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Mori BA, Coutu C, Erlandson MA, Hegedus DD. Characterization of the swede midge, Contarinia nasturtii, first instar larval salivary gland transcriptome. CURRENT RESEARCH IN INSECT SCIENCE 2023; 4:100064. [PMID: 37575317 PMCID: PMC10415697 DOI: 10.1016/j.cris.2023.100064] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 06/09/2023] [Accepted: 07/11/2023] [Indexed: 08/15/2023]
Abstract
Proteins in saliva of gall-forming insect larvae govern insect-host plant interactions. Contarinia nasturtii, the swede midge, is a pest of brassicaceous vegetables (cabbage, cauliflower, broccoli) and canola. We examined the salivary gland (SG) transcriptome of first instar larvae reared on Brassica napus and catalogued genes encoding secreted proteins that may contribute to the initial stages of larval establishment, the synthesis of plant growth hormones, extra-oral digestion and evasion of host defenses. A significant portion of the secreted proteins with unknown functions were unique to C. nasturtii and were often members of larger gene families organized in genomic clusters with conservation patterns suggesting that they are undergoing selection.
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Affiliation(s)
- Boyd A. Mori
- Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB T6G 2P5, Canada
| | - Cathy Coutu
- Agriculture and Agri-Food Canada, Saskatoon Research and Development Centre, Saskatoon, SK S7N 0×2, Canada
| | - Martin A. Erlandson
- Agriculture and Agri-Food Canada, Saskatoon Research and Development Centre, Saskatoon, SK S7N 0×2, Canada
| | - Dwayne D. Hegedus
- Agriculture and Agri-Food Canada, Saskatoon Research and Development Centre, Saskatoon, SK S7N 0×2, Canada
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Paulmann MK, Wegner L, Gershenzon J, Furch ACU, Kunert G. Pea Aphid ( Acyrthosiphon pisum) Host Races Reduce Heat-Induced Forisome Dispersion in Vicia faba and Trifolium pratense. PLANTS (BASEL, SWITZERLAND) 2023; 12:plants12091888. [PMID: 37176952 PMCID: PMC10181200 DOI: 10.3390/plants12091888] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2023] [Revised: 04/21/2023] [Accepted: 04/28/2023] [Indexed: 05/15/2023]
Abstract
Although phloem-feeding insects such as aphids can cause significant damage to plants, relatively little is known about early plant defenses against these insects. As a first line of defense, legumes can stop the phloem mass flow through a conformational change in phloem proteins known as forisomes in response to Ca2+ influx. However, specialized phloem-feeding insects might be able to suppress the conformational change of forisomes and thereby prevent sieve element occlusion. To investigate this possibility, we triggered forisome dispersion through application of a local heat stimulus to the leaf tips of pea (Pisum sativum), clover (Trifolium pratense) and broad bean (Vicia faba) plants infested with different pea aphid (Acyrthosiphon pisum) host races and monitored forisome responses. Pea aphids were able to suppress forisome dispersion, but this depended on the infesting aphid host race, the plant species, and the age of the plant. Differences in the ability of aphids to suppress forisome dispersion may be explained by differences in the composition and quantity of the aphid saliva injected into the plant. Various mechanisms of how pea aphids might suppress forisome dispersion are discussed.
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Affiliation(s)
- Maria K Paulmann
- Max Planck Institute for Chemical Ecology, Department of Biochemistry, Hans-Knöll-Str. 8, D-07745 Jena, Germany
- Plant Physiology, Matthias Schleiden Institute for Genetics, Bioinformatics and Molecular Botany, Faculty of Biological Science, Friedrich Schiller University Jena, Dornburger Straße 159, D-07743 Jena, Germany
| | - Linus Wegner
- Plant Physiology, Matthias Schleiden Institute for Genetics, Bioinformatics and Molecular Botany, Faculty of Biological Science, Friedrich Schiller University Jena, Dornburger Straße 159, D-07743 Jena, Germany
- Institute of Botany, Justus Liebig University, Heinrich-Buff-Ring 38, 35292 Giessen, Germany
| | - Jonathan Gershenzon
- Max Planck Institute for Chemical Ecology, Department of Biochemistry, Hans-Knöll-Str. 8, D-07745 Jena, Germany
| | - Alexandra C U Furch
- Plant Physiology, Matthias Schleiden Institute for Genetics, Bioinformatics and Molecular Botany, Faculty of Biological Science, Friedrich Schiller University Jena, Dornburger Straße 159, D-07743 Jena, Germany
| | - Grit Kunert
- Max Planck Institute for Chemical Ecology, Department of Biochemistry, Hans-Knöll-Str. 8, D-07745 Jena, Germany
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Sadon P, Corre MN, Lugan R, Boissot N. Aphid adaptation to cucurbits: sugars, cucurbitacin and phloem structure in resistant and susceptible melons. BMC PLANT BIOLOGY 2023; 23:239. [PMID: 37147560 PMCID: PMC10161555 DOI: 10.1186/s12870-023-04248-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Accepted: 04/25/2023] [Indexed: 05/07/2023]
Abstract
BACKGROUND Aphis gossypii, a strictly phloemophagaous aphid, colonize hundreds of plant families, and a group of clones formed a cucurbit-specialised host-race. Cucurbits are unique in having evolved a specific extra-fascicular phloem (EFP), which carries defence-related metabolites such as cucurbitacin, whereas the fascicular phloem (FP) is common to all higher plants and carries primary metabolites, such as raffinose-family oligosaccharides (RFOs). Both cucurbitacins (in the EFP) and galactinol (in the FP) have been suggested to be toxic to aphids. We investigated these hypotheses in cucurbit-specialized A. gossypii fed on melon plants with or without aphid-resistance conferred by the NLR gene Vat. We selected a plant-aphid system with (i) Vat-mediated resistance not triggered, (ii) Vat-mediated resistance triggered by an aphid clone adapted to the presence of Vat resistant alleles and (iii) Vat-mediated resistance triggered by a non-adapted aphid clone. RESULTS We quantified cucurbitacin B, its glycosylated derivative, and sugars, in melon plants and aphids that fed on. The level of cucurbitacin in plants was unrelated to both aphid infestation and aphid resistance. Galactinol was present at higher quantities in plants when Vat-mediated resistance was triggered, but its presence did not correlate with aphid performance. Finally, we showed that cucurbit-specialized A. gossypii fed from the FP but could also occasionally access the EFP without sustainably feeding from it. However, the clone not adapted to Vat-mediated resistance were less able to access the FP when the Vat resistance was triggered. CONCLUSION We concluded that galactinol accumulation in resistant plants does not affect aphids, but may play a role in aphid adaptation to fasting and that Cucurbitacin in planta is not a real threat to Aphis gossypii. Moreover, the specific phloem of Cucurbits is involved neither in A. gossypii cucurbit specialisation nor in adaptation to Vat-dependent resistance.
