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All Roads Lead to Susceptibility: The Many Modes of Action of Fungal and Oomycete Intracellular Effectors.
He, Q, McLellan, H, Boevink, PC, Birch, PRJ
Plant communications. 2020;(4):100050
Abstract
The ability to secrete effector proteins that can enter plant cells and manipulate host processes is a key determinant of what makes a successful plant pathogen. Here, we review intracellular effectors from filamentous (fungal and oomycete) phytopathogens and the host proteins and processes that are targeted to promote disease. We cover contrasting virulence strategies and effector modes of action. Filamentous pathogen effectors alter the fates of host proteins that they target, changing their stability, their activity, their location, and the protein partners with which they interact. Some effectors inhibit target activity, whereas others enhance or utilize it, and some target multiple host proteins. We discuss the emerging topic of effectors that target negative regulators of immunity or other plant proteins with activities that support susceptibility. We also highlight the commonly targeted host proteins that are manipulated by effectors from multiple pathogens, including those representing different kingdoms of life.
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RNAi-Based Biofungicides as a Promising Next-Generation Strategy for Controlling Devastating Gray Mold Diseases.
Islam, MT, Sherif, SM
International journal of molecular sciences. 2020;(6)
Abstract
Botrytis cinerea is one of the most critical agro-economic phytopathogens and has been reported to cause gray mold disease in more than 1000 plant species. Meanwhile, small interfering RNA (siRNA), which induce RNA interference (RNAi), are involved in both host immunity and pathogen virulence. B. cinerea has been reported to use both siRNA effectors and host RNAi machinery to facilitate the progression of gray mold in host species. Accordingly, RNAi-based biofungicides that use double-stranded RNA (dsRNA) to target essential fungal genes are considered an emerging approach for controlling devastating gray mold diseases. Furthermore, spray-induced gene silencing (SIGS), in which the foliar application of dsRNA is used to silence the pathogen virulence genes, holds great potential as an alternative to host-induced gene silencing (HIGS). Recently, SIGS approaches have attracted research interest, owing to their ability to mitigate both pre- and post-harvest B. cinerea infections. The RNAi-mediated regulation of host immunity and susceptibility in B. cinerea-host interactions are summarized in this review, along with the limitations of the current knowledge of RNAi-based biofungicides, especially regarding SIGS approaches for controlling gray mold diseases under field conditions.
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Plant immunity in signal integration between biotic and abiotic stress responses.
Saijo, Y, Loo, EP
The New phytologist. 2020;(1):87-104
Abstract
Plants constantly monitor and cope with the fluctuating environment while hosting a diversity of plant-inhabiting microbes. The mode and outcome of plant-microbe interactions, including plant disease epidemics, are dynamically and profoundly influenced by abiotic factors, such as light, temperature, water and nutrients. Plants also utilize associations with beneficial microbes during adaptation to adverse conditions. Elucidation of the molecular bases for the plant-microbe-environment interactions is therefore of fundamental importance in the plant sciences. Following advances into individual stress signaling pathways, recent studies are beginning to reveal molecular intersections between biotic and abiotic stress responses and regulatory principles in combined stress responses. We outline mechanisms underlying environmental modulation of plant immunity and emerging roles for immune regulators in abiotic stress tolerance. Furthermore, we discuss how plants coordinate conflicting demands when exposed to combinations of different stresses, with attention to a possible determinant that links initial stress response to broad-spectrum stress tolerance or prioritization of specific stress tolerance.
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Structural specificity in plant-filamentous pathogen interactions.
Lacaze, A, Joly, DL
Molecular plant pathology. 2020;(11):1513-1525
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Abstract
Plant diseases bear names such as leaf blights, root rots, sheath blights, tuber scabs, and stem cankers, indicating that symptoms occur preferentially on specific parts of host plants. Accordingly, many plant pathogens are specialized to infect and cause disease in specific tissues and organs. Conversely, others are able to infect a range of tissues, albeit often disease symptoms fluctuate in different organs infected by the same pathogen. The structural specificity of a pathogen defines the degree to which it is reliant on a given tissue, organ, or host developmental stage. It is influenced by both the microbe and the host but the processes shaping it are not well established. Here we review the current status on structural specificity of plant-filamentous pathogen interactions and highlight important research questions. Notably, this review addresses how constitutive defence and induced immunity as well as virulence processes vary across plant organs, tissues, and even cells. A better understanding of the mechanisms underlying structural specificity will aid targeted approaches for plant health, for instance by considering the variation in the nature and the amplitude of defence responses across distinct plant organs and tissues when performing selective breeding.
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PRRs and NB-LRRs: From Signal Perception to Activation of Plant Innate Immunity.
Noman, A, Aqeel, M, Lou, Y
International journal of molecular sciences. 2019;(8)
Abstract
To ward off pathogens and pests, plants use a sophisticated immune system. They use pattern-recognition receptors (PRRs), as well as nucleotide-binding and leucine-rich repeat (NB-LRR) domains, for detecting nonindigenous molecular signatures from pathogens. Plant PRRs induce local and systemic immunity. Plasma-membrane-localized PRRs are the main components of multiprotein complexes having additional transmembrane and cytosolic kinases. Topical research involving proteins and their interactive partners, along with transcriptional and posttranscriptional regulation, has extended our understanding of R-gene-mediated plant immunity. The unique LRR domain conformation helps in the best utilization of a surface area and essentially mediates protein-protein interactions. Genome-wide analyses of inter- and intraspecies PRRs and NB-LRRs offer innovative information about their working and evolution. We reviewed plant immune responses with relevance to PRRs and NB-LRRs. This article focuses on the significant functional diversity, pathogen-recognition mechanisms, and subcellular compartmentalization of plant PRRs and NB-LRRs. We highlight the potential biotechnological application of PRRs and NB-LRRs to enhance broad-spectrum disease resistance in crops.
