An analysis of plant-aphid interactions by different microarray hybridization strategies

Exogenous stimulation of Tanacetum vulgare roots with pipecolic acid leads to tissue-specific responses in terpenoid composition

Tanacetum vulgare L., tansy, is a perennial plant with highly variable terpenoid composition, with mono- and sesquiterpenoids being the most abundant. The high diversity of terpenoids plays an important role in mediating ecological interactions. However, the distribution of terpenoids in different tissues and inducibility of terpenoids in these tissues via biotic stress are poorly understood. We investigated changes in terpenoid profiles and concentrations in different organs following treatment of roots with pipecolic acid (Pip), a non-proteinogenic amino acid that triggers defence responses leading to induce systemic resistance (SAR) in plants. Tansy leaves and midribs contained mainly monoterpenoids, while coarse and fine roots contained mainly sesquiterpenoids. Rhizomes contained terpenoid profiles of both midribs and roots but also unique compounds. Treatment with Pip led to an increase in concentrations of mono- and sesquiterpenoids in all tissues except rhizomes. However, significantly more sesquiterpenoids was formed in root tissues in response to Pip treatment, compared to shoots. The metabolic atlas for terpenoids presented here shows that there is exceptionally strong differentiation of terpenoid patterns and terpenoid content in different tissues of tansy. This, together with differential inducibility by Pip, suggests that the chemical diversity of terpenoids may play an important role in tansy ecological interactions and defence against biotic stressors that feed on below- and aboveground organs.

Non-volatile metabolites mediate plant interactions with insect herbivores

Non-volatile metabolites constitute the bulk of plant biomass. From the perspective of plant-insect interactions, these structurally diverse compounds include nutritious core metabolites and defensive specialized metabolites. In this review, we synthesize the current literature on multiple scales of plant-insect interactions mediated by non-volatile metabolites. At the molecular level, functional genetics studies have revealed a large collection of receptors targeting plant non-volatile metabolites in model insect species and agricultural pests. By contrast, examples of plant receptors of insect-derived molecules remain sparse. For insect herbivores, plant non-volatile metabolites function beyond the dichotomy of core metabolites, classed as nutrients, and specialized metabolites, classed as defensive compounds. Insect feeding tends to elicit evolutionarily conserved changes in plant specialized metabolism, whereas its effect on plant core metabolism varies widely based the interacting species. Finally, several recent studies have demonstrated that non-volatile metabolites can mediate tripartite communication on the community scale, facilitated by physical connections established through direct root-to-root communication, parasitic plants, arbuscular mycorrhizae and the rhizosphere microbiome. Recent advances in both plant and insect molecular biology will facilitate further research on the role of non-volatile metabolites in mediating plant-insect interactions.

Defensive Resistance of Cowpea Vigna unguiculata Control Megalurothrips usitatus Mediated by Jasmonic Acid or Insect Damage

Vigna unguiculata is a vital vegetable crop in Southeast Asia, and Megalurothrips usitatus can cause huge damage to this crop. Enhancing the resistance of V. unguiculata against M. usitatus is a promising way to protect this crop; however, there is limited information regarding the mechanism underlying the resistance of V. unguiculata against M. usitatus. Here, a behavior assay was performed to explore the resistance of V. unguiculata against M. usitatus after insect damage or treatment by jasmonic acid (JA). Furthermore, transcriptome and metabonomics analysis was used to detect the putative mechanism underlying the resistance of V. unguiculata against M. usitatus. The pre-treatment of Vigna unguiculata with JA or infestation with Megalurothrips usitatus alleviated the damage resulting from the pest insect. We further identified differentially expressed genes and different metabolites involved in flavonoid biosynthesis and alpha-linolenic acid metabolism. Genes of chalcone reductase and shikimate O-hydroxycinnamoyltransferase involved in flavonoid biosynthesis, as well as lipoxygenase and acyl-CoA oxidase involved in alpha-linolenic acid metabolism, were upregulated in plants after herbivory or JA supplementation. The upregulation of these genes contributed to the high accumulation of metabolites involved in flavonoid biosynthesis and the alpha-linolenic acid metabolism pathway. These transcriptional and metabolite changes are potentially responsible for plant defense and a putative regulatory model is thus proposed to illustrate the cowpea defense mechanism against insect attack. Our study provides candidate targets for the breeding of varieties with resistance to insect herbivory by molecular technology.

Identification of Differentially Expressed Genes in Resistant Tetraploid Wheat (Triticum turgidum) under Sitobion avenae (F.) Infestation

The grain aphid Sitobion avenae (Fabricius) is one of the most destructive pests of wheat (Triticum aestivum). Deployment of resistant wheat germplasm appears as an excellent solution for this problem. Elite bread wheat cultivars only have limited resistance to this pest. The present study was carried out to investigate the potential of the tetraploid wheat (Triticum turgidum) variety Lanmai, which showed high resistance to S. avenae at both seedling and adult plant stages, as a source of resistance genes. Based on apterous adult aphids’ fecundity tests and choice bioassays, Lanmai has been shown to display antixenosis and antibiosis. Suppression subtractive hybridization (SSH) was employed to identify and isolate the putative candidate defense genes in Lanmai against S. avenae infestation. A total of 134 expressed sequence tags (ESTs) were identified and categorized based on their putative functions. RT-qPCR analysis of 30 selected genes confirmed their differential expression over time between the resistant wheat variety Lanmai and susceptible wheat variety Polan305 during S. avenae infestation. There were 11 genes related to the photosynthesis process, and only 3 genes showed higher expression in Lanmai than in Polan305 after S. avenae infestation. Gene expression analysis also revealed that Lanmai played a critical role in salicylic acid and jasmonic acid pathways after S. avenae infestation. This study provided further insights into the role of defense signaling networks in wheat resistance to S. avenae and indicates that the resistant tetraploid wheat variety Lanmai may provide a valuable resource for aphid tolerance improvement in wheat.

Transcriptomic Profiling Reveals Shared Signalling Networks Between Flower Development and Herbivory-Induced Responses in Tomato

Most flowering plants must defend themselves against herbivores for survival and attract pollinators for reproduction. Although traits involved in plant defence and pollinator attraction are often localised in leaves and flowers, respectively, they will show a diffuse evolution if they share the same molecular machinery and regulatory networks. We performed RNA-sequencing to characterise and compare transcriptomic changes involved in herbivory-induced defences and flower development, in tomato leaves and flowers, respectively. We found that both the herbivory-induced responses and flower development involved alterations in jasmonic acid signalling, suppression of primary metabolism and reprogramming of secondary metabolism. We identified 411 genes that were involved in both processes, a number significantly higher than expected by chance. Genetic manipulation of key regulators of induced defences also led to the expression changes in the same genes in both leaves and flowers. Targeted metabolomic analysis showed that among closely related tomato species, jasmonic acid and α-tomatine are correlated in flower buds and herbivory-induced leaves. These findings suggest that herbivory-induced responses and flower development share a common molecular machinery and likely have coevolved in nature.

Dynamics of Zea mays transcriptome in response to a polyphagous herbivore, Spodoptera litura

Zea mays defense response is well-crafted according to the physical and chemical weapons utilized by their invaders during the coevolutionary period. Maize plants employ diversified defense strategies and alter the spatiotemporal distribution of several classes of defensive compounds to affect insect herbivore performance. However, only little knowledge is available about the defense orchestration of maize in response to Spodoptera litura, a voracious Noctuidae pest. In order to decipher the defense status of Zea mays (African tall variety) against S. litura, a comparative feeding bioassay was executed, which revealed reduced performance of the herbivore on maize. In order to understand the molecular mechanism behind maize tolerance against S. litura, a microarray-based genome-wide expression analysis was performed. The comparative analysis displayed 792 differentially expressed genes (DEGs), wherein 357 genes were upregulated and 435 genes were downregulated at fold change ≥ 2 and p value ≤ 0.05. The upregulated genes were identified and categorized as defense-related, oxidative stress-related, transcription regulatory genes, protein synthesis genes, phytohormone-related, and primary and secondary metabolism-related. In contrast, downregulated genes were mainly associated with plant growth and development, indicating a balance of growth and defense response and utilization of a highly evolved C-diversion response were noticed. Maize plants showed better tolerance against herbivory and maintained its fitness using a combinatorial strategy. This peculiar response of Zea mays against S. litura offers an excellent possibility of managing polyphagous pests by spicing up the plant's defensive response with tolerance mechanism.

