Plant immunity to insect herbivores

The plant-beneficial fungus Trichoderma harzianum T22 modulates plant metabolism and negatively affects Nezara viridula

BACKGROUND

Plant-beneficial fungi play an important role in enhancing plant health and resistance against biotic and abiotic stresses. Although extensive research has focused on their role in eliciting plant defences against pathogens, their contribution to induced resistance against herbivorous insects and the underlying mechanisms remain poorly understood. In this study, we used insect bioassays and untargeted metabolomics to investigate the impact of root inoculation of sweet pepper with the plant-beneficial fungus Trichoderma harzianum T22 on direct defence responses against the insect herbivore Nezara viridula.

RESULTS

We observed reduced relative growth rate of N. viridula on leaves of fungus-inoculated plants, with no change in mortality. Untargeted metabolomic analyses revealed that inoculation with T. harzianum did not affect the leaf metabolome in the absence of herbivory five weeks after inoculation. However, compared to non-inoculated plants, inoculated plants exhibited significant metabolic alterations in herbivore-damaged leaves following N. viridula feeding, while changes in the metabolic profile of distant leaves were less pronounced. Notably, metabolites involved in the shikimate-phenylpropanoid pathway, known to be involved in plant defence responses, displayed higher accumulation in damaged leaves of inoculated plants compared to non-inoculated plants.

CONCLUSION

Our results indicate that root inoculation with T. harzianum T22 affects plant defences against N. viridula, leading to reduced insect performance. Metabolite-level effects were primarily observed in damaged leaves, suggesting that the priming effect mainly results in localized metabolite accumulation at the site of attack. Future research should focus on identifying the detected compounds and determining their role in impairing N. viridula performance.

Auxin-salicylic acid seesaw regulates the age-dependent balance between plant growth and herbivore defense

According to the plant vigor hypothesis, younger, more vigorous plants tend to be more susceptible to herbivores compared to older, mature plants, yet the molecular mechanisms underlying this dynamic remain elusive. Here, we uncover a hormonal cross-talk framework that orchestrates the age-related balance between plant growth and herbivore defense. We demonstrate that the accumulation of salicylic acid (SA), synthesized by Nicotiana benthamiana phenylalanine ammonia-lyase 6 (NbPAL6), dictates insect resistance in adult plants. NbPAL6 expression is driven by the key transcription factor, NbMYB42, which is regulated by two interacting auxin response factors, NbARF18La/b. In juvenile plants, higher auxin levels activate NbmiR160c, a microRNA that simultaneously silences NbARF18La/b, subsequently reducing NbMYB42 expression, lowering SA accumulation, and thus weakening herbivore defense. Excessive SA in juvenile plants enhances defense but antagonizes auxin signaling, impairing early growth. Our findings suggest a seesaw-like model that balances growth and defense depending on the plant's developmental stage.

GLR3.6T807I Mutation of Casuarina equisetifolia Is Associated With a Decreased JA Response to Insect Feeding by Lymantria xylina

Lymantria xylina is the most important defoliator, damaging the effective coastal windbreak tree species Casuarina equisetifolia. However, the underlying genetic mechanisms through which C. equisetifolia responds to L. xylina attacks remain unknown. Here, we compared the transcriptional, phytohormone and metabolic differences between susceptible (S) and resistant (R) C. equisetifolia cultivars in response to L. xylina feeding. The main L. xylina-induced resistance in C. equisetifolia was a jasmonate (JA) response and JA synthesis was highly induced by L. xylina feeding at both the transcriptional and metabolic levels, thus promoting flavonoid accumulation. The JA response was highly activated by L. xylina feeding on the R but not in the S cultivar, although the JA signalling pathway was intact in both cultivars. We found a single amino acid mutation in the homologues of glutamate receptor-like protein 3.6 (CeGLR3.6T807I) in the S cultivar. Compared with the GLR3.6 homologues in the R cultivar, phosphorylation of CeGLR3.6T807I was not induced by insect feeding, leading to a decreased JA response in the S cultivar. Collectively, this study provides new insights into the function of CeGLR3.6 in regulating the JA response of C. equisetifolia to L. xylina feeding.

Arabidopsis perceives caterpillar oral secretion to increase resistance by reactive oxygen species-enhanced glucosinolate hydrolysis

In Arabidopsis, the outbreaks of reactive oxygen species (ROS) occur upon pathogen recognition by pattern- and effector-triggered immunity (PTI and ETI, respectively), which plays a significant role in disease resistance. Here, we found that Arabidopsis also experiences two outbreaks of ROS (oral secretion (OS)-induced ROS (ROSOS)) upon the perception of OS from cotton bollworm (Helicoverpa armigera) and other lepidopterans. Oral secretion-induced ROS burst requires the PTI machinery, including BRI1-ASSOCIATED RECEPTOR KINASE1 (BAK1) and BOTRYTIS-INDUCED KINASE1 (BIK1). Oral secretion-induced ROS are primarily produced by respiratory burst oxidase homologue D (RBOHD) in the apoplast, and the double mutant, rbohdf, exhibits reduced resistance to lepidopterans. Insect biting rather than wounding induces the gene expressions of plant defense-associated respiratory burst and toxin catabolic processes, facilitating the breakdown of leaf glucosinolates into bioactive intermediates, like sulforaphane, thereby impeding insect herbivory. Our investigation demonstrates that Arabidopsis perceives insect OS in a BAK1-BIK1-dependent manner and employs RBOHD to produce ROS in the apoplast, thereby enhancing its insect resistance by accelerating glucosinolate hydrolysis.

Integrative transcriptome and metabolome analysis uncovers the Toxoptera aurantii (Hemiptera: Aphididae) response of two Camellia sinensis (Ericales: Theaceae) cultivars

The tea aphid Toxoptera aurantii Boyer (Hemiptera: Aphididae) is a destructive pest that infests tea plants. The resistance mechanisms of the tea plant against T. aurantii infestation are largely unexplored. This study investigates the defensive response of tea plants to T. aurantii feeding using an aphid-resistant Camellia sinensis cultivar 'Qiancha1' (QC1) and an aphid-susceptible C. sinensis cultivar 'Huangjinya' (HJY). Transcriptomics and metabolomics analyses were conducted on 4 samples: QCCK (T. aurantii non-infested QC1), HJYCK (T. aurantii non-infested HJY), QC24 (T. aurantii-infested QC1 for 24 h), and HJY24 (T. aurantii-infested HJY for 24 h). The results showed that the differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) in the 2 comparison groups (QCCK vs. QC24 and HJYCK vs. HJY24) were primarily enriched in metabolic pathways, including hormone signal transduction, phenylpropanoid biosynthesis and flavonoid biosynthesis. Following aphid infestation, the resistant cultivar QC1 exhibited more DEGs and DAMs than the susceptible cultivar HJY, indicating a stronger response to T. aurantii feeding stress. Additionally, the expression of phenylpropanoid- and flavonoid-related genes (CYP, 4CL, FLS, F3H, and LAR) was significantly upregulated in the resistant cultivar QC1 compared with that in the susceptible cultivar HJY. Metabolites involved in phenylpropanoid/flavonoid pathways, such as p-coumaroyl-CoA, caffeoylquinic acid, and feruloyl-CoA, were exclusively induced in QC1. These findings suggest that phenylpropanoid/flavonoid pathways play pivotal roles in tea plant resistance to T. aurantii infestation, providing valuable insights for the breeding and utilization of resistant germplasms.

Isoprene deters insect herbivory by priming plant hormone responses

Isoprene, emitted by some plants, deters insect herbivory. However, the associated biochemical and physiological responses that confer herbivory resistance remain unknown. We used engineered isoprene-emitting (IE) and non-emitting (NE) control tobacco plants to interpret isoprene-mediated defense against herbivory in plants. Hornworm larvae raised on IE plants exhibited stunted growth compared to those raised on NE plants. Worms preferred to feed on NE rather than IE leaves, indicating deterrent effects of isoprene on insect feeding. Worm feeding induced a greater increase in jasmonic acid (JA), a crucial hormone for insect resistance, in IE leaves compared to that in NE leaves. Assimilation rates were stably maintained in IE plants, suggesting a protective role of isoprene in preserving photosynthetic efficiency during insect herbivory. Wound-induced increase in isoprene emission correlated with the elevation of key metabolites of the isoprene biosynthesis pathway. Our results highlight JA-priming functions of isoprene and provide insights into isoprene-mediated defense against insect herbivory.

