Local and systemic effects of two herbivores with different feeding mechanisms on primary metabolism of cotton leaves

Spider mite herbivory induces an ABA-driven stomatal defense

Arthropod herbivory poses a serious threat to crop yield, prompting plants to employ intricate defense mechanisms against pest feeding. The generalist pest 2-spotted spider mite (Tetranychus urticae) inflicts rapid damage and remains challenging due to its broad target range. In this study, we explored the Arabidopsis (Arabidopsis thaliana) response to T. urticae infestation, revealing the induction of abscisic acid (ABA), a hormone typically associated with abiotic stress adaptation, and stomatal closure during water stress. Leveraging a Forster resonance energy transfer (FRET)-based ABA biosensor (nlsABACUS2-400n), we observed elevated ABA levels in various leaf cell types postmite feeding. While ABA's role in pest resistance or susceptibility has been debated, an ABA-deficient mutant exhibited increased mite infestation alongside intact canonical biotic stress signaling, indicating an independent function of ABA in mite defense. We established that ABA-triggered stomatal closure effectively hinders mite feeding and minimizes leaf cell damage through genetic and pharmacological interventions targeting ABA levels, ABA signaling, stomatal aperture, and density. This study underscores the critical interplay between biotic and abiotic stresses in plants, highlighting how the vulnerability to mite infestation arising from open stomata, crucial for transpiration and photosynthesis, reinforces the intricate relationship between these stress types.

Deep learning and targeted metabolomics-based monitoring of chewing insects in tea plants and screening defense compounds

Tea is an important cash crop that is often consumed by chewing pests, resulting in reduced yields and economic losses. It is important to establish a method to quickly identify the degree of damage to tea plants caused by leaf-eating insects and screen green control compounds. This study was performed through the combination of deep learning and targeted metabolomics, in vitro feeding experiment, enzymic analysis and transient genetic transformation. A small target damage detection model based on YOLOv5 with Transformer Prediction Head (TPH-YOLOv5) algorithm for the tea canopy level was established. Orthogonal partial least squares (OPLS) was used to analyze the correlation between the degree of damage and the phenolic metabolites. A potential defensive compound, (-)-epicatechin-3-O-caffeoate (EC-CA), was screened. In vitro feeding experiments showed that compared with EC and epicatechin gallate, Ectropis grisescens exhibited more significant antifeeding against EC-CA. In vitro enzymatic experiments showed that the hydroxycinnamoyl transferase (CsHCTs) recombinant protein has substrate promiscuity and can catalyze the synthesis of EC-CA. Transient overexpression of CsHCTs in tea leaves effectively reduced the degree of damage to tea leaves. This study provides important reference values and application prospects for the effective monitoring of pests in tea gardens and screening of green chemical control substances.

Induced responses contribute to rapid adaptation of Spirodela polyrhiza to herbivory by Lymnaea stagnalis

Herbivory-induced responses in plants are typical examples of phenotypic plasticity, and their evolution is thought to be driven by herbivory. However, direct evidence of the role of induced responses in plant adaptive evolution to herbivores is scarce. Here, we experimentally evolve populations of an aquatic plant (Spirodela polyrhiza, giant duckweed) and its native herbivore (Lymnaea stagnalis, freshwater snail), testing whether herbivory drives rapid adaptive evolution in plant populations using a combination of bioassays, pool-sequencing, metabolite analyses, and amplicon metagenomics. We show that snail herbivory drove rapid phenotypic changes, increased herbivory resistance, and altered genotype frequencies in the plant populations. Additional bioassays suggest that evolutionary changes of induced responses contributed to the rapid increase of plant resistance to herbivory. This study provides direct evidence that herbivory-induced responses in plants can be subjected to selection and have an adaptive role by increasing resistance to herbivores.

Systemic whitefly-induced metabolic responses in newly developed distal leaves of husk tomato plants (Physalis philadelphica) impairs whiteflies development

BACKGROUND

Metabolic reconfiguration in plants is a hallmark response to insect herbivory that occurs in the attack site and systemically in undamaged tissues. Metabolomic systemic responses can occur rapidly while the herbivore is still present and may persist in newly developed tissue to counterattack future herbivore attacks. This study analyzed the metabolic profile of local and newly developed distal (systemic) leaves of husk tomato (Physalis philadelphica) plants after whitefly Trialeurodes vaporariorum infestation. In addition, the effect of these metabolomic adjustments on whitefly oviposition and development was evaluated.

RESULTS

Our results indicate that T. vaporariorum infestation induced significant changes in husk tomato metabolic profiles, not only locally in infested leaves, but also systemically in distal leaves that developed after infestation. The distinctive metabolic profile produced in newly developed leaves affected whitefly nymphal development but did not affect female oviposition, suggesting that changes driven by whitefly herbivory persist in the young leaves that developed after the infestation event to avoid future herbivore attacks.

CONCLUSIONS

This report contributes to further understanding the plant responses to sucking insects by describing the metabolic reconfiguration in newly developed, undamaged systemic leaf tissues of husk tomato plants after whitefly infestation. © 2022 Society of Chemical Industry.