Differential defense responses of tropical grasses to Mahanarva spectabilis (Hemiptera: Cercopidae) infestation

The spittlebugs Mahanarva spectabilis economically challenges cattle production of neotropical regions, due to its voracious feeding on tropical grasses. Here, we evaluated biochemical responses of the interaction between M. spectabilis and the widely cultivated tropical grasses Brachiaria spp. (i.e., brizantha and decumbens) and elephant grasses (cvs. Roxo de Botucatu and Pioneiro), regarding lipoxygenases, protease inhibitors, phytohormones, and proteolytic activities in the midgut of M. spectabilis. The M. spectabilis-infested grasses increased lipoxygenases activity, except for cv. Pioneiro. The levels of the phytohormones jasmonic and abscisic acids were similarly low in all genotypes and increased under herbivory. Furthermore, salicylic acid concentration was constitutively higher in Brachiaria sp., increasing only in spittlebug-infested B. decumbens. M. spectabilis infestations did not induce increases of protease inhibitors in any forage grass type. The trypsin activity remained unaltered, and the total proteolytic activity increased only in B. decumbens-fed insects. Our findings revealed that most forage grasses exposed to spittlebugs activate the lipoxygenases pathway, resulting in increased abscisic and jasmonic acids. However, greater amounts of these hormones do not induce protease inhibitory activity in response to spittlebug attack. This knowledge certainly helps to guide future projects aiming at reducing the impact of spittlebugs on forage production.

Insects-plants-pathogens: Toxicity, dependence and defense dynamics

In a natural ecosystem, the pathogen-plant-insect relationship has diverse implications for each other. The pathogens as well as insect-pests consume plant tissues as their feed that mostly results in damage. In turn, plant species have evolved specialized defense system to not only protect themselves but reduce the damage also. Such tripartite interactions involve toxicity, metabolic modulations, resistance etc. among all participants of interaction. These attributes result in selection pressure among participants. Coevolution of such traits reveals need to focus and unravel multiple hidden aspects of insect-plant-pathogen interactions. The definite modulations during plant responses to biotic stress and the operating defense network against herbivores are vital to research areas. Different types of plant pathogens and herbivores are tackled with various changes in plants, e.g. changes in genes expression, glucosinolate metabolism detoxification, signal transduction, cell wall modifications, Ca²⁺dependent signaling. It is essential to clarify which chemical in plants can work as a defense signal or weapon in plant-pathogen-herbivore interactions. In spite of increased knowledge regarding signal transduction pathways regulating growth-defense balance, much more is needed to unveil the coordination of growth rate with metabolic modulations in bi-trophic interactions. Here, we addressed plant-pathogen-insect interaction for toxicity as well as dependnce along with plant defense dynamics against pathogens and insects with broad range effects at the physio-biochemical and molecular level. We have reviewed interfaces in plant-pathogen-insect research to show pulsating regulation of plant immunity for attuning survival and ecological equilibrium. An improved understanding of the systematic foundation of growth-defense stability has vital repercussions for enhancing crop yield, including insights into uncoupling of host-parasite tradeoffs for ecological and environmental sustainability.

The Multifunctional Roles of Polyphenols in Plant-Herbivore Interactions

There is no argument to the fact that insect herbivores cause significant losses to plant productivity in both natural and agricultural ecosystems. To counter this continuous onslaught, plants have evolved a suite of direct and indirect, constitutive and induced, chemical and physical defenses, and secondary metabolites are a key group that facilitates these defenses. Polyphenols—widely distributed in flowering plants—are the major group of such biologically active secondary metabolites. Recent advances in analytical chemistry and metabolomics have provided an opportunity to dig deep into extraction and quantification of plant-based natural products with insecticidal/insect deterrent activity, a potential sustainable pest management strategy. However, we currently lack an updated review of their multifunctional roles in insect-plant interactions, especially focusing on their insect deterrent or antifeedant properties. This review focuses on the role of polyphenols in plant-insect interactions and plant defenses including their structure, induction, regulation, and their anti-feeding and toxicity effects. Details on mechanisms underlying these interactions and localization of these compounds are discussed in the context of insect-plant interactions, current findings, and potential avenues for future research in this area.

Aphid-Responsive Defense Networks in Hybrid Switchgrass

Aphid herbivory elicits plant defense-related networks that are influenced by host genetics. Plants of the upland switchgrass (Panicum virgatum) cultivar Summer can be a suitable host for greenbug aphids (Schizaphis graminum; GB), and yellow sugarcane aphids (Sipha flava, YSA), whereas the lowland cultivar Kanlow exhibited multi-species resistance that curtails aphid reproduction. However, stabilized hybrids of Summer (♀) x Kanlow (♂) (SxK) with improved agronomics can be damaged by both aphids. Here, hormone and metabolite analyses, coupled with RNA-Seq analysis of plant transcriptomes, were utilized to delineate defense networks induced by aphid feeding in SxK switchgrass and pinpoint plant transcription factors (TFs), such as WRKYs that potentially regulate these responses. Abscisic acid (ABA) levels were significantly higher in GB infested plants at 5 and 10 days after infestation (DAI). ABA levels were highest at 15DAI in YSA infested plants. Jasmonic acid levels were significantly elevated under GB infestation, while salicylic acid levels were signifi40cantly elevated only at 15 DAI in YSA infested plants. Similarly, levels of several metabolites were altered in common or specifically to each aphid. YSA infestation induced a significant enrichment of flavonoids consistent with an upregulation of many genes associated with flavonoid biosynthesis at 15DAI. Gene co-expression modules that responded singly to either aphid or in common to both aphids were differentiated and linked to specific TFs. Together, these data provide important clues into the interplay of metabolism and transcriptional remodeling accompanying defense responses to aphid herbivory in hybrid switchgrass.

Characterization of STP4 promoter in Indian mustard Brassica juncea for use as an aphid responsive promoter

OBJECTIVE

Brassica juncea, a major oilseed crop, suffers substantial yield losses due to infestation by mustard aphids (Lipaphis erysimi). Unavailability of resistance genes within the accessible gene pool underpins significance of the transgenic strategy in developing aphid resistance. In this study, we aimed for the identification of an aphid-responsive promoter from B. juncea, based on the available genomic resources.

RESULTS

A monosaccharide transporter gene, STP4 in B. juncea was activated by aphids and sustained increased expression as the aphids colonized the plants. We cloned the upstream intergenic region of STP4 and validated its stand-alone aphid-responsive promoter activity. Further, deletion analysis identified the putative cis-elements important for the aphid responsive promoter activity.

CONCLUSION

The identified STP4 promoter can potentially be used for driving high level aphid-inducible expression of transgenes in plants. Use of aphid-responsive promoter instead of constitutive promoters can potentially reduce the metabolic burden of transgene-expression on the host plant.

Comprehensive transcriptome analysis of grafting onto Artemisia scoparia W. to affect the aphid resistance of chrysanthemum (Chrysanthemum morifolium T.)

BACKGROUND

Aphid (Macrosiphoniella sanbourni) stress drastically influences the yield and quality of chrysanthemum, and grafting has been widely used to improve tolerance to biotic and abiotic stresses. However, the effect of grafting on the resistance of chrysanthemum to aphids remains unclear. Therefore, we used the RNA-Seq platform to perform a de novo transcriptome assembly to analyze the self-rooted grafted chrysanthemum (Chrysanthemum morifolium T. 'Hangbaiju') and the grafted Artermisia-chrysanthemum (grafted onto Artemisia scoparia W.) transcription response to aphid stress.

RESULTS

The results showed that there were 1337 differentially expressed genes (DEGs), among which 680 were upregulated and 667 were downregulated, in the grafted Artemisia-chrysanthemum compared to the self-rooted grafted chrysanthemum. These genes were mainly involved in sucrose metabolism, the biosynthesis of secondary metabolites, the plant hormone signaling pathway and the plant-to-pathogen pathway. KEGG and GO enrichment analyses revealed the coordinated upregulation of these genes from numerous functional categories related to aphid stress responses. In addition, we determined the physiological indicators of chrysanthemum under aphid stress, and the results were consistent with the molecular sequencing results. All evidence indicated that grafting chrysanthemum onto A. scoparia W. upregulated aphid stress responses in chrysanthemum.