The Role of Phenylpropanoids and the Plant Microbiome in Defences of Ash Trees Against Invasive Emerald Ash Borer

Plants have coevolved with herbivorous insects for millions of years, resulting in variation in resistance both within and between species. Using a manipulative experiment combined with untargeted metabolomics, microbiome sequencing and transcriptomics approaches, we investigated the roles of plant metabolites and the microbiome in defence mechanisms in native resistant Manchurian ash (Fraxinus mandshurica) trees and non-native susceptible velvet ash (Fraxinus velutina) trees against the highly invasive emerald ash borer (EAB, Agrilus planipennis). Comparative transcriptomics and metabolomics analyses show that the phenylpropanoid pathway, which is enriched in differentially expressed genes and differentially abundant metabolites, may serve as a potential regulator of resistance. Additionally, the microbiome is distinctly shifted in two ash species. Indicator taxa analysis reveals that the distinct genera are dominant in the galleries of two ash species, for example, Pseudomonas in velvet, and Hafnia-Obesumbacterium in Manchurian. The strong correlation between indicator taxa and metabolites suggests that the chemical compounds might impact the microbial community in phloem directly or indirectly, or vice versa. This study significantly enhances our understanding of the variation in resistance between ash species and its contribution to the invasion success of EAB, providing valuable insights for the development of pest management strategies.

The role of salivary effector FoCA2 in modulating the interactions of the defense response of the kidney bean plant and the adaptability of Frankliniella occidentalis under dinotefuran exposure

Frankliniella occidentalis (Pergande) is a horticultural pest known for its overwhelming destructive power. Our previous study showed that dinotefuran significantly inhibited the feeding behavior of F. occidentalis on kidney bean plants. However, why dinotefuran suppressed feeding in F. occidentalis is unknown. Here, we analyzed differences in gene expression in the head (containing salivary glands) of F. occidentalis with or without dinotefuran LC25 stress using transcriptome sequencing. Eventually, a salivary protein gene belonging to the carbonic anhydrase (CA) family was obtained and named as FoCA2. The full-length cDNA of FoCA2 was obtained by cloning, and the role of FoCA2 in the F. occidentalis antidefense toward the kidney bean plant was investigated using RNA interference. The results showed that FoCA2 was highly expressed in the head of F. occidentalis and at the feeding stages (nymph and adult). Silencing FoCA2 significantly inhibited F. occidentalis feeding and decreased its fecundity and survival; activated jasmonic and salicylic acid signaling pathway-related genes and callose synthase genes; and induced callose accumulation. However, dinotefuran down-regulated the expression of FoCA2 thereby attenuating the suppression of plant defense responses by FoCA2, which ultimately reduced the adaptability of F. occidentalis. Taken together, our findings suggest that FoCA2 is a key effector protein involved in F. occidentalis feeding and host adaptation, providing a foundation for studying the interaction between F. occidentalis and its host plants, and providing insights into the role of dinotefuran on pests.

CeJAZ3 suppresses longifolene accumulation in Casuarina equisetifolia, affecting the host preference of Anoplophora chinensis

BACKGROUND

Casuarina equisetifolia, a crucial species of coastal windbreaks, is highly susceptible to infestation by Anoplophora chinensis. This stem-boring pest poses a significant threat to the health and sustainability of Casuarina equisetifolia forests. Understanding the molecular mechanisms underlying the host preference of A. chinensis to Casuarina equisetifolia is essential for developing effective pest management strategies.

RESULTS

Through field surveys, we identified two cultivars of Casuarina equisetifolia that exhibited differing levels of host preference for A. chinensis. Further analysis of multi-omics data (phenomics, transcriptomics, and metabolomics) from these cultivars revealed that longifolene plays a significant role in attracting A. chinensis to Casuarina equisetifolia. Additionally, the jasmonic acid (JA) signaling pathway was found to suppress longifolene accumulation, primarily through the interaction between the jasmonate ZIM-domain (JAZ) proteins and the terpene synthase (TPS) gene. Moreover, we identified a critical JAZ component, CeJAZ3, whose overexpression led to the down-regulation of TPS expression levels and, consequently, a reduced release of longifolene.

CONCLUSION

We confirmed that the negative regulator of host preference, CeJAZ3, in the JA signaling pathway can suppress the expression of TPSs, thereby down-regulating the accumulation of longifolene in Casuarina equisetifolia and indirectly suppressing the attraction of host plants to A. chinensis, which provides a basis for the integrated management of A. chinensis. © 2024 Society of Chemical Industry.

Biocontrol Mechanism of Bacillus thuringiensis GBAC46 Against Diseases and Pests Caused by Fusarium verticillioides and Spodoptera frugiperda

Bacillus thuringiensis (Bt) is widely recognized as the most important microbial pesticide controlling various insect pests and diseases due to its insecticidal crystal proteins (ICPs) and antimicrobial metabolites. The current study investigates the biocontrol potential of B. thuringiensis GBAC46 against the fungal pathogen Fusarium verticillioides and the insect pest Spodoptera frugiperda through multiple mechanisms. Phenotypic experiments revealed that GBAC46 effectively inhibited F. verticillioides growth by inducing reactive oxygen species (ROS) accumulation and showed enhanced larvicidal activity against second instar S. frugiperda larvae. Pot experiments showed that feeding by S. frugiperda enhanced F. verticillioides infection in maize. The Bt strain GBAC46 effectively controlled both pests and diseases in greenhouse maize seedlings. Applying the Bt strain GBAC46 reduced feeding damage from S. frugiperda, decreased leaf yellowing and wilting caused by F. verticillioides, and improved growth indicators such as plant height, fresh weight, and dry weight. RT-qPCR results revealed that the Bt strain GBAC46 induced key defense genes in maize involved in activating salicylic acid, jasmonic acid, and ethylene pathways. The overall study demonstrated and confirmed the GBAC46 strain as a promising microbial agent for disease and pest management.

Fall Armyworm Frass Induce Sorghum Defenses Against Insect Herbivores

The fall armyworm (FAW; Spodoptera frugiperda) is a global invasive agricultural pest. Sorghum (Sorghum bicolor), an important monocot crop cultivated worldwide, faces significant challenges from FAW, which has become a major threat to sorghum production. Plants have evolved a wide array of defense mechanisms to combat insect assault. Caterpillar secretions contain both elicitors and effectors, which can either amplify or suppress plant defenses, thereby influencing plant defense responses. In this study, we examined the role of FAW frass in modulating sorghum defenses. Our results suggest that frass application significantly induced sorghum defenses that impacted subsequent FAW herbivory. We also found that the exogenous frass application significantly elevated the phytohormone levels, specifically jasmonic acid and abscisic acid levels, potentially contributing to enhanced sorghum defense against FAW. Furthermore, FAW frass-treated plants exhibited transient increase in total flavonoids, a class of secondary metabolites, which was previously shown to have a detrimental impact on FAW growth and survival. FAW frass application on sorghum plants mitigated proliferation of specialist aphids (sugarcane aphids), though its effect on generalist aphids (greenbugs) was less pronounced. These findings highlight the role of FAW frass in mediating plant responses against both chewing and piercing-sucking insect pests, providing valuable insights into sorghum's defense mechanisms and its potential for pest management strategies.

Genome and Tissue-Specific Transcriptome of the Tropical Milkweed (Asclepias curassavica)

Tropical milkweed (Asclepias curassavica) serves as a host plant for monarch butterflies (Danaus plexippus) and other insect herbivores that can tolerate the abundant cardiac glycosides that are characteristic of this species. Cardiac glycosides, along with additional specialized metabolites, also contribute to the ethnobotanical uses of A. curassavica. To facilitate further research on milkweed metabolism, we assembled the 197-Mbp genome of a fifth-generation inbred line of A. curassavica into 619 contigs, with an N50 of 10 Mbp. Scaffolding resulted in 98% of the assembly being anchored to 11 chromosomes, which are mostly colinear with the previously assembled common milkweed (A. syriaca) genome. Assembly completeness evaluations showed that 98% of the BUSCO gene set is present in the A. curassavica genome assembly. The transcriptomes of six tissue types (young leaves, mature leaves, stems, flowers, buds, and roots), with and without defense elicitation by methyl jasmonate treatment, showed both tissue-specific gene expression and induced expression of genes that may be involved in cardiac glycoside biosynthesis. Expression of a CYP87A gene, the predicted first gene in the cardiac glycoside biosynthesis pathway, was observed only in the stems and roots and was induced by methyl jasmonate. Together, this genome sequence and transcriptome analysis provide important resources for further investigation of the ecological and medicinal uses of A. curassavica.