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Affiliation(s)
- Pierre Sadon
- Génétique et Amélioration des Fruits et Légumes, National Institute for Agriculture, Food and Environment, INRAE, Domaine St-Maurice, 84143, Montfavet, Cedex, France
| | - Marie-Noëlle Corre
- Génétique et Amélioration des Fruits et Légumes, National Institute for Agriculture, Food and Environment, INRAE, Domaine St-Maurice, 84143, Montfavet, Cedex, France
| | - Raphael Lugan
- Plantes et Systèmes de cultures Horticoles, National Institute for Agriculture, Food and Environment, INRAE, Domaine St Paul, 84914, Avignon, Cedex, France
| | - Nathalie Boissot
- Génétique et Amélioration des Fruits et Légumes, National Institute for Agriculture, Food and Environment, INRAE, Domaine St-Maurice, 84143, Montfavet, Cedex, France.
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Noll GA, Furch ACU, Rose J, Visser F, Prüfer D. Guardians of the phloem - forisomes and beyond. THE NEW PHYTOLOGIST 2022; 236:1245-1260. [PMID: 36089886 DOI: 10.1111/nph.18476] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Accepted: 07/27/2022] [Indexed: 06/15/2023]
Abstract
The phloem is a highly specialized vascular tissue that forms a fundamentally important transport and signaling pathway in plants. It is therefore a system worth protecting. The main function of the phloem is to transport the products of photosynthesis throughout the whole plant, but it also transports soluble signaling molecules and propagates electrophysiological signals. The phloem is constantly threatened by mechanical injuries, phloem-sucking pests and parasites, and the spread of pathogens, which has led to the evolution of efficient defense mechanisms. One such mechanism involves structural phloem proteins, which are thought to facilitate sieve element occlusion following injury and to defend the plant against pathogens. In leguminous plants, specialized structural phloem proteins known as forisomes form unique mechanoproteins via sophisticated molecular interaction and assembly mechanisms, thus enabling reversible sieve element occlusion. By understanding the structure and function of forisomes and other structural phloem proteins, we can develop a toolbox for biotechnological applications in material science and medicine. Furthermore, understanding the involvement of structural phloem proteins in plant defense mechanisms will allow phloem engineering as a new strategy for the development of crop varieties that are resistant to pests, pathogens and parasites.
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Affiliation(s)
- Gundula A Noll
- Institute of Plant Biology and Biotechnology, University of Muenster, Schlossplatz 8, 48143, Muenster, Germany
- Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Schlossplatz 8, 48143, Muenster, Germany
| | - Alexandra C U Furch
- Matthias Schleiden Institute for Genetics, Bioinformatics and Molecular Botany, Friedrich Schiller University Jena, Dornburger Straße 159, 07743, Jena, Germany
| | - Judith Rose
- Institute of Plant Biology and Biotechnology, University of Muenster, Schlossplatz 8, 48143, Muenster, Germany
| | - Franziska Visser
- Institute of Plant Biology and Biotechnology, University of Muenster, Schlossplatz 8, 48143, Muenster, Germany
| | - Dirk Prüfer
- Institute of Plant Biology and Biotechnology, University of Muenster, Schlossplatz 8, 48143, Muenster, Germany
- Fraunhofer Institute for Molecular Biology and Applied Ecology IME, Schlossplatz 8, 48143, Muenster, Germany
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Leybourne DJ, Aradottir GI. Common resistance mechanisms are deployed by plants against sap-feeding herbivorous insects: insights from a meta-analysis and systematic review. Sci Rep 2022; 12:17836. [PMID: 36284143 PMCID: PMC9596439 DOI: 10.1038/s41598-022-20741-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Accepted: 09/19/2022] [Indexed: 01/20/2023] Open
Abstract
Despite their abundance and economic importance, the mechanism of plant resistance to sap-feeding insects remains poorly understood. Here we deploy meta-analysis and data synthesis methods to evaluate the results from electrophysiological studies describing feeding behaviour experiments where resistance mechanisms were identified, focussing on studies describing host-plant resistance and non-host resistance mechanisms. Data were extracted from 108 studies, comprising 41 insect species across eight insect taxa and 12 host-plant families representing over 30 species. Results demonstrate that mechanisms deployed by resistant plants have common consequences on the feeding behaviour of diverse insect groups. We show that insects feeding on resistant plants take longer to establish a feeding site and have their feeding duration suppressed two-fold compared with insects feeding on susceptible plants. Our results reveal that traits contributing towards resistant phenotypes are conserved across plant families, deployed against taxonomically diverse insect groups, and that the underlying resistance mechanisms are conserved. These findings provide a new insight into plant-insect interaction and highlight the need for further mechanistic studies across diverse taxa.
