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Leucine-rich repeat receptor-like kinases (LRR-RLKs) are an important subfamily of receptor-like kinases (RLKs) in plants that play key roles in sensing different biotic and abiotic stress. However, the role of LRR-RLKs in herbivore-induced plant defense remains largely elusive. Here, we found that the expression of a rice gene, OsRLK7-1, was induced by mechanical wounding, but was slightly suppressed by the infestation of gravid females of brown planthopper (BPH, Nilaparvata lugens) or white-backed planthopper (WBPH, Sogatella furcifera). Through targeted disruption of OsRLK7-1 (resulting in the ko-rlk lines), we observed an augmentation in transcript levels of BPH-induced OsMPK3, OsWRKY30, OsWRKY33, and OsWRKY45, alongside heightened levels of planthopper-induced jasmonic acid, JA-isoleucine, and abscisic acid in plant tissues. These dynamic changes further facilitated the biosynthesis of multiple phenolamides within the rice plants, culminating in an enhanced resistance to planthopper infestations under both lab and field conditions. In addition, knocking out OsRLK7-1 impaired plant growth and reproduction. These results suggest that OsRLK7-1 plays an important role in regulating rice growth, development, and rice-planthopper interactions.

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It has been well documented that an infestation of the piercing-sucking herbivore, brown planthopper (BPH), Nilaparvata lugens, activates strong local defenses in rice. However, whether a BPH infestation elicits systemic responses in rice remains largely unknown. In this study, we investigated BPH-induced systemic defenses by detecting the change in expression levels of 12 JA- and/or SA-signaling-responsive marker genes in different rice tissues upon a BPH attack. We found that an infestation of gravid BPH females on rice leaf sheaths significantly increased the local transcript level of all 12 marker genes tested except OsVSP, whose expression was induced only weakly at a later stage of the BPH infestation. Moreover, an infestation of gravid BPH females also systemically up-regulated the transcription levels of three JA-signaling-responsive genes (OsJAZ8, OsJAMyb, and OsPR3), one SA-signaling-responsive gene (OsWRKY62), and two JA- and SA- signaling-responsive genes (OsPR1a and OsPR10a). Our results demonstrate that an infestation of gravid BPH females systemically activates JA- and SA-dependent defenses in rice, which may in turn influence the composition and structure of the community in the rice ecosystem.

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The fall armyworm (FAW), Spodoptera frugiperda, has become one of the most important pests on corn in China since it invaded in 2019. Although FAW has not been reported to cause widespread damage to rice plants in China, it has been sporadically found feeding in the field. If FAW infests rice in China, the fitness of other insect pests on rice may be influenced. However, how FAW and other insect pests on rice interact remains unknown. In this study, we found that the infestation of FAW larvae on rice plants prolonged the developmental duration of the brown planthopper (BPH, Nilaparvata lugens (Stål)) eggs and plants damaged by gravid BPH females did not induce defenses that influenced the growth of FAW larvae. Moreover, co-infestation by FAW larvae on rice plants did not influence the attractiveness of volatiles emitted from BPH-infested plants to Anagrus nilaparvatae, an egg parasitoid of rice planthoppers. FAW larvae were able to prey on BPH eggs laid on rice plants and grew faster compared to those larvae that lacked available eggs. Studies revealed that the delay in the development of BPH eggs on FAW-infested plants was probably related to the increase in levels of jasmonoyl-isoleucine, abscisic acid and the defensive compounds in the rice leaf sheaths on which BPH eggs were laid. These findings indicate that, if FAW invades rice plants in China, the population density of BPH may be decreased by intraguild predation and induced plant defenses, whereas the population density of FAW may be increased.

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Herbivory-induced plant volatiles (HIPVs) are involved in biotic interactions among plants as well as herbivorous and carnivorous arthropods. This review looks at the specificity in plant-carnivore communication mediated by specific blends of HIPVs as well as describes plant-herbivore and plant-plant communication mediated by specific HIPVs. Factors affecting the net benefits of HIPV production have also been examined. These specific means of communication results in high complexity in the 'interaction-information network', which should be explored further to elucidate the mechanism underlying the numerous species coexisting in ecosystems.