Caffeic acid O-methyltransferase-dependent flavonoid defenses promote sorghum resistance to fall armyworm infestation

Sorghum (Sorghum bicolor), one of the world's most important monocot crops, suffers severe yield losses due to attack by a polyphagous insect pest, fall armyworm (FAW; Spodoptera frugiperda). Here, we show that the Brown midrib 12 (Bmr12) gene, which encodes the caffeic acid O-methyltransferase (COMT) enzyme, promotes sorghum defense against FAW. Loss of Bmr12 function resulted in increased susceptibility, but enhanced resistance to FAW was observed in Bmr12-overexpression (OE) plants compared with wild-type (RTx430) plants. Although COMT is associated with modulating lignin levels, FAW infestation resulted in comparable lignin levels between bmr12 and Bmr12-OE sorghum plants. On the contrary, evidence presented here indicates that FAW feeding induced the accumulation of flavonoids, which was previously shown to have a negative impact on FAW growth and survival in Bmr12-OE plants compared with bmr12 and RTx430 plants. Furthermore, a combination of phytohormone profiling and transcriptomic analysis uncovered that COMT-mediated resistance to FAW depends on jasmonic acid (JA) and oxidative stress-associated pathways. Exogenous application of FAW oral secretions stimulated flavonoid accumulation in Bmr12-OE plants compared with bmr12 and RTx430 plants, indicating that COMT has an essential function in perceiving FAW oral cues. Taken together, the critical role of COMT in sorghum defense against FAW hinges upon the interplay between JA and its derivatives and hydrogen peroxide, which potentially helps to mount a robust flavonoid-based host defense upon caterpillar attack.

Transcriptomics integrated with metabolomics reveals the defense response of insect-resistant Zea mays infested with Spodoptera exigua

Maize (Zea mays) is one of the most important cereal crops worldwide. Insect control through host plant resistance plays an important part in improving both yield and quality of maize. Spodoptera exigua is a common insect pest causing destructive damages to maize. To comprehensively understand molecular mechanism of maize defense against S. exigua, integrated transcriptomics and metabolomics analyses were conducted in the insect-resistant maize inbred line CML139 infested with S. exigua for 24 h. 9845 differentially expressed genes and 34 significantly changed metabolites were identified in infested leaves. Maize transcriptional response to S. exigua infestation involved in genes encoding enzymes in biosynthetic process (ribosome, glycerolipid, glycerophospholipid metabolism), genes in valine, leucine and isoleucine degradation, phenylpropanoid pathway and transcription factors. By metabolism analysis, accumulations of amino acids, organic acids, phenylpropanoids and benzoxazinoids (Bxs) were significantly enhanced, with the exception of salicylic acid (SA) and jasmonic acid (JA). The integrated analysis of transcriptomic and metabolic data demonstrated that both transcripts and metabolites involved in phenylpropanoid and Bxs biosynthesis were differentially modulated in S. exigua infested leaves. This study is valuable in understanding the complex mechanism of interaction between plants and insect herbivores and provide a potential strategy to maize pest control.

Antagonistic systemin receptors integrate the activation and attenuation of systemic wound signaling in tomato

Pattern recognition receptor (PRR)-mediated perception of damage-associated molecular patterns (DAMPs) triggers the first line of inducible defenses in both plants and animals. Compared with animals, plants are sessile and regularly encounter physical damage by biotic and abiotic factors. A longstanding problem concerns how plants achieve a balance between wound defense response and normal growth, avoiding overcommitment to catastrophic defense. Here, we report that two antagonistic systemin receptors, SYR1 and SYR2, of the wound peptide hormone systemin in tomato act in a ligand-concentration-dependent manner to regulate immune homeostasis. Whereas SYR1 acts as a high-affinity receptor to initiate systemin signaling, SYR2 functions as a low-affinity receptor to attenuate systemin signaling. The expression of systemin and SYR2, but not SYR1, is upregulated upon SYR1 activation. Our findings provide a mechanistic explanation for how plants appropriately respond to tissue damage based on PRR-mediated perception of DAMP concentrations and have implications for uncoupling defense-growth trade-offs.

SlABCG9 Functioning as a Jasmonic Acid Transporter Influences Tomato Resistance to Botrytis cinerea

Jasmonic acid (JA) is crucial for plant stress responses, which rely on intercellular jasmonate transport. However, JA transporters have not been fully identified, especially in tomato (Solanum lycopersicum L.). This study reveals that plasma-membrane-localized protein SlABCG9 in tomato regulates fruit resistance to Botrytis cinerea. Transcriptomic analysis indicated that the SlABCG9 expression was significantly upregulated after B. cinerea infection. Assays using Xenopus oocytes, yeast cell sensitivity, and JA-inhibited primary root growth confirmed that SlABCG9 functions as a JA influx transporter. The knockout mutant lines of SlABCG9 showed decreased JA contents, suppressed defense gene PDF1.2's expression, reduced antioxidant enzyme activity, and severe disease symptoms compared to wild-type controls. Our findings provide new knowledge for understanding how the JA transporter and signaling pathway are involved in the biotic stress responses and improve the resistant ability against pathogen infections.

The concerted function of a novel class of transcription factors, ZBFs, in light, jasmonate, and abscisic acid signaling pathways

Several classes of transcription factors have been investigated in light signaling pathways that bind to the light-responsive elements (LREs) present in the promoters of light regulatory genes for transcriptional regulation. Some of these transcription factors have been shown to bind to numerous promoters through genome-wide ChIP-on-chip (ChIP-chip) studies. Furthermore, through the integration of ChIP-seq and RNA-seq techniques, it has been demonstrated that a transcription factor modifies the expression of numerous genes with which it interacts. However, the mode of action of these transcription factors and their dependency on other regulators in the pathway has just started to be unraveled. In this review, we focus on a particular class of transcription factors, ZBFs (Z-box-binding factors), and their associated partners within the same or other classes of transcription factors and regulatory proteins during photomorphogenesis. Moreover, we have further made an attempt to summarize the crosstalk of these transcription factors with jasmonic acid-, abscisic acid-, and salicylic acid-mediated defense signaling pathways. This review offers an in-depth insight into the manner in which ZBFs and their interactors reshape cellular functions and plant behavior. The underlying principles not only contribute to a comprehensive understanding but also establish a framework for analyzing the interplay between early developmental events and hormone signaling, a regulation orchestrated by the ZBF family.

Salicylic Acid Modulates Volatile Organic Compound Profiles During CEVd Infection in Tomato Plants

Background:Citrus Exocortis Viroid (CEVd) is a non-coding RNA pathogen capable of infecting a wide range of plant species, despite its lack of protein-coding ability. Viroid infections induce significant alterations in various physiological and biochemical processes, particularly impacting plant metabolism. This study shows the metabolic changes upon viroid infection in tomato plants (Solanum lycopersicum var. 'MoneyMaker') exhibiting altered levels of salicylic acid (SA), a key signal molecule involved in the plant defence against this pathogen. Methods: Transgenic RNAi_S5H lines, which have the salicylic acid 5-hydroxylase gene silenced to promote SA accumulation, and NahG lines, which overexpress a salicylate hydroxylase to degrade SA into catechol and prevent its accumulation, were used to establish different SA levels in plants, resulting in varying degrees of resistance to viroid infection. The analysis was performed by using gas chromatography-mass spectrometry (GC-MS) to explore the role of volatile organic compounds (VOCs) in plant immunity against this pathogen. Results: Our results revealed distinct volatile profiles associated with plant immunity, where RNAi_S5H-resistant plants showed significantly enhanced production of monoterpenoids upon viroid infection. Moreover, viroid-susceptible NahG plants emitted a broad range of VOCs, whilst viroid-tolerant RNAi_S5H plants exhibited less variation in VOC emission. Conclusions: This study demonstrates that SA levels significantly influence metabolic responses and immunity in tomato plants infected by CEVd. The identification of differential emitted VOCs upon CEVd infection could allow the development of biomarkers for disease or strategies for disease control.