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Affiliation(s)
- D. J. Leybourne
- grid.9122.80000 0001 2163 2777Zoological Biodiversity, Institute of Geobotany, Leibniz University of Hannover, 30167 Hannover, Germany
| | - G. I. Aradottir
- grid.17595.3f0000 0004 0383 6532Department of Plant Pathology and Entomology, NIAB, Cambridge, CB3 0LE UK
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Agaoua A, Rittener V, Troadec C, Desbiez C, Bendahmane A, Moquet F, Dogimont C. A single substitution in Vacuolar protein sorting 4 is responsible for resistance to Watermelon mosaic virus in melon. JOURNAL OF EXPERIMENTAL BOTANY 2022; 73:4008-4021. [PMID: 35394500 DOI: 10.1093/jxb/erac135] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/11/2021] [Accepted: 04/07/2022] [Indexed: 06/14/2023]
Abstract
In plants, introgression of genetic resistance is a proven strategy for developing new resistant lines. While host proteins involved in genome replication and cell to cell movement are widely studied, other cell mechanisms responsible for virus infection remain under investigated. Endosomal sorting complexes required for transport (ESCRT) play a key role in membrane trafficking in plants and are involved in the replication of several plant RNA viruses. In this work, we describe the role of the ESCRT protein CmVPS4 as a new susceptibility factor to the Potyvirus Watermelon mosaic virus (WMV) in melon. Using a worldwide collection of melons, we identified three different alleles carrying non-synonymous substitutions in CmVps4. Two of these alleles were shown to be associated with WMV resistance. Using a complementation approach, we demonstrated that resistance is due to a single non-synonymous substitution in the allele CmVps4P30R. This work opens up new avenues of research on a new family of host factors required for virus infection and new targets for resistance.
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Affiliation(s)
- Aimeric Agaoua
- Genetics and Breeding of Fruit and Vegetables (GAFL-INRAE), 84000 Avignon, France
| | - Vincent Rittener
- Genetics and Breeding of Fruit and Vegetables (GAFL-INRAE), 84000 Avignon, France
| | - Christelle Troadec
- Institute of Plant Sciences-Paris-Saclay (IPS2), 91190 Gif-sur-Yvette, France
| | | | | | | | - Catherine Dogimont
- Genetics and Breeding of Fruit and Vegetables (GAFL-INRAE), 84000 Avignon, France
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7
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Twayana M, Girija AM, Mohan V, Shah J. Phloem: At the center of action in plant defense against aphids. JOURNAL OF PLANT PHYSIOLOGY 2022; 273:153695. [PMID: 35468314 DOI: 10.1016/j.jplph.2022.153695] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2021] [Revised: 04/04/2022] [Accepted: 04/08/2022] [Indexed: 06/14/2023]
Abstract
The location of the phloem deep inside the plant, the high hydrostatic pressure in the phloem, and the composition of phloem sap, which is rich in sugar with a high C:N ratio, allows phloem sap feeding insects to occupy a unique ecological niche. The anatomy and physiology of aphids, a large group of phytophagous insects that use their mouthparts, which are modified into stylets, to consume large amounts of phloem sap, has allowed aphids to successfully exploit this niche, however, to the detriment of agriculture and horticulture. The ability to reproduce asexually, a short generation time, the development of resistance to commonly used insecticides, and their ability to vector viral diseases makes aphids among the most damaging pests of plants. Here we review how plants utilize their ability to occlude sieve elements and accumulate antibiotic and antinutritive factors in the phloem sap to limit aphid infestation. In addition, we summarize progress on understanding how plants perceive aphids to activate defenses in the phloem.
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Affiliation(s)
- Moon Twayana
- Department of Biological Sciences and BioDiscovery Institute, University of North Texas, Denton, TX, 76210, USA.
| | - Anil M Girija
- Department of Biological Sciences and BioDiscovery Institute, University of North Texas, Denton, TX, 76210, USA.
| | - Vijee Mohan
- Department of Biological Sciences and BioDiscovery Institute, University of North Texas, Denton, TX, 76210, USA.
| | - Jyoti Shah
- Department of Biological Sciences and BioDiscovery Institute, University of North Texas, Denton, TX, 76210, USA.
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8
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Carpane P, Catalano MI. Probing behavior of the corn leafhopper Dalbulus maidis on susceptible and resistant maize hybrids. PLoS One 2022; 17:e0259481. [PMID: 35639741 PMCID: PMC9154111 DOI: 10.1371/journal.pone.0259481] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Accepted: 05/12/2022] [Indexed: 11/24/2022] Open
Abstract
The corn leafhopper Dalbulus maidis is the main vector of the pathogens that cause corn stunt, a major disease of maize in the Americas. In line with plant resistance being an efficient tool to control diseases, the findings of a previous work showed that some corn hybrids are resistant to D. maidis. In this work, we assessed the probing behavior of D. maidis on susceptible and resistant corn hybrids using EPG (Electrical Penetration Graph) technology. Feeding of fifteen-day-old, non-inoculative females was recorded for 20 hours, with access to hybrids DK390, DK670, DK79-10, and DK72-10. Compared to the susceptible hybrid DK670, the other hybrids shifted D. maidis probing behavior in a way consistent with plant resistance to insects. This shift consisted of a higher number of probes of short duration, difficulties in attaining phloem ingestion and increase in xylem ingestion. In addition to this common shift in probing behavior, a phloem-located resistance factor was inferred in DK72-10 based on the longer time spent in phloem conditioning to attain phloem ingestion. In contrast, DK390 expressed the highest level of mesophyll and phloem-based resistance, in both cases seen with repeated attempts of short duration, a behavior typically associated with failed attempts to ingest. These findings support and are consistent with previous research, providing useful information to characterize maize hybrids resistant to D. maidis, and consequently to corn stunt.