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Jasmonic acid (JA) and its derivatives, collectively known as jasmonates (JAs), are important signaling hormones for plant responses against chewing herbivores. In JA signaling networks, jasmonate ZIM-domain (JAZ) proteins are transcriptional repressors that regulate JA-modulated downstream herbivore defenses. JAZ repressors are widely presented in land plants, however, there is only limited information about the regulation/function of JAZ proteins in maize. In this study, we performed a comprehensive expression analysis of ZmJAZ genes with other selected genes in the jasmonate pathway in response to feeding by fall armyworm (Spodoptera frugiperda, FAW), mechanical wounding, and exogenous hormone treatments in two maize genotypes differing in FAW resistance. Results showed that transcript levels of JAZ genes and several key genes in JA-signaling and biosynthesis pathways were rapidly and abundantly expressed in both genotypes in response to these various treatments. However, there were key differences between the two genotypes in the expression of ZmJAZ1 and ZmCOI1a, these two genes were expressed significantly rapidly and abundantly in the resistant line which was tightly regulated by endogenous JA level upon feeding. For instance, transcript levels of ZmJAZ1 increase dramatically within 30 min of FAW-fed Mp708 but not Tx601, correlating with the JA accumulation. The results also demonstrated that wounding or JA treatment alone was not as effective as FAW feeding; this suggests that insect-derived factors are required for optimal defense responses.

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A potential barrier to the establishment of weed biological control agents is interference from other management tactics that induce plant defenses. Methods that suppress the weed such as feeding by other biological control agents or mechanical removal are especially disposed to inducing plant defenses and potentially limiting agent establishment. Here, we focused on the invasive weed Lygodium microphyllum (Cav.) R. Br. (Schizaeales: Lygodiaceae, Old World climbing fern) and one of its biological control agents, the mite Floracarus perrepae Knihinicki and Boczek (Acariformes: Eriophyidae). We experimentally induced plant defenses in potted plants via damage or application of jasmonic acid, a hormone typically involved in plant defenses, and measured the responses of the mite in a screenhouse. Localized damage to the pinnae (e.g., leaflets) via cutting or larval feeding from a second biological control agent, Neomusotima conspurcatalis (Warren) (Lepidoptera; Crambidae), reduced F. perrepae gall formation, but not the number of mites per gall. In contrast, damage to rachises (e.g., stems) did not affect galling, likely because plant defense responses were not systemic. Application of jasmonic acid reduced gall formation but not the numbers of mites within galls. Taken together, we found that localized damage interfered with gall formation but not within-gall reproduction. However, these effects on the mite from induced plant defenses are likely short-lived, and therefore interference between management tactics is unlikely to affect F. perrepae establishment and performance.

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Insect-associated microbes, including pathogens, parasites, and symbionts, influence the interactions of herbivorous insects and pollinators with their host plants. Moreover, herbivory-induced changes in plant resource allocation and defensive chemistry can influence pollinator behavior. This suggests that the outcomes of interactions between herbivores, their microbes and host plants could have implications for pollinators. As epizootic diseases occur at high population densities, pathogen and parasite-mediated effects on plants could have landscape-level impacts on foraging pollinators. The goal of this minireview is to highlight the potential for an herbivore's multitrophic interactions to trigger plant-mediated effects on the immunity and health of pollinators. We highlight the importance of plant quality and gut microbiomes in bee health, and how caterpillars as model herbivores interact with pathogens, parasites, and symbionts to affect plant quality, which forms the centerpiece of multitrophic interactions between herbivores and pollinators. We also discuss the impacts of other herbivore-associated factors, such as agricultural inputs aimed at decreasing herbivorous pests, on pollinator microbiomes.