Plant Defense Responses to Insect Herbivores Through Molecular Signaling, Secondary Metabolites, and Associated Epigenetic Regulation

Over millions of years of interactions, plants have developed complex defense mechanisms to counteract diverse insect herbivory strategies. These defenses encompass morphological, biochemical, and molecular adaptations that mitigate the impacts of herbivore attacks. Physical barriers, such as spines, trichomes, and cuticle layers, deter herbivores, while biochemical defenses include the production of secondary metabolites and volatile organic compounds (VOCs). The initial step in the plant's defense involves sensing mechanical damage and chemical cues, including herbivore oral secretions and herbivore-induced VOCs. This triggers changes in plasma membrane potential driven by ion fluxes across plant cell membranes, activating complex signal transduction pathways. Key hormonal mediators, such as jasmonic acid, salicylic acid, and ethylene, orchestrate downstream defense responses, including VOC release and secondary metabolites biosynthesis. This review provides a comprehensive analysis of plant responses to herbivory, emphasizing early and late defense mechanisms, encompassing physical barriers, signal transduction cascades, secondary metabolites synthesis, phytohormone signaling, and epigenetic regulation.

Effects of Defoliation Timing and Intensity on Yield Components and Grain Quality of Quinoa (Chenopodium quinoa Willd.)

Understanding plant tolerance to defoliation is crucial for sustainable pest management and reducing pesticide use in food production. This study explores quinoa's (Chenopodium quinoa Willd.) responses to foliar damage, which have been largely unexamined. Over two seasons, quinoa plants were subjected to mechanical defoliation at different pre-reproductive stages and intensities (0-60%) in the first season, and both mechanical and insect-induced (Trichoplusia ni (Hübner), Lepidoptera: Noctuidae) defoliation in the second. The results showed that quinoa plants consistently tolerated defoliation without reductions in grain number, weight, above-ground biomass, or harvest index. These compensatory responses were independent of the defoliation method, timing, or intensity. In the first season, overcompensatory effects were observed, leading to increased plant biomass at 60% early defoliation and 40% late defoliation. Additionally, early defoliation at 20% and 60%, as well as late defoliation at 60%, led to an increase in grain number without affecting grain weight. Defoliation did not significantly alter the phenolic content, sapogenins, or antioxidant capacity of the grains, preserving their phytochemical quality. These findings enhance the understanding of quinoa's resilience to herbivory, suggesting that it can withstand defoliation stress without compromising yield or quality.

Feeding Preferences and Salivary Protein Profiles of Spodoptera frugiperda on Saccharum Species

The invasion of the fall armyworm poses substantial threats to local agricultural safety, including the sugarcane industry. Exploring the insect-resistance mechanism is crucial for breeding resistant varieties. This study selected three representative materials from the Saccharum genus─Saccharum officinarum L. (Badila), S. spp. hybrid (GT58), and Saccharum spontaneum (SES208), to investigate feeding preferences and developmental fitness of Spodoptera frugiperda. Larvae exhibited a strong preference and highest fitness parameters in Badila leaves compared to SES208. Additionally, proteomic analyses of larval saliva from insects feeding on Badila and SES208 were carried out to test the types and abundance of proteins on different hosts. Furthermore, we identified fatty acid-binding protein 1-like activates plant defense responses, while aldehyde dehydrogenase negatively suppressed plant defense response. Our findings suggest that the plasticity of salivary proteins induced by different host plants, and also offer new insights into the molecular interactions between S. frugiperda and plants.

Influence of Bemisia tabaci-Induced Plant Volatiles on the Host-Choice Behavior of Tuta absoluta

Plants respond to attacks by insects by releasing herbivore-induced plant volatiles (HIPVs), which are known to influence the behavior of natural enemies, conspecific and heterospecific insects. However, little is known about how HIPVs induced by one insect species influence the behavior of an allospecific insect species, particularly if these insects belong to different feeding guilds. Here, using the interaction of two co-occurring insects with different feeding guilds - Bemisia tabaci (a sap sucking insect) and Tuta absoluta (a leaf mining insect) - on potato plants, we report that T. absoluta significantly preferred potato plants infested by B. tabaci. This preference is attributed to the B. tabaci-induced potato plant volatiles. Gas chromatography coupled with mass spectroscopy (GC-MS) analysis further revealed notable alterations in volatile composition between B. tabaci-infested and uninfested plants. Additionally, gas chromatography coupled with electroantennogram detector (GC-EAD) analysis identified four compounds - undecane, β-caryophyllene, β-farnesene and germacrene D - in B. tabaci-induced potato plant volatiles that elicited responses from T. absoluta antennae. Our findings emphasize how B. tabaci infestation alters potato plant volatile composition, making them attractive to T. absoluta. Understanding the chemical ecology interactions between allospecific insects with different feeding guilds is crucial for understanding how different insect groups affect the host location of one another through HIPVs. This knowledge can contribute to the development of more effective pest management strategies against these economically important pests.

The role of light in regulating plant growth, development and sugar metabolism: a review

Light provides the necessary energy for plant photosynthesis, which allows plants to produce organic matter and energy conversion, during plant growth and development. Light provides material energy to plants as the basis for cell division and differentiation, chlorophyll synthesis, tissue growth and stomatal movement, and light intensity, photoperiod, and light quality play important roles in these processes. There are several regulatory mechanisms involved in sugar metabolism in plants, and light, as one of the regulatory factors, affects cell wall composition, starch granules, sucrose synthesis, and vascular bundle formation. Similarly, sugar species and genes are affected in the context of light-regulated sugar metabolism. We searched the available databases and found that there are fewer relevant reviews. Therefore, this paper provides a summary of the effects of light on plant growth and development and sugar metabolism, further elaborates on the mechanisms of light effects on plants, and provides some new insights for a better understanding of how plant growth is regulated under different light conditions.

Managing Friends and Foes: Sanctioning Mutualists in Mixed-Infection Nodules Trades off With Defense Against Antagonists

Successful plant growth requires plants to minimize harm from antagonists and maximize benefit from mutualists. However, these outcomes may be difficult to achieve simultaneously, since plant defenses activated in response to antagonists can compromise mutualism function, and plant resources allocated to defense may trade off with resources allocated to managing mutualists. Here, we investigate how antagonist attack affects plant ability to manage mutualists with sanctions, in which a plant rewards cooperative mutualists and/or punishes uncooperative mutualists. We studied interactions among wild and domesticated pea plants, pea aphids, an aphid-vectored virus (Pea Enation Mosaic Virus, PEMV), and mutualistic rhizobial bacteria that fix nitrogen in root nodules. Using isogenic rhizobial strains that differ in their ability to fix nitrogen and express contrasting fluorescent proteins, we found that peas demonstrated sanctions in both singly-infected nodules and mixed-infection nodules containing both strains. However, the plant's ability to manage mutualists in mixed-infection nodules traded off with its ability to defend against antagonists: when plants were attacked by aphids, they stopped sanctioning within mixed-infection nodules, and plants that exerted stricter sanctions within nodules during aphid attack accumulated higher levels of the aphid-vectored virus, PEMV. Our findings suggest that plants engaged in defense against antagonists suffer a reduced ability to select for the most beneficial symbionts in mixed-infection tissues. Mixed-infection tissues may be relatively common in this mutualism, and reduced plant sanctions in these tissues could provide a refuge for uncooperative mutualists and compromise the benefit that plants obtain from mutualistic symbionts during antagonist attack. Understanding the conflicting selective pressures plants face in complex biotic environments will be crucial for breeding crop varieties that can maximize benefits from mutualists even when they encounter antagonists.

Spraying calcium chloride helps to enhance the resistance of kidney bean plants to western flower thrips

BACKGROUND

The western flower thrips (WFT), Frankliniella occidentalis (Thysanoptera: Thripidae), is a significant pest in horticulture and ornamental agriculture. While exogenous calcium (Ca) has been shown to confer plant immune responses against thrips, the detailed mechanisms of this interaction remain to be elucidated for improved thrips management strategies. This study aimed to assess the impact of exogenous Ca on WFT feeding behavior and to explore its role in enhancing the defense mechanisms of kidney bean plants against WFT attacks. We compared WFT feeding preferences and efficiency on kidney bean plants treated with H2O or Ca, and examined whether exogenous Ca improves plant defense responses to thrips attack.

RESULTS

WFT exhibited less preference for feeding on Ca-treated plants over H2O-treated ones. The total duration of WFT's long-ingestion probes was significantly reduced on Ca-treated plants, indicating impaired feeding efficiency. Furthermore, WFT infestation activated both jasmonic acid (JA) and salicylic acid (SA) signaling pathways in kidney bean plants, and exogenous Ca application led to elevated levels of endogenous Ca2+ and CaM, up-regulation of genes associated with JA and SA pathways (LOX, AOS, PAL, and β-1,3-glucanase), and increased accumulation of JA, SA, flavonoids, and alkaloids.

