How do plants achieve immunity? Defence without specialized immune cells
TL;DR: Recent developments point towards a multilayered plant innate immune system comprised of self-surveillance, systemic signalling and chromosomal changes that together establish effective immunity.
Abstract: Vertebrates have evolved a sophisticated adaptive immune system that relies on an almost infinite diversity of antigen receptors that are clonally expressed by specialized immune cells that roam the circulatory system. These immune cells provide vertebrates with extraordinary antigen-specific immune capacity and memory, while minimizing self-reactivity. Plants, however, lack specialized mobile immune cells. Instead, every plant cell is thought to be capable of launching an effective immune response. So how do plants achieve specific, self-tolerant immunity and establish immune memory? Recent developments point towards a multilayered plant innate immune system comprised of self-surveillance, systemic signalling and chromosomal changes that together establish effective immunity.
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TL;DR: This review focuses on molecular processes at the interface between plant roots and ISR-eliciting mutualists, and on the progress in the understanding of ISR signaling and systemic defense priming.
Abstract: Beneficial microbes in the microbiome of plant roots improve plant health. Induced systemic resistance (ISR) emerged as an important mechanism by which selected plant growth–promoting bacteria and fungi in the rhizosphere prime the whole plant body for enhanced defense against a broad range of pathogens and insect herbivores. A wide variety of root-associated mutualists, including Pseudomonas, Bacillus, Trichoderma, and mycorrhiza species sensitize the plant immune system for enhanced defense without directly activating costly defenses. This review focuses on molecular processes at the interface between plant roots and ISR-eliciting mutualists, and on the progress in our understanding of ISR signaling and systemic defense priming. The central role of the root-specific transcription factor MYB72 in the onset of ISR and the role of phytohormones and defense regulatory proteins in the expression of ISR in aboveground plant parts are highlighted. Finally, the ecological function of ISR-inducing microbes in the root microbiome is discussed.
1,856 citations
Cites background from "How do plants achieve immunity? Def..."
...Over the years, SAR has been extensively reviewed (139, 171), so here we only discuss the important principles and recent findings....
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...This well-characterized form of pathogen-induced resistance is commonly known as systemic acquired resistance (SAR) (139, 171) and confers enhanced resistance against a broad spectrum of pathogens (Figure 1)....
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TL;DR: This review will provide an update of recent findings related to the integration of ROS signals with an array of signalling pathways aimed at regulating different responses in plants and address signals that confer systemic acquired resistance (SAR) or systemic acquired acclimation (SAA) in plants.
Abstract: Reactive oxygen species (ROS) play an integral role as signalling molecules in the regulation of numerous biological processes such as growth, development, and responses to biotic and/or abiotic stimuli in plants. To some extent, various functions of ROS signalling are attributed to differences in the regulatory mechanisms of respiratory burst oxidase homologues (RBOHs) that are involved in a multitude of different signal transduction pathways activated in assorted tissue and cell types under fluctuating environmental conditions. Recent findings revealed that stress responses in plants are mediated by a temporal-spatial coordination between ROS and other signals that rely on production of stress-specific chemicals, compounds, and hormones. In this review we will provide an update of recent findings related to the integration of ROS signals with an array of signalling pathways aimed at regulating different responses in plants. In particular, we will address signals that confer systemic acquired resistance (SAR) or systemic acquired acclimation (SAA) in plants.
1,414 citations
Cites background from "How do plants achieve immunity? Def..."
...…acclimation (SAA), respectively , and both play an important role in preventing further infection or damage to the entire plant (Karpinski et al., 1999; Rossel et al., 2007; Carr et al., 2010; Szechynska-Hebda et al., 2010; Dempsey and Klessig, 2012; Spoel and Dong, 2012; Shah and Zeier, 2013)....
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TL;DR: High-throughput technologies are revealing interactions between these complex communities and their hosts in unprecedented detail, with significant implications for plant health and productivity.
Abstract: Plant genomes contribute to the structure and function of the plant microbiome, a key determinant of plant health and productivity. High-throughput technologies are revealing interactions between these complex communities and their hosts in unprecedented detail.
1,028 citations
TL;DR: In plant innate immunity, effector-triggered immunity displays remarkable robustness against pathogen disturbance, in part by employing compensatory mechanisms within the defense network.
Abstract: In plant innate immunity, individual cells have the capacity to sense and respond to pathogen attack. Intracellular recognition mechanisms have evolved to intercept perturbations by pathogen virulence factors (effectors) early in host infection and convert it to rapid defense. One key to resistance success is a polymorphic family of intracellular nucleotide-binding/leucine-rich-repeat (NLR) receptors that detect effector interference in different parts of the cell. Effector-activated NLRs connect, in various ways, to a conserved basal resistance network in order to transcriptionally boost defense programs. Effector-triggered immunity displays remarkable robustness against pathogen disturbance, in part by employing compensatory mechanisms within the defense network. Also, the mobility of some NLRs and coordination of resistance pathways across cell compartments provides flexibility to fine-tune immune outputs. Furthermore, a number of NLRs function close to the nuclear chromatin by balancing actions of def...
912 citations
TL;DR: Recent advances in the identification of upstream receptors/sensors and downstream MAPK substrates revealed the molecular mechanisms underlying MAPK functions in plant disease resistance and emerged as battlegrounds of plant-pathogen interactions.