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The search behavior and parasitism of trichogrammatids can be affected by volatile compounds emitted by plants under herbivory and/or oviposition. Our aim was to evaluate the chemotactic behavior and parasitism rates of Trichogramma pretiosum Riley (Hymenoptera: Trichogrammatidae) females against two varieties of corn and one of rice that underwent herbivory or oviposition by Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae). In a glass Y-tube olfactometer, the parasitoids were given the choice between plants damaged by either herbivory or oviposition, with and without sentinel eggs, against those without damage. We also evaluated the average of parasitized eggs and the parasitoid emergence in sentinel eggs, which were next to plants that underwent herbivory contrasted with eggs next to undamaged plants. Trichogramma pretiosum was more attracted to rice and corn plants evaluated 24 h after herbivory compared to undamaged plants. Parasitoids preferred oviposited rice plants over control plants. Oviposited corn plants after 48 h were more attractive than non-oviposited plants without sentinel eggs. In the presence of sentinel eggs on the olfactometer tests, there was no difference in oviposition preference in corn. Parasitism was higher in sentinel eggs located near plants damaged by herbivory. This suggested that the egg parasitoid T. pretiosum not only uses chemical clues from rice and corn plants, damaged by herbivory, but also uses them as a strategy to search and increase parasitism in S. frugiperda eggs. However, the results of oviposition tests showed that plants of different species and varieties might respond differently to this type of damage.

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Synthetic chemical elicitors, so called plant strengtheners, can protect plants from pests and pathogens. Most plant strengtheners act by modifying defense signaling pathways, and little is known about other mechanisms by which they may increase plant resistance. Moreover, whether plant strengtheners that enhance insect resistance actually enhance crop yields is often unclear. Here, we uncover how a mechanism by which 4-fluorophenoxyacetic acid (4-FPA) protects cereals from piercing-sucking insects and thereby increases rice yield in the field. Four-FPA does not stimulate hormonal signaling, but modulates the production of peroxidases, H2O2, and flavonoids and directly triggers the formation of flavonoid polymers. The increased deposition of phenolic polymers in rice parenchyma cells of 4-FPA-treated plants is associated with a decreased capacity of the white-backed planthopper (WBPH) Sogatella furcifera to reach the plant phloem. We demonstrate that application of 4-PFA in the field enhances rice yield by reducing the abundance of, and damage caused by, insect pests. We demonstrate that 4-FPA also increases the resistance of other major cereals such as wheat and barley to piercing-sucking insect pests. This study unravels a mode of action by which plant strengtheners can suppress herbivores and increase crop yield. We postulate that this represents a conserved defense mechanism of plants against piercing-sucking insect pests, at least in cereals.

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Plants respond to insect infestation with defenses targeting insect eggs on their leaves and the feeding insects. Upon perceiving cues indicating imminent herbivory, such as damage-induced leaf odors emitted by neighboring plants, they are able to prime their defenses against feeding insects. Yet it remains unknown whether plants can amplify their defenses against insect eggs by responding to cues indicating imminent egg deposition. Here, we tested the hypothesis that a plant strengthens its defenses against insect eggs by responding to insect sex pheromones. Our study shows that preexposure of Pinus sylvestris to pine sawfly sex pheromones reduces the survival rate of subsequently laid sawfly eggs. Exposure to pheromones does not significantly affect the pine needle water content, but results in increased needle hydrogen peroxide concentrations and increased expression of defense-related pine genes such as SOD (superoxide dismutase), LOX (lipoxygenase), PAL (phenylalanine ammonia lyase), and PR-1 (pathogenesis related protein 1) after egg deposition. These results support our hypothesis that plant responses to sex pheromones emitted by an herbivorous insect can boost plant defensive responses to insect egg deposition, thus highlighting the ability of a plant to mobilize its defenses very early against an initial phase of insect attack, the egg deposition.