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Affiliation(s)
- Pablo Carpane
- Bayer CropScience, Fontezuela, Buenos Aires, Argentina
- * E-mail:
| | - María Inés Catalano
- Centro de BioInvestigaciones (Universidad Nacional del Noroeste de la Provincia de Buenos Aires-CICBA), Pergamino, Buenos Aires, Argentina
- Centro de Investigaciones y Transferencias del Noroeste de la Provincia de Buenos Aires (CITNOBA-CONICET), Pergamino, Buenos Aires, Argentina
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9
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Jayasinghe WH, Akhter MS, Nakahara K, Maruthi MN. Effect of aphid biology and morphology on plant virus transmission. PEST MANAGEMENT SCIENCE 2022; 78:416-427. [PMID: 34478603 DOI: 10.1002/ps.6629] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/22/2021] [Accepted: 09/03/2021] [Indexed: 06/13/2023]
Abstract
Aphids severely affect crop production by transmitting many plant viruses. Viruses are obligate intracellular pathogens that mostly depend on vectors for their transmission and survival. A majority of economically important plant viruses are transmitted by aphids. They transmit viruses either persistently (circulative or non-circulative) or non-persistently. Plant virus transmission by insects is a process that has evolved over time and is strongly influenced by insect morphological features and biology. Over the past century, a large body of research has provided detailed knowledge of the molecular processes underlying virus-vector interactions. In this review, we discuss how aphid biology and morphology can affect plant virus transmission. © 2021 Society of Chemical Industry.
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Affiliation(s)
- Wikum H Jayasinghe
- Department of Agricultural Biology, Faculty of Agriculture, University of Peradeniya, Peradeniya, Sri Lanka
| | - Md Shamim Akhter
- Laboratory of Pathogen-Plant Interactions, Research Faculty of Agriculture, Hokkaido University, Sapporo, Japan
- Plant Pathology Division, Bangladesh Agricultural Research Institute (BARI), Joydebpur, Bangladesh
| | - Kenji Nakahara
- Laboratory of Pathogen-Plant Interactions, Research Faculty of Agriculture, Hokkaido University, Sapporo, Japan
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10
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Walker GP. Sieve element occlusion: Interactions with phloem sap-feeding insects. A review. JOURNAL OF PLANT PHYSIOLOGY 2022; 269:153582. [PMID: 34953413 DOI: 10.1016/j.jplph.2021.153582] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/02/2021] [Revised: 10/30/2021] [Accepted: 11/25/2021] [Indexed: 06/14/2023]
Abstract
Phloem sieve element (SE) occlusion has been hypothesized for decades to be a mechanism of resistance against phloem sap-feeding insects. Few studies have tested this hypothesis although it is likely a widespread phenomenon. This review focuses on SE occlusion by callose and P-proteins. Both are reversible, which would allow the plant to defend itself against phloem sap-feeders when SEs are penetrated and resume normal function when the insects give up and withdraw their stylets. Callose (β-1,3 glucans with some β-1,6 branches) serves many roles in plant physiology in many different tissues, each being under the control of different callose synthase genes; only callose deposited in SE sieve pores is relevant to SE occlusion. The amount of callose in sieve pores (and consequently how much it impedes sap flow) is determined by the balance in activity between callose synthase and β-1,3 glucanase. Sieve pore callose deposition has been shown to provide resistance to some phloem sap-feeders in a few studies, and in one, the difference in resistance between a susceptible and resistant rice variety was due to the ability or inability of the insect to upregulate the plants' β-1,3 glucanase that degrades the callose deposition. P-proteins occur only in dicotyledons and include a variety of proteins, not all of which are involved in SE occlusion. In some plants, P-proteins form distinct bodies in mature functional SEs. In papilionid legumes, these discrete bodies, called forisomes can expand and contract. In their expanded state, they effectively plug SEs and stop the flow of sap while in their contracted state, they provide negligible resistance to sap flow. Expansion of forisomes is triggered by an influx of Ca2+ into the SE. Penetration of a legume (Vicia faba) SE by a generalist aphid not adapted to legumes triggers forisome expansion which occludes the SE and prevents the aphid from ingesting sap. In contrast, a legume specialist aphid, Acyrthosiphon pisum, does not trigger forisome expansion and readily ingests sap from V. faba. P-protein bodies in SEs of non-legumes do not appear to be involved in SE occlusion. In most dicotyledons, P-proteins do not form discrete bodies, but rather occur as filamentous aggregations adhering to the parietal margins of the SE and in response to damage, are released into the lumen where they are carried by the flow of sap to the downstream sieve plate where they back up and clog the sieve pores. Their effectiveness at actually stopping the flow of sap is controversial. In one study, they seemed to provide little resistance to the flow of sap while in other studies, they provided considerable resistance. In response to injury in melon, they completely stop the flow of sap, and in an aphid-resistant melon, penetration of SEs by the melon aphid, Aphis gossypii, triggers P-protein occlusion which prevents the aphids from ingesting sap. The first P-protein described, PP1, occurs only in the genus Cucurbita, and although it has been often cited to function as a SE occlusion protein, experimental evidence suggests it does not play a significant role in SE occlusion. The most common strategy for phloem sap-feeders to mitigate P-protein occlusion seems to be avoid triggering it. A widely cited in vitro study suggested that aphid saliva can reverse P-protein occlusion, but a subsequent study demonstrated that saliva was ineffective at reversing P-protein occlusion in vivo. Lastly, SE callose deposition in wheat triggered by Russian wheat aphid has been hypothesized to create an artificial sink that benefits the aphid, but additional studies are needed to test that hypothesis.