CONCLUSION

In summary, our study presents a genome-wide transcript profile of the self-rooted grafted chrysanthemum and the grafted Artemisia-chrysanthemum and provides insights into the molecular mechanisms of C. morifolium T. in response to aphid infestation. These data will contribute to further studies of aphid tolerance and the exploration of new candidate genes for chrysanthemum molecular breeding.

Plant Genes Benefitting Aphids-Potential for Exploitation in Resistance Breeding

Aphids are phloem sap-feeding insects common as pests in various crops. Here we review 62 omics studies of aphid/plant interactions to search for indications of how aphids may manipulate the plants to make them more suitable as hosts, i.e. more susceptible. Our aim is to try to reveal host plant susceptibility (S) genes, knowledge which can be exploited for making a plant more resistant to its pest by using new plant breeding techniques to knock out or down such S genes. S genes may be of two types, those that are involved in reducing functional plant defense and those involved in further increasing plant factors that are positive to the aphid, such as facilitated access to food or improved nutritional quality. Approximately 40% of the omics studies we have reviewed indicate how aphids may modify their host to their advantage. To exploit knowledge obtained so far, we suggest knocking out/down candidate aphid S genes using CRISPR/Cas9 or RNAi techniques in crops to evaluate if this will be sufficient to keep the aphid pest at economically viable levels without severe pleiotropic effects. As a complement, we also propose functional studies of recessively inherited resistance previously discovered in some aphid-crop combinations, to potentially identify new types of S genes that later could be knocked out or down also in other crops to improve their resistance to aphids.

Metabotype variation in a field population of tansy plants influences aphid host selection

It is well known that plant volatiles influence herbivores in their selection of a host plant; however, less is known about how the nonvolatile metabolome affects herbivore host selection. Metabolic diversity between intraspecific plants can be characterized using non-targeted mass spectrometry that gives us a snapshot overview of all metabolic processes occurring within a plant at a particular time. Here, we show that non-targeted metabolomics can be used to reveal links between intraspecific chemical diversity and ecological processes in tansy (Tanacetum vulgare). First, we show that tansy plants can be categorized into five subgroups based up on their metabolic profiles, and that these "metabotypes" influenced natural aphid colonization in the field. Second, this grouping was not due to induced metabolomic changes within the plant due to aphid feeding but rather resulted from constitutive differences in chemical diversity between plants. These findings highlight the importance of intraspecific chemical diversity within one plant population and provide the first report of a non-targeted metabolomic field study in chemical ecology.

Green leaf volatile production by plants: a meta-analysis

666 I. Introduction 667 II. Biosynthesis 667 III. Meta-analysis 669 IV. The type of stress influences the total amount of GLVs released 669 V. Herbivores can modulate the wound-induced release of GLVs 669 VI. Fungal infection greatly induces GLV production 672 VII. Monocots and eudicots respond differentially to different types of stress 673 VIII. The type of stress does not influence the proportion of GLVs per chemical class 673 IX. The type of stress does influence the isomeric ratio within each chemical class 674 X. GLVs: from signal perception to signal transduction 676 XI. GLVs influence the C/N metabolism 677 XII. Interaction with plant hormones 678 XIII. General conclusions and unanswered questions 678 Acknowledgements 679 References 679 SUMMARY: Plants respond to stress by releasing biogenic volatile organic compounds (BVOCs). Green leaf volatiles (GLVs), which are abundantly produced across the plant kingdom, comprise an important group within the BVOCs. They can repel or attract herbivores and their natural enemies; and they can induce plant defences or prime plants for enhanced defence against herbivores and pathogens and can have direct toxic effects on bacteria and fungi. Unlike other volatiles, GLVs are released almost instantly upon mechanical damage and (a)biotic stress and could thus function as an immediate and informative signal for many organisms in the plant's environment. We used a meta-analysis approach in which data from the literature on GLV production during biotic stress responses were compiled and interpreted. We identified that different types of attackers and feeding styles add a degree of complexity to the amount of emitted GLVs, compared with wounding alone. This meta-analysis illustrates that there is less variation in the GLV profile than we presumed, that pathogens induce more GLVs than insects and wounding, and that there are clear differences in GLV emission between monocots and dicots. Besides the meta-analysis, this review provides an update on recent insights into the perception and signalling of GLVs in plants.

Pea aphid infestation induces changes in flavonoids, antioxidative defence, soluble sugars and sugar transporter expression in leaves of pea seedlings

The perception of aphid infestation induces highly coordinated and sequential defensive reactions in plants at the cellular and molecular levels. The aim of the study was to explore kinetics of induced antioxidative defence responses in leaf cells of Pisum sativum L.cv. Cysterski upon infestation of the pea aphid Acyrthosiphon pisum at varying population sizes, including accumulation of flavonoids, changes of carbon metabolism, and expression of nuclear genes involved in sugar transport. Within the first 96 h, after A. pisum infestation, flavonoid accumulation and increased peroxidase activity were observed in leaves. The level of pisatin increased after 48 h of infestation and reached a maximum at 96 h. At this time point, a higher concentration of flavonols was observed in the infested tissue than in the control. Additionally, strong post-infestation accumulation of chalcone synthase (CHS) and isoflavone synthase (IFS) transcription products was also found. The levels of sucrose and fructose in 24-h leaves infested by 10, 20, and 30 aphids were significantly lower than in the control. Moreover, in leaves infested by 30 aphids, the reduced sucrose level observed up to 48 h was accompanied by a considerable increase in the expression level of the PsSUT1 gene encoding the sucrose transporter. In conclusion, A. pisum infestation on pea leads to stimulation of metabolic pathways associated with defence.

Genome-wide identification of calcium-dependent protein kinases in soybean and analyses of their transcriptional responses to insect herbivory and drought stress

Calcium-dependent protein kinases (CDPKs) are plant-specific calcium sensors that play important roles in various aspects of plant physiology. Here, we investigated phylogenic relationships, chromosomal locations, gene structures, and tissue-specific, herbivory- and drought-induced expression profiles of soybean (Glycine max) GmCDPKs. Fifty GmCDPK genes were identified, which phylogenetically grouped into 4 distinct clusters and distributed across 13 sub-clusters. Individual classes of GmCDPKs harbor highly conserved mRNA splicing sites, and their exon numbers and lengths were consistent with the phylogenetic relationships, suggesting that at least 13 ancestral CDPK genes had emerged before the split of monocots and eudicots. Gene expression analysis indicated that several GmCDPKs were tissue-specific expressed. GmCDPKs' transcript levels changed after wounding, exhibited specific expression patterns after simulated Spodoptera exigua feeding or soybean aphid (Aphis glycines) herbivory, and were largely independent of the phytohormones jasmonic acid and salicylic acid. The most pronounced transcriptional responses were detected after drought and abscisic acid treatments with more than half of all GmCDPKs being upregulated, suggesting their important roles during abiotic stress responses in soybean. Our data provide an important foundation for further functional dissection of GmCDPKs, especially in the context of soybean-insect interactions and drought stress adaptation.

QTL Mapping by SLAF-seq and Expression Analysis of Candidate Genes for Aphid Resistance in Cucumber

Cucumber, a very important vegetable crop worldwide, is easily damaged by pests. Aphid is one of the most serious cucumber pests and frequently cause severe damage to commercially produced crops. Understanding the genetic mechanisms underlying pest resistance is important for aphid-resistant cucumber varieties breeding. In this study, two parental cucumber lines, JY30 (aphid susceptible) and EP6392 (aphid resistant), and pools of resistant and susceptible (n = 50 each) plants from 1000 F2 individuals derived from crossing JY30 with EP6392, were used to detect genomic regions associated with aphid resistance in cucumbers. The analysis was performed using specific length amplified fragment sequencing (SLAF-seq), bulked segregant analysis (BSA), and single nucleotide polymorphism index (SNP-index) methods. A main effect QTL (quantitative trait locus) of 0.31 Mb on Chr5, including 43 genes, was identified by association analysis. Sixteen of the 43 genes were identified as potentially associated with aphid resistance through gene annotation analysis. The effect of aphid infestation on the expression of these candidate genes screened by SLAF-seq was investigated in EP6392 plants by qRT-PCR. The results indicated that seven genes including encoding transcription factor MYB59-like (Csa5M641610.1), auxin transport protein BIG-like (Csa5M642140.1), F-box/kelch-repeat protein At5g15710-like (Csa5M642160.1), transcription factor HBP-1a-like (Csa5M642710.1), beta-glucan-binding protein (Csa5M643380.1), endo-1,3(4)-beta-glucanase 1-like (Csa5M643880.1), and proline-rich receptor-like protein kinase PERK10-like (Csa5M643900.1), out of the 16 genes were down regulated after aphid infestation, whereas 5 genes including encoding probable leucine-rich repeat (LRR) receptor-like serine/threonine-protein kinase At5g15730-like (Csa5M642150.1), Stress-induced protein KIN2 (Csa5M643240.1 and Csa5M643260.1), F-box family protein (Csa5M643280.1), F-box/kelch-repeat protein (Csa5M643290.1), were up-regulated after aphid infestation. The gene Csa5M642150.1, encoding probable LRR receptor-like serine/threonine-protein kinase At5g15730-like, was most likely a key candidate gene in cucumber plants in response to infestation. This study provides a certain theoretical basis of molecular biology for genetic improvement of cucumber aphid resistance and aphid resistant variety breeding.

