Plant, Insect and...
Follow
Find
2.4K views | +1 today
Plant, Insect and Microbe Interactions
New and old articles on plant-insect-microbe interactions
Your new post is loading...
Your new post is loading...
Scooped by The aphid team@INRA Rennes
Scoop.it!

Two host clades, two bacterial arsenals: evolution through gene losses in facultative endosymbionts

Abstract

Bacterial endosymbiosis is an important evolutionary process in insects, which can harbor both obligate and facultative symbionts. The evolution of these symbionts is driven by evolutionary convergence, and they exhibit among the tiniest genomes in prokaryotes. The large host spectrum of facultative symbionts and the high diversity of strategies they use to infect new hosts probably impacts the evolution of their genome and explains why they undergo less severe genomic erosion than obligate symbionts. Candidatus Hamiltonella defensa is suitable for the investigation of the genomic evolution of facultative symbionts because the bacteria are engaged in specific relationships in two clades of insects. In aphids, H. defensa is found in several species with an intermediate prevalence and confers protection against parasitoids. In whiteflies, H. defensa is almost fixed in some species of Bemisia tabaci, which suggests an important role of and a transition towards obligate symbiosis. In the present study, comparisons of the genome of H. defensa present in two B. tabaci species (MEAM1 and MED) and in the aphid Acyrthosiphon pisum revealed that they belong to two distinct clades and underwent specific gene losses. In aphids, it contains highly virulent factors that could allow protection and horizontal transfers. In whiteflies, the genome lost these factors and seems to have a limited ability to acquire genes. However it contains genes that could be involved in the production of essential nutrients, which is consistent with a primordial role for this symbiont. In conclusion, while both lineages of H. defensa have mutualistic interactions with their hosts, their genomes follow distinct evolutionary trajectories that reflect their phenotype and could have important consequences on their evolvability.

more...
No comment yet.
Rescooped by The aphid team@INRA Rennes from Plants and Microbes
Scoop.it!

MPMI: Focus on The Good, the Bad and the Unknown: Genomics-Enabled Discovery of Plant-Associated Microbial Processes and Diversity (2015)

MPMI: Focus on The Good, the Bad and the Unknown: Genomics-Enabled Discovery of Plant-Associated Microbial Processes and Diversity (2015) | Plant, Insect and Microbe Interactions | Scoop.it

MPMI has played a leading role in disseminating new insights into plant-microbe interactions and promoting new approaches. Articles in this Focus Issue highlight the power of genomic studies in uncovering novel determinants of plant interactions with microbial symbionts (good), pathogens (bad), and complex microbial communities (unknown). Many articles also illustrate how genomics can support translational research by quickly advancing our knowledge of important microbes that have not been widely studied.

 

Click on Next Article or Table of Contents above to view the articles in this Focus Issue. (From the mobile site, go to the MPMI March 2015 issue.)


Via Kamoun Lab @ TSL
more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Full crop protection from an insect pest by expression of long double-stranded RNAs in plastids

Double-stranded RNAs (dsRNAs) targeted against essential genes can trigger a
lethal RNA interference (RNAi) response in insect pests. The application of this
concept in plant protection is hampered by the presence of an endogenous plant
RNAi pathway that processes dsRNAs into short interfering RNAs.We found that long
dsRNAs can be stably produced in chloroplasts, a cellular compartment that appears to
lack an RNAi machinery. When expressed from the chloroplast genome, dsRNAs accumulated
to as much as 0.4% of the total cellular RNA.Transplastomic potato plants producing dsRNAs
targeted against the b-actin gene of the Colorado potato beetle, a notorious agricultural
pest, were protected from herbivory and were lethal to its larvae. Thus, chloroplast
expression of long dsRNAs can provide crop protection without chemical pesticides.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

A Massive Expansion of Effector Genes Underlies Gall-Formation in the Wheat Pest Mayetiola destructor: Current Biology

Highlights•The plant-galling Mayetiola destructor genome is replete with putative effector genes•The SSGP-71 effector gene family is the largest known arthropod gene family•SSGP-71 genes encode E3-ubiquitin-ligase mimics•Two SSGP-71 genes elicit effector-triggered immunity in resistant wheatSummary