Abstract: Mitogen-activated protein kinase (MAPK) cascades are highly conserved signaling modules downstream of receptors/sensors that transduce extracellular stimuli into intracellular responses in eukaryotes. Plant MAPK cascades play pivotal roles in signaling plant defense against pathogen attack. In this review, we summarize recent advances in the identification of upstream receptors/sensors and downstream MAPK substrates. These findings revealed the molecular mechanisms underlying MAPK functions in plant disease resistance. MAPK cascades have also emerged as battlegrounds of plant-pathogen interactions. Activation of MAPKs is one of the earliest signaling events after plant sensing of pathogen/microbe-associated molecular patterns (PAMPs/MAMPs) and pathogen effectors. MAPK cascades are involved in signaling multiple defense responses, including the biosynthesis/signaling of plant stress/defense hormones, reactive oxygen species (ROS) generation, stomatal closure, defense gene activation, phytoalexin biosynthes...
897 citations
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TL;DR: A detailed understanding of plant immune function will underpin crop improvement for food, fibre and biofuels production and provide extraordinary insights into molecular recognition, cell biology and evolution across biological kingdoms.
Abstract: Many plant-associated microbes are pathogens that impair plant growth and reproduction. Plants respond to infection using a two-branched innate immune system. The first branch recognizes and responds to molecules common to many classes of microbes, including non-pathogens. The second responds to pathogen virulence factors, either directly or through their effects on host targets. These plant immune systems, and the pathogen molecules to which they respond, provide extraordinary insights into molecular recognition, cell biology and evolution across biological kingdoms. A detailed understanding of plant immune function will underpin crop improvement for food, fibre and biofuels production.
10,539 citations
TL;DR: A draft sequence of the rice genome for the most widely cultivated subspecies in China, Oryza sativa L. ssp.indica, by whole-genome shotgun sequencing is produced, with a large proportion of rice genes with no recognizable homologs due to a gradient in the GC content of rice coding sequences.
Abstract: We have produced a draft sequence of the rice genome for the most widely cultivated subspecies in China, Oryza sativa L. ssp. indica, by whole-genome shotgun sequencing. The genome was 466 megabases in size, with an estimated 46,022 to 55,615 genes. Functional coverage in the assembled sequences was 92.0%. About 42.2% of the genome was in exact 20-nucleotide oligomer repeats, and most of the transposons were in the intergenic regions between genes. Although 80.6% of predicted Arabidopsis thaliana genes had a homolog in rice, only 49.4% of predicted rice genes had a homolog in A. thaliana. The large proportion of rice genes with no recognizable homologs is due to a gradient in the GC-content of rice coding sequences.
4,064 citations
TL;DR: Current evidence indicates that MAMPs, DAMPs, and effectors are all perceived as danger signals and induce a stereotypic defense response, and the importance of MAMP/PRR signaling for plant immunity is highlighted.
Abstract: Microbe-associated molecular patterns (MAMPs) are molecular signatures typical of whole classes of microbes, and their recognition plays a key role in innate immunity. Endogenous elicitors are similarly recognized as damage-associated molecular patterns (DAMPs). This review focuses on the diversity of MAMPs/DAMPs and on progress to identify the corresponding pattern recognition receptors (PRRs) in plants. The two best-characterized MAMP/PRR pairs, flagellin/FLS2 and EF-Tu/EFR, are discussed in detail and put into a phylogenetic perspective. Both FLS2 and EFR are leucine-rich repeat receptor kinases (LRR-RKs). Upon treatment with flagellin, FLS2 forms a heteromeric complex with BAK1, an LRR-RK that also acts as coreceptor for the brassinolide receptor BRI1. The importance of MAMP/PRR signaling for plant immunity is highlighted by the finding that plant pathogens use effectors to inhibit PRR complexes or downstream signaling events. Current evidence indicates that MAMPs, DAMPs, and effectors are all perceived as danger signals and induce a stereotypic defense response.
2,801 citations
TL;DR: A model describing the sequence of events leading from initial infection to the induction of defense genes is presented and exciting new data suggest that the mobile signal for SAR might be a lipid molecule.
Abstract: Systemic acquired resistance (SAR) is a mechanism of induced defense that confers long-lasting protection against a broad spectrum of microorganisms. SAR requires the signal molecule salicylic acid (SA) and is associated with accumulation of pathogenesis-related proteins, which are thought to contribute to resistance. Much progress has been made recently in elucidating the mechanism of SAR. Using the model plant Arabidopsis, it was discovered that the isochorismate pathway is the major source of SA during SAR. In response to SA, the positive regulator protein NPR1 moves to the nucleus where it interacts with TGA transcription factors to induce defense gene expression, thus activating SAR. Exciting new data suggest that the mobile signal for SAR might be a lipid molecule. We discuss the molecular and genetic data that have contributed to our understanding of SAR and present a model describing the sequence of events leading from initial infection to the induction of defense genes.
2,744 citations
TL;DR: Deep sequencing of smRNAs revealed a direct relationship between the location of sm RNAs and DNA methylation, perturbation of smRNA biogenesis upon loss of CpG DNA methylisation, and a tendency for smRN as to direct strand-specific DNA methylations in regions of RNA-DNA homology.
2,349 citations