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BACKGROUND: Plants and insects have coexisted for million years and evolved a set of interactions which affect both organisms at different levels. Plants have developed various morphological and biochemical adaptations to cope with herbivores attacks. However, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) has become the major pest threatening tomato crops worldwide and without the appropriated management it can cause production losses between 80 to 100%. RESULTS: The aim of this study was to investigate the in vivo effect of a serine proteinase inhibitor (BTI-CMe) and a cysteine proteinase inhibitor (Hv-CPI2) from barley on this insect and to examine the effect their expression has on tomato defensive responses. We found that larvae fed on tomato transgenic plants co-expressing both proteinase inhibitors showed a notable reduction in weight. Moreover, only 56% of these larvae reached the adult stage. The emerged adults showed wings deformities and reduced fertility. We also investigated the effect of proteinase inhibitors ingestion on the insect digestive enzymes. Our results showed a decrease in larval trypsin activity. Transgenes expression had no harmful effect on Nesidiocoris tenuis (Reuter) (Heteroptera: Miridae), a predator of Tuta absoluta, despite transgenic tomato plants attracted the mirid. We also found that barley cystatin expression promoted plant defense by inducing the expression of the tomato endogenous wound inducible Proteinase inhibitor 2 (Pin2) gene, increasing the production of glandular trichomes and altering the emission of volatile organic compounds. CONCLUSION: Our results demonstrate the usefulness of the co-expression of different proteinase inhibitors for the enhancement of plant resistance to Tuta absoluta.

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Silicon (Si) is important in plant defenses that operate in a direct manner against herbivores, and work in rice (Oryza sativa) has established that this is mediated by the jasmonate signaling pathway. Plant defenses also operate indirectly, by the production of herbivore induced plant volatiles (HIPVs) that attract predators and parasitoids of herbivores. These indirect defenses too are mediated by the jasmonate pathway but no earlier work has demonstrated an effect of Si on HIPVs. In this study, we tested the effect of Si supplementation versus Si deprivation to rice plants on subsequent HIPV production following feeding by the important pest, rice leaffolder (Cnaphalocrocis medinalis). Gas chromatography-mass spectrometry analyses showed lower production of α-bergamotene, ß-sesquiohellandrene, hexanal 2-ethyl, and cedrol from +Si herbivore-infested plants compared with -Si infested plants. These changes in plant chemistry were ecologically significant in altering the extent to which parasitoids were attracted to infested plants. Adult females of Trathala flavo-orbitalis and Microplitis mediator both exhibited greater attraction to the HIPV blend of +Si plants infested with their respective insect hosts compared to -Si infested plants. In equivalent studies using RNAi rice plants in which jasmonate perception was silenced there was no equivalent change to the HIPV blend associated with Si treatment; indicating that the effects of Si on HIPVs are modulated by the jasmonate pathway. Further, this work demonstrates that silicon alters the HIPV blend of herbivore-infested rice plants. The significance of this finding is that there are no earlier-published studies of this phenomenon in rice or any other plant species. Si treatment to crops offers scope for enhancing induced, indirect defenses and associated biological control of pests because parasitoids are more strongly attracted by the HIPVs produced by +Si plants.

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The interactions of vector-virus-plant have important ecological and evolutionary implications. While the tripartite interactions have received some attention, little is known about whether vector infestation affects subsequent viral transmission and infection. Working with the whitefly Bemisia tabaci, begomovirus and tobacco/tomato, we demonstrate that pre-infestation of plants by the whitefly vector reduced subsequent plant susceptibility to viral transmission. Pre-infestation by the cotton bollworm, a nonvector of the virus, likewise repressed subsequent viral transmission. The two types of insects, with piercing and chewing mouthparts, respectively, activated different plant signaling pathways in the interactions. Whitefly pre-infestation activated the salicylic acid (SA) signaling pathway, leading to deposition of callose that inhibited begomovirus replication/movement. Although cotton bollworm infestation elicited the jasmonic acid (JA) defense pathway and was beneficial to virus replication, the pre-infested plants repelled whiteflies from feeding and so decreased virus transmission. Experiments using a pharmaceutical approach with plant hormones or a genetic approach using hormone transgenic or mutant plants further showed that SA played a negative but JA played a positive role in begomovirus infection. These novel findings indicate that both vector and nonvector insect feeding of a plant may have substantial negative consequences for ensuing viral transmission and infection.