Abiotic and Herbivory Combined Stress in Tomato: Additive, Synergic and Antagonistic Effects and Within-Plant Phenotypic Plasticity

Background: Drought, N deficiency and herbivory are considered the most important stressors caused by climate change in the agro- and eco-systems and varied in space and time shaping highly dynamic and heterogeneous stressful environments. This study aims to evaluate the tomato morpho-physiological and metabolic responses to combined abiotic and herbivory at different within-plant spatial levels and temporal scales. Methods: Leaf-level morphological, gas exchange traits and volatile organic compounds (VOCs) profiles were measured in tomato plants exposed to N deficiency and drought, Tuta absoluta larvae and their combination. Additive, synergistic or antagonistic effects of the single stress when combined were also evaluated. Morpho-physiological traits and VOCs profile were also measured on leaves located at three different positions along the shoot axes. Results: The combination of the abiotic and biotic stress has been more harmful than single stress with antagonistic and synergistic but non-additive effects for the morpho-physiological and VOCs tomato responses, respectively. Combined stress also determined a high within-plant phenotypic plasticity of the morpho-physiological responses. Conclusions: These results suggested that the combined stress in tomato determined a “new stress state” and a higher within-plant phenotypic plasticity which could permit an efficient use of the growth and defense resources in the heterogeneous and multiple stressful environmental conditions.

Stomata at the crossroad of molecular interaction between biotic and abiotic stress responses in plants

Increasing global food production is threatened by harsh environmental conditions along with biotic stresses, requiring massive new research into integrated stress resistance in plants. Stomata play a pivotal role in response to many biotic and abiotic stresses, but their orchestrated interactions at the molecular, physiological, and biochemical levels were less investigated. Here, we reviewed the influence of drought, pathogen, and insect herbivory on stomata to provide a comprehensive overview in the context of stomatal regulation. We also summarized the molecular mechanisms of stomatal response triggered by these stresses. To further investigate the effect of stomata-herbivore interaction at a transcriptional level, integrated transcriptome studies from different plant species attacked by different pests revealed evidence of the crosstalk between abiotic and biotic stress. Comprehensive understanding of the involvement of stomata in some plant-herbivore interactions may be an essential step towards herbivores' manipulation of plants, which provides insights for the development of integrated pest management strategies. Moreover, we proposed that stomata can function as important modulators of plant response to stress combination, representing an exciting frontier of plant science with a broad and precise view of plant biotic interactions.

Characterizing serotonin biosynthesis in Setaria viridis leaves and its effect on aphids

A combined transcriptomic and metabolic analysis of Setaria viridis leaves responding to aphid infestation was used to identify genes related to serotonin biosynthesis. Setaria viridis (green foxtail), a short life-cycle C4 plant in the Poaceae family, is the wild ancestor of Setaria italica (foxtail millet), a resilient crop that provides good yields in dry and marginal land. Although S. viridis has been studied extensively in the last decade, the molecular mechanisms of insect resistance in this species remain under-investigated. To address this issue, we performed a metabolic analysis of S. viridis and discovered that these plants accumulate the tryptophan-derived compounds tryptamine and serotonin. To elucidate the defensive functions of serotonin, Rhophalosiphum padi (bird cherry-oat aphids) were exposed to this compound, either by exogenous application to the plant medium or with artificial diet bioassays. In both cases, exposure to serotonin increased aphid mortality. To identify genes that are involved in serotonin biosynthesis, we conducted a transcriptome analysis and identified several predicted S. viridis tryptophan decarboxylase (TDC) and tryptamine 5-hydroxylase (T5H) genes. Two candidate genes were ectopically expressed in Nicotiana tabacum, where SvTDC1 (Sevir.6G066200) had tryptophan decarboxylase activity, and SvT5H1 (Sevir.8G219600) had tryptamine hydroxylase activity. Moreover, the function of the SvTDC1 gene was validated using virus-induced gene silencing in S. italica, which caused a reduction in serotonin levels. This study provides the first evidence of serotonin biosynthesis in Setaria leaves. The biosynthesis of serotonin may play an important role in defense responses and could prove to be useful for developing more pest-tolerant Setaria italica cultivars.

Isolation and functional analysis of OsAOS1 promoter for resistance to Nilaparvata lugens Stål infestation in rice

Insect pests have a great impact on the yield and quality of crops. Insecticide applications are an effective method of pest control, however, they also have adverse effects on the environment. Using insect-inducible promoters to drive insect-resistant genes in transgenic crops is a potential sustainable pest management strategy, but insect-inducible promoters have been rarely reported. In this study, we found rice allene oxide synthase gene (AOS, LOC_Os03g12500) can be highly upregulated following brown planthopper (Nilaparvata lugens Stål, BPH) infestation. Then, we amplified the promoter of OsAOS1 and the β- glucuronidase reporter gene was used to analyze the expression pattern of the promoter. Through a series of 5' truncated assays, three positive regulatory regions in response to BPH infestation in the promoter were identified. The transgenic plants, P1R123-min 35S and P1TR1-min 35S promoter-driven snowdrop lectin (Galanthus nivalis agglutinin, GNA) gene, demonstrated the highest expression levels of GNA and lowest BPH survival. Our work identified a BPH-inducible promoter and three positive regions within it. Transgenic rice with GNA driven by OsAOS1 promoter and positive regions exhibited an expected lethal effect on BPH. This study proved the application potential of BPH-inducible promoter and provided a novel path for the selection of insect-resistant tools in the future.

Stomata-mediated interactions between plants, herbivores, and the environment

Stomata play a central role in plant responses to abiotic and biotic stresses. Existing knowledge regarding the roles of stomata in plant stress is centered on abiotic stresses and plant-pathogen interactions, but how stomata influence plant-herbivore interactions remains largely unclear. Here, we summarize the functions of stomata in plant-insect interactions and highlight recent discoveries of how herbivores manipulate plant stomata. Because stomata are linked to interrelated physiological processes in plants, herbivory-induced changes in stomatal dynamics might have cellular, organismic, and/or even community-level impacts. We summarize our current understanding of how stomata mediate plant responses to herbivory and environmental stimuli, propose how herbivores may influence these responses, and identify key knowledge gaps in plant-herbivore interactions.