Gall-forming arthropods are highly specialized herbivores that, in combination with their hosts, produce extended phenotypes with unique morphologies [ 1 ]. Many are economically important, and others have improved our understanding of ecology and adaptive radiation [ 2 ]. However, the mechanisms that these arthropods use to induce plant galls are poorly understood. We sequenced the genome of the Hessian fly (Mayetiola destructor; Diptera: Cecidomyiidae), a plant parasitic gall midge and a pest of wheat (Triticum spp.), with the aim of identifying genic modifications that contribute to its plant-parasitic lifestyle. Among several adaptive modifications, we discovered an expansive reservoir of potential effector proteins. Nearly 5% of the 20,163 predicted gene models matched putative effector gene transcripts present in the M. destructor larval salivary gland. Another 466 putative effectors were discovered among the genes that have no sequence similarities in other organisms. The largest known arthropod gene family (family SSGP-71) was also discovered within the effector reservoir. SSGP-71 proteins lack sequence homologies to other proteins, but their structures resemble both ubiquitin E3 ligases in plants and E3-ligase-mimicking effectors in plant pathogenic bacteria. SSGP-71 proteins and wheat Skp proteins interact in vivo. Mutations in different SSGP-71 genes avoid the effector-triggered immunity that is directed by the wheat resistance genes H6 and H9. Results point to effectors as the agents responsible for arthropod-induced plant gall formation.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Aphid salivary proteases are capable of degrading sieve-tube proteins

Aphid salivary proteases are capable of degrading sieve-tube proteins | Plant, Insect and Microbe Interactions | Scoop.it

Sieve tubes serve as transport conduits for photo-assimilates and other resources in angiosperms and are profitable targets for piercing–sucking insects such as aphids. Sieve-tube sap also contains significant amounts of proteins with diverse functions, for example in signalling, metabolism, and defence. The identification of salivary proteases in Acyrthosiphon pisum led to the hypothesis that aphids might be able to digest these proteins and by doing so suppress plant defence and access additional nitrogen sources. Here, the scarce knowledge of proteases in aphid saliva is briefly reviewed. In order to provide a better platform for discussion, we conducted a few tests on in vitro protease activity and degradation of sieve-tube sap proteins of Cucurbita maxima by watery saliva. Inhibition of protein degradation by EDTA indicates the presence of different types of proteases (e.g. metalloproteses) in saliva of A. pisum. Proteases in the watery saliva from Macrosiphum euphorbiae and A. pisum were able to degrade the most abundant phloem protein, which is phloem protein 1. Our results provide support for the breakdown of sieve-element proteins by aphid saliva in order to suppress/neutralize the defence responses of the plant and to make proteins of sieve-tube sap accessible as a nitrogen source, as is discussed in detail. Finally, we discuss whether glycosylation of sieve-element proteins and the presence of protease inhibitors may confer partial protection against the proteolytic activity of aphid saliva.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Density-Dependent Interference of Aphids with Caterpillar-Induced Defenses in Arabidopsis: Involvement of Phytohormones and Transcription Factors

Density-Dependent Interference of Aphids with Caterpillar-Induced Defenses in Arabidopsis: Involvement of Phytohormones and Transcription Factors | Plant, Insect and Microbe Interactions | Scoop.it

In nature, plants are exposed to attacks by multiple herbivore species at the same time. To cope with these attacks, plants regulate defenses with the production of hormones such as salicylic acid (SA) and jasmonic acid (JA). Because herbivore densities are dynamic in time, this may affect plant-mediated interactions between different herbivores attacking at the same time. In Arabidopsis thaliana, feeding by Brevicoryne brassicae aphids interferes with induced defenses against Plutella xylostella caterpillars. This is density dependent: at a low aphid density, the growth rate of P. xylostella was increased, whereas caterpillars feeding on plants colonized by aphids at a high density have a reduced growth rate. Growth of P. xylostella larvae was unaffected on sid2-1 or on dde2-2 mutant plants when feeding simultaneously with a low or high aphid density. This shows that aphid interference with caterpillar-induced defenses requires both SA and JA signal transduction pathways. Transcriptional analysis revealed that simultaneous feeding by caterpillars and aphids at a low density induced the expression of the SA transcription factor gene WRKY70 whereas expression of WRKY70 was lower in plants induced with both caterpillars and a high aphid density. Interestingly, the expression of the JA transcription factor gene MYC2 was significantly higher in plants simultaneously attacked by aphids at a high density and caterpillars. These results indicate that a lower expression level of WRKY70 leads to significantly higher MYC2 expression through SA–JA cross-talk. Thus, plant-mediated interactions between aphids and caterpillars are density dependent and involve phytohormonal cross-talk and differential activation of transcription factors.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Cheaper is not always worse: strongly protective isolates of a defensive symbiont are less costly to the aphid host

