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1.
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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2.
Harnessing the microbiome to control plant parasitic weeds.
Masteling, R, Lombard, L, de Boer, W, Raaijmakers, JM, Dini-Andreote, F
Current opinion in microbiology. 2019;:26-33
Abstract
Microbiomes can significantly expand the genomic potential of plants, contributing to nutrient acquisition, plant growth promotion and tolerance to (a)biotic stresses. Among biotic stressors, root parasitic weeds (RPWs), mainly of the genera Orobanche, Phelipanche and Striga, are major yield-limiting factors of a wide range of staple crops, particularly in developing countries. Here, we provide a conceptual synthesis of putative mechanisms by which soil and plant microbiomes could be harnessed to control RPWs. These mechanisms are partitioned in direct and indirect modes of action and discussed in the context of past and present studies on microbe-mediated suppression of RPWs. Specific emphasis is given to the large but yet unexplored potential of root-associated microorganisms to interfere with the chemical signalling cascade between the host plant and the RPWs. We further provide concepts and ideas for future research directions and prospective designs of novel control strategies.
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3.
Development of Targeting Induced Local Lesions IN Genomes (TILLING) Populations in Small Grain Crops by Ethyl Methanesulfonate Mutagenesis.
Singh, L, Schoen, A, Mahlandt, A, Chhabra, B, Steadham, J, Tiwari, V, Rawat, N
Journal of visualized experiments : JoVE. 2019;(149)
Abstract
Targeting Induced Local Lesions IN Genomes (TILLING) is a powerful reverse genetics tool that includes chemical mutagenesis and detection of sequence variation in target genes. TILLING is a highly valuable functional genomics tool for gene validation, especially in small grains in which transformation-based approaches hold serious limitations. Developing a robust mutagenized population is key to determining the efficiency of a TILLING-based gene validation study. A TILLING population with a low overall mutation frequency indicates that an impractically large population must be screened to find desired mutations, whereas a high mutagen concentration leads to high mortality in the population, leading to an insufficient number of mutagenized individuals. Once an effective population is developed, there are multiple ways to detect mutations in a gene of interest, and the choice of platform depends upon the experimental scale and availability of resources. The Cel-1 assay and agarose gel-based approach for mutant identification is convenient, reproducible, and a less resource-intensive platform. It is advantageous in that it is simple, requiring no computational knowledge, and it is especially suitable for validation of a small number of genes with basic lab equipment. In the present article, described are the methods for development of a good TILLING population, including preparation of the dosage curve, mutagenesis and maintenance of the mutant population, and screening of the mutant population using the PCR-based Cel-1 assay.
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4.
Organ-specific differences in endogenous phytohormone and antioxidative responses in potato upon PSTVd infection.
Milanović, J, Oklestkova, J, Majdandžić, A, Novák, O, Mihaljević, S
Journal of plant physiology. 2019;:107-114
Abstract
Although structurally simple, viroids can trigger numerous changes in host plants and cause loss of yield in agronomically important crops. This study investigated changes in the endogenous status of phytohormones and antioxidant enzyme activity in Solanum tuberosum cv. Désirée in response to Potato spindle tuber viroid (PSTVd) infection. Phytohormone analysis showed that the content of endogenous jasmonic acid (JA) and its precursor cis-OPDA significantly increased in leaves, while the content of castasterone (CS) increased in both leaves and tubers of systemically infected plants compared to mock-inoculated control plants at 8 weeks post-inoculation. The indole-3-acetic acid content moderately increased only in tubers, while no differences in salicylic acid and abscisic acid content were observed between infected and control plants. Changes in endogenous phytohormone content were associated with upregulated expression of genes involved in the biosynthesis of JA and brassinosteroids, and the metabolism of auxins. Additionally, PSTVd infection provoked overproduction of hydrogen peroxide, which coincided with increased activity of guaiacol peroxidase in leaves and ascorbate peroxidase in potato tubers. The activity of catalase decreased in leaves, while superoxide dismutase activity remained steady regardless of the treatment and organ type. Total ascorbate and glutathione did not change significantly, although a shift towards oxidized forms was observed. Results suggest the existence of organ-specific differences in phytohormone and antioxidative responses in potato upon PSTVd infection. Possible effects of the observed changes on symptom development are discussed.
