https://www.cell.com/trends/immunology/pdf/S1471-4906(14)00094-5.pdf

Plant pattern-recognition receptors.

Plants are constantly exposed to would-be pathogens and pests, and thus have a sophisticated immune system to ward off these threats, which otherwise can have devastating ecological and economic consequences on ecosystems and agriculture. Plants employ receptor kinases (RKs) and receptor-like proteins (RLPs) as pattern recognition receptors (PRRs) to monitor their apoplastic environment and detect non-self and damaged-self patterns as signs of potential danger. Plant PRRs contribute to both basal and non-host resistances, and treatment with pathogen-/microbe-associated molecular patterns (PAMPs/MAMPs) or damage-associated molecular patterns (DAMPs) recognized by plant PRRs induces both local and systemic immunity. Here, we comprehensively review known PAMPs/DAMPs recognized by plants as well as the plant PRRs described to date. In particular, we describe the different methods that can be used to identify PAMPs/DAMPs and PRRs. Finally, we emphasize the emerging biotechnological potential use of PRRs to improve broad-spectrum, and potentially durable, disease resistance in crops.

Function, Discovery, and Exploitation of Plant Pattern Recognition Receptors for Broad-Spectrum Disease Resistance

Plants solely rely on innate immunity of each individual cell to deal with a diversity of microbes in the environment. Extracellular recognition of microbe- and host damage-associated molecular patterns leads to the first layer of inducible defenses, termed pattern-triggered immunity (PTI). In plants, pattern recognition receptors (PRRs) described to date are all membrane-associated receptor-like kinases or receptor-like proteins, reflecting the prevalence of apoplastic colonization of plant-infecting microbes. An increasing inventory of elicitor-active patterns and PRRs indicates that a large number of them are limited to a certain range of plant groups/species, pointing to dynamic and convergent evolution of pattern recognition specificities. In addition to common molecular principles of PRR signaling, recent studies have revealed substantial diversification between PRRs in their functions and regulatory mechanisms. This serves to confer robustness and plasticity to the whole PTI system in natural infections, wherein different PRRs are simultaneously engaged and faced with microbial assaults. We review the functional significance and molecular basis of PRR-mediated pathogen recognition and disease resistance, and also an emerging role for PRRs in homeostatic association with beneficial or commensal microbes.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/tpj.13808

Pattern recognition receptors and signaling in plant-microbe interactions.

Virus Diseases of Peanut

We identified a glycoside hydrolase family 12 (GH12) protein, XEG1, produced by the soybean pathogen Phytophthora sojae that exhibits xyloglucanase and β-glucanase activity. It acts as an important virulence factor during P. sojae infection but also acts as a pathogen-associated molecular pattern (PAMP) in soybean (Glycine max) and solanaceous species, where it can trigger defense responses including cell death. GH12 proteins occur widely across microbial taxa, and many of these GH12 proteins induce cell death in Nicotiana benthamiana. The PAMP activity of XEG1 is independent of its xyloglucanase activity. XEG1 can induce plant defense responses in a BAK1-dependent manner. The perception of XEG1 occurs independently of the perception of ethylene-inducing xylanase. XEG1 is strongly induced in P. sojae within 30 min of infection of soybean and then slowly declines. Both silencing and overexpression of XEG1 in P. sojae severely reduced virulence. Many P. sojae RXLR effectors could suppress defense responses induced by XEG1, including several that are expressed within 30 min of infection. Therefore, our data suggest that PsXEG1 contributes to P. sojae virulence, but soybean recognizes PsXEG1 to induce immune responses, which in turn can be suppressed by RXLR effectors. XEG1 thus represents an apoplastic effector that is recognized via the plant’s PAMP recognition machinery.

/pdf/a-phytophthora-sojae-glycoside-hydrolase-12-protein-is-a-361c5dy55h.pdf

A Phytophthora sojae Glycoside Hydrolase 12 Protein Is a Major Virulence Factor during Soybean Infection and Is Recognized as a PAMP

LepR3, found in the Brassica napus cv 'Surpass 400', provides race-specific resistance to the fungal pathogen Leptosphaeria maculans, which was overcome after great devastation in Australia in 2004. We investigated the LepR3 locus to identify the genetic basis of this resistance interaction. We employed a map-based cloning strategy, exploiting collinearity with the Arabidopsis thaliana and Brassica rapa genomes to enrich the map and locate a candidate gene. We also investigated the interaction of LepR3 with the L. maculans avirulence gene AvrLm1 using transgenics. LepR3 was found to encode a receptor-like protein (RLP). We also demonstrated that avirulence towards LepR3 is conferred by AvrLm1, which is responsible for both the Rlm1 and LepR3-dependent resistance responses in B. napus. LepR3 is the first functional B. napus disease resistance gene to be cloned. AvrLm1's interaction with two independent resistance loci, Rlm1 and LepR3, highlights the need to consider redundant phenotypes in 'gene-for-gene' interactions and offers an explanation as to why LepR3 was overcome so rapidly in parts of Australia.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.12043

N.J. Larkan

Papers

The Brassica napus blackleg resistance gene LepR3 encodes a receptor-like protein triggered by the Leptosphaeria maculans effector AVRLM1.