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Affiliation(s)
- G P Walker
- Department of Entomology, University of California, Riverside, United States.
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11
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Different Host Plants Distinctly Influence the Feeding Ability of the Brown Citrus Aphid Toxoptera citricida. INSECTS 2021; 12:insects12100864. [PMID: 34680633 PMCID: PMC8538693 DOI: 10.3390/insects12100864] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 09/13/2021] [Accepted: 09/17/2021] [Indexed: 12/04/2022]
Abstract
Simple Summary The brown citrus aphid, Toxoptera citricida, is an important pest of citrus and causes serious damage in the main production areas. Host plant resistance is an environmentally friendly method to manage aphid infestations and is becoming increasingly important as aphids develop greater resistance to insecticides. The aim of this study was to assess T. citricida resistance on seven widespread and common hosts using electropenetrography combined with a population development test. We showed that the feeding parameters of the brown citrus aphid differed significantly depending on the host plants. Toxoptera citricida spent more time in the pathway stage and less time in the phloem stage on Eureka, while the opposite was observed on Yuzu and Rough Lemon. Measurements of population development of aphids showed that on the Eureka, aphids developed more slowly. Our data suggest that different host plants distinctly influence the ability of T. citricida to feed. The brown citrus aphid did not prefer to feed on Eureka Lemon compared to the other six host plants. Abstract Piercing–sucking insects are important crop pests, and an understanding of their feeding behavior and population development plays a crucial role in studying insect population dynamics and crop resistance. In our study, we examined the probing behavior of the brown citrus aphid, Toxoptera citricida, using electropenetrography and assessed its population development after 8 days on seven host plants: Yuzu, Citrus junos Sieb. ex Tanaka; Rough Lemon, C. jambhiri Lush.; ‘Luofu’ kumquat, Fortunella margarita Swingle; ‘Olinda’ valencia orange, C. sinensis (L.) Osbeck; ‘Yanxiwanlu’ Ponkan, C. reticulata Blanco; ‘Rohde Red’ valencia orange, C. sinensis; and ‘Eureka’ lemon, C. limon (L.) Osbeck. The results demonstrated that probing by the brown citrus aphid differed significantly according to the target hosts. Toxoptera citricida produced significantly more pathway activities on Eureka than on Rough Lemon and Yuzu. Toxoptera citricida spent more time from the first probe to first salivation into phloem sieve elements on Eureka compared to Yuzu. In addition, the total duration of ingestion from sieve cells of each aphid in the phloem-feeding phase was shortest on Eureka, and this was significantly shorter than that on Yuzu, Rough Lemon, Luofu, and Olinda. The population number of T. citricida on Eureka after 8 days was significantly lower than that on the other hosts. Overall, Eureka was found to have obvious resistance to T. citricida, whereas Yuzu and Rough Lemon were susceptible host plants. These results provide a theoretical basis for exploring aphid-resistant fruit tree resources using resistant varieties.
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Kloth KJ, Shah P, Broekgaarden C, Ström C, Albrectsen BR, Dicke M. SLI1 confers broad-spectrum resistance to phloem-feeding insects. PLANT, CELL & ENVIRONMENT 2021; 44:2765-2776. [PMID: 33837973 PMCID: PMC8360143 DOI: 10.1111/pce.14064] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/11/2021] [Revised: 03/30/2021] [Accepted: 04/02/2021] [Indexed: 05/13/2023]
Abstract
Resistance (R) genes usually compete in a coevolutionary arms race with reciprocal effectors to confer strain-specific resistance to pathogens or herbivorous insects. Here, we investigate the specificity of SLI1, a recently identified R gene in Arabidopsis that encodes a small heat shock-like protein involved in resistance to Myzus persicae aphids. In a panel with several aphid and whitefly species, SLI1 compromised reproductive rates of three species: the tobacco aphid M. persicae nicotianae, the cabbage aphid Brevicoryne brassicae and the cabbage whitefly Aleyrodes proletella. Electrical penetration graph recording of aphid behaviour, revealed shorter salivations and a 3-to-5-fold increase in phloem feeding on sli1 loss-of-function plants. The mustard aphid Lipaphis erysimi and Bemisia tabaci whitefly were not affected by SLI1. Unlike the other two aphid species, L. erysimi exhibited repetitive salivations preceding successful phloem feeding, indicating a role of salivary effectors in overcoming SLI1-mediated resistance. Microscopic characterization showed that SLI1 proteins localize in the sieve tubes of virtually all above- and below-ground tissues and co-localize with the aphid stylet tip after penetration of the sieve element plasma membrane. These observations reveal an unconventional R gene that escapes the paradigm of strain specificity and confers broad-spectrum quantitative resistance to phloem-feeding insects.
