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<p>Co-evolution between cereals and pathogenic grass powdery mildew fungi is exemplified by sequence diversification of an allelic series of barley resistance genes encoding Mildew Locus A (MLA) nucleotide-binding leucine-rich repeat (NLR) immunoreceptors with an N-terminal coiled-coil domain (CNLs). Each immunoreceptor recognises a matching, strain-specific powdery mildew effector encoded by an avirulence gene (<i>AVR</i><sub><i>a</i></sub>). We present here the cryo-EM structure of barley MLA13 in complex with its cognate effector AVR<sub>A13</sub>-1. The effector adopts an RNase-like fold when bound to MLA13 in planta, similar to crystal structures of other RNase-like AVR<sub>A</sub> effectors unbound to receptors. AVR<sub>A13</sub>-1 interacts via its basal loops with MLA13 C-terminal leucine-rich repeats (LRRs) and the central winged helix domain (WHD). Co-expression of structure-guided MLA13 and AVR<sub>A13</sub>-1 substitution variants show that the receptor–effector interface plays an essential role in mediating immunity-associated plant cell death. Furthermore, by combining structural information from the MLA13–AVR<sub>A13</sub>-1 heterocomplex with sequence alignments of other MLA receptors, we engineered a single amino acid substitution in MLA7 that enables expanded effector detection of AVR<sub>A13</sub>-1 and the virulent variant AVR<sub>A13</sub>-V2. In contrast to the pentameric conformation of previously reported effector-activated CNL resistosomes, MLA13 was purified and resolved as a stable heterodimer from an in planta expression system. Our study suggests a common structural principle for RNase-like effector binding to MLAs and highlights the utility of structure-guided engineering of plant immune receptors for broadening their pathogen effector recognition capabilities.</p>

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The barley MLA13-AVRA13 heterodimer reveals principles for immunoreceptor recognition of RNase-like powdery mildew effectors

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年2月13日

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  • Aaron W Lawson,
  • Andrea Flores-Ibarra,
  • Yu Cao,
  • Chunpeng An,
  • Ulla Neumann,
  • Monika Gunkel,
  • Isabel M L Saur,
  • Jijie Chai,
  • Elmar Behrmann,
  • Paul Schulze-Lefert

摘要

Co-evolution between cereals and pathogenic grass powdery mildew fungi is exemplified by sequence diversification of an allelic series of barley resistance genes encoding Mildew Locus A (MLA) nucleotide-binding leucine-rich repeat (NLR) immunoreceptors with an N-terminal coiled-coil domain (CNLs). Each immunoreceptor recognises a matching, strain-specific powdery mildew effector encoded by an avirulence gene (AVRa). We present here the cryo-EM structure of barley MLA13 in complex with its cognate effector AVRA13-1. The effector adopts an RNase-like fold when bound to MLA13 in planta, similar to crystal structures of other RNase-like AVRA effectors unbound to receptors. AVRA13-1 interacts via its basal loops with MLA13 C-terminal leucine-rich repeats (LRRs) and the central winged helix domain (WHD). Co-expression of structure-guided MLA13 and AVRA13-1 substitution variants show that the receptor–effector interface plays an essential role in mediating immunity-associated plant cell death. Furthermore, by combining structural information from the MLA13–AVRA13-1 heterocomplex with sequence alignments of other MLA receptors, we engineered a single amino acid substitution in MLA7 that enables expanded effector detection of AVRA13-1 and the virulent variant AVRA13-V2. In contrast to the pentameric conformation of previously reported effector-activated CNL resistosomes, MLA13 was purified and resolved as a stable heterodimer from an in planta expression system. Our study suggests a common structural principle for RNase-like effector binding to MLAs and highlights the utility of structure-guided engineering of plant immune receptors for broadening their pathogen effector recognition capabilities.