Cheaper is not always worse: strongly protective isolates of a defensive symbiont are less costly to the aphid host | Plant, Insect and Microbe Interactions | Scoop.it

Defences against parasites are typically associated with costs to the host that contribute to the maintenance of variation in resistance. This also applies to the defence provided by the facultative bacterial endosymbiont Hamiltonella defensa, which protects its aphid hosts against parasitoid wasps while imposing life-history costs. To investigate the cost–benefit relationship within protected hosts, we introduced multiple isolates of H. defensa to the same genetic backgrounds of black bean aphids, Aphis fabae, and we quantified the protection against their parasitoid Lysiphlebus fabarum as well as the costs to the host (reduced lifespan and reproduction) in the absence of parasitoids. Surprisingly, we observed the opposite of a trade-off. Strongly protective isolates of H. defensa reduced lifespan and lifetime reproduction of unparasitized aphids to a lesser extent than weakly protective isolates. This finding has important implications for the evolution of defensive symbiosis and highlights the need for a better understanding of how strain variation in protective symbionts is maintained

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

An Experimental Test of whether the Defensive Phenotype of an Aphid Facultative Symbiont Can Respond to Selection within a Host Lineage

An Experimental Test of whether the Defensive Phenotype of an Aphid Facultative Symbiont Can Respond to Selection within a Host Lineage | Plant, Insect and Microbe Interactions | Scoop.it

An experiment was conducted to test whether parasitoid resistance within a single clonal line of pea aphid (Acyrthosiphon pisum) might increase after exposure to the parasitoid wasp Aphidius ervi. Any change in resistance was expected to occur through an increase in the density of protective symbiotic bacteria rather than genetic change within the aphid or the bacterial symbiont. Six aphid lineages were exposed to high parasitoid attack rates over nine generations, each line being propagated from individuals that had survived attack; a further six lineages were maintained without parasitoids as a control. At the end of the experiment the strength of resistance of aphids from treatment and control lines were compared. No differences in resistance were found.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Gene amplification and microsatellite polymorphism underlie a recent insect host shift

Gene amplification and microsatellite polymorphism underlie a recent insect host shift | Plant, Insect and Microbe Interactions | Scoop.it

Insect host shifts may lead to sympatric speciation and can create new crop pests, however identifying the genetic changes involved has proved elusive. We studied a subspecies of the aphid Myzus persicae that has recently host shifted to tobacco and are resistant to the plant alkaloid nicotine. We found these races overexpress a cytochrome P450 enzyme (CYP6CY3) that allows them to detoxify nicotine and also certain synthetic insecticides. Overexpression of CYP6CY3 is caused by gene amplification (up to 100 copies) and expansion of a dinucleotide microsatellite in the promoter. Our findings provide insights into the molecular drivers of insect host shifts.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Plant–insect interactions under bacterial influence: ecological implications and underlying mechanisms

Plant–insect interactions under bacterial influence: ecological implications and underlying mechanisms | Plant, Insect and Microbe Interactions | Scoop.it

Plants and insects have been co-existing for more than 400 million years, leading to intimate and complex relationships. Throughout their own evolutionary history, plants and insects have also established intricate and very diverse relationships with microbial associates. Studies in recent years have revealed plant- or insect-associated microbes to be instrumental in plant–insect interactions, with important implications for plant defences and plant utilization by insects. Microbial communities associated with plants are rich in diversity, and their structure greatly differs between below- and above-ground levels. Microbial communities associated with insect herbivores generally present a lower diversity and can reside in different body parts of their hosts including bacteriocytes, haemolymph, gut, and salivary glands. Acquisition of microbial communities by vertical or horizontal transmission and possible genetic exchanges through lateral transfer could strongly impact on the host insect or plant fitness by conferring adaptations to new habitats. Recent developments in sequencing technologies and molecular tools have dramatically enhanced opportunities to characterize the microbial diversity associated with plants and insects and have unveiled some of the mechanisms by which symbionts modulate plant–insect interactions. Here, we focus on the diversity and ecological consequences of bacterial communities associated with plants and herbivorous insects. We also highlight the known mechanisms by which these microbes interfere with plant–insect interactions. Revealing such mechanisms in model systems under controlled environments but also in more natural ecological settings will help us to understand the evolution of complex multitrophic interactions in which plants, herbivorous insects, and micro-organisms are inserted.

more...
No comment yet.
Rescooped by The aphid team@INRA Rennes from Plant Biology Teaching Resources (Higher Education)
Scoop.it!