Leaf-mining by Phyllonorycter blancardella reprograms the host-leaf transcriptome to modulate phytohormones associated with nutrient mobilization and plant defense

Phytohormones have long been hypothesized to play a key role in the interactions between plant-manipulating organisms and their host-plants such as insect-plant interactions that lead to gall or 'green-islands' induction. However, mechanistic understanding of how phytohormones operate in these plant reconfigurations is lacking due to limited information on the molecular and biochemical phytohormonal modulation following attack by plant-manipulating insects. In an attempt to fill this gap, the present study provides an extensive characterization of how the leaf-miner Phyllonorycter blancardella modulates the major phytohormones and the transcriptional activity of plant cells in leaves of Malus domestica. We show here, that cytokinins strongly accumulate in mined tissues despite a weak expression of plant cytokinin-related genes. Leaf-mining is also associated with enhanced biosynthesis of jasmonic acid precursors but not the active form, a weak alteration of the salicylic acid pathway and a clear inhibition of the abscisic acid pathway. Our study consolidates previous results suggesting that insects may produce and deliver cytokinins to the plant as a strategy to manipulate the physiology of the leaf to create a favorable nutritional environment. We also demonstrate that leaf-mining by P. blancardella leads to a strong reprogramming of the plant phytohormonal balance associated with increased nutrient mobilization, inhibition of leaf senescence and mitigation of plant direct and indirect defense.

Identification of differentially expressed genes related to aphid resistance in cucumber (Cucumis sativus L.)

Cucumber, a very important vegetable crop worldwide, is easily damaged by pests. Aphids (Aphis gossypii Glover) are among the most serious pests in cucumber production and often cause severe loss of yield and make fruit quality get worse. Identifying genes that render cucumbers resistant to aphid-induced damage and breeding aphid-resistant cucumber varieties have become the most promising control strategies. In this study, a Illumina Genome Analyzer platform was applied to monitor changes in gene expression in the whole genome of the cucumber cultivar 'EP6392' which is resistant to aphids. Nine DGE libraries were constructed from infected and uninfected leaves. In total, 49 differentially expressed genes related to cucumber aphid resistance were screened during the treatment period. These genes are mainly associated with signal transduction, plant-pathogen interactions, flavonoid biosynthesis, amino acid metabolism and sugar metabolism pathways. Eight of the 49 genes may be associated with aphid resistance. Finally, expression of 9 randomly selected genes was evaluated by qRT-PCR to verify the results for the tag-mapped genes. With the exception of 1-aminocyclopropane-1-carboxylate oxidase homolog 6, the expression of the chosen genes was in agreement with the results of the tag-sequencing analysis patterns.

Aphid salivary proteases are capable of degrading sieve-tube proteins

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.

Systematic analysis of phloem-feeding insect-induced transcriptional reprogramming in Arabidopsis highlights common features and reveals distinct responses to specialist and generalist insects

Phloem-feeding insects (PFIs), of which aphids are the largest group, are major agricultural pests causing extensive damage to crop plants. In contrast to chewing insects, the nature of the plant response to PFIs remains poorly characterized. Scrutiny of the literature concerning transcriptional responses of model and crop plant species to PFIs reveals surprisingly little consensus with respect to the transcripts showing altered abundance following infestation. Nevertheless, core features of the transcriptional response to PFIs can be defined in Arabidopsis thaliana. This comparison of the PFI-associated transcriptional response observed in A. thaliana infested by the generalists Myzus persicae and Bemisia tabaci with the specialist Brevicoryne brassicae highlights the importance of calcium-dependent and receptor kinase-associated signalling. We discuss these findings within the context of the complex cross-talk between the different hormones regulating basal immune response mechanisms in plants. We identify PFI-responsive genes, highlighting the importance of cell wall-associated kinases in plant-PFI interactions, as well as the significant role of kinases containing the domain of unknown function 26. A common feature of plant-PFI interaction is enhanced abundance of transcripts encoding WRKY transcription factors. However, significant divergence was observed with respect to secondary metabolism dependent upon the insect attacker. Transcripts encoding enzymes and proteins associated with glucosinolate metabolism were decreased following attack by the generalist M. persicae but not by the specialist B. brassicae. This analysis provides a comprehensive overview of the molecular patterns associated with the plant response to PFIs and suggests that plants recognize and respond to perturbations in the cell wall occurring during PFI infestation.

Gene expression profiles responses to aphid feeding in chrysanthemum (Chrysanthemum morifolium)

BACKGROUND

Chrysanthemum is an important ornamental plant all over the world. It is easily attacked by aphid, Macrosiphoniella sanbourni. The molecular mechanisms of plant defense responses to aphid are only partially understood. Here, we investigate the gene expression changes in response to aphid feeding in chrysanthemum leaf by RNA-Seq technology.

RESULTS

Three libraries were generated from pooled leaf tissues of Chrysanthemum morifolium 'nannongxunzhang' that were collected at different time points with (Y) or without (CK) aphid infestations and mock puncture treatment (Z), and sequenced using an Illumina HiSeqTM 2000 platform. A total of 7,363,292, 7,215,860 and 7,319,841 clean reads were obtained in library CK, Y and Z, respectively. The proportion of clean reads was >97.29% in each library. Approximately 76.35% of the clean reads were mapped to a reference gene database including all known chrysanthemum unigene sequences. 1,157, 527 and 340 differentially expressed genes (DEGs) were identified in the comparison of CK-VS-Y, CK-VS-Z and Z-VS-Y, respectively. These DEGs were involved in phytohormone signaling, cell wall biosynthesis, photosynthesis, reactive oxygen species (ROS) pathway and transcription factor regulatory networks, and so on.

CONCLUSIONS

Changes in gene expression induced by aphid feeding are shown to be multifaceted. There are various forms of crosstalk between different pathways those genes belonging to, which would allow plants to fine-tune its defense responses.

Response of Solanum tuberosum to Myzus persicae infestation at different stages of foliage maturity

Young leaves of the potato Solanum tuberosum L. cultivar Kardal contain resistance factors to the green peach aphid Myzus persicae (Sulzer) (Hemiptera: Aphididae) and normal probing behavior is impeded. However, M. persicae can survive and reproduce on mature and senescent leaves of the cv. Kardal plant without problems. We compared the settling of M. persicae on young and old leaves and analyzed the impact of aphids settling on the plant in terms of gene expression. Settling, as measured by aphid numbers staying on young or old leaves, showed that after 21 h significantly fewer aphids were found on the young leaves. At earlier time points there were no difference between young and old leaves, suggesting that the young leaf resistance factors are not located at the surface level but deeper in the tissue. Gene expression was measured in plants at 96 h postinfestation, which is at a late stage in the interaction and in compatible interactions this is long enough for host plant acceptance to occur. In old leaves of cv. Kardal (compatible interaction), M. persicae infestation elicited a higher number of differentially regulated genes than in young leaves. The plant response to aphid infestation included a larger number of genes induced than repressed, and the proportion of induced versus repressed genes was larger in young than in old leaves. Several genes changing expression seem to be involved in changing the metabolic state of the leaf from source to sink.