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Affiliation(s)
- Karen J. Kloth
- Laboratory of EntomologyWageningen University & ResearchWageningenThe Netherlands
| | - Parth Shah
- Laboratory of EntomologyWageningen University & ResearchWageningenThe Netherlands
| | | | - Cecilia Ström
- Department of Plant Physiology, Umeå Plant Science CentreUmeå UniversityUmeåSweden
| | | | - Marcel Dicke
- Laboratory of EntomologyWageningen University & ResearchWageningenThe Netherlands
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Jiménez J, Moreno A, Fereres A. Semipersistently Transmitted, Phloem Limited Plant Viruses Are Inoculated during the First Subphase of Intracellular Stylet Penetrations in Phloem Cells. Viruses 2021; 13:v13010137. [PMID: 33478068 PMCID: PMC7835983 DOI: 10.3390/v13010137] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Revised: 01/14/2021] [Accepted: 01/15/2021] [Indexed: 11/16/2022] Open
Abstract
The green peach aphid Myzus persicae Sulzer is the main vector of the semipersistently transmitted and phloem-limited Beet yellows virus (BYV, Closterovirus). Studies monitoring the M. persicae probing behavior by using the Electrical penetration graphs (EPG) technique revealed that inoculation of BYV occurs during unique brief intracellular punctures (phloem-pds) produced in companion and/or sieve element cells. Intracellular stylet punctures (or pds) are subdivided in three subphases (II-1, II-2 and II-3), which have been related to the delivery or uptake of non-phloem limited viruses transmitted in a non-persistent or semipersistent manner. As opposed to non-phloem limited viruses, the specific pd subphase(s) involved in the successful delivery of phloem limited viruses by aphids remain unknown. Therefore, we monitored the feeding process of BYV-carrying M. persicae individuals in sugar beet plants by the EPG technique and the feeding process was artificially terminated at each phloem-pd subphase. Results revealed that aphids that only performed the subphase II-1 of the phloem-pd transmitted BYV at similar efficiency than those allowed to perform subphase II-2 or the complete phloem-pd. This result suggests that BYV inoculation occurs during the first subphase of the phloem-pd. The specific transmission mechanisms involved in BYV delivery in phloem cells are discussed.
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14
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Huang W, Reyes-Caldas P, Mann M, Seifbarghi S, Kahn A, Almeida RPP, Béven L, Heck M, Hogenhout SA, Coaker G. Bacterial Vector-Borne Plant Diseases: Unanswered Questions and Future Directions. MOLECULAR PLANT 2020; 13:1379-1393. [PMID: 32835885 PMCID: PMC7769051 DOI: 10.1016/j.molp.2020.08.010] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 08/18/2020] [Accepted: 08/18/2020] [Indexed: 06/01/2023]
Abstract
Vector-borne plant diseases have significant ecological and economic impacts, affecting farm profitability and forest composition throughout the world. Bacterial vector-borne pathogens have evolved sophisticated strategies to interact with their hemipteran insect vectors and plant hosts. These pathogens reside in plant vascular tissue, and their study represents an excellent opportunity to uncover novel biological mechanisms regulating intracellular pathogenesis and to contribute to the control of some of the world's most invasive emerging diseases. In this perspective, we highlight recent advances and major unanswered questions in the realm of bacterial vector-borne disease, focusing on liberibacters, phytoplasmas, spiroplasmas, and Xylella fastidiosa.
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Affiliation(s)
- Weijie Huang
- Department of Crop Genetics, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
| | - Paola Reyes-Caldas
- Department of Plant Pathology, University of California, Davis, CA, 95616, USA
| | - Marina Mann
- Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY 14853, USA
| | - Shirin Seifbarghi
- Department of Plant Pathology, University of California, Davis, CA, 95616, USA
| | - Alexandra Kahn
- Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA
| | - Rodrigo P P Almeida
- Department of Environmental Science, Policy and Management, University of California, Berkeley, CA 94720, USA
| | - Laure Béven
- UMR 1332 Biologie du Fruit et Pathologie, Univ. Bordeaux, INRAE, Villenave d'Ornon 33882 France
| | - Michelle Heck
- Department of Plant Pathology and Plant-Microbe Biology, Cornell University, Ithaca, NY 14853, USA; Boyce Thompson Institute, Ithaca, NY 14853, USA; Emerging Pests and Pathogens Research Unit, Robert W. Holley Center, USDA ARS, Ithaca, NY 14853, USA
| | - Saskia A Hogenhout
- Department of Crop Genetics, John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK; School of Environmental Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK
| | - Gitta Coaker
- Department of Plant Pathology, University of California, Davis, CA, 95616, USA.
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15
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Greenbug (Schizaphis graminum) herbivory significantly impacts protein and phosphorylation abundance in switchgrass (Panicum virgatum). Sci Rep 2020; 10:14842. [PMID: 32908168 PMCID: PMC7481182 DOI: 10.1038/s41598-020-71828-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2020] [Accepted: 08/19/2020] [Indexed: 02/06/2023] Open
Abstract
Switchgrass (Panicum virgatum L.) is an important crop for biofuel production but it also serves as host for greenbugs (Schizaphis graminum Rondani; GB). Although transcriptomic studies have been done to infer the molecular mechanisms of plant defense against GB, little is known about the effect of GB infestation on the switchgrass protein expression and phosphorylation regulation. The global response of the switchgrass cultivar Summer proteome and phosphoproteome was monitored by label-free proteomics shotgun in GB-infested and uninfested control plants at 10 days post infestation. Peptides matching a total of 3,594 proteins were identified and 429 were differentially expressed proteins in GB-infested plants relative to uninfested control plants. Among these, 291 and 138 were up and downregulated by GB infestation, respectively. Phosphoproteome analysis identified 310 differentially phosphorylated proteins (DP) from 350 phosphopeptides with a total of 399 phosphorylated sites. These phosphopeptides had more serine phosphorylated residues (79%), compared to threonine phosphorylated sites (21%). Overall, KEGG pathway analysis revealed that GB feeding led to the enriched accumulation of proteins important for biosynthesis of plant defense secondary metabolites and repressed the accumulation of proteins involved in photosynthesis. Interestingly, defense modulators such as terpene synthase, papain-like cysteine protease, serine carboxypeptidase, and lipoxygenase2 were upregulated at the proteome level, corroborating previously published transcriptomic data.