An Optical Clearing Technique for Plant Tissues Allowing Deep Imaging and Compatible with Fluorescence Microscopy

An Optical Clearing Technique for Plant Tissues Allowing Deep Imaging and Compatible with Fluorescence Microscopy | Plant, Insect and Microbe Interactions | Scoop.it

In this new article in Plant Physiology, an effective new tissue clearing method is used in plants with impressive results. I think this could be easily incorporated for use by undergraduate students. Previously developed as "Scale" method for use in animal tissues, the results were similarly effective (http://www.nature.com/neuro/journal/v14/n11/full/nn.2928.html). See a stunning image of a cleared mouse embryo here: http://www.riken.jp/en/pr/press/2011/20110830_3/.


Via Mary Williams
more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Low Levels of Mitochondrial DNA and Symbiont Diversity in the Worldwide Agricultural Pest, the Greenhouse Whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae)

Low Levels of Mitochondrial DNA and Symbiont Diversity in the Worldwide Agricultural Pest, the Greenhouse Whitefly Trialeurodes vaporariorum (Hemiptera: Aleyrodidae) | Plant, Insect and Microbe Interactions | Scoop.it

Trialeurodes vaporariorum, the greenhouse whitefly, is a cosmopolitan agricultural pest. Little is known about the genetic diversity of T. vaporariorum and the bacterial symbionts associated with this species. Here, we undertook a large phylogeographic study by investigating both the mitochondrial (mt) diversity and the infection status of 38 T. vaporariorum collections from 18 countries around the world. Genetic diversity of T. vaporariorum was studied by analyzing sequence data from the mt cytochrome oxidase I, cytochrome b, and NADH dehydrogenase subunit 5 genes. Maximum-likelihood (ML) phylogeny reconstruction delineated 2 clades characterized by limited sequence divergence: one clade comprised samples only from the Northern hemisphere whereas the other comprised samples from a broader geographical range. The presence of secondary symbionts was determined by PCR using primers specific for Hamiltonella, Rickettsia, Arsenophonus, Cardinium, Wolbachia, and Fritschea. Most individuals examined harbored at least one secondary endosymbiont, and Arsenophonus was detected in almost all male and female individuals. Wolbachia was present at a much lower frequency, and Cardinium was detected in only a few individuals from Greece. Rickettsia, Hamiltonella, and Fritschea were not found. Additionally, we set out to further analyze Arsenophonus diversity by multilocus sequence typing analysis; however, the Arsenophonus sequences did not exhibit any polymorphism. Our results revealed remarkably low diversity in both mtDNA and symbionts in this worldwide agricultural pest, contrasting sharply with that of the ecologically similar Bemisia tabaci.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

The Facultative Symbiont Rickettsia Protects an Invasive Whitefly Against Entomopathogenic Pseudomonas syringae Strains

Facultative endosymbionts can benefit insect hosts in a variety of ways, including context dependent roles such as providing defense against pathogens. The role of some symbionts in defense may be overlooked, however, when pathogen infection is transient, sporadic, or asymptomatic. The facultative endosymbiont Rickettsia increases the fitness of the sweet potato whitefly (Bemisia tabaci) in some populations through mechanisms that are not yet understood. In this study we investigated the role of Rickettsia in mediating the interaction between the sweet potato whitefly and Pseudomonas syringae, a common environmental bacterium, some strains of which are pathogenic to aphids. Our results show that P. syringae multiplies within whiteflies leading to host death and that whiteflies infected with Rickettsia show a decreased rate of death due to P. syringae. Experiments using plants coated with P. syringae confirmed that whiteflies can acquire the bacteria at a low rate while feeding, leading to increased mortality, particularly when the whiteflies are not infected with Rickettsia. These results suggest that P. syringae may affect whitefly populations in nature and that Rickettsia can ameliorate this effect. This study highlights the possible importance of interactions among opportunistic environmental pathogens and endosymbionts of insects.

more...
No comment yet.
Rescooped by The aphid team@INRA Rennes from Plants and Microbes
Scoop.it!

