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 ...

Recognition of endogenous molecules acting as 'damage-associated molecular patterns' (DAMPs) is a key feature of immunity in both animals and plants. Oligogalacturonides (OGs), i.e. fragments derived from the hydrolysis of homogalacturonan, a major component of pectin are a well known class of DAMPs that activate immunity and protect plants against several microbes. However, hyper-accumulation of OGs severely affects growth, eventually leading to cell death and clearly pointing to OGs as players in the growth-defence trade-off. Here we report a mechanism that may control the homeostasis of OGs avoiding their deleterious hyper-accumulation. By combining affinity chromatography on acrylamide-trapped OGs and other procedures, an Arabidopsis thaliana enzyme that specifically oxidizes OGs was purified and identified. The enzyme was named OG OXIDASE 1 (OGOX1) and shown to be encoded by the gene At4g20830. As a typical flavo-protein, OGOX1 is a sulphite-sensitive H O -producing enzyme that displays maximal activity on OGs with a degree of polymerization >4. OGOX1 belongs to a large gene family of mainly apoplastic putative FAD-binding proteins [Berberine Bridge Enzyme-like (BBE-like); 27 members], whose biochemical and biological function is largely unexplored. We have found that at least four BBE-like enzymes in Arabidopsis are OG oxidases (OGOX1-4). Oxidized OGs display a reduced capability of activating the immune responses and are less hydrolysable by fungal polygalacturonases. Plants overexpressing OGOX1 are more resistant to Botrytis cinerea, pointing to a crucial role of OGOX enzymes in plant immunity.

Summary The plant cell wall is the barrier that pathogens must overcome to cause a disease, and to this end they secrete enzymes that degrade the various cell wall components. Due to the complexity of these components, several types of oligosaccharide fragments may be released during pathogenesis and some of these can act as damage‐associated molecular patterns (DAMPs). Well‐known DAMPs are the oligogalacturonides (OGs) released upon degradation of homogalacturonan and the products of cellulose breakdown, i.e. the cellodextrins (CDs). We have previously reported that four Arabidopsis berberine bridge enzyme‐like (BBE‐like) proteins (OGOX1–4) oxidize OGs and impair their elicitor activity. We show here that another Arabidopsis BBE‐like protein, which is expressed coordinately with OGOX1 during immunity, specifically oxidizes CDs with a preference for cellotriose (CD3) and longer fragments (CD4–CD6). Oxidized CDs show a negligible elicitor activity and are less easily utilized as a carbon source by the fungus Botrytis cinerea. The enzyme, named CELLOX (cellodextrin oxidase), is encoded by the gene At4 g20860. Plants overexpressing CELLOX display an enhanced resistance to B. cinerea, probably because oxidized CDs are a less valuable carbon source. Thus, the capacity to oxidize and impair the biological activity of cell wall‐derived oligosaccharides seems to be a general trait of the family of BBE‐like proteins, which may serve to homeostatically control the level of DAMPs to prevent their hyperaccumulation.

Bacterial CRISPR systems have been widely adopted to create operator-specified site-specific nucleases. Such nuclease action commonly results in loss-of-function alleles, facilitating functional analysis of genes and gene families We conducted a systematic comparison of components and T-DNA architectures for CRISPR-mediated gene editing in Arabidopsis, testing multiple promoters, terminators, sgRNA backbones and Cas9 alleles. We identified a T-DNA architecture that usually results in stable (i.e. homozygous) mutations in the first generation after transformation. Notably, the transcription of sgRNA and Cas9 in head-to-head divergent orientation usually resulted in highly active lines. Our Arabidopsis data may prove useful for optimization of CRISPR methods in other plants.