Metabolic response to larval herbivory in three Physalis species

The Physalis genus includes species of commercial importance due to their ornamental, edible and medicinal properties. These qualities stem from their variety of biologically active compounds. We performed a metabolomic analysis of three Physalis species, i.e., P. angulata, P. grisea, and P. philadelphica, differing in domestication stage and cultivation practices, to determine the degree of inter-species metabolite variation and to test the hypothesis that these related species mount a common metabolomic response to foliar damage caused by Trichoplusia ni larvae. The results indicated that the metabolomic differences detected in the leaves of these species were species-specific and remained even after T. ni herbivory. They also show that each Physalis species displayed a unique response to insect herbivory. This study highlighted the metabolite variation present in Physalis spp. and the persistence of this variability when faced with biotic stressors. Furthermore, it sets an experimental precedent from which highly species-specific metabolites could be identified and subsequently used for plant breeding programs designed to increase insect resistance in Physalis and related plant species.

Foliar herbivory increases sucrose concentration in bracteal extrafloral nectar of cotton

Cultivated cotton, such as Gossypium hirsutum L., produces extrafloral (EF) nectar on leaves (foliar) and reproductive structures (bracteal) as an indirect anti-herbivore defense. In exchange for this carbohydrate-rich substance, predatory insects such as ants protect the plant against herbivorous insects. Some EF nectar-bearing plants respond to herbivory by increasing EF nectar production. For instance, herbivore-free G. hirsutum produces more bracteal than foliar EF nectar, but increases its foliar EF nectar production in response to herbivory. This study is the first to test for systemically induced changes to the carbohydrate composition of bracteal EF nectar in response to foliar herbivory on G. hirsutum. We found that foliar herbivory significantly increased the sucrose content of bracteal EF nectar while glucose and fructose remained unchanged. Sucrose content is known to influence ant foraging behavior and previous studies of an herbivore-induced increase to EF nectar caloric content found that it led to increased ant activity on the plant. As a follow-up to our finding, ant recruitment to mock EF nectar solutions that varied in sucrose content was tested in the field. The ants did not exhibit any preference for either solution, potentially because sucrose is a minor carbohydrate component in G. hirsutum EF nectar: total sugar content was not significantly affected by the increase in sucrose. Nonetheless, our findings raise new questions about cotton’s inducible EF nectar responses to herbivory. Further research is needed to determine whether an herbivore-induced increase in sucrose content is typical of Gossypium spp., and whether it constitutes a corollary of systemic sucrose induction, or a potentially adaptive mechanism which enhances ant attraction to the plant

Elicitation of biomolecules as host defense arsenals during insect attacks on tea plants (Camellia sinensis (L.) Kuntze)

The most consumed and economically important beverage plant, tea (Camellia sinensis), and its pests have coevolved so as to maintain the plant-insect interaction. In this review, findings of different research groups on pest responsive tolerance mechanisms that exist in tea manifested through the production of secondary metabolites and their inducers are presented. The phytochemicals of C. sinensis have been categorized into volatiles, nonvolatiles, enzymes, and phytohormones for convenience. Two types of pests, namely the piercing-sucking pests and chewing pests, are associated with tea. Both the insect groups can trigger the production of those metabolites and inducers through several primary and secondary biosynthetic pathways. These induced biomolecules can act as insect repellents and most of them are associated with lowering the nutrient quality of plant tissue and increasing the indigestibility in the pest's gut. Moreover, some of them also act as predator attractants of particular pests. The herbivore-induced plant volatiles secreted from tea plants during pest infestation were (E)-nerolidol, α-farnesene, (Z)-3-hexenol, (E)-4,8-dimethyl-1,3,7-nonatriene, indole, benzyl nitrile (BN), linalool, and ocimenes. The nonvolatiles like theaflavin and L-theanine were increased in response to the herbivore attack. Simultaneously, S-adenosyl-L-methionine synthase, caffeine synthase activities were affected, whereas flavonoid synthesis and wax formation were elevated. Defense responsive enzymes like peroxidase, polyphenol oxidase, phenylalanine ammonia-lyase, ascorbate peroxidase, and catalase are involved in pest prevention mechanisms. Phytohormones like jasmonic acid, salicylic acid, abscisic acid, and ethylene act as the modulator of the defense system. The objective of this review is to discuss the defensive roles of these metabolites and their inducers against pest infestation in tea with an aim to develop environmentally sustainable pesticides in the future.Key points• Herbivore-induced volatile signals and their effects on neighboring tea plant protection• Stereochemical conversion of volatiles, effects of nonvolatiles, expression of defense-responsive enzymes, and phytohormones due to pest attack• Improved understanding of metabolites for bio-sustainable pesticide development.

Induced defense and its cost in two bryophyte species

PREMISE

Current knowledge about defense strategies in plants under herbivore pressure is predominantly based on vascular plants. Bryophytes are rarely consumed by herbivores since they have ample secondary metabolites. However, it is unknown whether bryophytes have induced defenses against herbivory and whether there is a trade-off between growth and defense in bryophytes.

METHODS

In an experiment with two peatland bryophytes, Sphagnum magellanicum Brid. and S. fuscum (Schimp.) H. Klinggr., two kinds of herbivory, clipping with scissors and grazing by mealworms (Tenebrio molitor L.) were simulated. At the end of the experiment, we measured growth traits, carbon-based defense compounds (total phenolics and cellulose) and storage compounds (total nonstructural carbohydrates) of these two Sphagnum species.