Nature Biotechnology: Engineering insect-free cereals (2015)

Nature Biotechnology: Engineering insect-free cereals (2015) | Plant, Insect and Microbe Interactions | Scoop.it

A cluster of three rice lectin receptor kinases confers resistance to planthopper insects.

 

Insect pests reduce yields of crops worldwide through direct damage and because they spread devastating viral diseases. In Asia, the brown planthopper (BPH) decimates rice (Oryza sativa) crops, causing the loss of billions of dollars annually1. In this issue, Liu et al.2 report the cloning of a rice genetic locus that confers broad-spectrum resistance to BPH and at least one other planthopper species (white back planthopper). Introducing this locus into plant genomes is likely to provide an effective means of combating insect pests of rice and of other cereals such as maize.

 

In modern rice agriculture, BPH damage is controlled through breeding and the application of vast amounts of chemical pesticides1. Pesticides are not a sustainable approach, however, owing to high costs, harmful environmental effects and rapid development of resistant insects. Breeding programs have identified more than 20 genetic loci in cultivated or wild rice species that confer BPH resistance1. However, these Bph loci are usually only effective against specific BPH biotypes, and newly evolved BPH populations have rapidly overcome several Bph resistance loci deployed in the field..

 

Of the >20 identified Bph loci, only Bph14 and Bph26 have been cloned. Both of these loci encode coiled-coil, nucleotide-binding and leucine-rich repeat proteins3, 4, the main class of plant intracellular immune receptors5. Bph3 is a resistance locus that was first pinpointed genetically in the Sri Lankan rice indica cultivar Rathu Heenati. Notably, unlike most other Bph loci, including Bph14 and Bph26, Bph3 confers broad-spectrum resistance to many BPH biotypes as well as to the white back planthopper1, 2. The success of Bph3 as a resistance locus might be linked to the fact that it acts against BPH at an early stage of the feeding cycle, before the insect can deploy its arsenal of virulence proteins that circumvent plant defenses.

 

Despite the huge potential of Bph3 for rice agriculture, its molecular identity has been unknown. Liu et al.2 now identify Bph3 through map-based cloning in a cross between the resistant indica cultivar Rathu Heenati and the susceptible japonica cultivar 02428. Bph3 maps to a 79-kb genomic region that contains a cluster of three lectin receptor kinases, OsLecRK1–3 (ref. 2) (Fig. 1). The authors find that single-nucleotide polymorphisms in these genes are associated with BPH resistance in different cultivated rice accessions. They also show that ectopic expression of the OsLecRK1–3 gene cluster in the susceptible japonica Kitaake cultivar confers BPH resistance.

 

See Liu et al. Nature Biotechnology http://www.nature.com/nbt/journal/v33/n3/full/nbt.3069.html


Via Kamoun Lab @ TSL
more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Insecticidal RNA, the long and short of it

Insecticidal RNA, the long and short of it | Plant, Insect and Microbe Interactions | Scoop.it

Insects cost the agricultural sector billions of dollars every year in lost crop yields and insecticide expenditures. The continued use of chemical insecticides has inadvertently selected for more resistant pest strains, prompting higher doses and more frequent applications to control them. The advent of transgenic plants, such as those expressing insecticidal Bacillus thuringiensis (Bt) toxins, reduces the use of chemicals while offering protection to some crops (1), but not all insects are affected by Bt toxins, and continued use of Bt technologies will eventually see the rise of Bt-resistant insects. To stay ahead of the pests will require additional technologies. On page 991 of this issue, Zhang et al. (2) describe a clever modification to an existing transgenic plant technology that produces insecticidal RNAs. The trick is to express lethal RNA in the plant's photosynthetic organelles, the chloroplasts.

more...
No comment yet.
Rescooped by The aphid team@INRA Rennes from Plants and Microbes
Scoop.it!