Near-isogenic lines of Triticum aestivum with distinct modes of resistance exhibit dissimilar transcriptional regulation during Diuraphis noxia feeding

Russian wheat aphid (Diuraphis noxia, Kurdjumov) feeding on susceptible Triticum aestivum L. leads to leaf rolling, chlorosis and plant death - symptoms not present in resistant lines. Although the effects of several D. noxia (Dn) resistance genes are known, none have been isolated or characterized. Wheat varieties expressing different Dn genes exhibit distinct modes of D. noxia resistance, such as antibiosis (Dn1), tolerance (Dn2), and antixenosis (Dn5). However, the mechanism whereby feeding aphids are perceived, and how subsequent transcriptional responses are partitioned into resistance categories, remains unclear. Here we report on downstream events in near-isogenic wheat lines containing different Dn genes after D. noxia biotype SA1 feeding. Transcripts involved in stress, signal transduction, photosynthesis, metabolism and gene regulation were differentially regulated during D. noxia feeding. Expression analyses using RT-qPCR and RNA hybridization, as well as enzyme activity profiling, provide evidence that the timing and intensity of pathways induced are critical in the development of particular modes of resistance. Pathways involved include the generation of kinase signalling cascades that lead to a sustained oxidative burst, and a hypersensitive response that is active during antibiosis. Tolerance is a passive resistance mechanism that acts through repair or de novo synthesis of photosystem proteins. Results further suggest that ethylene-mediated pathways are possibly involved in generating volatile compounds and cell wall fortification during the antixenosic response.

Hypervirulent Diuraphis noxia (Hemiptera: Aphididae) biotype SAM avoids triggering defenses in its host (Triticum aestivum) (Poales: Poaceae) during feeding

In the molecular arms race between aphids and plants, both organisms rely on adaptive strategies to outcompete their evolutionary rival. In the current study, we investigated the difference in elicited defense responses of wheat (Triticum aestivum L.) near-isogenic lines with different Dn resistance genes, upon feeding by an avirulent and hypervirulent Diuraphis noxia Kurdjumov biotype. After measuring the activity of a suite of enzymes associated with plant defense, it became apparent that the host does not recognize the invasion by the hypervirulent aphid because none of these were induced, while feeding by the avirulent biotype did result in induction of enzyme activity. Genomic plasticity in D. noxia may be a likely explanation for the observed differences in virulence between D. noxia biotype SA1 and SAM, as demonstrated in the current study.

Differential induction of Pisum sativum defense signaling molecules in response to pea aphid infestation

This study demonstrates the sequence of enhanced generation of signal molecules such as phytohormones, i.e. jasmonic acid (JA), ethylene (ET), salicylic acid (SA), and a relatively stable free radical, nitric oxide (NO), in response of Pisum sativum L. cv. Cysterski seedling leaves to the infestation of pea aphid Acyrthosiphon pisum (Harris) at a varied population size. In time from 0 to 96h after A. pisum infestation these signal molecules accumulated transiently. Moreover, the convergence of these signaling pathways occurred. JA and its methyl derivative MeJA reached the first maximum of generation at 24th hour of infestation. An increase in ET and NO generation was observed at 48th hour of infestation. The increase in SA, JA/MeJA and ET concentrations in aphid-infested leaves occurred from the 72nd to 96th hour. In parallel, an increase was demonstrated for the activities of enzymes engaged in the biosynthesis of SA, such as phenylalanine ammonia-lyase (PAL) and benzoic acid 2-hydroxylase (BA2H). Additionally, a considerable post-infestation accumulation of transcripts for PAL was observed. An increase in the activity of lipoxygenase (LOX), an important enzyme in the biosynthesis of JA was noted. This complex signaling network may contribute to the coordinated regulation of gene expression leading to specific defence responses.

Plant resistance to aphid feeding: behavioral, physiological, genetic and molecular cues regulate aphid host selection and feeding

Aphids damage major world food and fiber crops through direct feeding and transmission of plant viruses. Fortunately, the development of many aphid-resistant crop plants has provided both ecological and economic benefits to food production. Plant characters governing aphid host selection often dictate eventual plant resistance or susceptibility to aphid herbivory, and these phenotypic characters have been successfully used to map aphid resistance genes. Aphid resistance is often inherited as a dominant trait, but is also polygenic and inherited as recessive or incompletely dominant traits. Most aphid-resistant cultivars exhibit constitutively expressed defenses, but some cultivars exhibit dramatic aphid-induced responses, resulting in the overexpression of large ensembles of putative aphid resistance genes. Two aphid resistance genes have been cloned. Mi-1.2, an NBS-LRR gene from wild tomato, confers resistance to potato aphid and three Meloidogyne root-knot nematode species, and Vat, an NBS-LRR gene from melon, controls resistance to the cotton/melon aphid and to some viruses. Virulence to aphid resistance genes of plants occurs in 17 aphid species--more than half of all arthropod biotypes demonstrating virulence. The continual appearance of aphid virulence underscores the need to identify new sources of resistance of diverse sequence and function in order to delay or prevent biotype development.

Large-scale analysis of differential gene expression in coffee genotypes resistant and susceptible to leaf miner-toward the identification of candidate genes for marker assisted-selection

BACKGROUND

A successful development of herbivorous insects into plant tissues depends on coordination of metabolic processes. Plants have evolved complex mechanisms to recognize such attacks, and to trigger a defense response. To understand the transcriptional basis of this response, we compare gene expression profiles of two coffee genotypes, susceptible and resistant to leaf miner (Leucoptera coffella). A total of 22000 EST sequences from the Coffee Genome Database were selected for a microarray analysis. Fluorescence probes were synthesized using mRNA from the infested and non-infested coffee plants. Array hybridization, scanning and data normalization were performed using Nimble Scan® e ArrayStar® platforms. Genes with foldchange values +/-2 were considered differentially expressed. A validation of 18 differentially expressed genes was performed in infected plants using qRT-PCR approach.

RESULTS

The microarray analysis indicated that resistant plants differ in gene expression profile. We identified relevant transcriptional changes in defense strategies before insect attack. Expression changes (>2.00-fold) were found in resistant plants for 2137 genes (1266 up-regulated and 873 down-regulated). Up-regulated genes include those responsible for defense mechanisms, hypersensitive response and genes involved with cellular function and maintenance. Also, our analyses indicated that differential expression profiles between resistant and susceptible genotypes are observed in the absence of leaf-miner, indicating that defense is already build up in resistant plants, as a priming mechanism. Validation of selected genes pointed to four selected genes as suitable candidates for markers in assisted-selection of novel cultivars.

CONCLUSIONS

Our results show evidences that coffee defense responses against leaf-miner attack are balanced with other cellular functions. Also analyses suggest a major metabolic reconfiguration that highlights the complexity of this response.

Transcriptomic and proteomic analysis of a compatible tomato-aphid interaction reveals a predominant salicylic acid-dependent plant response

BACKGROUND

Aphids are among the most destructive pests in temperate climates, causing significant damage on several crops including tomato. We carried out a transcriptomic and proteomic study to get insights into the molecular mechanisms and dynamics of the tomato response to the Macrosyphum euphorbiae aphid.

RESULTS

The time course analysis of aphid infestation indicated a complex, dynamic pattern of gene expression. Several biological functions were affected and genes related to the stress and defence response were the most represented. The Gene Ontology categories of the differentially expressed genes (899) and identified proteins (57) indicated that the tomato response is characterized by an increased oxidative stress accompanied by the production of proteins involved in the detoxification of oxygen radicals. Aphids elicit a defense reaction based on the cross-communication of different hormone-related signaling pathways such as those related to the salicylic acid (SA), jasmonic acid (JA), ethylene and brassinosteroids. Among them, the SA-signaling pathway and stress-responsive SA-dependent genes play a dominant role. Furthermore, tomato response is characterized by a reduced accumulation of photosynthetic proteins and a modification of the expression of various cell wall related genes.

CONCLUSIONS

Our work allowed a more comprehensive understanding of the signaling events and the defense dynamics of the tomato response to aphids in a compatible interaction and, based on experimental data, a model of the tomato-aphid molecular interaction was proposed. Considering the rapid advancement of tomato genomics, this information will be important for the development of new protection strategies.