RESULTS

Grazing but not clipping increased total phenolics and C:N ratio and reduced biomass production and height increment. A negative relationship between biomass production and total phenolics was found in S. magellanicum but not in S. fuscum, indicating a growth-defense trade-off that is species-specific. Grazing reduced the sugar starch content of S. magellanicum and the sugar of S. fuscum. Either clipping or grazing had no effect on chlorophyll fluorescence (including actual and maximum photochemical efficiency of photosystem II) except that a significant effect of clipping on actual photochemical efficiency in S. fuscum was observed.

CONCLUSIONS

Our results suggest that Sphagnum can have induced defense against herbivory and that this defense can come at a cost of growth. These findings advance our knowledge about induced defense in bryophytes, the earliest land plants.

The Price of the Induced Defense Against Pests: A Meta-Analysis

Plants and phytophagous arthropods have co-evolved for millions of years. During this long coexistence, plants have developed defense mechanisms including constitutive and inducible defenses. In an effort to survive upon herbivore attack, plants suffer a resource reallocation to facilitate the prioritization of defense toward growth. These rearrangements usually end up with a penalty in plant growth, development or reproduction directly linked to crop losses. Achieving the balance to maximize crop yield requires a fine tune regulation specific for each host-arthropod combination, which remains to be fully elucidated. The purpose of this work is to evaluate the effects of induced plant defenses produced upon pest feeding on plant fitness and surrogate parameters. The majority of the studies are focused on specific plant-pest interactions based on artificial herbivory damage or simulated defoliation on specific plant hosts. In this meta-analysis, the relevance of the variables mediating plant-pest interactions has been studied. The importance of plant and pest species, the infestation conditions (plant age, length/magnitude of infestation) and the parameters measured to estimate fitness (carbohydrate content, growth, photosynthesis and reproduction) in the final cost have been analyzed through a meta-analysis of 209 effects sizes from 46 different studies. Herbivore infestation reduced growth, photosynthesis and reproduction but not carbohydrate content. When focusing on the analyses of the variables modulating plant-pest interactions, new conclusions arise. Differences on the effect on plant growth and photosynthesis were observed among different feeding guilds or plant hosts, suggesting that these variables are key players in the final effects. Regarding the ontogenetic stage of a plant, negative effects were reported only in infestations during the vegetative stage of the plant, while no effect was observed during the reproductive stage. In addition, a direct relation was found between the durability and magnitude of the infestation, and the final negative effect on plant fitness. Among the parameters used to estimate the cost, growth and photosynthesis revealed more differences among subgroups than reproduction parameters. Altogether, this information on defense-growth trade-offs should be of great help for the scientific community to design pest management strategies reducing costs.

Comparative transcriptome analysis of defense response of rice to Nilaparvata lugens and Chilo suppressalis infestation

The brown planthopper (BPH, Nilaparvata lugens) and striped stem borer (SSB, Chilo suppressalis) are two of the most devastating insect pests in rice, causing significant losses of rice yield. Plants evolve multiple defense responses in the process of coexisting with pests. According to different pest infestation, the plants selectively activate related pathways and downstream gene expression. However, there are very few reports of differences in defense signaling pathways after rice was attacked by BPH or SSB. We determined the transcriptional responses of rice infested with BPH and SSB for 3 and 6 h using Illumina sequencing. By comparing the difference in gene changes caused by BPH and SSB infestation in rice, multiple signal pathways and gene expression patterns, including phytohormones, secondary metabolites, plant-pathogen interaction, reactive oxygen species, defense response, transcription factors, protease inhibitor and chitinase were found significantly different. Our results provide a basis for further exploring the molecular mechanism of rice defense response caused by BPH and SSB infestation, which will add to further understanding the interactions between plants and insects, and could provide valuable resources that could be applied in insect-resistant crop breeding.

Cloning and functional identification of a Chilo suppressalis-inducible promoter of rice gene, OsHPL2

BACKGROUND

Promoters play a key role in driving insect-resistant genes during breeding of transgenic plants. In current transgenic procedures for breeding rice resistance to striped stem borer (Chilo suppressalis Walker, SSB), the constitutive promoter is used to drive the insect-resistant gene. To reduce the burden of constitutive promoters on plant growth, isolation and identification of insect-inducible promoters are particularly important. However, few promoters are induced specifically by insect feeding.

RESULTS

We found rice hydroperoxide lyase gene (OsHPL2) (LOC_Os02g12680) was upregulated after feeding by SSB. We subsequently cloned the promoter of OsHPL2 and analysed its expression pattern using the β-glucuronidase (GUS) reporter gene. Histochemical assays and quantitative analyses of GUS activity confirmed that P _HPL2 :GUS was activated by SSB, but did not respond to brown planthopper (Nilaparvata lugens Stål, BPH) infestation, mechanical wounding or phytohormone treatments. A series of 5' truncated assays were conducted and three positive regulatory regions (-1452 to -1213, -903 to -624, and -376 to -176) induced by SSB infestation were identified. P2R123-min 35S and P2TR2-min 35S promoters linked with cry1C of transgenic plants showed the highest levels of Cry1C protein expression and SSB larval mortality.

CONCLUSION

We identified an SSB-inducible promoter and three positive internal regions. Transgenic rice plants with the OsHPL2 promoter and its positive regions driving cry1C exhibited the expected larvicidal effect on SSB. Our study is the first report of an SSB-inducible promoter that could be used as a potential resource for breeding insect-resistant transgenic crops. © 2020 Society of Chemical Industry.