Current Opinion in Insect Science: Disruption of insect transmission of plant viruses (2015)

Current Opinion in Insect Science: Disruption of insect transmission of plant viruses (2015) | Plant, Insect and Microbe Interactions | Scoop.it

Plant-infecting viruses are transmitted by a diverse array of organisms including insects, mites, nematodes, fungi, and plasmodiophorids. Virus interactions with these vectors are diverse, but there are some commonalities. Generally the infection cycle begins with the vector encountering the virus in the plant and the virus is acquired by the vector. The virus must then persist in or on the vector long enough for the virus to be transported to a new host and delivered into the plant cell. Plant viruses rely on their vectors for breaching the plant cell wall to be delivered directly into the cytosol. In most cases, viral capsid or membrane glycoproteins are the specific viral proteins that are required for transmission and determinants of vector specificity. Specific molecules in vectors also interact with the virus and while there are few-identified to no-identified receptors, candidate recognition molecules are being further explored in these systems. Due to the specificity of virus transmission by vectors, there are defined steps that represent good targets for interdiction strategies to disrupt the disease cycle. This review focuses on new technologies that aim to disrupt the virus–vector interaction and focuses on a few of the well-characterized virus–vector interactions in the field. In closing, we discuss the importance of integration of these technologies with current methods for plant virus disease control.


Via Kamoun Lab @ TSL
more...
Steve Marek's curator insight, February 26, 9:27 AM

Not fungal, but still an excellent review with great insights on important plant pathosystems.

Bharat Employment's curator insight, February 27, 4:46 AM

http://www.bharatemployment.com/

Scooped by The aphid team@INRA Rennes
Scoop.it!

Cryptic Virulence and Avirulence Alleles Revealed by Controlled Sexual Recombination in Pea Aphids

Although aphids are worldwide crop pests, little is known about aphid effector genes underlying virulence and avirulence. Here we show that controlling the genetics of both aphid and host can reveal novel recombinant genotypes with previously undetected allelic variation in both virulence and avirulence functions. Clonal F1 progeny populations were derived from reciprocal crosses and self-matings between two parental genotypes of pea aphid (Acyrthosiphon pisum) differing in virulence on a Medicago truncatula host carrying the RAP1 and RAP2 resistance genes. These populations showed Mendelian segregation consistent with aphid performance being controlled largely by a dominant virulence allele derived from only one parent. Altered segregation ratios on near-isogenic host genotypes differing in the region carrying RAP1 were indicative of additional heritable functions likely related to avirulence genes originating from both parents. Unexpectedly, some virulent F1 progeny were recovered from selfing of an avirulent parent, suggesting a reservoir of cryptic alleles. Host chlorosis was associated with virulence, whereas necrotic hypersensitive-like response was not. No maternal inheritance was found for any of these characteristics, ruling out sex-linked, cytoplasmic, and endosymbiotic factors. Our results demonstrate the tractability of dissecting the genetic basis of pest-host resistance mechanisms and indicate that the annual sexual cycle in aphids may lead to frequent novel genotypes with both increased and decreased virulence. Availability of genomes for both pest and host can facilitate definition of cognate gene-for-gene relationships, potentially leading to selection of crop genotypes with multiple resistance traits.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

The global distribution of diet breadth in insect herbivores

The global distribution of diet breadth in insect herbivores | Plant, Insect and Microbe Interactions | Scoop.it

Understanding variation in resource specialization is important for progress on issues that include coevolution, community assembly, ecosystem processes, and the latitudinal gradient of species richness. Herbivorous insects are useful models for studying resource specialization, and the interaction between plants and herbivorous insects is one of the most common and consequential ecological associations on the planet. However, uncertainty persists regarding fundamental features of herbivore diet breadth, including its relationship to latitude and plant species richness. Here, we use a global dataset to investigate host range for over 7,500 insect herbivore species covering a wide taxonomic breadth and interacting with more than 2,000 species of plants in 165 families. We ask whether relatively specialized and generalized herbivores represent a dichotomy rather than a continuum from few to many host families and species attacked and whether diet breadth changes with increasing plant species richness toward the tropics. Across geographic regions and taxonomic subsets of the data, we find that the distribution of diet breadth is fit well by a discrete, truncated Pareto power law characterized by the predominance of specialized herbivores and a long, thin tail of more generalized species. Both the taxonomic and phylogenetic distributions of diet breadth shift globally with latitude, consistent with a higher frequency of specialized insects in tropical regions. We also find that more diverse lineages of plants support assemblages of relatively more specialized herbivores and that the global distribution of plant diversity contributes to but does not fully explain the latitudinal gradient in insect herbivore specialization.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Experimental replacement of an obligate insect symbiont