CONCLUSION

Our findings demonstrate that the application of exogenous Ca enhances endogenous Ca2+, JA, and SA signaling pathways in kidney bean plants. This enhancement results in an up-regulation of the biosynthesis of flavonoid and alkaloid, thereby equipping the plants with an enhanced defense against WFT infestation. © 2024 Society of Chemical Industry.

Jasmonate induces translation of the Arabidopsis transfer RNA-binding protein YUELAO1, which activates MYC2 in jasmonate signaling

Jasmonate is ubiquitous in the plant kingdom and regulates multiple physiological processes. Although jasmonate signaling has been thoroughly investigated in Arabidopsis thaliana, most studies have focused on the transcriptional mechanisms underlying various jasmonate responses. It remains unclear whether (and how) translation-related pathways help improve transcription efficiency to modulate jasmonate signaling, which may enable plants to respond to stressful conditions effectively. Here, we demonstrate that jasmonate induces translation of the transfer RNA (tRNA)-binding protein YUELAO 1 (YL1) via a specific region in its 3' untranslated region (3' UTR). YL1 and its homolog YL2 redundantly stimulate jasmonate responses such as anthocyanin accumulation and root growth inhibition, with the YL1 3' UTR being critical for YL1-promoted jasmonate responses. Once translated, YL1 acts as an activator of the MYC2 transcription factor through direct interaction, and disrupting YL1 3' UTR impairs the YL1-mediated transcriptional activation of MYC2. YL1 enhances jasmonate responses mainly in a MYC2-dependent manner. Together, these findings reveal a translational mechanism involved in jasmonate signaling and advance our understanding of the transcriptional regulation of jasmonate signaling. The YL1 3' UTR acts as a crucial signal transducer that integrates translational and transcriptional regulation, allowing plants to respond to jasmonate in a timely fashion.

Mitogen-activated protein kinase 4 phosphorylates MYC2 transcription factors to regulate jasmonic acid signaling and herbivory responses in maize

Regulation of responses induced by herbivory and jasmonic acid (JA) remains poorly understood in the important staple crop maize (Zea mays). MYC2 is the key transcription factor regulating many aspects of JA signaling, while mitogen-activated protein kinases (MAPKs or MPKs) play important roles in various plant physiological processes. Using a combination of reverse genetics, transcriptome analysis, and biochemical assays, we elucidated the important role of mitogen-activated protein kinase 4 (MPK4) in maize resistance to insects and in JA signaling. Silencing MPK4 increased the JA and jasmonoyl-isoleucine levels elicited by wounding or simulated herbivory but decreased maize resistance to armyworm (Mythimna separata) larvae. We showed that MPK4 is required for transcriptional regulation of many genes responsive to methyl jasmonate, indicating the important role of maize MPK4 in JA signaling. Biochemical analyses indicated that MPK4 directly phosphorylates MYC2s at Thr115 of MYC2a and Thr112 of MYC2b. Compared with nonphosphorylated MYC2s, phosphorylated MYC2s were more prone to degradation and exhibited enhanced transactivation activity against the promoters of several benzoxazinoid biosynthesis genes, which are important for maize defense against insects. This study reveals the essential role of maize MPK4 in JA signaling and provides insights into the functions of MAPKs in maize.

Comparative Transcriptome Analysis Highlights the Role of NlABCG14 in the Honeydew Production of Virulent Brown Planthoppers (Nilaparvata lugens Stål) to Resistant Rice Variety

Brown planthoppers (BPHs, Nilaparvata lugens Stål) are a major threat to rice cultivation in Asia, necessitating the development of pest-resistant varieties for effective management. However, the adaptability of BPHs has resulted in the development of virulent populations, such as biotype Y BPHs, which exhibit significant virulence against the rice variety YHY15 that harbors the resistance gene Bph15. The various response mechanisms of BPH populations to resistant rice varieties are critical yet underexplored. Via RNA sequencing, the present study identified distinct transcriptional profiles in avirulent (biotype 1) and virulent (biotype Y) BPH nymphs both before and after feeding on YHY15 rice. Our findings revealed differential expression patterns of gene clusters involved in protein synthesis, hydrolysis, fatty acid biosynthesis, metabolism, cuticle composition, and translocation. Further analysis elucidated changes in the expression of genes associated with longevity and structural components of cuticles, highlighting specific disruptions in both biotype 1 and biotype Y BPHs. Moreover, the two biotypes showed differences in the expression level of genes involved in ATP-binding cassette (ABC) transporters. A functional assessment of ABC transporter genes revealed a role of NlABCG14 in the honeydew production of biotype Y BPHs to YHY15 rice, without impacting their survival and developmental dynamics. These insights deepen our understanding of the mechanisms of virulent BPHs response to resistant rice varieties and highlight potential targets for improving pest management strategies.

Induced biochemical variations in maize parental lines affect the life table and age-specific reproductive potential of Spodoptera frugiperda (J.E. Smith)

In recent years, the fall armyworm, Spodoptera frugiperda has rapidly emerged as a global invasive pest, challenging the maize production and leading to considerable economic losses. Developing resistant hybrids is essential for sustainable maize cultivation, which requires a comprehensive understanding of resistance traits and the underlying mechanisms in parental lines. To address this need, the present study aimed to identify the sources of resistance, age and stage-specific effects and role of phytochemicals in plant defense against S. frugiperda in thirty diverse maize parental lines [17 female (A) and 13 male (R) lines]. The study revealed that the larvae fed on maize A-lines CML 565, AI 501, AI 544 and PDIM 639, and R-lines AI 125, AI 542, AI 155, AI 1100 and PML 105 exhibited a reduced intrinsic (r) and finite rate of increase (λ), and net (R0) and gross reproduction rates (GRR); while, increased mean generation time (T) and doubling time (DT). Among these, A-lines CML 565, PDIM 639 and AI 544, and R-lines AI 125, AI 155 and AI 1100 showed higher detrimental effect on reproductive value of S. frugiperda. Aforesaid A- and R-lines were also found with greater increase in insect-induced test phytochemicals compared to other lines, accounting for 25.0 to 72.8% variation in the life table parameters, indicating antibiosis effect on S. frugiperda. Among the test phytochemicals, tannins, CAT, PAL, TAL and APX inflicted greater effect, indicating their role in induced-biochemical defense against S. frugiperda.

Identification and odor exposure regulation of odorant-binding proteins in Picromerus lewisi

The highly developed sensitive olfactory system is essential for Picromerus lewisi Scott (Hemiptera: Pentatomidae) adults, an widely distributed natural predatory enemy, to locate host plants. During this process, odorant-binding proteins (OBPs) are thought to have significant involvement in the olfactory recognition. However, the roles of OBPs in the olfactory perception of P. lewisi are not frequently reported. Here, we conducted odor exposure and transcriptome sequencing experiments using healthy and Spodoptera litura-infested tobacco plants as odor sources. The transcriptomic data revealed that the alteration in the expression of mRNA levels upon exposure to odor was sex-dependent. As the expression profiles differed significantly between male and female adults of P. lewisi. A total of 15 P. lewisi OBPs (PlewOBPs) were identified from the P. lewisi transcriptome. Sequence and phylogenetic analysis indicated that PlewOBPs can be classified into two subfamilies (classic OBP and plus-C OBP). The qRT-PCR results showed that the transcript abundance of 8 PlewOBPs substantially altered following exposure to S. litura-infested tobacco plants, compared to the blank control or healthy plants. This implies that these PlewOBPs may have an olfactory function in detecting S. litura-infested tobacco plants. This study establishes the foundation for further understanding of the olfactory recognition mechanism of P. lewisi and helps discover novel targets for functional characterization in future research.

bHLH19 and bHLH20 repress jasmonate-mediated plant defense against insect herbivores in Arabidopsis

Plants are attacked by various insect herbivores. Upon attack-triggered biosynthesis of the phytohormone jasmonates (JAs), the JA receptor CORONATINE INSENSITIVE 1 recruits the JA-ZIM domain (JAZ) repressors for ubiquitination, releases the MYC-MYB transcription factor (TF) complexes, and enhances glucosinolates (GSs) biosynthesis to promote defense against insects in Arabidopsis. However, the negative regulation of JA-regulated defense remains largely unclear. Here, we found that Arabidopsis IVa bHLH TFs bHLH19 and bHLH20 interacted with JAZs. The bhlh19/20 mutations enhanced defense against the insects Spodoptera frugiperda and S. exigua, while their overexpression inhibited defense. bHLH19/20 repressed defense via at least two layers of regulation: first, bHLH19/20 interacted with the members MYC2/3/4/5 and MYB34/51/122 of MYC-MYB complexes, and inhibited the interaction/transcription activity of MYC2-MYB34; second, bHLH19/20 activated the RNA level of nitrile-specifier protein 1, which converts GSs into the less toxic nitriles. bhlh19/20 exhibited no penalty in JA-regulated growth inhibition. Collectively, our findings reveal the molecular mechanism for negatively regulating JA-mediated defense against insects in Arabidopsis without growth penalty by the pair of bHLH19/20 TFs.