Source-to-sink transport of sugar and regulation by environmental factors

Source-to-sink transport of sugar is one of the major determinants of plant growth and relies on the efficient and controlled distribution of sucrose (and some other sugars such as raffinose and polyols) across plant organs through the phloem. However, sugar transport through the phloem can be affected by many environmental factors that alter source/sink relationships. In this paper, we summarize current knowledge about the phloem transport mechanisms and review the effects of several abiotic (water and salt stress, mineral deficiency, CO2, light, temperature, air, and soil pollutants) and biotic (mutualistic and pathogenic microbes, viruses, aphids, and parasitic plants) factors. Concerning abiotic constraints, alteration of the distribution of sugar among sinks is often reported, with some sinks as roots favored in case of mineral deficiency. Many of these constraints impair the transport function of the phloem but the exact mechanisms are far from being completely known. Phloem integrity can be disrupted (e.g., by callose deposition) and under certain conditions, phloem transport is affected, earlier than photosynthesis. Photosynthesis inhibition could result from the increase in sugar concentration due to phloem transport decrease. Biotic interactions (aphids, fungi, viruses…) also affect crop plant productivity. Recent breakthroughs have identified some of the sugar transporters involved in these interactions on the host and pathogen sides. The different data are discussed in relation to the phloem transport pathways. When possible, the link with current knowledge on the pathways at the molecular level will be highlighted.

Vitamin C and the abscisic acid-insensitive 4 transcription factor are important determinants of aphid resistance in Arabidopsis

AIMS

Aphids, like other insects, are probably unable to synthesize vitamin C (ascorbic acid), which is therefore an essential dietary nutrient that has to be obtained from the host plant. Plant responses to aphids involve hormones such as salicylic acid (SA), jasmonic acid (JA), and abscisic acid (ABA), but hormone/redox interactions remain poorly characterized. We therefore investigated hormone/redox signaling in the response of Arabidopsis thaliana to infestation by the aphid Myzus persicae, focusing on the interactions between ascorbic acid and ABA, together with the influence of altered ascorbate and ABA signaling on the SA- and JA-dependent pathways.

RESULTS

Whole-genome microarray analysis revealed highly dynamic transcriptional responses to aphid infestation with extensive differences between transcript profiles of infested and systemic leaves, revealing aphid-dependent effects on the suites of transcripts involved in the redox, SA, and ABA responses. Central roles for ascorbate, ABA-insensitive 4 (ABI4), and oxidative signal-inducible 1 in plant resistance to aphids were demonstrated by altered fecundity on respective mutants. However, ABA had a negative effect on aphid resistance, as did ABI4 or redox-responsive transcription factor 1. The decrease in aphid fecundity observed in mutants defective in ascorbate accumulation (vtc2) was absent from abi4vtc2 double mutants that are also deficient in ABA signaling (abi4). Aphid-dependent transcriptome responses reveal a role for ascorbate-regulated receptor-like kinases in plant defenses against aphids.

INNOVATION

Vitamin C deficiency enhances plant resistance to aphids through redox signaling pathways rather than dietary requirements.

CONCLUSION

ABI4 is a linchpin of redox regulation of the innate immune response to aphids.

Comparative transcriptome analysis of Gossypium hirsutum L. in response to sap sucking insects: aphid and whitefly

Background

Cotton (Gossypium hirsutum L.) is a major fiber crop that is grown worldwide; it faces extensive damage from sap-sucking insects, including aphids and whiteflies. Genome-wide transcriptome analysis was performed to understand the molecular details of interaction between Gossypium hirsutum L. and sap-sucking pests, namely Aphis gossypii (Aphid) and Bemisia tabacci (Whiteflies). Roche’s GS-Titanium was used to sequence transcriptomes of cotton infested with aphids and whiteflies for 2 h and 24 h.

Results

A total of 100935 contigs were produced with an average length of 529 bp after an assembly in all five selected conditions. The Blastn of the non-redundant (nr) cotton EST database resulted in the identification of 580 novel contigs in the cotton plant. It should be noted that in spite of minimal physical damage caused by the sap-sucking insects, they can change the gene expression of plants in 2 h of infestation; further change in gene expression due to whiteflies is quicker than due to aphids. The impact of the whitefly 24 h after infestation was more or less similar to that of the aphid 2 h after infestation. Aphids and whiteflies affect many genes that are regulated by various phytohormones and in response to microbial infection, indicating the involvement of complex crosstalk between these pathways. The KOBAS analysis of differentially regulated transcripts in response to aphids and whiteflies indicated that both the insects induce the metabolism of amino acids biosynthesis specially in case of whiteflies infestation at later phase. Further we also observed that expression of transcript related to photosynthesis specially carbon fixation were significantly influenced by infestation of Aphids and Whiteflies.

Conclusions

A comparison of different transcriptomes leads to the identification of differentially and temporally regulated transcripts in response to infestation by aphids and whiteflies. Most of these differentially expressed contigs were related to genes involved in biotic, abiotic stresses and enzymatic activities related to hydrolases, transferases, and kinases. The expression of some marker genes such as the overexpressors of cationic peroxidase 3, lipoxygenase I, TGA2, and non-specific lipase, which are involved in phytohormonal-mediated plant resistance development, was suppressed after infestation by aphids and whiteflies, indicating that insects suppressed plant resistance in order to facilitate their infestation. We also concluded that cotton shares several pathways such as phagosomes, RNA transport, and amino acid metabolism with Arabidopsis in response to the infestation by aphids and whiteflies.

Comparative analysis of Solanum stoloniferum responses to probing by the green peach aphid Myzus persicae and the potato aphid Macrosiphum euphorbiae

Plants protect themselves against aphid attacks by species-specific defense mechanisms. Previously, we have shown that Solanum stoloniferum Schlechtd has resistance factors to Myzus persicae Sulzer (Homoptera: Aphididae) at the epidermal/mesophyll level that are not effective against Macrosiphum euphorbiae Thomas (Homoptera: Aphididae). Here, we compare the nymphal mortality, the pre-reproductive development time, and the probing behavior of M. persicae and M. euphorbiae on S. stoloniferum and Solanum tuberosum L. Furthermore, we analyze the changes in gene expression in S. stoloniferum 96 hours post infestation by either aphid species. Although the M. euphorbiae probing behavior shows that aphids encounter more probing constrains on phloem activities-longer probing and salivation time- on S. stoloniferum than on S. tuberosum, the aphids succeeded in reaching a sustained ingestion of phloem sap on both plants. Probing by M. persicae on S. stoloniferum plants resulted in limited feeding only. Survival of M. euphorbiae and M. persicae was affected on young leaves, but not on senescent leaves of S. stoloniferum. Infestation by M. euphorbiae changed the expression of more genes than M. persicae did. At the systemic level both aphids elicited a weak response. Infestation of S. stoloniferum plants with a large number of M. persicae induced morphological changes in the leaves, leading to the development of pustules that were caused by disrupted vascular parenchyma and surrounding tissue. In contrast, an infestation by M. euphorbiae had no morphological effects. Both plant species can be regarded as good host for M. euphorbiae, whereas only S. tuberosum is a good host for M. persicae and S. stoloniferum is not. Infestation of S. stoloniferum by M. persicae or M. euphorbiae changed the expression of a set of plant genes specific for each of the aphids as well as a set of common genes.

Wounding, insect chewing and phloem sap feeding differentially alter the leaf proteome of potato, Solanum tuberosum L

Background

Various factors shape the response of plants to herbivorous insects, including wounding patterns, specific chemical effectors and feeding habits of the attacking herbivore. Here we performed a comparative proteomic analysis of the plant's response to wounding and herbivory, using as a model potato plants (Solanum tuberosum L.) subjected to mechanical wounding, defoliation by the Colorado potato beetle Leptinotarsa decemlineata Say, or phloem sap feeding by the potato aphid Macrosiphum euphorbiae Thomas.

Results

Out of ~500 leaf proteins monitored by two-dimensional gel electrophoresis (2-DE), 31 were up- or downregulated by at least one stress treatment compared to healthy control plants. Of these proteins, 29 were regulated by beetle chewing, 8 by wounding and 8 by aphid feeding. Some proteins were up- or downregulated by two different treatments, while others showed diverging expression patterns in response to different treatments. A number of modulated proteins identified by mass spectrometry were typical defense proteins, including wound-inducible protease inhibitors and pathogenesis-related proteins. Proteins involved in photosynthesis were also modulated, notably by potato beetle feeding inducing a strong decrease of some photosystem I proteins. Quantitative RT PCR assays were performed with nucleotide primers for photosynthesis-related proteins to assess the impact of wounding and herbivory at the gene level. Whereas different, sometimes divergent, responses were observed at the proteome level in response to wounding and potato beetle feeding, downregulating effects were systematically observed for both treatments at the transcriptional level.