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5.
Pid3-I1 is a race-specific partial-resistance allele at the Pid3 blast resistance locus in rice.
Inukai, T, Nagashima, S, Kato, M
TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik. 2019;(2):395-404
Abstract
The rice blast resistance QTL detected on chromosome 6 in MC276 is Pid3-I1, one of the multiple alleles at the Pid3 locus. Pid3-I1 shows race-specific partial resistance. Many of the quantitative trait loci (QTLs) for rice blast resistance reported to date remain unidentified. In the present study, we focused on qBRM6.2, a known blast-resistance QTL in experimental resistant rice line MC276. A CO39 near-isogenic line (NIL) carrying qBRM6.2 from MC276 was developed here, and we showed that qBRM6.2 resistance was partial but race specific to Japanese blast isolates using the NIL. Because defense genes in the NIL were expressed sooner than those in CO39 after inoculation with a blast isolate, qBRM6.2 resistance appeared to be an induced resistance. Next, we demonstrated that qBRM6.2 was located within a 123-kb interval on chromosome 6. Among the six genes annotated in the interval, only four genes appeared to be functional. Among these four, a polymorphism between CO39 and the NIL for qBRM6.2 at the amino acid sequence level was detected only in Os06g0330400 that encodes a fatty acid hydroxylase domain-containing protein and in Os06g0330100, the blast resistance locus Pid3, that encodes a nucleotide-binding site-leucine-rich repeat protein. Moreover, the allele at the Pid3 locus in the NIL was Pid3-I1, originally identified as a complete blast resistance gene in Kasalath. To clarify whether Pid3-I1 is qBRM6.2, we investigated the resistance phenotype of Pid3-I1 to Japanese isolates using Nipponbare transgenic lines that express Pid3-I1. The results showed that Pid3-I1 was a race-specific but partial-resistance allele at the Pid3 locus, suggesting strongly that Pid3-I1 is qBRM6.2. The discrepancy in the phenotype of Pid3-I1 between the present and previous reports is also discussed.
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6.
Trichoderma/pathogen/plant interaction in pre-harvest food security.
Silva, RN, Monteiro, VN, Steindorff, AS, Gomes, EV, Noronha, EF, Ulhoa, CJ
Fungal biology. 2019;(8):565-583
Abstract
Large losses before crop harvesting are caused by plant pathogens, such as viruses, bacteria, oomycetes, fungi, and nematodes. Among these, fungi are the major cause of losses in agriculture worldwide. Plant pathogens are still controlled through application of agrochemicals, causing human disease and impacting environmental and food security. Biological control provides a safe alternative for the control of fungal plant pathogens, because of the ability of biocontrol agents to establish in the ecosystem. Some Trichoderma spp. are considered potential agents in the control of fungal plant diseases. They can interact directly with roots, increasing plant growth, resistance to diseases, and tolerance to abiotic stress. Furthermore, Trichoderma can directly kill fungal plant pathogens by antibiosis, as well as via mycoparasitism strategies. In this review, we will discuss the interactions between Trichoderma/fungal pathogens/plants during the pre-harvest of crops. In addition, we will highlight how these interactions can influence crop production and food security. Finally, we will describe the future of crop production using antimicrobial peptides, plants carrying pathogen-derived resistance, and plantibodies.
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7.
Transposable Elements Adaptive Role in Genome Plasticity, Pathogenicity and Evolution in Fungal Phytopathogens.