In many invertebrates, development depends on obligate bacterial symbionts that are confined to specialized host cells and are transmitted directly from mother to progeny. A primary model for this kind of symbiosis is the Buchnera/pea aphid association, which has been maintained for more than 100 million years through strict maternal transmission. The intimacy of this symbiosis has thwarted experiments aimed at dissecting how symbiont and host genotypes contribute to overall phenotype and ecological tolerances. Using a selectable Buchnera phenotype combined with microinjection, we successfully replaced Buchnera within a matriline, thus generating matrilines with identical aphid genotypes but distinct Buchnera genotypes. Buchnera replacement dramatically increased heat tolerance of the aphid matriline, demonstrating directly that symbiont genotype can affect host ecology.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Cannibalism in the pea aphid, Acyrthosiphon pisum. - PubMed - NCBI

An experiment was conducted to test whether parasitoid resistance within a single clonal line of pea aphid (Acyrthosiphon pisum) might increase after exposure to the parasitoid wasp Aphidius ervi. Any change in resistance was expected to occur through an increase in the density of protective symbiotic bacteria rather than genetic change within the aphid or the bacterial symbiont. Six aphid lineages were exposed to high parasitoid attack rates over nine generations, each line being propagated from individuals that had survived attack; a further six lineages were maintained without parasitoids as a control. At the end of the experiment the strength of resistance of aphids from treatment and control lines were compared. No differences in resistance were found.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

BMC Genomics | Full text | Adenine methylation may contribute to endosymbiont selection in a clonal aphid population

BMC Genomics | Full text | Adenine methylation may contribute to endosymbiont selection in a clonal aphid population | Plant, Insect and Microbe Interactions | Scoop.it
The pea aphid Acyrthosiphon pisum has two modes of reproduction: parthenogenetic during the spring and summer and sexual in autumn. This ability to alternate between reproductive modes and the emergence of clonal populations under favorable conditions make this organism an interesting model for genetic and epigenetic studies. The pea aphid hosts different types of endosymbiotic bacteria within bacteriocytes which help the aphids survive and adapt to new environmental conditions and habitats. The obligate endosymbiont Buchnera aphidicola has a drastically reduced and stable genome, whereas facultative endosymbionts such as Regiella insecticola have large and dynamic genomes due to phages, mobile elements and high levels of genetic recombination. In previous work, selection toward cold adaptation resulted in the appearance of parthenogenetic A. pisum individuals characterized by heavier weights and remarkable green pigmentation.
more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Pea aphid biotype performance on diverse Medicago host genotypes in... - PubMed - NCBI

Bull Entomol Res. 2014 Dec;104(6):689-701. doi: 10.1017/S0007485314000443.

Aphid-plant interactions depend on genotypes of both organisms, which determine the two-way molecular exchange that leads to compatible or incompatible outcomes. The underlying genes are mostly unknown, making it difficult to predict likelihood of aphid success or host resistance, and hampering crop genetic improvement. Here we screened eight pea aphid clonal genotypes collected from diverse legume hosts, on a species-wide panel of Medicago truncatula (Mt) genotypes. Aphid virulence was measured by survival, fecundity and growth rate, together with scores for chlorosis and necrosis as host response indicators. Outcomes were highly dependent on the specific aphid-host genotype combinations. Only one Mt line was fully resistant against all clones. Aphid-induced host chlorosis and necrosis varied greatly, but correlated with resistance only in a few combinations. Bi-clustering analysis indicated that all aphid clones could be distinguished by their performance profiles across the host genotypes tested, with each clone being genetically differentiated and potentially representing a distinct biotype. Clones originating from Medicago sativa ranged from highly virulent to almost completely avirulent on both Medicago species, indicating that some were well adapted, whereas others were most likely migrants. Comparisons of closely related pairs of Australian Mt genotypes differing in aphid resistance revealed no enhanced resistance to European pea aphid clones. Based on the extensive variation in pea aphid adaptation even on unfamiliar hosts, most likely reflecting multiple biotype-specific gene-for-gene interactions, we conclude that robust defences require an arsenal of appropriate resistance genes.

more...
No comment yet.
Rescooped by The aphid team@INRA Rennes from Plants and Microbes
Scoop.it!