The combined impacts of wheat spatial position and phenology on cereal aphid abundance

Background

Wheat is a staple crop that suffers from massive yield losses caused by cereal aphids. Many factors can determine the abundance of cereal aphids and the damage they cause to plants; among them are the plant’s genetic background, as well as environmental conditions such as spatial position within the plot, the composition and the distance from neighboring vegetation. Although the effects of these factors have been under scrutiny for many years, the combined effect of both factors on aphid populations is not fully understood. The goal of this study was to examine the collective impact of genotype and environment on wheat phenology (developmental stages), chemical diversity (metabolites), and insect susceptibility, as manifested by cereal aphid abundance.

Methods

To determine the influence of plant genotype on the metrics mentioned above, we measured the phenology, chemical profile, and aphid abundance of four wheat genotypes, including the tetraploid wild emmer (Triticum turgidum ssp. dicoccoides cv. Zavitan), tetraploid durum (Triticum turgidum ssp. durum cv. Svevo), and two hexaploid spring bread (Triticum aestivum), ‘Rotem’ and ‘Chinese Spring’. These genotypes are referred to as “focal” plants. To evaluate the impact of the environment, we scored the distance of each focal plant (spatial position) from two neighboring vegetation types: (i) natural resource and (ii) monoculture wheat resource.

Results

The results demonstrated that the wild emmer wheat was the most aphid-resistant, while the bread wheat Rotem was most aphid-susceptible. Aphids were more abundant in plants that matured early. The spatial position analysis demonstrated that aphids were more abundant in focal plants located closer to the margin monoculture wheat resource rather than to the natural resource, suggesting a resource concentration effect. The analysis of metabolic diversity showed that the levels of three specialized metabolites from the flavonoid class, differed between the wheat genotypes and some minor changes in central metabolites were shown as well. Altogether, these results demonstrate a combined effect of genetic background and spatial position on wheat phenology and aphid abundance on plants. This exposes the potential role of the marginal vegetation environment in shaping the insect population of desirable crops. These findings highlight the importance of maintaining plant intra-specific variation in the agriculture system because of its potential applications in reducing pest density.

Defence priming in Arabidopsis - a Meta-Analysis

Defence priming by organismal and non-organismal stimulants can reduce effects of biotic stress in plants. Thus, it could help efforts to enhance the sustainability of agricultural production by reducing use of agrochemicals in protection of crops from pests and diseases. We have explored effects of applying this approach to both Arabidopsis plants and seeds of various crops in meta-analyses. The results show that its effects on Arabidopsis plants depend on both the priming agent and antagonist. Fungi and vitamins can have strong priming effects, and priming is usually more effective against bacterial pathogens than against herbivores. Moreover, application of bio-stimulants (particularly vitamins and plant defence elicitors) to seeds can have promising defence priming effects. However, the published evidence is scattered, does not include Arabidopsis, and additional studies are required before we can draw general conclusions and understand the molecular mechanisms involved in priming of seeds' defences. In conclusion, defence priming of plants has clear potential and application of bio-stimulants to seeds may protect plants from an early age, promises to be both labour- and resource-efficient, poses very little environmental risk, and is thus both economically and ecologically promising.

Effect of Major Tea Insect Attack on Formation of Quality-Related Nonvolatile Specialized Metabolites in Tea ( Camellia sinensis) Leaves

Insect attack is known to induce a high accumulation of volatile metabolites in tea ( Camellia sinensis). However, little information is available concerning the effect of insect attack on tea quality-related nonvolatile specialized metabolites. This study aimed to investigate the formation of characteristic nonvolatile specialized metabolites in tea leaves in response to attack by major tea insects, namely, tea green leafhoppers and tea geometrids, and determine the possible involvement of phytohormones in metabolite formation resulting from insect attack. Both tea green leafhopper and tea geometrid attacks increased the jasmonic acid and salicylic acid contents. The abscisic acid content was only increased under tea green leafhopper attack, perhaps due to special continuous piercing-sucking wounding. Tea green leafhopper attack induced the formation of theaflavins from catechins under the action of polyphenol oxidase, while tea geometrid attack increased the l-theanine content. Exogenous phytohormone treatments can affect the caffeine and catechin contents. These results will help to determine the influence of major tea pest insects on important tea quality-related metabolites and enhance understanding of the relationship of phytohormones and quality-related nonvolatile metabolite formation in tea exposed to tea pest insect attacks.

Reduced caterpillar damage can benefit plant bugs in Bt cotton

Bt cotton was genetically modified to produce insecticidal proteins targeting Lepidopteran pests and is therefore only minimally affected by caterpillar damage. This could lead to reduced levels of inherent, systemically inducible defensive compounds in Bt cotton which might benefit other important cotton herbivores such as plant bugs. We studied the effects of plant defense induction on the performance of the plant bug Lygus hesperus by caging nymphs on different food sources (bolls/squares) of Bt and non-Bt cotton which were either undamaged, damaged by Bt tolerant caterpillars, or treated with jasmonic acid (JA). Terpenoid induction patterns of JA-treated and L. hesperus-damaged plants were characterized for different plant structures and artificial diet assays using purified terpenoids (gossypol/heliocide H1/4) were conducted. Nymphs were negatively affected if kept on plants damaged by caterpillars or sprayed with JA. Performance of nymphs was increased if they fed on squares and by the Bt-trait which had a positive effect on boll quality as food. In general, JA-sprayed plants (but not L. hesperus infested plants) showed increased levels of terpenoids in the plant structures analyzed, which was especially pronounced in Bt cotton. Nymphs were not negatively affected by terpenoids in artificial diet assays indicating that other inducible cotton responses are responsible for the found negative effects on L. hesperus. Overall, genetically engineered plant defenses can benefit plant bugs by releasing them from plant-mediated indirect competition with lepidopterans which might contribute to increasing numbers of hemipterans in Bt cotton.