Mat Razali, N, Cheah, BH, Nadarajah, K
International journal of molecular sciences. 2019;(14)
Abstract
Transposable elements (TEs) are agents of genetic variability in phytopathogens as they are a source of adaptive evolution through genome diversification. Although many studies have uncovered information on TEs, the exact mechanism behind TE-induced changes within the genome remains poorly understood. Furthermore, convergent trends towards bigger genomes, emergence of novel genes and gain or loss of genes implicate a TE-regulated genome plasticity of fungal phytopathogens. TEs are able to alter gene expression by revamping the cis-regulatory elements or recruiting epigenetic control. Recent findings show that TEs recruit epigenetic control on the expression of effector genes as part of the coordinated infection strategy. In addition to genome plasticity and diversity, fungal pathogenicity is an area of economic concern. A survey of TE distribution suggests that their proximity to pathogenicity genes TEs may act as sites for emergence of novel pathogenicity factors via nucleotide changes and expansion or reduction of the gene family. Through a systematic survey of literature, we were able to conclude that the role of TEs in fungi is wide: ranging from genome plasticity, pathogenicity to adaptive behavior in evolution. This review also identifies the gaps in knowledge that requires further elucidation for a better understanding of TEs' contribution to genome architecture and versatility.
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8.
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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9.
Rapid burst of ethylene evolution by premature seed: A warning sign for the onset of spongy tissue disorder in Alphonso mango fruit?
Shivashankar, S, Sumathi, M
Journal of biosciences. 2019;(6)
Abstract
Moisture stress induced in premature seeds due to the breakdown of funiculus in Alphonso mango led to the burst of ethylene evolution, which in turn caused a sudden increase of polyphenol oxidase activity in the pulp, resulting in the development of a black spot near the seed base. Reduced levels of very long chain fatty acids in 70% mature seeds with black spots were associated with a sudden increase of cytokinins followed by a rapid rise of starch-metabolizing enzymes culminating in the onset of pre-germination events. Concurrently, an overproduction of p-OH benzoic acid inhibited amylase and polygalacturonase enzymes and led to partial degradation of the stored starch and pectin in the pulp. A parallel drop in climacteric ethylene production by the pulp led to incomplete ripening coupled with changes in composition, texture and aroma of the pulp, characteristic of spongy tissue. The results have provided strong experimental evidence to support the fact that increased competition for resources among developing fruits for the synthesis of seed fat plays a critical role in spongy tissue formation in Alphonso mango. The major highlight of the study is that rapid ethylene evolution by premature seed is an early warning sign for the initiation of spongy tissue formation in Alphonso mango.
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10.
Coinfection Organizes Epidemiological Networks of Viruses and Hosts and Reveals Hubs of Transmission.
McLeish, M, Sacristán, S, Fraile, A, García-Arenal, F
Phytopathology. 2019;(6):1003-1010
Abstract
Multiple virus infections affect the competence of host plants to transmit disease. The effects of coinfection on transmission are expected to produce ecologically complex pathogen and host-pathogen interactions. However, the prediction of disease risk will rely on untangling nonrandom from random patterns of infection to identify underlying processes that drive these interactions. Are the spatial distributions of infections in complex multispecies systems random or not? For the first time, we use an empirical evaluation of this basic but nontrivial question to test the hypothesis that coinfection contributes to (i) nonrandom ecological interactions between hosts and viruses and (ii) structuring infection distributions. We use a novel approach that decomposed the ecological interactions of 11 generalist viruses in 47 host species in four habitats of an agroecosystem into single-infection and coinfection "modes." Then, we relate ecological structuring in infection networks to the distribution of infection using generalized regression models. The network analyses of coinfection showed that virus-host interactions occurred more often than expected at random in one of the four habitats, Edge. A pattern of specific interactions was shared between Edge and the ecosystem, indicating scale invariance. The regression modeling also showed that the plant community characteristics of Edge were unique in explaining infection distributions. The results showed that the spatial distribution of infection at the ecosystem level was not only a species-specific phenomenon but also, strongly structured by specific virus-virus and host-virus interactions. The evidence of scale invariance and the special role of Edge as a reservoir suggest that ecological interactions were less strongly structured by community differences among habitats than by wider-scale processes and traits underlying the interactions. Addressing whether reservoir communities significantly contribute to epidemiological processes at the ecosystem scale is a promising avenue for future research.