HcCYP6AE178 plays a crucial role in facilitating Hyphantria cunea's adaptation to a diverse range of host plants

Strong multi-host adaptability significantly contributes to the rapid dissemination of Hyphantria cunea. The present study explores the involvement of cytochrome P450 monooxygenase (P450) in the multi-host adaptation of H. cunea and aims to develop RNA pesticides targeting essential P450 genes to disrupt this adaptability. The results showed that inhibiting P450 activity notably reduced larval weight and food-intake across seven plants groups. The P450 gene HcCYP6AE178 was highly upregulated in H. cunea larvae from medium- and low-preference host plant groups. Silencing HcCYP6AE178 significantly decreased H. cunea larval body weight, increased larval mortality, inhibited energy metabolism genes expression and interfered with growth regulatory genes expression. Overexpression of HcCYP6AE178 enhanced the tolerance of Drosophila and Sf9 cells to the plant defensive substances cytisine and coumarin. The RNA pesticide CS-dsHcCYP6AE178 constructed using chitosan (CS) exhibited remarkable stability. Treatment with CS-dsHcCYP6AE178 effectively reduced H. cunea larval body weight, heightened larval mortality, and disrupted growth regulatory genes expression in low-preference host plant groups. Combined treatment of CS-dsHcCYP6AE178 and coumarin significantly elevated H. cunea larval mortality compared to coumarin alone, accompanied by the inhibition of growth regulatory genes expression and an abnormal increase in energy metabolism genes expression. Taken together, HcCYP6AE178 is essential for the adaptation of H. cunea to multiple host plants, and RNA pesticides targeting HcCYP6AE178 can effectively impair the performance of H. cunea in different host plants.

Root inoculation with soil-borne microorganisms alters gut bacterial communities and performance of the leaf-chewer Spodoptera exigua

Soil-borne microorganisms can impact leaf-chewing insect fitness by modifying plant nutrition and defence. Whether the altered insect performance is linked to changes in microbial partners of caterpillars remains unclear. We investigated the effects of root inoculation with soil bacteria or fungi on the gut bacterial community and biomass of the folivore Spodoptera exigua. We also explored the potential correlation between both parameters. We performed herbivory bioassay using leaves of tomato plants (Solanum lycopersicum), measured caterpillar weight gain and characterized the gut bacterial communities via 16S rRNA gene metabarcoding. All soil microbes modified the gut bacterial communities, but the extent of these changes depended on the inoculated species. Rhizophagus irregularis and Bacillus amyloliquefaciens had opposite effects on S. exigua weight. While plant inoculation with the fungus influenced gut bacterial diversity, B. amyloliquefaciens also affected the community composition. A reduced abundance of two S. exigua enterococcal symbionts correlated with decreased insect biomass. Our results show that soil microorganisms can induce plant-mediated changes in the gut bacterial community of foliar-feeding caterpillars. We propose that the impact of these alterations on insect performance might rely on specific adaptations within the gut bacteria, rather than solely on the occurrence of changes.

Genetic Warfare: The Plant Genome's Role in Fending Off Insect Invaders

The plant defense against insects is multiple layers of interactions. They defend through direct defense and indirect defense. Direct defenses include both physical and chemical barriers that hinder insect growth, development, and reproduction. In contrast, indirect defenses do not affect insects directly but instead suppress them by releasing volatile compounds that attract the natural enemies of herbivores. Insects overcome plant defenses by deactivating biochemical defenses, suppressing defense signaling through effectors, and altering their behavior through chemical regulation. There is always a genetic war between plants and insects. In this genetic war, plant-insect co-evolution act as both weapons and messengers. Because plants always look for new strategies to avoid insects by developing adaptation. There are molecular processes that regulate the interaction between plants and insect. Here, we examine the genes and proteins involved in plant-insect interactions and explore how their discovery has shaped the current model of the plant genome's role. Plants detect damage-associated and herbivore-associated molecular patterns through receptors, which trigger early signaling pathways involving Ca2+, reactive oxygen species, and MAP kinases. The specific defense mechanisms are activated through gene signaling pathways, including phytohormones, secondary metabolites, and transcription factors. Expanding plant genome approaches to unexplored dimensions in fending off insects should be a future priority in order to develop management strategies.

Catechol acetylglucose: a newly identified benzoxazinoid-regulated defensive metabolite in maize

An enormous diversity of specialized metabolites is produced in the plant kingdom, with each individual plant synthesizing thousands of these compounds. Previous research showed that benzoxazinoids, the most abundant class of specialized metabolites in maize, also function as signaling molecules by regulating the production callose as a defense response. We searched for additional benzoxazinoid-regulated specialized metabolites, characterized them, examined whether they too function in herbivore protection, and determined how Spodoptera frugiperda (fall armyworm), a prominent maize pest, copes with these metabolites. We identified catechol acetylglucose (CAG) as a benzoxazinoid-regulated metabolite that is produced from salicylic acid via catechol and catechol glucoside. Genome-wide association studies of CAG abundance identified a gene encoding a predicted acetyltransferase. Knockout of this gene resulted in maize plants that lack CAG and over-accumulate catechol glucoside. Upon tissue disruption, maize plants accumulate catechol, which inhibits S. frugiperda growth. Analysis of caterpillar frass showed that S. frugiperda detoxifies catechol by glycosylation, and the efficiency of catechol glycosylation was correlated with S. frugiperda growth on a catechol-containing diet. Thus, the success of S. frugiperda as an agricultural pest may depend partly on its ability to detoxify catechol, which is produced as a defensive metabolite by maize.

CRISPR-Cas9-mediated construction of a cotton CDPK mutant library for identification of insect-resistance genes

Calcium-dependent protein kinases (CDPKs) act as key signal transduction enzymes in plants, especially in response to diverse stresses, including herbivory. In this study, a comprehensive analysis of the CDPK gene family in upland cotton revealed that GhCPKs are widely expressed in multiple cotton tissues and respond positively to various biotic and abiotic stresses. We developed a strategy for screening insect-resistance genes from a CRISPR-Cas9 mutant library of GhCPKs. The library was created using 246 single-guide RNAs targeting the GhCPK gene family to generate 518 independent T0 plants. The average target-gene coverage was 86.18%, the genome editing rate was 89.49%, and the editing heritability was 82%. An insect bioassay in the field led to identification of 14 GhCPK mutants that are resistant or susceptible to insects. The mutant that showed the clearest insect resistance, cpk33/74 (in which the homologous genes GhCPK33 and GhCPK74 were knocked out), was selected for further study. Oral secretions from Spodoptera litura induced a rapid influx of Ca2+ in cpk33/74 leaves, resulting in a significant increase in jasmonic acid content. S-adenosylmethionine synthase is an important protein involved in plant stress response, and protein interaction experiments provided evidence for interactions of GhCPK33 and GhCPK74 with GhSAMS1 and GhSAM2. In addition, virus-induced gene silencing of GhSAMS1 and GhSAM2 in cotton impaired defense against S. litura. This study demonstrates an effective strategy for constructing a mutant library of a gene family in a polyploid plant species and offers valuable insights into the role of CDPKs in the interaction between plants and herbivorous insects.