Conclusions

These observations illustrate the differential impacts of wounding and insect herbivory on defense- and photosynthesis-related components of the potato leaf proteome, likely associated with the perception of distinct physical and chemical cues in planta.

Stress inducible proteinase inhibitor diversity in Capsicum annuum

BACKGROUND

Wound-inducible Pin-II Proteinase inhibitors (PIs) are one of the important plant serine PIs which have been studied extensively for their structural and functional diversity and relevance in plant defense against insect pests. To explore the functional specialization of an array of Capsicum annuum (L.) proteinase inhibitor (CanPIs) genes, we studied their expression, processing and tissue-specific distribution under steady-state and induced conditions. Inductions were performed by subjecting C. annuum leaves to various treatments, namely aphid infestation or mechanical wounding followed by treatment with either oral secretion (OS) of Helicoverpa armigera or water.

RESULTS

The elicitation treatments regulated the accumulation of CanPIs corresponding to 4-, 3-, and 2-inhibitory repeat domains (IRDs). Fourty seven different CanPI genes composed of 28 unique IRDs were identified in total along with those reported earlier. The CanPI gene pool either from uninduced or induced leaves was dominated by 3-IRD PIs and trypsin inhibitory domains. Also a major contribution by 4-IRD CanPI genes possessing trypsin and chymotrypsin inhibitor domains was specifically revealed in wounded leaves treated with OS. Wounding displayed the highest number of unique CanPIs while wounding with OS treatment resulted in the high accumulation of specifically CanPI-4, -7 and -10. Characterization of the PI protein activity through two dimensional gel electrophoresis revealed tissue and induction specific patterns. Consistent with transcript abundance, wound plus OS or water treated C. annuum leaves exhibited significantly higher PI activity and isoform diversity contributed by 3- and 4-IRD CanPIs. CanPI accumulation and activity was weakly elicited by aphid infestation yet resulted in the higher expression of CanPI-26, -41 and -43.

CONCLUSIONS

Plants can differentially perceive various kinds of insect attacks and respond appropriately through activating plant defenses including regulation of PIs at transcriptional and post-translational levels. Based on the differentially elicited CanPI accumulation patterns, it is intriguing to speculate that generating sequence diversity in the form of multi-IRD PIs is a part of elaborative plant defense strategy to obtain a diverse pool of functional units to confine insect attack.

Mechanisms of plant defense against insect herbivores

Plants respond to herbivory through various morphological, biochemicals, and molecular mechanisms to counter/offset the effects of herbivore attack. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by induced responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be engineered genetically, so that the defensive compounds are constitutively produced in plants against are challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.

Arabidopsis thaliana-Aphid Interaction

Aphids are important pests of plants that use their stylets to tap into the sieve elements to consume phloem sap. Besides the removal of photosynthates, aphid infestation also alters source-sink patterns. Most aphids also vector viral diseases. In this chapter, we will summarize on recent significant findings in plant-aphid interaction, and how studies involving Arabidopsis thaliana and Myzus persicae (Sülzer), more commonly known as the green peach aphid (GPA), are beginning to provide important insights into the molecular basis of plant defense and susceptibility to aphids. The recent demonstration that expression of dsRNA in Arabidopsis can be used to silence expression of genes in GPA has further expanded the utility of Arabidopsis for evaluating the contribution of the aphid genome-encoded proteins to this interaction.

Toward a mechanistic understanding of competition in vascular-feeding herbivores: an empirical test of the sink competition hypothesis

Recent evidence suggests that competitive interactions among herbivores are mostly indirect and mediated by plant responses to herbivory. Most studies, however, emphasize chewing insects and secondary chemistry, thus ignoring the diverse group of vascular-parasites that may be more likely to compete through induced changes in phytonutrients. Using an aboveground phloem-feeding aphid (Myzus persicae) and a belowground gall-forming nematode (Meloidogyne incognita) on tobacco plants, we assessed the importance of competition via induced host-plant sinks. In a series of experimental trials, nematode root herbivory caused 55 and 72% declines in the growth and fecundity of aphids, respectively. Aphids, on the other hand, did not impact nematode performance. Therefore, we predicted that nematodes out-compete M. persicae by attenuating the magnitude of aphid-induced sinks. Through a combination of invertase enzyme measurements and stable isotope ((13)C and (15)N) enrichment, we found evidence that both herbivores act as mobilizing sinks. Aphids attracted photoassimilates to feeding aggregations on leaves and nematode galls accumulated resources in the roots. Levels of invertase enzymes, for example, were more than fourfold higher in nematode galls than in surrounding root tissue. Yet we found no evidence supporting a sink competition model for aphid-nematode interactions. The strength of aphid-induced leaf sinks was entirely unaffected by nematode presence, and vice versa. Thus, induced host-plant sinks appear to be a common strategy employed by vascular parasites to manipulate the physiology of their host, but multi-sink competition may be limited to herbivores that co-occur on the same tissue type and/or plants under growth-limited abiotic conditions.

Herbivore-specific elicitation of photosynthesis by mirid bug salivary secretions in the wild tobacco Nicotiana attenuata

Herbivory is thought to be detrimental to plant fitness and commonly results in a metabolic shift in the plant: photosynthetic processes are typically down-regulated, while resource allocation to defenses is increased in herbivore-attacked plants, resulting in fitness costs of induced plant responses. Wild tobacco, Nicotiana attenuata, attacked by Tupiocoris notatus mirid bugs becomes resistant against more damaging herbivores through mirid-induced direct and indirect defenses. However, mirid-induced resistance and tissue loss do not result in a reduction of plant fitness. These findings suggest induced metabolic responses allowing the plant to compensate for the lost tissue and resources allocated to defenses. While feeding by Manduca sexta larvae results in a strong down-regulation of photosynthesis, we demonstrate a specific induction of elevated photosynthetic activity in N. attenuata leaves by elicitors in mirid salivary secretions. The elevated CO(2) assimilation rate is sufficient to compensate for the loss of photosynthetically active tissue and balances the net photosynthesis of infested leaves. We discuss the observed increase in the plant's primary metabolic activity as a mechanism that allows plants to alleviate negative fitness effects of mirid attack and mediates the vaccination effects that result in a net benefit in environments with multiple herbivores.

TREHALOSE PHOSPHATE SYNTHASE11-dependent trehalose metabolism promotes Arabidopsis thaliana defense against the phloem-feeding insect Myzus persicae

Agricultural productivity is limited by the removal of sap, alterations in source-sink patterns, and viral diseases vectored by aphids, which are phloem-feeding pests. Here we show that TREHALOSE PHOSPHATE SYNTHASE11 (TPS11) gene-dependent trehalose metabolism regulates Arabidopsis thaliana defense against Myzus persicae (Sülzer), commonly known as the green peach aphid (GPA). GPA infestation of Arabidopsis resulted in a transient increase in trehalose and expression of the TPS11 gene, which encodes a trehalose-6-phosphate synthase/phosphatase. Knockout of TPS11 function abolished trehalose increases in GPA-infested leaves of the tps11 mutant plant and attenuated defense against GPA. Trehalose application restored resistance in the tps11 mutant, confirming that the lack of trehalose accumulation is associated with the inability of the tps11 mutant to control GPA infestation. Resistance against GPA was also higher in the trehalose hyper-accumulating tre1 mutant and in bacterial otsB gene-expressing plants, further supporting the conclusion that trehalose plays a role in Arabidopsis defense against GPA. Evidence presented here indicates that TPS11-dependent trehalose regulates expression of the PHYTOALEXIN DEFICIENT4 gene, which is a key modulator of defenses against GPA. TPS11 also promotes the re-allocation of carbon into starch at the expense of sucrose, the primary plant-derived carbon and energy source for the insect. Our results provide a framework for the signaling function of TPS11-dependent trehalose in plant stress responses, and also reveal an important contribution of starch in controlling the severity of aphid infestation.

