New insights into plant cell surface immune receptor function and evolution
University Tübingen, Center of Plant Molecular Biology, Department of Plant Biochemistry
Plants employ cell surface and intracellular immune receptors with leucine rich-repeat (LRRs) to detect pathogens. LRR receptor kinases (LRR-RKs) and LRR receptor-like proteins (LRR-RPs) sense extracellular microbe-derived molecules to confer pattern-triggered immunity (PTI), while nucleotide-binding LRR (NLR) proteins detect microbial effectors inside the cell to confer effector-triggered immunity (ETI). Despite PTI and ETI signalling being initiated in different compartments, both rely on the transcriptional activation of similar sets of genes, suggesting convergence in signalling upstream of nuclear events. We have identified two sets of molecules, helper NLRs from the ADR1 (ACTIVATED DISEASE RESISTANCE 1) family as well as lipase-like proteins EDS1 (ENHANCED DISEASE SUSCEPTIBILITY 1) and PAD4 (PHYTOALEXIN DEFICIENT 4), to be required not only for ETI, but also for PTI. We find that the LRR-RK SUPPRESSOR OF BRASSINOSTEROID INSENSITIVE 1 (BRI1)-ASSOCIATED KINASE (BAK1)-INTERACTING RECEPTOR KINASE 1 (SOBIR1) directly links LRR-RPs with the ADR1 helper NLR as well as EDS1 and PAD4, suggesting the formation of constitutive supramolecular signalosome complexes at the inner side of the plasma membrane. We suggest that the EDS1-PAD4-ADR1 node is an essential component and convergence point for immune signaling cascades activated by both surface-resident LRR-RP receptors and intracellular NLR receptors. We further report the identification of two novel pattern recognition receptors implicated in plant immunity to bacterial or oomycete infection.
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Fan L et al. 2022. Nature Commun., 13:1294.