Nitrogen nutrition of tomato plant alters leafminer dietary intake dynamics

The leafminer Tuta absoluta (Meyrick) is a major pest of the tomato crop and its development rate is known to decline when nitrogen availability for crop growth is limited. Because N limitation reduces plant primary metabolism but enhances secondary metabolism, one can infer that the slow larval development arises from lower leaf nutritive value and/or higher plant defence. As an attempt to study the first alternative, we examined the tomato-T. absoluta interaction in terms of resource supply by leaves and intake by larvae. Tomato plants were raised under controlled conditions on N-sufficient vs. N-limited complete nutrient solutions. Plants were kept healthy or artificially inoculated with larvae for seven days. Serial harvests were taken and the N, C, dry mass and water contents were determined in roots, stems and leaves. Leaf and mine areas were also measured and the N, C, dry mass and water surface densities were calculated in order to characterize the diet of the larvae. The infestation of a specific leaf lessened its local biomass by 8-26%, but this effect was undetectable at the whole plant scale. Infestation markedly increased resource density per unit leaf area (water, dry mass, C and N) suggesting that the insect induced changes in leaf composition. Nitrogen limitation lessened whole plant growth (by 50%) and infested leaflet growth (by 32-44%). It produced opposite effects on specific resource density per unit area, increasing that of dry mass and C while decreasing water and N. These changes were ineffective on insect mining activity, but slowed down larval development. Under N limitation, T. absoluta consumed less water and N but more dry mass and C. The resulting consequences were a 50-70% increase of C:N stoichiometry in their diet and the doubling of faeces excretion. The observed limitation of larval development is therefore consistent with a trophic explanation caused by low N and/or water intakes.

Interrelated responses of tomato plants and the leaf miner Tuta absoluta to nitrogen supply

Plant-insect interactions are strongly modified by environmental factors. This study evaluates the influence of nitrogen fertilisation on the tomato (Solanum lycopersicum L.) cv. Santa clara and the leafminer (Tuta absoluta (Meyrick), Lepidoptera: Gelechiidae). Greenhouse-grown tomato plants were fed hydroponically on a complete nutrient solution containing either a high nitrogen concentration (HN) sustaining maximum growth or a low nitrogen concentration (LN) limiting plant growth. Insect-free plants were compared with plants attacked by T. absoluta. Seven and 14 days after artificial oviposition leading to efficacious hatching and larvae development, we measured total carbon, nitrogen and soluble protein as well as defence compounds (phenolics, glycoalkaloids, polyphenol oxidase activity) in the HN versus LN plants. Only in the HN treatment did T. absoluta infestation slightly impair leaf growth and induce polyphenol oxidase (PPO) activity in the foliage. Neither the concentration of phenolic compounds and proteins nor the distribution of nitrogen within the plant was affected by T. absoluta infestation. In contrast, LN nutrition impaired T. absoluta-induced PPO activity. It decreased protein and total nitrogen concentration of plant organs and enhanced the accumulation of constitutive phenolics and tomatine. Moreover, LN nutrition impaired T. absoluta development by notably decreasing pupal weight and lengthening the development period from egg to adult. Adjusting the level of nitrogen nutrition may thus be a means of altering the life cycle of T. absoluta. This study provides a comprehensive dataset concerning interrelated responses of tomato plants and T. absoluta to nitrogen nutrition.

Sucrose and Saccharomyces cerevisiae: a relationship most sweet

Sucrose is an abundant, readily available and inexpensive substrate for industrial biotechnology processes and its use is demonstrated with much success in the production of fuel ethanol in Brazil. Saccharomyces cerevisiae, which naturally evolved to efficiently consume sugars such as sucrose, is one of the most important cell factories due to its robustness, stress tolerance, genetic accessibility, simple nutrient requirements and long history as an industrial workhorse. This minireview is focused on sucrose metabolism in S. cerevisiae, a rather unexplored subject in the scientific literature. An analysis of sucrose availability in nature and yeast sugar metabolism was performed, in order to understand the molecular background that makes S. cerevisiae consume this sugar efficiently. A historical overview on the use of sucrose and S. cerevisiae by humans is also presented considering sugarcane and sugarbeet as the main sources of this carbohydrate. Physiological aspects of sucrose consumption are compared with those concerning other economically relevant sugars. Also, metabolic engineering efforts to alter sucrose catabolism are presented in a chronological manner. In spite of its extensive use in yeast-based industries, a lot of basic and applied research on sucrose metabolism is imperative, mainly in fields such as genetics, physiology and metabolic engineering.