Aphids alter host-plant nitrogen isotope fractionation

Plant sap-feeding insects and blood-feeding parasites are frequently depleted in (15)N relative to their diet. Unfortunately, most fluid-feeder/host nitrogen stable-isotope studies simply report stable-isotope signatures, but few attempt to elucidate the mechanism of isotopic trophic depletion. Here we address this deficit by investigating the nitrogen stable-isotope dynamics of a fluid-feeding herbivore-host plant system: the green peach aphid, Myzus persicae, feeding on multiple brassicaceous host plants. M. persicae was consistently more than 6‰ depleted in (15)N relative to their hosts, although aphid colonized plants were 1.5‰ to 2.0‰ enriched in (15)N relative to uncolonized control plants. Isotopic depletion of aphids relative to hosts was strongly related to host nitrogen content. We tested whether the concomitant aphid (15)N depletion and host (15)N enrichment was coupled by isotopic mass balance and determined that aphid (15)N depletion and host (15)N enrichment are uncoupled processes. We hypothesized that colonized plants would have higher nitrate reductase activity than uncolonized plants because previous studies had demonstrated that high nitrate reductase activity under substrate-limiting conditions can result in increased plant δ(15)N values. Consistent with our hypothesis, nitrate reductase activity in colonized plants was twice that of uncolonized plants. This study offers two important insights that are likely applicable to understanding nitrogen dynamics in fluid-feeder/host systems. First, isotopic separation of aphid and host depends on nitrogen availability. Second, aphid colonization alters host nitrogen metabolism and subsequently host nitrogen stable-isotope signature. Notably, this work establishes a metabolic framework for future hypothesis-driven studies focused on aphid manipulation of host nitrogen metabolism.

Wheat gene expression is differentially affected by a virulent Russian wheat aphid biotype

An improved understanding of the complex interactions between plants and aphids is emerging. Recognition of aphid feeding in plant tissues involves production of several defense response signaling pathways and downstream production of defense and detoxification compounds. Feeding by Russian wheat aphid, Diuraphis noxia (Kurdjumov), a serious pest of cereal crops worldwide, induces foliar deformity and chlorophyll loss during compatible wheat-D. noxia interactions. Experiments described here revealed significant differences in level and pattern of gene expression in defense response signaling and metabolic pathways between compatible and incompatible D. noxia-wheat interactions. The jasmonate (JA)-signaling genes LOX, AOS, and AOC were significantly more upregulated (~3- to 7 fold) in incompatible interactions than in compatible interactions (~2.5 to 3.5 fold) as early as 1 h post D. noxia infestation (hpi). Cellulose synthase, responsible for strengthening plant cell walls via cellulose production, was also more upregulated in incompatible interactions (4 to 7 fold) than in compatible interactions (1 to 3.5 fold). In contrast, glycolysis and citric acid cycle genes were significantly downregulated (~1.5 to 2 fold) in incompatible interactions and upregulated or less downregulated in compatible interactions from 6 to 72 hpi. Differences in expression of JA-signaling genes between feeding site tissues and non-feeding site tissues suggest that D. noxia defense response signals in wheat are restricted primarily to aphid feeding sites in the initial 6 hpi. This is the first report of differential upregulation of plant genes at 1 hpi in incompatible interactions involving aphid herbivory. Early wheat plant defense responses in incompatible D. noxia interactions at 1, 3, and 6 hpi appear to be important aspects of D. noxia resistance in wheat.

Virus-induced gene silencing of WRKY53 and an inducible phenylalanine ammonia-lyase in wheat reduces aphid resistance

Although several wheat genes differentially expressed during the Russian wheat aphid resistance response have recently been identified, their requirement for and specific role in resistance remain unclear. Progress in wheat-aphid interaction research is hampered by inadequate collections of mutant germplasm and difficulty in transforming hexaploid wheat. Virus-induced gene silencing (VIGS) technology is emerging as a viable reverse genetics approach in cereal crops. However, the potential of VIGS for determining aphid defence gene function in wheat has not been evaluated. We report on the use of recombinant barley stripe mosaic virus (BSMV) to target and silence a WRKY53 transcription factor and an inducible phenylalanine ammonia-lyase (PAL) gene, both predicted to contribute to aphid defence in a genetically resistant wheat line. After inoculating resistant wheat with the VIGS constructs, transcript abundance was reduced to levels similar to that observed in susceptible wheat. Notably, the level of PAL expression was also suppressed by the WKRY53 construct, suggesting that these genes operate in the same defence response network. Both knockdowns exhibited a susceptible phenotype upon aphid infestation, and aphids feeding on silenced plants exhibited a significant increase in fitness compared to aphids feeding on control plants. Altered plant phenotype and changes in aphid behaviour after silencing imply that WKRY53 and PAL play key roles in generating a successful resistance response. This study is the first report on the successful use of VIGS to investigate genes involved in wheat-insect interactions.

Differential expression pattern of an acidic 9/13-lipoxygenase in flower opening and senescence and in leaf response to phloem feeders in the tea plant

BACKGROUND

Lipoxygenase (LOXs) is a large family of plant enzymes that catalyse the hydroperoxidation of free polyunsaturated fatty acids into diverse biologically active compounds, collectively named phyto-oxylipins. Although multiple isoforms of LOXs have been identified in a wide range of annual herbaceous plants, the genes encoding these enzymes in perennial woody plants have not received as much attention. In Camellia sinensis (L.) O. Kuntze, no LOX gene of any type has been isolated, and its possible role in tea plant development, senescence, and defence reaction remains unknown. The present study describes the isolation, characterization, and expression of the first tea plant LOX isoform, namely CsLOX1, and seeks to clarify the pattern of its expression in the plant's defence response as well as in flower opening and senescence.

RESULTS

Based on amino acid sequence similarity to plant LOXs, a LOX was identified in tea plant and named CsLOX1, which encodes a polypeptide comprising 861 amino acids and has a molecular mass of 97.8 kDa. Heterologous expression in yeast analysis showed that CsLOX1 protein conferred a dual positional specificity since it released both C-9 and C-13 oxidized products in equal proportion and hence was named 9/13-CsLOX1. The purified recombinant CsLOX1 protein exhibited optimum catalytic activity at pH 3.6 and 25°C. Real-time quantitative PCR analysis showed that CsLOX1 transcripts were detected predominantly in flowers, up-regulated during petal senescence, and down-regulated during flower bud opening. In leaves, the gene was up-regulated following injury or when treated with methyl jasmonate (MeJA), but salicylic acid (SA) did not induce such response. The gene was also rapidly and highly induced following feeding by the tea green leafhopper Empoasca vitis, whereas feeding by the tea aphid Toxoptera aurantii resulted in a pattern of alternating induction and suppression.

CONCLUSIONS

Analysis of the isolation and expression of the LOX gene in tea plant indicates that the acidic CsLOX1 together with its primary and end products plays an important role in regulating cell death related to flower senescence and the JA-related defensive reaction of the plant to phloem-feeders.

Molecular, biochemical, and organismal analyses of tomato plants simultaneously attacked by herbivores from two feeding guilds

Previous work identified aphids and caterpillars as having distinct effects on plant responses to herbivory. We sought to decipher these interactions across different levels of biological organization, i.e., molecular, biochemical, and organismal, with tomato plants either damaged by one 3rd-instar beet armyworm caterpillar (Spodoptera exigua), damaged by 40 adult potato aphids (Macrosiphum euphorbiae), simultaneous damaged by both herbivores, or left undamaged (controls). After placing insects on plants, plants were transferred to a growth chamber for 5 d to induce a systemic response. Subsequently, individual leaflets from non-damaged parts of plants were excised and used for gene expression analysis (microarrays and quantitative real-time PCR), C/N analysis, total protein analysis, proteinase inhibitor (PI) analysis, and for performance assays. At the molecular level, caterpillars up-regulated 56 and down-regulated 29 genes systemically, while aphids up-regulated 93 and down-regulated 146 genes, compared to controls. Although aphids induced more genes than caterpillars, the magnitude of caterpillar-induced gene accumulation, particularly for those associated with plant defenses, was often greater. In dual-damaged plants, aphids suppressed 27% of the genes regulated by caterpillars, while caterpillars suppressed 66% of the genes regulated by aphids. At the biochemical level, caterpillars induced three-fold higher PI activity compared to controls, while aphids had no effects on PIs either alone or when paired with caterpillars. Aphid feeding alone reduced the foliar C/N ratio, but not when caterpillars also fed on the plants. Aphid and caterpillar feeding alone had no effect on the amount of protein in systemic leaves; however, both herbivores feeding on the plant reduced the amount of protein compared to aphid-damaged plants. At the organismal level, S. exigua neonate performance was negatively affected by prior caterpillar feeding, regardless of whether aphids were present or absent. This study highlights areas of concordance and disjunction between molecular, biochemical, and organismal measures of induced plant resistance when plants are attacked by multiple herbivores. In general, our data produced consistent results when considering each herbivore separately but not when considering them together.