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16
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Sun M, Voorrips RE, Vosman B. Aphid populations showing differential levels of virulence on Capsicum accessions. INSECT SCIENCE 2020; 27:336-348. [PMID: 30353689 PMCID: PMC7379501 DOI: 10.1111/1744-7917.12648] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/11/2018] [Revised: 09/14/2018] [Accepted: 10/09/2018] [Indexed: 05/27/2023]
Abstract
The green peach aphid, Myzus persicae, is one of the most threatening pests in pepper cultivation and growers would benefit from resistant varieties. Previously, we identified two Capsicum accessions as susceptible and three as resistant to M. persicae using an aphid population originating from the Netherlands (NL). Later on we identified an aphid population originating from a different geographical region (Switserland, SW) that was virulent on all tested Capsicum accessions. The objective of the current work is to describe in detail different aspects of the interaction between two aphid populations and two selected Capsicum accessions (one that was susceptible [PB2013046] and one that was resistant [PB2013071] to population NL), including biochemical processes involved. Electrical penetration graph (EPG) recordings showed similar feeding activities for both aphid populations on PB2013046. On accession PB2013071 the aphid population SW was able to devote significantly more time to phloem ingestion than population NL. We also studied plant defense response and found that plants of accession PB2013046 could not induce an accumulation of reactive oxygen species and callose formation after infestation with either aphid population. However, plants of PB2013071 induced a stronger defense response after infestation by population NL than after infestation by population SW. Based on these results, population SW of M. persicae seems to have overcome the resistance of PB2013071 that prevented feeding of aphids from NL population. The potential mechanism by which SW population overcomes the resistance is discussed.
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Affiliation(s)
- Mengjing Sun
- Plant BreedingWageningen University & ResearchWageningenThe Netherlands
| | | | - Ben Vosman
- Plant BreedingWageningen University & ResearchWageningenThe Netherlands
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17
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Priming Melon Defenses with Acibenzolar- S-methyl Attenuates Infections by Phylogenetically Distinct Viruses and Diminishes Vector Preferences for Infected Hosts. Viruses 2020; 12:v12030257. [PMID: 32111005 PMCID: PMC7150938 DOI: 10.3390/v12030257] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2019] [Revised: 02/07/2020] [Accepted: 02/21/2020] [Indexed: 02/03/2023] Open
Abstract
Plant virus management is mostly achieved through control of insect vectors using insecticides. However, insecticides are only marginally effective for preventing virus transmission. Furthermore, it is well established that symptoms of virus infections often encourage vector visitation to infected hosts, which exacerbates secondary spread. Plant defense elicitors, phytohormone analogs that prime the plant immune system against attack, may be a viable approach for virus control that complements insecticide use by disrupting pathologies that attract vectors. To explore this, we tested the effect of a commercial plant elicitor, acibenzolar-S-methyl (ASM), on infection rates, virus titers, and symptom development in melon plants inoculated with one of two virus species, Cucumber mosaic virus (CMV) and Cucurbit yellow stunting disorder virus (CYSDV). We also conducted behavioral assays to assess the effect of ASM treatment and virus inoculation on vector behavior. For both pathogens, ASM treatment reduced symptom severity and delayed disease progression. For CYSDV, this resulted in the attenuation of symptoms that encourage vector visitation and virion uptake. We did observe slight trade-offs in growth vs. defense following ASM treatment, but these effects did not translate into reduced yields or plant performance in the field. Our results suggest that immunity priming may be a valuable tool for improving management of insect-transmitted plant viruses.
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18
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Sun M, Voorrips RE, van Kaauwen M, Visser RGF, Vosman B. The ability to manipulate ROS metabolism in pepper may affect aphid virulence. HORTICULTURE RESEARCH 2020; 7:6. [PMID: 31908809 PMCID: PMC6938493 DOI: 10.1038/s41438-019-0231-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 11/13/2019] [Accepted: 12/04/2019] [Indexed: 05/14/2023]
Abstract
Myzus persicae has severe economic impact on pepper (Capsicum) cultivation. Previously, we identified two populations of M. persicae, NL and SW, that were avirulent and virulent, respectively on C. baccatum accession PB2013071. The transcriptomics approach used in the current study, which is the first study to explore the pepper-aphid interaction at the whole genome gene expression level, revealed genes whose expression is differentially regulated in pepper accession PB2013071 upon infestation with these M. persicae populations. The NL population induced ROS production genes, while the SW population induced ROS scavenging genes and repressed ROS production genes. We also found that the SW population can induce the removal of ROS which accumulated in response to preinfestion with the NL population, and that preinfestation with the SW population significantly improved the performance of the NL population. This paper supports the hypothesis that M. persicae can overcome the resistance in accession PB2013071 probably because of its ability to manipulate plant defense response especially the ROS metabolism and such ability may benefit avirulent conspecific aphids.