Mirids secrete a TOPLESS targeting protein to enhance JA-mediated defense and gossypol accumulation for antagonizing cotton bollworms on cotton plants

Most coexisting insect species exhibit stunted growth compared to individual species on plants. This phenomenon reflects an interspecific antagonism drawing extensive attention, while the underlying mechanisms remain largely uncharacterized. Mirids (Apolygus lucorum) and cotton bollworms (Helicoverpa armigera) are two common cotton pests. We identified a secretory protein, ASP1, from the oral secretion of mirids, found in the nucleus of mirid-infested cotton leaves. ASP1 specifically targets the transcriptional co-repressor TOPLESS (TPL) and inhibits NINJA-mediated recruitment of TPL, promoting plant defense response and gossypol accumulation in cotton glands. ASP1-enhanced defense inhibits the growth of cotton bollworms on cotton plants, while having limited impact on mirids. The mesophyll-feeding characteristic allows mirids to avoid most cotton glands, invalidating cotton defense. Our investigation reveals the molecular mechanism by which mirids employ cotton defense to selectively inhibit the feeding of cotton bollworms.

Arbuscular mycorrhizal fungi influence belowground interactions between a specialist root-feeder and its natural enemy

As primary producers, plants play a central role in mediating interactions across trophic levels. Although plants are the primary food source for herbivorous insects, they can protect themselves from herbivore damage. Many plants produce toxic compounds that directly reduce herbivore feeding, but plants also protect themselves indirectly by attracting natural enemies of the attacking herbivore through volatile signaling. These so-called tri-trophic interactions have historically been documented aboveground in aerial plant parts but are also known to occur belowground in root systems. In addition to herbivores, plants directly interact with other organisms, which can influence the outcomes of tri-trophic interactions. Arbuscular mycorrhizal fungi (AMF) are symbiotic soil microbes that colonize the roots of plants and facilitate nutrient uptake. These microbes can alter plant chemistry and subsequent resistance to herbivores. Few studies, however, have shown how AMF affect tri-trophic interactions above- or belowground. This study examines how AMF colonization affects the emission of root volatiles when plants are under attack by western corn rootworm, a problematic pest of corn, and subsequent attraction of entomopathogenic nematodes, a natural enemy of western corn rootworm. Mycorrhizal fungi increased rootworm survival but decreased larval weight. Differences were detected across root volatile profiles, but there was not a clear link between volatile signaling and nematode behavior. Nematodes were more attracted to non-mycorrhizal plants without rootworms and AMF alone in soil, suggesting that AMF may interfere with cues that are used in combination with volatiles which nematodes use to locate prey.

Combined transcriptome and metabolome analysis identifies triterpenoid-induced defense responses in Myzus persicae Sülzer-infested peach

Piercing/sucking insects such as green peach aphid (GPA) (Myzus persicae) cause direct damage by obtaining phloem nutrients and indirect damage by spreading plant viruses. To investigate the response of peach trees (Prunus persica) to aphids, the leaf transcriptome and metabolome of two genotypes with different sensitivities to GPA were studied. The gene expression of aphid-susceptible plants infested with aphids was similar to that of control plants, whereas the gene expression of aphid-resistant plants infested with aphids showed strong induced changes in gene expression compared with control plants. Furthermore, gene transcripts in defense-related pathways, including plant-pathogen interaction, MAPK signaling, and several metabolic pathways, were strongly enriched upon aphid infestation. Untargeted secondary metabolite profiling confirmed that aphid infestation induced larger changes in aphid-resistant than in aphid-susceptible peaches. Consistent with transcriptomic alterations, nine triterpenoids showed highly significant GPA-induced accumulation in aphid-resistant peaches, whereas triterpenoid abundance remained predominantly unchanged or undetected in aphid-susceptible peaches. Furthermore, some types of transcription factors (including WRKYs, ERFs, and NACs) were strongly induced upon GPA infestation in aphid-resistant, but not in aphid-susceptible peaches. These results suggested that the accumulation of specialized triterpenoids and the corresponding pathway transcripts may play a key role in peach GPA resistance.

Mathematical modeling predicts that endemics by generalist insects are eradicated if nearly all plants produce constitutive defense

Plants with constitutive defense chemicals exist widely in nature. The phenomenon is backed by abundant data from plant chemical ecology. Sufficient data are also available to conclude that plant defenses act as deterrent and repellent to attacking herbivores, particularly deleterious generalist insects. In the wild, generalist species are usually not endemic, meaning they are not restricted to certain plant species in a region. Therefore, our objective is to inspect theoretically whether evolution of chemical defenses in all plant species eradicate an endemic by any generalist species. The objective is addressed by developing deterministic ordinary differential equations under the following conditions: Plants without constitutive defenses are susceptible to oviposition by generalist insects, while they become defended against generalists by storing chemical defenses. From the models, we explicitly obtain that a generalist-free stable state is only possible if the vast majority of all plant individuals have chemical defenses. The model also allows one to predict the highest possible percentage of undefended plant individuals, which may be considered as free-riders.

ApCarE4 and ApPOD3 participate in the adaptation of pea aphids to different alfalfa varieties

The adaptability of insects to hosts has long been a focal point in the study of insect-plant interactions. The pea aphid (Acythosiphon pisum), a significant pest of numerous leguminous crops, not only inflicts direct economic losses but also disseminates various plant viruses. To understand how pea aphids adapt to diverse alfalfa varieties. We analyzed the differentially expressed genes (DEGs) of pea aphids in distinct alfalfa varieties using transcriptome sequencing, and subsequently conducted functional validation of these genes. Comparative analysis between pea aphids feeding on susceptible and resistant strains revealed that DEGs in aphids feeding on resistant strains were primarily associated with transcriptional enrichment in the sugar, amino acid, protein, and lipid metabolism pathways. Fourteen DEGs related to adaptation of the pea aphid to alfalfa were chosen, including five carboxylesterases (CarE), four cytochrome P450s, three glutathione S-transferases, and two peroxidases (POD). RT-qPCR results indicated significant up-regulation of two carboxylesterase genes and two peroxidase genes after 24 h of feeding resistant alfalfa (Gannong 5, GN5) compared to the susceptible varieties (Hunter River, LRH), particularly highlighting the high expression levels of ApCarE4 and ApPOD3. Simultaneously, RNAi-induced knockdown of ApCarE4 and ApPOD3 led to a higher mortality of pea aphids in the alfalfa Hunter River. These results indicate that ApPOD3 and ApCarE4 are involved in the detoxification of metabolic functions in the adaptation of pea aphids to host switching. These findings contribute to the understanding of pea aphid adaptation to host plants and lay a foundation for further exploration of the physiological roles of carboxylesterase and peroxidase genes in pea aphids.

Different multicellular trichome types coordinate herbivore mechanosensing and defense in tomato

Herbivore-induced wounding can elicit a defense response in plants. However, whether plants possess a surveillance system capable of detecting herbivore threats and initiating preparatory defenses before wounding occurs remains unclear. In this study, we reveal that tomato (Solanum lycopersicum) trichomes can detect and respond to the mechanical stimuli generated by herbivores. Mechanical stimuli are preferentially perceived by long trichomes, and this mechanosensation is transduced via intra-trichome communication. This communication presumably involves calcium waves, and the transduced signals activate the jasmonic acid (JA) signaling pathway in short glandular trichomes, resulting in the upregulation of the Woolly (Wo)-SlMYC1 regulatory module for terpene biosynthesis. This induced defense mechanism provides plants with an early warning system against the threat of herbivore invasion. Our findings represent a perspective on the role of multicellular trichomes in plant defense and the underlying intra-trichome communication.

Inducible defense phytohormones in annual bluegrass (Poa annua) and creeping bentgrass (Agrostis stolonifera) in response to annual bluegrass weevil (Listronotus maculicollis) infestation

The annual bluegrass weevil (Listronotus maculicollis) is the most damaging insect pest of short-mown turfgrass on golf courses in eastern North America. Listronotus maculicollis larvae cause limited visible damage as stem-borers (L1-3), compared to the crown-feeding (L4-5) developmental instars. Prolonged larval feeding results in discoloration and formation of irregular patches of dead turf, exposing soil on high-value playing surfaces (fairways, collars, tee boxes, and putting greens). Annual bluegrass (Poa annua) is highly susceptible to L. maculicollis compared to a tolerant alternate host plant, creeping bentgrass (Agrostis stolonifera). This study explored whether defense signaling phytohormones contribute to A. stolonifera tolerance in response to L. maculicollis. Concentrations (ng/g) of salicylic acid (SA), jasmonic acid (JA), jasmonic-isoleucine (JA-Ile), 12-oxophytodienoic acid (OPDA), and abscisic acid (ABA) were extracted from turfgrass (leaf, stem, and root) tissue samples as mean larval age reached 2nd (L2), 3rd (L3), and 4th (L4) instar. Poa annua infested with L. maculicollis larvae (L2-4) possessed significantly greater SA in above-ground tissues than A. stolonifera. Levels of constitutive JA, JA-Ile, OPDA, and ABA were significantly higher within non-infested A. stolonifera aboveground tissues compared to P. annua. Inducible defense phytohormones may play a role in P. annua susceptibility to L. maculicollis but are unlikely to provide tolerance in A. stolonifera. Additional studies in turfgrass breeding, particularly focusing on cultivar selection for increased constitutive JA content, could provide a non-chemical alternative management strategy for L. maculicollis for turfgrass managers.