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BACKGROUND: Herbivore-induced changes in plant traits can cause indirect interactions between spatially and/or temporally separated herbivores that share the same host plant. Feeding modes of the herbivores is one of the major factors that influence the outcome of such interactions. Here, we tested whether the effects of transient aboveground herbivory for seven days by herbivores of different feeding guilds on tomato plants (Solanum lycopersicum) alters their interaction with spatially as well as temporally separated belowground herbivores. RESULTS: The transient aboveground herbivory by both chewing caterpillars (Spodoptera exigua) and sucking aphids (Myzus persicae) had significant impacts on plant traits such as plant growth, resource allocation and phytohormone contents. While the changes in plant traits did not affect the overall performance of the root-knot nematodes (Meloidogyne incognita) in terms of total number of galls, we found that the consequences of aboveground herbivory for the plants can be altered by the subsequent nematode herbivory. For example, plants that had hosted aphids showed compensatory growth when they were later challenged by nematodes, which was not apparent in plants that had hosted only aphids. In contrast, plants that had been fed by S. exigua larvae did not show such compensatory growth even when challenged by nematodes. CONCLUSION: The results suggest that the earlier aboveground herbivory can modify plant responses to subsequent herbivores, and such modifications may depend upon identity and/or feeding modes of the aboveground herbivores.

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Costs of defense are central to our understanding of interactions between organisms and their environment, and defensive phenotypes of plants have long been considered to be constrained by trade-offs that reflect the allocation of limiting resources. Recent advances in uncovering signal transduction networks have revealed that defense trade-offs are often the result of regulatory "decisions" by the plant, enabling it to fine-tune its phenotype in response to diverse environmental challenges. We place these results in the context of classic studies in ecology and evolutionary biology, and propose a unifying framework for growth-defense trade-offs as a means to study the plant's allocation of limiting resources. Pervasive physiological costs constrain the upper limit to growth and defense traits, but the diversity of selective pressures on plants often favors negative correlations at intermediate trait levels. Despite the ubiquity of underlying costs of defense, the current challenge is using physiological and molecular approaches to predict the conditions where they manifest as detectable trade-offs.

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WRKY transcription factors play a central role not only in plant growth and development but also in plant stress responses. However, the role of WRKY transcription factors in herbivore-induced plant defenses and their underlying mechanisms, especially in rice, remains largely unclear. Here, we cloned a rice WRKY gene OsWRKY45, whose expression was induced by mechanical wounding, by infestation of the brown planthopper (BPH, Nilaparvata lugens) and by treatment with jasmonic acid (JA) or salicylic acid (SA). The antisense expression of OsWRKY45 (as-wrky) enhanced BPH-induced levels of H2O2 and ethylene, reduced feeding and oviposition preference as well as the survival rate of BPH, and delayed the development of BPH nymphs. Consistently, lower population densities of BPH on as-wrky lines, compared to those on wild-type (WT) plants, were observed in field experiments. On the other hand, as-wrky lines in the field had lower susceptibility to sheath blight (caused by Rhizoctonia solani) but higher susceptibility to rice blast (caused by Magnaporthe oryzae) than did WT plants. These findings suggest that OsWRKY45 plays important but contrasting roles in regulating the resistance of rice to pathogens and herbivores, and attention should be paid if OsWRKY45 is used to develop disease or herbivore-resistant rice.

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Jasmonic acid (JA) and related metabolites play a key role in plant defense and growth. JA carboxyl methyltransferase (JMT) may be involved in plant defense and development by methylating JA to methyl jasmonate (MeJA) and thus influencing the concentrations of JA and related metabolites. However, no JMT gene has been well characterized in monocotyledon defense and development at the molecular level. After we cloned a rice JMT gene, OsJMT1, whose encoding protein was localized in the cytosol, we found that the recombinant OsJMT1 protein catalyzed JA to MeJA. OsJMT1 is up-regulated in response to infestation with the brown planthopper (BPH; Nilaparvata lugens). Plants in which OsJMT1 had been overexpressed (oe-JMT plants) showed reduced height and yield. These oe-JMT plants also exhibited increased MeJA levels but reduced levels of herbivore-induced JA and jasmonoyl-isoleucine (JA-Ile). The oe-JMT plants were more attractive to BPH female adults but showed increased resistance to BPH nymphs, probably owing to the different responses of BPH female adults and nymphs to the changes in levels of H2 O2 and MeJA in oe-JMT plants. These results indicate that OsJMT1, by altering levels of JA and related metabolites, plays a role in regulating plant development and herbivore-induced defense responses in rice.