Quantity over quality: light intensity, but not red/far-red ratio, affects extrafloral nectar production in Senna mexicana var. chapmanii

Extrafloral nectar (EFN) mediates food‐for‐protection mutualisms between plants and insects and provides plants with a form of indirect defense against herbivory. Understanding sources of variation in EFN production is important because such variations affect the number and identity of insect visitors and the effectiveness of plant defense. Light represents a potentially crucial tool for regulating resource allocation to defense, as it not only contributes energy but may help plants to anticipate future conditions. Low red/far‐red (R/FR) light ratios can act as a signal of the proximity of competing plants. Exposure to such light ratios has been shown to promote competitive behaviors that coincide with reduced resource allocation to direct chemical defenses. Little is known, however, about how such informational light signals might affect indirect defenses such as EFN, and the interactions that they mediate. Through controlled glasshouse experiments, we investigated the effects of light intensity, and R/FR light ratios, on EFN production in Senna mexicana var. chapmanii. Plants in light‐limited conditions produced significantly less EFN, and leaf damage elicited increased EFN production regardless of light conditions. Ratios of R/FR light, however, did not appear to affect EFN production in either damaged or undamaged plants. Understanding the effects of light on indirect defenses is of particular importance for plants in the threatened pine rockland habitats of south Florida, where light conditions are changing in predictable ways following extensive fragmentation and subsequent mismanagement. Around 27% of species in these habitats produce EFN and may rely on insect communities for defense.

Arginine metabolism of Arabidopsis thaliana is modulated by Heterodera schachtii infection

The plant-parasitic cyst nematode Heterodera schachtii induces syncytial feeding structures in the roots of host plants. These syncytia provide all required nutrients, water and solutes to the parasites. Previous studies on the composition of primary metabolites in syncytia revealed significantly increased amino acid levels. However, mainly due to technical limitations, little is known about the role of arginine in plant-nematode interactions. This free amino acid plays a central role in the plant primary metabolism and serves as substrate for metabolites involved in plant stress responses. Thus, in the present work, expression of genes coding for the enzymes of arginine metabolism were studied in nematode-induced syncytia compared to non-infected control roots of Arabidopsis thaliana. Further, amiRNA lines were constructed and T-DNA lines were isolated to test their effects on nematode development. While the silencing of genes involved in arginine synthesis increased nematode development, most T-DNA lines did not show any significant difference from the wild type. Amino acid analyses of syncytia showed that they accumulate high arginine levels. In addition, manipulating arginine cycling had a global effect on the local amino acid composition in syncytia as well as on the systemic amino acid levels in roots and shoots.

Dynamic extrafloral nectar production: the timing of leaf damage affects the defensive response in Senna mexicana var. chapmanii (Fabaceae)

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PREMISE OF THE STUDY

Extrafloral nectar (EFN) mediates food for protection mutualisms between plants and defensive insects. Understanding sources of variation in EFN production is important because such variations may affect the number and identity of visitors and the effectiveness of plant defense. We investigated the influence of plant developmental stage, time of day, leaf age, and leaf damage on EFN production in Senna mexicana var. chapmanii. The observed patterns of variation in EFN production were compared with those predicted by optimal defense theory.•

METHODS

Greenhouse experiments with potted plants were conducted to determine how plant age, time of day, and leaf damage affected EFN production. A subsequent field study was conducted to determine how leaf damage, and the resulting increase in EFN production, affected ant visitation in S. chapmanii.•

KEY RESULTS

More nectar was produced at night and by older plants. Leaf damage resulted in increased EFN production, and the magnitude of the response was greater in plants damaged in the morning than those damaged at night. Damage to young leaves elicited a stronger defensive response than damage to older leaves, in line with optimal defense theory. Damage to the leaves of S. chapmanii also resulted in significantly higher ant visitation in the field.•

CONCLUSIONS

Extrafloral nectar is an inducible defense in S. chapmanii. Developmental variations in its production support the growth differentiation balance hypothesis, while within-plant variations and damage responses support optimal defense theory.

Application of an improved proteomics method for abundant protein cleanup: molecular and genomic mechanisms study in plant defense

High abundance proteins like ribulose-1,5-bisphosphate carboxylase oxygenase (Rubisco) impose a consistent challenge for the whole proteome characterization using shot-gun proteomics. To address this challenge, we developed and evaluated Polyethyleneimine Assisted Rubisco Cleanup (PARC) as a new method by combining both abundant protein removal and fractionation. The new approach was applied to a plant insect interaction study to validate the platform and investigate mechanisms for plant defense against herbivorous insects. Our results indicated that PARC can effectively remove Rubisco, improve the protein identification, and discover almost three times more differentially regulated proteins. The significantly enhanced shot-gun proteomics performance was translated into in-depth proteomic and molecular mechanisms for plant insect interaction, where carbon re-distribution was used to play an essential role. Moreover, the transcriptomic validation also confirmed the reliability of PARC analysis. Finally, functional studies were carried out for two differentially regulated genes as revealed by PARC analysis. Insect resistance was induced by over-expressing either jacalin-like or cupin-like genes in rice. The results further highlighted that PARC can serve as an effective strategy for proteomics analysis and gene discovery.

Susceptibility and physiological responses of Jatropha curcas accessions to broad mite infestation

The broad mite Polyphagotarsonemus latus is a key pest of physic nut (Jatropha curcas L.). The purpose of this study was to identify physic nut accessions that are less susceptible to P. latus, in support of the breeding program of J. curcas. We first evaluated population growth rate and injury symptoms of P. latus on different J. curcas accessions and then carried out physiological analyses on P. latus-infested and uninfested accessions. From the germplasm bank of the Federal University of Viçosa, 15 physic nut accessions with high seed oil content, with different genetic background, were tested. The following traits were evaluated: instantaneous population growth rate of P. latus (r i ), injury symptoms, relative leaf water content, specific leaf area, gas exchange, photosynthetic pigments, nitrogen and biomass of the aerial part. Significant differences were observed for P. latus population growth rate and injury symptoms among accessions. A positive correlation between P. latus growth rate and injury was found. The UFVJC72 accession stood out as the more resistant, considering P. latus growth rate and injury symptoms, compared with most accessions. Physiological responses did not vary among accessions, but did between infested and uninfested plants. In P. latus-infested plants, net photosynthesis was on average 50.5 % lower than in uninfested plants, whereas stomatal conductance and transpiration decreased by 46.2 and 51.6 %, respectively.