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Affiliation(s)
- Mengjing Sun
- Plant Breeding, Wageningen University & Research, P.O. Box 386, 6700 AJ Wageningen, Netherlands
| | - Roeland E. Voorrips
- Plant Breeding, Wageningen University & Research, P.O. Box 386, 6700 AJ Wageningen, Netherlands
| | - Martijn van Kaauwen
- Plant Breeding, Wageningen University & Research, P.O. Box 386, 6700 AJ Wageningen, Netherlands
| | - Richard G. F. Visser
- Plant Breeding, Wageningen University & Research, P.O. Box 386, 6700 AJ Wageningen, Netherlands
| | - Ben Vosman
- Plant Breeding, Wageningen University & Research, P.O. Box 386, 6700 AJ Wageningen, Netherlands
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19
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Silva-Sanzana C, Celiz-Balboa J, Garzo E, Marcus SE, Parra-Rojas JP, Rojas B, Olmedo P, Rubilar MA, Rios I, Chorbadjian RA, Fereres A, Knox P, Saez-Aguayo S, Blanco-Herrera F. Pectin Methylesterases Modulate Plant Homogalacturonan Status in Defenses against the Aphid Myzus persicae. THE PLANT CELL 2019; 31:1913-1929. [PMID: 31126981 PMCID: PMC6713307 DOI: 10.1105/tpc.19.00136] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/06/2019] [Revised: 04/29/2019] [Accepted: 05/20/2019] [Indexed: 05/18/2023]
Abstract
Because they suck phloem sap and act as vectors for phytopathogenic viruses, aphids pose a threat to crop yields worldwide. Pectic homogalacturonan (HG) has been described as a defensive element for plants during infections with phytopathogens. However, its role during aphid infestation remains unexplored. Using immunofluorescence assays and biochemical approaches, the HG methylesterification status and associated modifying enzymes during the early stage of Arabidopsis (Arabidopsis thaliana) infestation with the green peach aphid (Myzus persicae) were analyzed. Additionally, the influence of pectin methylesterase (PME) activity on aphid settling and feeding behavior was evaluated by free choice assays and the Electrical Penetration Graph technique, respectively. Our results revealed that HG status and HG-modifying enzymes are significantly altered during the early stage of the plant-aphid interaction. Aphid infestation induced a significant increase in total PME activity and methanol emissions, concomitant with a decrease in the degree of HG methylesterification. Conversely, inhibition of PME activity led to a significant decrease in the settling and feeding preference of aphids. Furthermore, we demonstrate that the PME inhibitor AtPMEI13 has a defensive role during aphid infestation, since pmei13 mutants are significantly more susceptible to M. persicae in terms of settling preference, phloem access, and phloem sap drainage.
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Affiliation(s)
- Christian Silva-Sanzana
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Jonathan Celiz-Balboa
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Elisa Garzo
- Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas, Madrid 28006, Spain
| | - Susan E Marcus
- Centre for Plant Sciences, Faculty of Biological Sciences, University of Leeds, Leeds LS2 9JT, United Kingdom
| | - Juan Pablo Parra-Rojas
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Barbara Rojas
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Patricio Olmedo
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Miguel A Rubilar
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Ignacio Rios
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Rodrigo A Chorbadjian
- Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago 7820436, Chile
| | - Alberto Fereres
- Instituto de Ciencias Agrarias, Consejo Superior de Investigaciones Científicas, Madrid 28006, Spain
| | - Paul Knox
- Facultad de Agronomía e Ingeniería Forestal, Pontificia Universidad Católica de Chile, Santiago 7820436, Chile
| | - Susana Saez-Aguayo
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
| | - Francisca Blanco-Herrera
- Centro de Biotecnología Vegetal, Facultad de Ciencias de la Vida, Universidad Andres Bello, Santiago 8370186, Chile
- Millennium Institute for Integrative Biology, Santiago 7500565, Chile
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20
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Turnip Mosaic Virus Is a Second Example of a Virus Using Transmission Activation for Plant-to-Plant Propagation by Aphids. J Virol 2019; 93:JVI.01822-18. [PMID: 30760573 DOI: 10.1128/jvi.01822-18] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Accepted: 02/06/2019] [Indexed: 12/16/2022] Open
Abstract
Cauliflower mosaic virus (CaMV; family Caulimoviridae) responds to the presence of aphid vectors on infected plants by forming specific transmission morphs. This phenomenon, coined transmission activation (TA), controls plant-to-plant propagation of CaMV. A fundamental question is whether other viruses rely on TA. Here, we demonstrate that transmission of the unrelated turnip mosaic virus (TuMV; family Potyviridae) is activated by the reactive oxygen species H2O2 and inhibited by the calcium channel blocker LaCl3 H2O2-triggered TA manifested itself by the induction of intermolecular cysteine bonds between viral helper component protease (HC-Pro) molecules and by the formation of viral transmission complexes, composed of TuMV particles and HC-Pro that mediates vector binding. Consistently, LaCl3 inhibited intermolecular HC-Pro cysteine bonds and HC-Pro interaction with viral particles. These results show that TuMV is a second virus using TA for transmission but using an entirely different mechanism than CaMV. We propose that TuMV TA requires reactive oxygen species (ROS) and calcium signaling and that it is operated by a redox switch.IMPORTANCE Transmission activation, i.e., a viral response to the presence of vectors on infected hosts that regulates virus acquisition and thus transmission, is an only recently described phenomenon. It implies that viruses contribute actively to their transmission, something that has been shown before for many other pathogens but not for viruses. However, transmission activation has been described so far for only one virus, and it was unknown whether other viruses also rely on transmission activation. Here we present evidence that a second virus uses transmission activation, suggesting that it is a general transmission strategy.
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