggressively than those with beneficial activities but also dominate in natural root samples. We identified and validated the pectin degrading enzyme family PL1_7 as a key component linking aggressiveness of endophytic colonization to plant health.

microbiology↗

bioRxiv2020

Infrared fiber optic spectroscopy detects bovine articular cartilage degeneration

Articular cartilage (AC) is a soft connective tissue that covers the ends of articulating bones. Joint injuries may lead to degeneration of cartilage tissue and initiate development of post-traumatic osteoarthritis (OA). Arthroscopic surgeries can be used to treat joint injuries, but arthroscopic evaluation of cartilage quality is subjective. Therefore, new methods are needed for objective assessment of cartilage degeneration. Fourier transform infrared (FTIR) spectroscopy can be used to assess tissue composition based on the fundamental molecular vibrations. When combined with fiber optics and attenuated total reflectance (ATR) crystal, the measurements can be done flexibly without any sample processing. We hypothesize that Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy can detect enzymatically and mechanically induced changes similar to changes occurring during progression of OA. Fresh bovine patellar cartilage plugs (n = 60) were extracted and degraded enzymatically and mechanically. Adjacent untreated control samples (n = 60) were utilized as controls. Enzymatic degradation was implemented by 90-min and 24-hour collagenase as well as 30-min trypsin treatments. Mechanical damage was induced by: 1) dropping a weight impactor on the cartilage plugs, and 2) abrading the cartilage surface with a rotating sandpaper. Fiber optic FTIR-ATR spectroscopic measurements were conducted for control and degraded samples, and spectral changes were assessed with random forest (RF), partial least squares discriminant analysis (PLS-DA), and support vector machine (SVM) classifiers. RF (accuracy 93.1 % to 79.2 %), PLS-DA (accuracy 95.8% to 81.9%), and SVM (accuracy 91.7% to 80.6%) all had excellent classification performance for detecting the different enzymatic and mechanical damage on cartilage matrix. The results suggest that fiber optic FTIR-ATR spectroscopy is a viable way to detect minor degeneration of AC.

biophysics↗

bioRxiv2019

Target Of Rapamycin pathway in the white-rot fungus Phanerochaete chrysosporium

The Target Of Rapamycin (TOR) signaling pathway is known to regulate growth in response to nutrient availability and stress in eukaryotic cells. In the present study, we have investigated the TOR pathway in the white-rot fungus Phanerochaete chrysosporium. Inhibition of TOR activity by rapamycin affects conidia germination and hyphal growth highlighting the conserved mechanism of susceptibility to rapamycin. Interestingly, the secreted protein content is also affected by the rapamycin treatment. Finally, homologs of the components of TOR pathway can be identified in P. chrysosporium. Altogether, those results indicate that the TOR pathway of P. chrysosporium plays a central role in this fungus.

microbiology↗

bioRxiv2017

The hydrophobin-like OmSSP1 may be an effector in the ericoid mycorrhizal symbiosis

Mutualistic and pathogenic plant-colonizing fungi use effector molecules to manipulate the host cell metabolism to allow plant tissue invasion. Some small secreted proteins (SSPs) have been identified as fungal effectors in both ectomycorrhizal and arbuscular mycorrhizal fungi, but it is currently unknown whether SSPs also play a role as effectors in other mycorrhizal associations. Ericoid mycorrhiza is a specific endomycorrhizal type that involves symbiotic fungi mostly belonging to the Leotiomycetes (Ascomycetes) and plants in the family Ericaceae. Genomic and RNASeq data from the ericoid mycorrhizal fungus Oidiodendron maius led to the identification of several symbiosis-upregulated genes encoding putative SSPs. OmSSP1, the most highly symbiosis up-regulated SSP, was found to share some features with fungal hydrophobins, even though it lacks the Pfam hydrophobin domain. Sequence alignment with other hydrophobins and hydrophobin-like fungal proteins placed OmSSP1 within Class I hydrophobins. However, the predicted features of OmSSP1 may suggest a distinct type of hydrophobin-like proteins. The presence of a predicted signal peptide and a yeast-based signal sequence trap assay demonstrate that OmSSP1 is secreted during symbiosis. OmSSP1 null-mutants showed a reduced capacity to form ericoid mycorrhiza with Vaccinium myrtillus roots, suggesting a role as effectors in the ericoid mycorrhizal interaction.

plant biology↗