Biology subjects

Balcke, G. U.

Publications and source records attributed to Balcke, G. U..

9 recordsLinked to original sources

bioRxiv2026

Prion-like domains control plastid targeting of PEPSI effectors and PEPSI6-mediated modulation of DXR during root symbiosis

Microbial effectors often act in the apoplast or cytosol, but how they reach host organelles during beneficial plant-fungal interactions remains poorly understood. Here, we identify a class of secreted prion-like effector proteins from the mutualistic root endophyte Serendipita indica, termed PEPSIs. These proteins contain prion-like domains (PrLDs) embedded within intrinsically disordered regions, and three tested PEPSIs require these domains for plastid localization. Focusing on PEPSI6, we show that plastid targeting depends on its PrLD and is associated with engagement of plastid import and proteostasis machinery. In plastids, PEPSI6 associates with 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), promotes DXR accumulation, alters methylerythritol phosphate pathway metabolites, and enhances tolerance to the DXR inhibitor fosmidomycin. PEPSI6 also undergoes apoplastic C-terminal CAP-domain processing, and its colonization-promoting activity persists after PrLD deletion, indicating a plastid-targeting-independent function. Overall, this work identifies PrLDs as noncanonical plastid-targeting elements in PEPSI effectors and reveals DXR as a target of fungal manipulation during root symbiosis. HighlightsO_LIPrion-like domains control plastid targeting of selected PEPSI effectors. C_LIO_LIPEPSI6 associates with DXR and promotes its accumulation in plastids. C_LIO_LIPEPSI6 alters MEP-pathway metabolites and increases tolerance to fosmidomycin. C_LIO_LIApoplastic processing reveals a plastid-independent PEPSI6 activity during root symbiosis. C_LI

plant biology↗

bioRxiv2025

Cytokinin-mediated trichome initiation in Nicotiana benthamiana upon Agrobacterium tumefaciens infiltration

Infiltration of Agrobacterium tumefaciens in leaves of Nicotiana benthamiana has become a standard method for transient expression in plants. Like many Solanaceae species, N. benthamiana develops on its leaf surface capitate glandular trichomes that produce and secrete acylsugars. We observed that A. tumefaciens strain GV3101 harboring the disarmed Ti plasmid pMP90 induces de novo formation of GTs and increased production of acylsugars when infiltrated in N. benthamiana leaves. In contrast, other strains, such as AGL1 or LBA4404, do not induce GTs. We demonstrate that the presence of the gene coding for the trans-zeatin synthase (tzs) present on pMP90 is responsible for the de novo trichome initiation and that infiltration of cytokinins such as trans-zeatin or benzylaminopurine is sufficient to induce GTs, establishing a direct link between cytokinins and trichome initiation. While these results provide an opportunity to better understand the development of GTs, they make us aware that Agrobacterium infiltration has developmental, biochemical and physiological consequences. To avoid or minimize potential interference of Agrobacterium on the outcome of the infiltration experiments, we recommend testing several strains when establishing a transient assay. Plain Language summaryAgrobacterium infiltration of tobacco leaves is a method of choice for transient expression in plants. Agrobacterium strains that produce cytokinins induce glandular trichome initiation and acylsugar production, providing a new angle for studying trichome development and highlighting side effects of Agro-infiltration that should be considered when designing transient assays.

plant biology↗

bioRxiv2025

Cooperation between a root fungal endophyte and host-derived coumarin scopoletin mediates Arabidopsis iron nutrition

O_LIIron acquisition is a critical challenge for plants, especially in iron-deficient soils. Recent research underscores the importance of root-exuded coumarins in modulating the root microbiome community structure and facilitating iron uptake. However, interactions between root-associated fungi and coumarins in plant iron nutrition remain unknown. We investigated the mechanism by which a fungal endophyte, Macrophomina phaseolina (F80), enhances Arabidopsis iron nutrition. C_LIO_LIFungal-coumarin interactions were assessed by profiling metabolites and measuring iron mobilisation in F80 cultures supplemented with specific coumarins, alongside quantifying growth performance and iron content in Arabidopsis coumarin-biosynthesis mutants inoculated with F80. C_LIO_LIOur findings reveal that an interaction between the coumarin scopoletin and F80 in the rhizosphere rescues plant growth under iron-limiting conditions by resolving the iron mobility bottleneck. F80 exhibits a capacity to modify scopoletin into iron-chelating catechol coumarin esculetin, thereby releasing available iron. C_LIO_LIWe conclude that Arabidopsis-produced scopoletin functions as a precursor for fungal conversion into iron-chelating coumarins. By extending the role of coumarins from bacterial to fungal members of the root microbiota, this study places coumarins at the centre of commensal-mediated enhancement of plant iron nutrition across microbial kingdoms. C_LI

plant biology↗

bioRxiv2024

Metabolome and transcriptome profiling of root chicory provide insights into laticifer development and specialized metabolism