Journal of Experimental Botany: Persistence and transgenerational effect of plant-mediated RNAi in aphids (2014)

Journal of Experimental Botany: Persistence and transgenerational effect of plant-mediated RNAi in aphids (2014) | Plant, Insect and Microbe Interactions | Scoop.it

Plant-mediated RNA interference (RNAi) has been successfully used as a tool to study gene function in aphids. The persistence and transgenerational effects of plant-mediated RNAi in the green peach aphid (GPA) Myzus persicae were investigated, with a focus on three genes with different functions in the aphid. Rack1 is a key component of various cellular processes inside aphids, while candidate effector genes MpC002and MpPIntO2 (Mp2) modulate aphid–plant interactions. The gene sequences and functions did not affect RNAi-mediated down-regulation and persistence levels in the aphids. Maximal reduction of gene expression was ~70% and this was achieved at between 4 d and 8 d of exposure of the aphids to double-stranded RNA (dsRNA)-producing transgenic Arabidopsis thaliana. Moreover, gene expression levels returned to wild-type levels within ~6 d after removal of the aphids from the transgenic plants, indicating that a continuous supply of dsRNA is required to maintain the RNAi effect. Target genes were also down-regulated in nymphs born from mothers exposed to dsRNA-producing transgenic plants, and the RNAi effect lasted twice as long (12–14 d) in these nymphs. Investigations of the impact of RNAi over three generations of aphids revealed that aphids reared on dsMpC002 transgenic plants experienced a 60% decline in aphid reproduction levels compared with a 40% decline of aphids reared on dsRack1 and dsMpPIntO2 plants. In a field setting, a reduction of the aphid reproduction by 40–60% would dramatically decrease aphid population growth, contributing to a substantial reduction in agricultural losses.


Via Kamoun Lab @ TSL
more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

Faba bean forisomes can function in defense against generalist aphids - MEDINA-ORTEGA - Plant, Cell & Environment - Wiley Online Library

Faba bean forisomes can function in defense against generalist aphids - MEDINA-ORTEGA - Plant, Cell & Environment - Wiley Online Library | Plant, Insect and Microbe Interactions | Scoop.it
Abstract

Phloem sieve elements have shut-off mechanisms that prevent loss of nutrient-rich phloem sap when the phloem is damaged. Some phloem proteins, such as the proteins that form forisomes in legume sieve elements are one such mechanism, and in response to damage, they instantly form occlusions that stop the flow of sap. It has long been hypothesized that one function of phloem proteins is defense against phloem sap-feeding insects such as aphids. This study provides the first experimental evidence that aphid feeding can induce phloem protein occlusion and that the aphid-induced occlusions inhibit phloem sap ingestion. The great majority of phloem penetrations in Vicia faba by the generalist aphids Myzus persicae and Macrosiphum euphorbiae triggered forisome occlusion, and the aphids eventually withdrew their stylets without ingesting phloem sap. This contrasts starkly with a previous study on the legume specialist aphid, Acyrthosiphon pisum, where penetration of faba bean sieve elements did not trigger forisome occlusion, and the aphids readily ingested phloem sap. Next, forisome occlusion was demonstrated to be the cause of failed phloem ingestion attempts by M. persicae: when occlusion was inhibited by the calcium channel blocker lanthanum, M. persicae readily ingested faba bean phloem sap.

more...
No comment yet.
Scooped by The aphid team@INRA Rennes
Scoop.it!

The Vat Locus Encodes for a CC-NBS-LRR Protein that Confers Resistance to Aphis gossypii Infestation and A. gossypii-Mediated Virus Resistance - Dogimont - The Plant Journal - Wiley Online Library

Abstract:
Aphis gossypii is a polyphagous sucking aphid and a vector for many viruses. In Cucumis melo, a dominant locus, Vat, confers a high level of resistance to Aphis gossypii infestation and to viruses transmitted by this vector. To investigate the mechanism underlying this double resistance, we first genetically dissected the Vat locus. We delimited the double resistance to a single gene that encodes for a CC-NBS-LRR protein type. To validate the genetic data, transgenic lines expressing the Vat gene were generated and assessed for the double resistance. In this analysis, Vat-transgenic plants were resistant to A. gossypii infestation as well as A. gossypii-mediated virus transmission. When the plants were infected mechanically, virus infection occurred on both transgenic and non-transgenic control plants. These results confirmed that the cloned CC-NBS-LRR gene mediates both resistance to aphid infestation and virus infection using A. gossypii as a vector. This resistance also invokes a separate recognition and response phases in which the recognition phase involves the interaction of an elicitor molecule from the aphid and Vat from the plant. The response phase is not specific and blocks both aphid infestation and virus infection. Sequence analysis of Vat alleles suggests a major role of an unusual conserved LRR repeat in the recognition of A. gossypii.

more...
No comment yet.