Specific response to herbivore-induced de novo synthesized plant volatiles provides reliable information for host plant selection in a moth

Animals depend on reliable sensory information for accurate behavioural decisions. For herbivorous insects it is crucial to find host plants for feeding and reproduction, and these insects must be able to differentiate suitable from unsuitable plants. Volatiles are important cues for insect herbivores to assess host plant quality. It has previously been shown that female moths of the Egyptian cotton leafworm, Spodoptera littoralis (Lepidoptera: Noctuidae), avoid oviposition on damaged cotton Gossypium hirsutum, which may mediated by herbivore-induced plant volatiles (HIPVs). Among the HIPVs, some volatiles are released following any type of damage while others are synthesized de novo and released by the plants only in response to herbivore damage. In behavioural experiments we here show that oviposition by S. littoralis on undamaged cotton plants was reduced by adding volatiles collected from plants with ongoing herbivory. Gas chromatography-electroantennographic detection (GC-EAD) recordings revealed that antennae of mated S. littoralis females responded to 18 compounds from a collection of headspace volatiles of damaged cotton plants. Among these compounds, a blend of the seven de novo synthesized volatile compounds was found to reduce oviposition in S. littoralis on undamaged plants under both laboratory and ambient (field) conditions in Egypt. Volatile compounds that are not produced de novo by the plants did not affect oviposition. Our results show that ovipositing females respond specifically to the de novo synthesized volatiles released from plants under herbivore attack. We suggest that these volatiles provide reliable cues for ovipositing females to detect plants that could provide reduced quality food for their offspring and an increased risk of competition and predation.

Herbivore-induced changes in tomato (Solanum lycopersicum) primary metabolism: a whole plant perspective

Induced changes in primary metabolism are important plant responses to herbivory, providing energy and metabolic precursors for defense compounds. Metabolic shifts also can lead to reallocation of leaf resources to storage tissues, thus increasing a plant's tolerance. We characterized whole-plant metabolic responses of tomato (Solanum lycopersicum) 24 h after leaf herbivory by two caterpillars (the generalist Helicoverpa zea and the specialist Manduca sexta) by using GC-MS. We measured 56 primary metabolites across the leaves, stems, roots, and apex, comparing herbivore-attacked plants to undamaged plants and mechanically damaged plants. Induced metabolic change, in terms of magnitude and number of individual concentration changes, was stronger in the apex and root tissues than in undamaged leaflets of damaged leaves, indicating rapid and significant whole-plant responses to damage. Helicoverpa zea altered many more metabolites than M. sexta across most tissues, suggesting an enhanced plant response to H. zea herbivory. Helicoverpa zea herbivory strongly affected concentrations of defense-related metabolites (simple phenolics and precursor amino acids), while M. sexta altered metabolites associated with carbon and nitrogen transport. We conclude that herbivory induces many systemic primary metabolic changes in tomato, and that changes often are specific to a single tissue or type of herbivore. The potential implications of primary metabolic changes are discussed in relation to resistance and tolerance.

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.

Methyl jasmonate elicits rapid changes in carbon and nitrogen dynamics in tomato

• Evidence is emerging to support the notion that in response to herbivory, plants undergo changes in their primary metabolism and are able to fine-tune the allocation of new and existing resources and temporarily direct them to storage organs. • We hypothesized that simulated herbivory increases the export of resources out of the affected tissues and increases allocation to roots. We used short-lived radioisotopes to study in vivo the dynamics of newly incorporated (11)CO(2) and (13)NH(3). Methyl jasmonate (MeJA), a known defense elicitor, was applied to the foliage of tomato plants and 4 h later we monitored leaf uptake, export and whole-plant allocation of [(11)C]photosynthate and [(13)N]amino acids. • There was a marginally significant decrease in the fixation of (11)CO(2), and an increase in the export of newly acquired carbon and nitrogen out of MeJA-treated leaves. The proportion of nitrogen allocated to roots increased, whereas the proportion of carbon did not change. • These results are in agreement with our hypotheses, showing a change in the allocation of resources after treatment with MeJA; this may reduce the chance of resources being lost to herbivores and act as a buffer to biotic stress by increasing the potential for plant regrowth and survival after the attack.

Metabolic profiling reveals local and systemic responses of host plants to nematode parasitism

The plant parasitic beet cyst nematode Heterodera schachtii induces syncytial feeding structures in Arabidopsis roots. The feeding structures form strong sink tissues that have been suggested to be metabolically highly active. In the present study, metabolic profiling and gene targeted expression analyses were performed in order to study the local and systemic effects of nematode infection on the plant host. The results showed increased levels of many amino acids and phosphorylated metabolites in syncytia, as well as high accumulation of specific sugars such as 1-kestose that do not accumulate naturally in Arabidopsis roots. A correlation-based network analysis revealed highly activated and coordinated metabolism in syncytia compared to non-infected control roots. An integrated analysis of the central primary metabolism showed a clear coherence of metabolite and transcript levels, indicating transcriptional regulation of specific pathways. Furthermore, systemic effects of nematode infection were demonstrated by correlation-based network analysis as well as independent component analysis. 1-kestose, raffinose, alpha,alpha-trehalose and three non-identified analytes showed clear systemic accumulation, indicating future potential for diagnostic and detailed metabolic analyses. Our studies open the door towards understanding the complex remodelling of plant metabolism in favour of the parasitizing nematode.