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Biological control has long been considered a potential alternative to pesticidal strategies for pest management but its impact and level of use globally remain modest and inconsistent. A rapidly expanding range of molecular - particularly DNA-related - techniques is currently revolutionizing many life sciences. This review identifies a series of constraints on the development and uptake of conservation biological control and considers the contemporary and likely future influence of molecular methods on these constraints. Molecular approaches are now often used to complement morphological taxonomic methods for the identification and study of biological control agents including microbes. A succession of molecular techniques has been applied to 'who eats whom' questions in food-web ecology. Polymerase chain reaction (PCR) approaches have largely superseded immunological approaches such as enzyme-linked immunosorbent assay (ELISA) and now - in turn - are being overtaken by next generation sequencing (NGS)-based approaches that offer unparalleled power at a rapidly diminishing cost. There is scope also to use molecular techniques to manipulate biological control agents, which will be accelerated with the advent of gene editing tools, the CRISPR/Cas9 system in particular. Gene editing tools also offer unparalleled power to both elucidate and manipulate plant defense mechanisms including those that involve natural enemy attraction to attacked plants. Rapid advances in technology will allow the development of still more novel pest management options for which uptake is likely to be limited chiefly by regulatory hurdles.

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Plants can respond to insect egg deposition and thus resist attack by herbivorous insects from the beginning of the attack, egg deposition. We review ecological effects of plant responses to insect eggs and differentiate between egg-induced plant defenses that directly harm the eggs and indirect defenses that involve egg parasitoids. Furthermore, we discuss the ability of plants to take insect eggs as warning signals; the eggs indicate future larval feeding damage and trigger plant changes that either directly impair larval performance or attract enemies of the larvae. We address the questions of how egg-associated cues elicit plant defenses, how the information that eggs have been laid is transmitted within a plant, and which molecular and chemical plant responses are induced by egg deposition. Finally, we highlight evolutionary aspects of the interactions between plants and insect eggs and ask how the herbivorous insect copes with egg-induced plant defenses and may avoid them by counteradaptations.

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Jasmonate- and salicylate-mediated signaling pathways play significant roles in induced plant defenses, but there is no sufficient evidence for their roles in monocots against aphids. We exogenously applied methyl jasmonate (MeJA) and salicylic acid (SA) on wheat seedlings and examined biochemical responses in wheat and effects on the grain aphid, Sitobion avenae (Fab.). Application of MeJA significantly increased levels of wheat's polyphenol oxidase, peroxidase and proteinase inhibitor 1, 2 and 6 days after treatment. In two-choice tests, adult aphids preferred control wheat leaves to MeJA- or SA-treated leaves. Electrical penetration graph (EPG) recordings of aphid probing behavior revealed that on MeJA-treated plants, the duration of aphid's first probe was significantly shorter and number of probes was significantly higher than those on control plants. Also total duration of probing on MeJA-treated plants was significantly shorter than on control plants. Total duration of salivation period on SA-treated plants was significantly longer, while mean phloem ingestion period was significantly shorter than on control plants. However, no significant difference in total duration of phloem sap ingestion period was observed among treatments. The EPG data suggest that MeJA-dependent resistance factors might be due to feeding deterrents in mesophyll, whereas the SA-mediated resistance may be phloem-based. We did not observe any significant difference of MeJA and SA application on aphid development, daily fecundity, intrinsic growth rate and population growth. The results indicate that both MeJA- and SA-induced defenses in wheat deterred S. avenae colonization processes and feeding behavior, but had no significant effects on its performance.

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