iHEAD
Research Initiative
A barley MLA receptor is targeted by a nonribosomal peptide effector of the necrotrophic spot blotch fungus for disease susceptibility
The evolutionary history of plant interactions with necrotrophic pathogens that feed on dying host cells and their virulence mechanisms remains fragmentary. We isolated barley Scs6, which is required for the necrotrophic fungus Bipolaris sorokiniana isolate ND90Pr to cause spot blotch disease. Scs6 is located at the Mla resistance locus and encodes an intracellular nucleotide-binding leucine-rich repeat receptor (NLR). In transgenic barley, Scs6 is sufficient to confer susceptibility to ND90Pr in accessions naturally lacking the receptor, resulting in infection-associated host cell death. Expression of Scs6 in evolutionarily distant Nicotiana benthamiana or human embryonic kidney (HEK293) cells reconstitutes a cell death to an uncharacterized non-ribosomal peptide effector produced by ND90Pr-specific non-ribosomal peptide synthetases (NRPSs) encoded at the VHv1 virulence locus, suggesting that the effector directly activates SCS6. Scs6-mediated cell death in HEK293 cells is independent of known vertebrate cell death pathways, but dependent on extracellular calcium. Scs6 is an allelic variant of functionally diversified Mla resistance genes each conferring strain-specific immunity to barley powdery mildew isolates with a matching proteinaceous pathogen effector. Domain swaps between MLA and SCS6 NLRs and expression of the resulting hybrid proteins in N. benthamiana reveal that the SCS6 leucine-rich repeat domain is a specificity determinant for the NRPS-derived effector to activate the receptor. Similarly, four substitutions in an MLA member unresponsive to ND90Pr render the receptor sensitive to the NRPS-derived effector, leading to cell death. Thus, Mla is subject to contrasting evolutionary selection, recognition of biotrophic pathogen effectors and evasion of targeting by a necrotrophic pathogen effector.
In iHEAD, we aim to i) purify and characterize the NRPS metabolite product derived from B. sorokiniana ND90Pr by mass spectrometry and ii) clarify how the effector activates SCS6 using structural biology approaches.
Publications published within the framework of iHEAD:
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Lawson, A.W. et al. Purifying recombinant proteins from Nicotiana benthamiana for structural studies. Nat Protoc (2025). https://doi.org/10.1038/s41596-025-01249-2
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Lawson, A. W. et al. EMBO J (2025). https://doi.org/ 10.1038/s44318-025-00373-9
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Leng, Y & Kümmel, F et al. A barley MLA immune receptor is activated by a fungal nonribosomalpeptide effector for disease susceptibility. New Phyt (2024). https://doi.org/10.1111/nph.20289
Prof. Dr. Elmar Behrmann
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Since 2000 he is head of the Department of Plant Microbe Interactions at the Max-Planck-Institute for Plant Breeding Research (MPIPZ), Cologne, and Honorary Professor at the University of Cologne since 2003.
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elected EMBO member since April 2006, an elected member of the National Academy of Sciences, USA since 2010, an elected member of the German National Academy of Sciences, Leopoldina since 2010, and an elected member of the American Academy of Microbiology, USA since 2011.
Dr. Aaron Lawson
Aaron joined the iHEAD initiative in 2024 and was invited to present his research at the international IS-MPMI Conference 2025 in Cologne.