Chicory roots produce inulin, a dietary fiber, as well as large quantities of bitter sesquiterpene lactones (STLs), which have valuable biological activities. In an effort to understand the compartmentalization of metabolism within chicory roots and the molecular basis of the development of laticifers that produce the chicory latex, we performed metabolomics and transcriptomics profiling. GC-MS and LC-MS identified a total of 22 580 features of which 135 were differentially abundant between cell types. Further analysis indicated that the major STLs accumulated primarily in the latex. Gene expression of known STL pathway genes indicates a compartmentalization of the biosynthesis across multiple tissues, with implications regarding the trafficking of pathway intermediates. Phytohormone measurements and gene expression analysis point to a major role for jasmonate signaling in the development and differentiation of laticifers. Furthermore, inulin accumulates mostly outside the laticifers but expression of inulin metabolic genes also point to a complex distribution and trafficking of inulin or inulin precursors across different root compartments. Altogether, the data presented here constitute a unique resource to investigate several biological processes in chicory roots, including laticifer development, STL biosynthesis and transport and inulin biosynthesis regulation. Significance statementA combination of transcriptomics, targeted and untargeted metabolomics of different tissues of chicory roots was generated. These data constitute a resource basis for the investigation of various processes taking place in chicory taproots, including sesquiterpene lactone biosynthesis, laticifer development and inulin biosynthesis and trafficking.

plant biology↗

bioRxiv2023

Metabolic arms race between a plant and a fungal pathogen

In this work, we uncover a metabolite interaction between barley and the fungal pathogen Bipolaris sorokiniana (Bs), involving hordedanes, a previously undescribed set of labdane-related diterpenoids with antimicrobial properties. Bs infection of barley roots elicits hordedane synthesis from a 600-kb gene cluster. Heterologous reconstruction of the synthesis pathway in yeast produced several hordedanes, including one of the most advanced products 19-b-hydroxy-hordetrienoic acid (19-OH-HTA). Barley mutants in the diterpene synthase genes of the cluster are unable to produce hordedanes but, unexpectedly, show reduced Bs colonization. Accordingly, 19-OH-HTA enhances both germination and growth of Bs, while it inhibits other fungi, and Bs chemically modifies 19-OH-HTA. Thus, plant and pathogen molecular interactions extend beyond protein-protein recognition and the simple detoxification of plant antimicrobial metabolites. One-Sentence SummaryA fungal pathogen uses barley diterpenoid phytoalexins to facilitate root colonization.

plant biology↗

bioRxiv2023

The Arabidopsis Concert of Metabolic Acclimation to High Light Stress

In plants, exposure to high light irradiation induces various stress responses, which entail complex metabolic rearrangements. To systematically study such dynamic changes, we conducted time course experiments from 2 minutes to 72 hours with Arabidopsis thaliana plants exposed to high and control light conditions. We performed comparative metabolomics, transcriptomics, redox proteomics and stable isotope labelling on leaf rosettes. Our data analysis identifies a set of synchronous and successive responses that provide a deeper insight into well-orchestrated mechanisms contributing to high light acclimation. We observe a downregulation of genes encoding light harvesting proteins and a transient restriction of genes involved in linear electron flow through photosystem I. C4 acids, produced via anaplerotic routes, strongly accumulate under high light conditions. Redox homeostasis is tightly balanced by reduced NADPH production, enhanced subcellular redistribution of reducing equivalents across several subcellular compartments via photorespiration and activation of processes that quench reactive oxygen species. In this well-orchestrated network, methylerythritol 2,4-cyclodiphosphate, fulfills a dual function as intermediate of plastidic isoprenoid production and as a stress signal molecule.

plant biology↗

bioRxiv2022

Auxin-dependent acceleration of cell division rates regulates root growth at elevated temperature

Roots are highly plastic organs enabling plants to acclimate to a changing below-ground environment. In addition to abiotic factors like nutrients or mechanical resistance, plant roots also respond to temperature variation. Below the heat stress threshold, Arabidopsis thaliana seedlings react to elevated temperature by promoting primary root growth, possibly to reach deeper soil regions with potentially better water saturation. While above-ground thermomorphogenesis is enabled by thermo-sensitive cell elongation, it was unknown how temperature modulates root growth. We here show that roots are able to sense and respond to elevated temperature independent of shoot-derived signals. A yet unknown root thermosensor seems to employ auxin as a messenger to promote primary root growth. Growth is primarily achieved by accelerating cell division rates in the root apical meristem, likely maintained via temperature-sensitive organization of the polar auxin transport system. Hence, the primary cellular target of elevated ambient temperature differs fundamentally between root and shoot tissues, while the messenger auxin that relays temperature information to elongating or dividing cells, respectively, remains the same.

