Plants deploy cell-surface and intracellular leucine rich-repeat domain (LRR) immune receptors to detect pathogens 1 . LRR receptor kinases and LRR receptor proteins at the plasma membrane recognize microorganism-derived molecules to elicit pattern-triggered immunity (PTI), whereas nucleotide-binding LRR proteins detect microbial effectors inside cells to confer effector-triggered immunity (ETI). Although PTI and ETI are initiated in different host cell compartments, they rely on the transcriptional activation of similar sets of genes 2 , suggesting pathway convergence upstream of nuclear events. Here we report that PTI triggered by the Arabidopsis LRR receptor protein RLP23 requires signalling-competent dimers of the lipase-like proteins EDS1 and PAD4, and of ADR1 family helper nucleotide-binding LRRs, which are all components of ETI. The cell-surface LRR receptor kinase SOBIR1 links RLP23 with EDS1, PAD4 and ADR1 proteins, suggesting the formation of supramolecular complexes containing PTI receptors and transducers at the inner side of the plasma membrane. We detected similar evolutionary patterns in LRR receptor protein and nucleotide-binding LRR genes across Arabidopsis accessions; overall higher levels of variation in LRR receptor proteins than in LRR receptor kinases are consistent with distinct roles of these two receptor families in plant immunity. We propose that the EDS1-PAD4-ADR1 node is a convergence point for defence signalling cascades, activated by both surface-resident and intracellular LRR receptors, in conferring pathogen immunity.Arabidopsis thaliana (hereafter Arabidopsis) cell-surface LRR receptor kinases (LRR-RKs) and LRR receptor protein (LRR-RP)-SOBIR1 complexes recruit the co-receptor BAK1 and signal through receptor-like cytoplasmic kinases (RLCKs) to elicit PTI 3 . Intracellular coiled-coil (CC)-nucleotide-binding LRR (NLR) or TOLL-INTERLEUKIN 1 RECEP-TOR (TIR)-NLR receptors 4 require ADR1-type and NRG1-type helper NLRs (hNLRs) and the lipase-like EDS1 family proteins EDS1, PAD4 and SAG101 to confer ETI 5,6 . While the defence outputs for PTI and ETI are qualitatively similar 2 , where and how pathways activated in different cell compartments converge remain unclear. Effective plant defence relies on mutual potentiation of PTI and ETI pathways 7,8 , suggesting mechanistic links between these two tiers of the plant immune system. RLCKs PBL30 and PBL31 mediate PTIThe Arabidopsis class VII RLCK (RLCK-VII) BIK1 promotes LRR-RK-mediated PTI but is a negative regulator of LRR-RP-mediated PTI 9 . To identify RLCK-VII members with positive roles in LRR-RP-dependent PTI, we screened an Arabidopsis RLCK-VII transfer DNA mutant library 10 for ethylene production elicited by fungal pg13(At) 11 , oomycete nlp20 and bacterial eMax (which are recognized by RLP42, RLP23 and RLP1, respectively) 3 (Extended Data Fig. 1a). A pbl31 mutant was defective in response to these elicitors compared with wild-type plants (Columbia-0 (Col-0)) (Extended Data Fig. 1a). PBL31 belongs to RLCK-VII subfamily 7, together ...

Plants deploy numerous cell surface-localized pattern-recognition receptors (PRRs) to perceive host- and microbe-derived molecular patterns that are specifically released during infection and activate defense responses. The activation of the mitogen-activated protein kinases MPK3, MPK4, and MPK6 (MPK3/4/6) is a hallmark of immune system activation by all known PRRs and is crucial for establishing disease resistance. The MAP kinase kinase kinase (MAPKKK) MEKK1 controls MPK4 activation, but the MAPKKKs responsible for MPK3/6 activation downstream of diverse PRRs and how the perception of diverse molecular patterns leads to the activation of MAPKKKs remain elusive. Here, we show that two highly related MAPKKKs, MAPKKK3 and MAPKKK5, mediate MPK3/6 activation by at least four PRRs and confer resistance to bacterial and fungal pathogens in The receptor-like cytoplasmic kinases VII (RLCK VII), which act downstream of PRRs, directly phosphorylate MAPKKK5 Ser-599, which is required for pattern-triggered MPK3/6 activation, defense gene expression, and disease resistance. Surprisingly, MPK6 further phosphorylates MAPKKK5 Ser-682 and Ser-692 to enhance MPK3/6 activation and disease resistance, pointing to a positive feedback mechanism. Finally, MEKK1 Ser-603 is phosphorylated by both RLCK VII and MPK4, which is required for pattern-triggered MPK4 activation. These findings illustrate central mechanisms by which multiple PRRs activate MAPK cascades and disease resistance.