Receptor Biochemistry

Aphids are small insects that have developed specialized mouthparts and effector proteins to establish long-term relationships with plants. The peach-potato aphid Myzus persicae is a generalist, feeding on many plant species and capable of transmitting numerous pathogens. This study reveals how host-responsive cathepsin B (CathB) proteins in the oral secretions of M. persicae facilitate aphid survival by modulating plant immune responses. Host-responsive CathB proteins localize to plant processing bodies (p-bodies), cytoplasmic ribonucleoprotein granules involved in messenger RNA storage or decay. Upon localization, these CathB proteins recruit key immune regulators EDS1, PAD4, and ADR1 to these bodies, suppressing plant defenses. A plant protein, Acd28.9 (Hsp20 family), counteracts this CathB activity and contributes to plant resistance to aphids. These findings highlight an unexpected role for p-bodies in plant immunity and uncover a plant resistance mechanism to aphid infestation.

Genome engineering technologies allow the generation of crops with increased disease resistance, though selecting suitable targets remains challenging. Our team has published two recent studies that highlight the potential of engineering plant immune proteases as an alternative approach to generating disease resistant plants.

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Plant pathogens have evolved multiple strategies to avoid being perceived by the host, and many of these aim to disrupt the function of immune receptors. A new study describes a strategy in which the oomycete Phytophthora sojae deploys a protease to cleave the extracellular part of the universal co-receptor BAK1, thereby suppressing plant immunity.

SummaryProcessing by proteases irreversibly regulates the fate of plant proteins and hampers the production of recombinant proteins in plants, yet only few processing events have been described in agroinfiltrated Nicotiana benthamiana, which has emerged as the main transient protein expression platform in plant science and molecular pharming.Here, we used in‐gel digests and mass spectrometry to monitor the migration and topography of 5040 plant proteins within a protein gel. By plotting the peptides over the gel slices, we generated peptographs that reveal where which part of each protein was detected within the protein gel. These data uncovered that 60% of the detected proteins have proteoforms that migrate at lower than predicted molecular weights, implicating extensive proteolytic processing. This analysis confirms the proteolytic removal and degradation of autoinhibitory prodomains of most but not all proteases, and revealed differential processing within pectinemethylesterase and lipase families. This analysis also uncovered intricate processing of glycosidases and uncovered that ectodomain shedding might be common for a diverse range of receptor‐like kinases. Transient expression of double‐tagged candidate proteins confirmed processing events in vivo. This large proteomic dataset implicates an elaborate proteolytic machinery shaping the proteome of N. benthamiana.

Secreted immune proteases Rcr3 (Required for Cladosporium resistance-3) and Pip1 (Phytophthora- inhibited protease-1) of tomato (Solanum lycopersicum) are both inhibited by Avr2 from the fungal plant pathogen Cladosporium fulvum. However, only Rcr3 acts as a decoy co-receptor that detects Avr2 in the presence of the Cf-2 immune receptor. Here, we identified crucial residues in tomato Rcr3 that are required for Cf-2-mediated signalling and bioengineered various proteases to trigger Avr2/Cf-2-dependent immunity. Despite substantial divergence in Rcr3 orthologs from eggplant (Solanum melongena) and tobacco (Nicotiana spp.), minimal alterations were sufficient to trigger Avr2/Cf-2-mediated immune signalling. By contrast, tomato Pip1 was bioengineered with 16 Rcr3-specific residues to initiate Avr2/Cf-2-triggered immune signalling. These residues cluster on one side of the protein next to the substrate-binding groove, indicating a potential Cf-2 interaction site. Our findings also revealed that Rcr3 and Pip1 have distinct substrate preferences determined by two variant residues, and that both are suboptimal for binding Avr2. This study advances our understanding of Avr2 perception and opens avenues to bioengineer proteases to broaden pathogen recognition in other crops.

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Fungal pathogens deploy a set of molecules (proteins, specialized metabolites, and sRNA), so called effectors, to aid the infection process. In comparison to other plant pathogens, smut fungi have small genomes and secretomes of 20 Mb and around 500 proteins, respectively.. Previous comparative genomic studies have shown that many secreted effector proteins without known domains i.e., novel, are conserved only in the Ustilaginaceae family. By analyzing the secretome of 11 species within Ustilaginaceae, we identified 53 core homologous groups commonly present in this lineage. By collecting existing mutants and generating additional ones, we gathered 44 Ustilago maydis strains lacking single core effectors as well as 9 strains contain-ing multiple deletions of core effector gene families. Pathogenicity assays revealed that 20 of these 53 mutant strains were affected in virulence. Among the 33 mutants that had no obvious phenotypic changes, 13 carried additional, sequence-divergent, structurally similar paralogs. We report a virulence contribution of seven previously uncharacterized single core effectors and of one effector family. Our results help to prioritize effectors for understanding U. maydis virulence and provide genetic re-sources for further characterization.