plant biology↗

bioRxiv2022

A fungal endophyte-generated nucleoside signal regulates host cell death and promotes root colonization

The intracellular colonization of plant roots by the beneficial fungal endophyte Serendipita indica follows a biphasic strategy. After an early biotrophic phase, the interaction transitions to a host cell death phase restricted to the epidermal and cortex layers of the root. Host cell death contributes to the successful accommodation of the fungus during the beneficial interaction in Arabidopsis thaliana. How host cell death is initiated and controlled is largely unknown. Here we show that two fungal enzymes, the ecto-5-nucleotidase SiE5NT and the nuclease SiNucA, act synergistically in the plant apoplast at the onset of cell death to produce deoxyadenosine (dAdo), a potent cell death inducer in animal systems. The uptake of extracellular dAdo, but not the structurally related adenosine (Ado), activates a previously undescribed cell death mechanism in A. thaliana. Mutation of the equilibrative nucleoside transporter ENT3 in A. thaliana results in resistance to cell death triggered by extracellular dAdo and reduced fungal-mediated cell death during root colonization. A library screen of A. thaliana T-DNA insertion lines identified a toll/interleukin-1 receptor nucleotide-binding leucine-rich repeat (TIR-NLR) protein as an additional intracellular component in dAdo-triggered cell death. Mutation of this previously uncharacterised TIR-NLR, which we have named ISI (induced by S. indica), affects host cell death, fungal colonization and growth promotion, suggesting a key role in the regulation of root cell death and plant-microbe interaction. Our data show that the combined activity of two fungal apoplastic enzymes leads to the production of a metabolite that, upon uptake, triggers TIR-NLR-modulated plant cell death, providing a link to immunometabolism in plants. Short summaryEfficient intraradical colonization by the beneficial fungal endophyte Serendipita indica requires restricted host cell death. How this symbiotic host cell death is initiated and controlled is largely unknown. Here we show that two fungal enzymes, the ecto-5-nucleotidase SiE5NT and the nuclease SiNucA, act synergistically in the apoplast at the onset of cell death to produce deoxyadenosine (dAdo), a potent cell death inducer in animal systems. Uptake of extracellular dAdo activates a previously undescribed cell death mechanism in plants. Mutation of the A. thaliana equilibrative nucleoside transporter ENT3 leads to resistance to cell death triggered by uptake of extracellular dAdo and to reduced fungal-mediated cell death during colonization. A library screen of A. thaliana T-DNA insertion lines identified a TIR-NLR protein as an additional intracellular component in dAdo-triggered cell death, providing a link to immunometabolism in plants. In a nutshellRegulated host cell death is part of the plant defense strategy against pathogens, but it is also involved in the accommodation of certain beneficial microbes in the roots. We have identified extracellular metabolites and intracellular metabolic signals that contribute to colonization by beneficial root fungal endophytes and uncovered a conserved cell death mechanism likely co-opted for establishing plant-endophyte symbiosis.

plant biology↗

bioRxiv2021

A barley gene cluster for the biosynthesis of diterpenoid phytoalexins

Phytoalexins are specialized metabolites that are induced upon pathogen infection and contribute to the defense arsenal of plants. Maize and rice produce multiple diterpenoid phytoalexins and there is evidence from genomic sequences that other monocots may also produce diterpenoid phytoalexins. Here we report on the identification and characterization of a gene cluster in barley (Hordeum vulgare cv. Golden Promise) that is involved in the production of a set of labdane-related diterpenoids upon infection of roots by the fungal pathogen Bipolaris sorokiniana. The cluster is localized on chromosome 2, covers over 600 kb and comprises genes coding for a (+)-copalyl diphosphate synthase (HvCPS2), a kaurene synthase like (HvKSL4) and several cytochrome P450 oxygenases (CYPs). Expression of HvCPS2 and HvKSL4 in yeast and Nicotiana benthamiana resulted in the production of a single major product, whose structure was determined to be of the cleistanthane type and was named hordediene. Co-expression of HvCPS2, HvKSL4 and one of the CYPs from the cluster (CYP89E31) afforded two additional products, hordetriene and 11-hydroxy-hordetriene. Both of these compounds could be detected in extracts of barley roots infected by B. sorokiniana, validating the function of these genes in planta. Furthermore, diterpenoids with multiple oxidations and with molecular masses of 316, 318 and 332 were induced in infected barley roots and secreted in the medium, indicating that additional oxidases, possibly from the same genomic cluster are involved in the production of these phytoalexins. Our results provide the basis for further investigation of the role of this gene cluster in the defense of barley against pathogens and more generally in the interaction with the microbiome.

plant biology↗