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Stressed Out About Hormones: How Plants Orchestrate Immunity.
Bürger, M, Chory, J
Cell host & microbe. 2019;(2):163-172
Abstract
Plants are under relentless challenge by pathogenic bacteria, fungi, and oomycetes, for whom they provide a resource of living space and nutrients. Upon detection of pathogens, plants carry out multiple layers of defense response, orchestrated by a tightly organized network of hormones. In this review, we provide an overview of the phytohormones involved in immunity and the ways pathogens manipulate their biosynthesis and signaling pathways. We highlight recent developments, including the discovery of a defense signaling molecule, new insights into hormone biosynthesis, and the increasing importance of signaling hubs at which hormone pathways intersect.
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A Report on Fungal (1→3)-α-d-glucans: Properties, Functions and Application.
Złotko, K, Wiater, A, Waśko, A, Pleszczyńska, M, Paduch, R, Jaroszuk-Ściseł, J, Bieganowski, A
Molecules (Basel, Switzerland). 2019;(21)
Abstract
The cell walls of fungi are composed of glycoproteins, chitin, and α- and β-glucans. Although there are many reports on β-glucans, α-glucan polysaccharides are not yet fully understood. This review characterizes the physicochemical properties and functions of (1→3)-α-d-glucans. Particular attention has been paid to practical application and the effect of glucans in various respects, taking into account unfavourable effects and potential use. The role of α-glucans in plant infection has been proven, and collected facts have confirmed the characteristics of Aspergillus fumigatus infection associated with the presence of glucan in fungal cell wall. Like β-glucans, there are now evidence that α-glucans can also stimulate the immune system. Moreover, α-d-glucans have the ability to induce mutanases and can thus decompose plaque.
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Structural, Functional, and Genomic Diversity of Plant NLR Proteins: An Evolved Resource for Rational Engineering of Plant Immunity.
Monteiro, F, Nishimura, MT
Annual review of phytopathology. 2018;:243-267
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Abstract
Plants employ a diverse intracellular system of NLR (nucleotide binding-leucine-rich repeat) innate immune receptors to detect pathogens of all types. These receptors represent valuable agronomic traits that plant breeders rely on to maximize yield in the face of devastating pathogens. Despite their importance, the mechanistic underpinnings of NLR-based disease resistance remain obscure. The rapidly increasing numbers of plant genomes are revealing a diverse array of NLR-type immune receptors. In parallel, mechanistic studies are describing diverse functions for NLR immune receptors. In this review, we intend to broadly describe how the structural, functional, and genomic diversity of plant immune receptors can provide a valuable resource for rational engineering of plant immunity.
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Plant cell wall-mediated immunity: cell wall changes trigger disease resistance responses.
Bacete, L, Mélida, H, Miedes, E, Molina, A
The Plant journal : for cell and molecular biology. 2018;(4):614-636
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Abstract
Plants have evolved a repertoire of monitoring systems to sense plant morphogenesis and to face environmental changes and threats caused by different attackers. These systems integrate different signals into overreaching triggering pathways which coordinate developmental and defence-associated responses. The plant cell wall, a dynamic and complex structure surrounding every plant cell, has emerged recently as an essential component of plant monitoring systems, thus expanding its function as a passive defensive barrier. Plants have a dedicated mechanism for maintaining cell wall integrity (CWI) which comprises a diverse set of plasma membrane-resident sensors and pattern recognition receptors (PRRs). The PRRs perceive plant-derived ligands, such as peptides or wall glycans, known as damage-associated molecular patterns (DAMPs). These DAMPs function as 'danger' alert signals activating DAMP-triggered immunity (DTI), which shares signalling components and responses with the immune pathways triggered by non-self microbe-associated molecular patterns that mediate disease resistance. Alteration of CWI by impairment of the expression or activity of proteins involved in cell wall biosynthesis and/or remodelling, as occurs in some plant cell wall mutants, or by wall damage due to colonization by pathogens/pests, activates specific defensive and growth responses. Our current understanding of how these alterations of CWI are perceived by the wall monitoring systems is scarce and few plant sensors/PRRs and DAMPs have been characterized. The identification of these CWI sensors and PRR-DAMP pairs will help us to understand the immune functions of the wall monitoring system, and might allow the breeding of crop varieties and the design of agricultural strategies that would enhance crop disease resistance.
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Multiple strategies for pathogen perception by plant immune receptors.
Cesari, S
The New phytologist. 2018;(1):17-24
Abstract
Contents Summary 17 I. Introduction 17 II. Pathogen perception by NLRs: from direct recognition to integrated decoys 18 III. Multiple activation and signaling pathways for NLRs 18 IV. How to engineer NLR-mediated disease resistance? 21 V. Conclusion 23 Acknowledgements 23 References 23 SUMMARY Plants have evolved a complex immune system to protect themselves against phytopathogens. A major class of plant immune receptors called nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs) is ubiquitous in plants and is widely used for crop disease protection, making these proteins critical contributors to global food security. Until recently, NLRs were thought to be conserved in their modular architecture and functional features. Investigation of their biochemical, functional and structural properties has revealed fascinating mechanisms that enable these proteins to perceive a wide range of pathogens. Here, I review recent insights demonstrating that NLRs are more mechanistically and structurally diverse than previously thought. I also discuss how these findings provide exciting future prospects to improve plant disease resistance.