Two Structural Analogs of Kairomones are Detected by an Odorant Receptor HvarOR28 in the Coccinellid Hippodamia variegata

In natural environments, general plant volatiles and herbivore-induced plant volatiles (HIPVs) serve as critical clues for predatory natural enemies in the search for prey. The insect olfactory system plays a vital role in perceiving plant volatiles including HIPVs. In this study, we found that HIPV (E,E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene (TMTT) and the plant volatile geranyl acetate (GA), two structurally similar chemicals, displayed electrophysiological activities on the antennae of the ladybird Hippodamia variegata, but were only attractive to adult females in behavior. Moreover, mated female ladybirds laid a significantly higher number of eggs on TMTT-treated and GA-treated cotton leaves compared to controls. Screening of female-biased odorant receptors (ORs) from the antennal transcriptomes, performing Xenopus oocytes expression coupled with two-electrode voltage clamp recordings, suggested that HvarOR28 specifically tuned to TMTT and GA. Molecular docking and site-directed mutagenesis revealed that the amino acid residues Tyr143 and Phe81 of HvarOR28 are the key site for binding with TMTT and GA. Furthermore, RNA interference (RNAi) assay demonstrated that HvarOR28-silenced individuals demonstrated a notable decrease in electrophysiological responses, even female adults almost lost behavioral preference for the two compounds. Thus, it could be concluded that HvarOR28 in H. variegata contributes to facilitating egg laying through the perception of TMTT and GA. These findings may help to develop new olfactory modulators based on the behaviorally active ligands of HvarOR28.

An RdDM-independent function of Pol V transcripts in gene regulation and plant defence

RNA polymerase V (Pol V) and Pol IV are known to be specialized for RNA-directed DNA methylation (RdDM). Here we report that Pol V, but not Pol IV, regulates hundreds of genes including jasmonic acid-responsive genes and confers plant defence to Botrytis cinerea and Spodoptera exigua. About half of the Pol V-regulated genes are associated with Pol V transcripts (PVTs). We thus hypothesized that some PVTs could regulate gene expression in an RdDM-independent manner. To test this hypothesis, we studied three PVTs, PVT-ERF5a/b and PVT-ERF6, as models. PVT-ERF5a/b and PVT-ERF6 are transcribed from the upstream regions of ERF5 and ERF6 and positively regulate their transcription, thereby regulating plant defence. Such regulation involves PVT-dependent H3K4me3 deposition and requires the DRD1-DMS3-RDM1 complex that mediates Pol V recruitment to the target loci. These findings highlight an unprecedented role for PVTs in regulating gene transcription, apart from serving as scaffold RNAs to direct DNA methylation.

Arabidopsis WRKY55 Transcription Factor Enhances Soft Rot Disease Resistance with ORA59

Pectobacterium is a major bacterial causal agent leading to soft rot disease in host plants. With the Arabidopsis-Pectobacterium pathosystem, we investigated the function of an Arabidopsis thaliana WRKY55 during defense responses to Pectobacterium carotovorum ssp. carotovorum (Pcc). Pcc-infection specifically induced WRKY55 gene expression. The overexpression of WRKY55 was resistant to the Pcc infection, while wrky55 knockout plants compromised the defense responses against Pcc. WRKY55 expression was mediated via Arabidopsis COI1-dependent signaling pathway showing that WRKY55 can contribute to the gene expression of jasmonic acid-mediated defense marker genes such as PDF1.2 and LOX2. WRKY55 physically interacts with Arabidopsis ORA59 facilitating the expression of PDF1.2</i. Our results suggest that WRKY55 can function as a positive regulator for resistance against Pcc in Arabidopsis.

Niche construction and niche choice by aphids infesting wheat ears

The niche of aphids is largely defined by their consumption of plant phloem sap and its composition, including nutrients and specialized metabolites. Niche construction is the change of the environment by organisms, which may influence the fitness of these organisms and their offspring. To better understand interactions between plants and aphids, it is necessary to investigate whether aphids modify the chemical composition of the phloem sap of their host plants and whether conspecifics are affected by previous infestation. In the current study, ears of wheat (Triticum aestivum) plants were infested with clonal lineages of the English grain aphid (Sitobion avenae) or were left uninfested. The metabolic composition of ear phloem sap exudates was analyzed through amino acid profiling and metabolic fingerprinting. Aphids of the clonal lineages were either put on previously aphid-infested or on uninfested ears and their colony sizes followed over time. Furthermore, it was investigated whether aphids choose one treatment group over another. Sitobion avenae infestation affected the relative concentrations of some metabolites in the phloem exudates of the ears. Compared to uninfested plants, the relative concentration of asparagine was higher after aphid infestation. Colonies grew significantly larger on previously aphid-infested ears, which the aphids also clearly chose in the choice experiment. The pronounced positive effect of previous infestation on aphid colonies indicates niche construction, while the choice of these constructed niches reveals niche choice by S. avenae on wheat. The interplay between these different niche realization processes highlights the complexity of interactions between aphids and their hosts.

Transcriptomic and coexpression network analyses revealed the regulatory mechanism of Cydia pomonella infestation on the synthesis of phytohormones in walnut husks

The codling moth (Cydia pomonella) has a major effect on the quality and yield of walnut fruit. Plant defences respond to insect infestation by activating hormonal signalling and the flavonoid biosynthetic pathway. However, little is known about the role of walnut husk hormones and flavonoid biosynthesis in response to C. pomonella infestation. The phytohormone content assay revealed that the contents of salicylic acid (SA), abscisic acid (ABA), jasmonic acid (JA), jasmonic acid-isoleucine conjugate (JA-ILE), jasmonic acid-valine (JA-Val) and methyl jasmonate (MeJA) increased after feeding at different time points (0, 12, 24, 36, 48, and 72 h) of walnut husk. RNA-seq analysis of walnut husks following C. pomonella feeding revealed a temporal pattern in differentially expressed genes (DEGs), with the number increasing from 3,988 at 12 h to 5,929 at 72 h postfeeding compared with the control at 0 h postfeeding. Walnut husks exhibited significant upregulation of genes involved in various defence pathways, including flavonoid biosynthesis (PAL, CYP73A, 4CL, CHS, CHI, F3H, ANS, and LAR), SA (PAL), ABA (ZEP and ABA2), and JA (AOS, AOC, OPR, JAZ, and MYC2) pathways. Three gene coexpression networks that had a significant positive association with these hormonal changes were constructed based on the basis of weighted gene coexpression network analysis (WGCNA). We identified several hub transcription factors, including the turquoise module (AIL6, MYB4, PRE6, WRKY71, WRKY31, ERF003, and WRKY75), the green module (bHLH79, PCL1, APRR5, ABI5, and ILR3), and the magenta module (ERF27, bHLH35, bHLH18, TIFY5A, WRKY31, and MYB44). Taken together, these findings provide useful genetic resources for exploring the defence response mediated by phytohormones in walnut husks.

Suprathreshold Water Spray Stimulus Enhances Plant Defenses against Biotic Stresses in Tomato

Mechanical stimuli can affect plant growth, development, and defenses. The role of water spray stimulation, as a prevalent mechanical stimulus in the environment, in crop growth and defense cannot be overlooked. In this study, the effects of water spray on tomato plant growth and defense against the chewing herbivore Helicoverpa armigera and necrotrophic fungus Botrytis cinerea were investigated. Suprathreshold water spray stimulus (LS) was found to enhance tomato plant defenses against pests and pathogens while concurrently modifying plant architecture. The results of the phytohormone and chemical metabolite analysis revealed that LS improved the plant defense response via jasmonic acid (JA) signaling. LS significantly elevated the level of a pivotal defensive metabolite, chlorogenic acid, and reduced the emissions of volatile organic compounds (VOCs) from tomato plants, thereby defending against pest and pathogen attacks. The most obvious finding to emerge from this study is that LS enhances tomato plant defenses against biotic stresses, which will pave the way for further work on the application of mechanical stimuli for pest management.