Phytocytokine signalling reopens stomata in plant immunity and water loss.

Stomata exert considerable effects on global carbon and water cycles by mediating gas exchange and water vapour1,2. Stomatal closure prevents water loss in response to dehydration and limits pathogen entry3,4. However, prolonged stomatal closure reduces photosynthesis and transpiration and creates aqueous apoplasts that promote colonization by pathogens. How plants dynamically regulate stomatal reopening in a changing climate is unclear. Here we show that the secreted peptides SMALL PHYTOCYTOKINES REGULATING DEFENSE AND WATER LOSS (SCREWs) and the cognate receptor kinase PLANT SCREW UNRESPONSIVE RECEPTOR (NUT) counter-regulate phytohormone abscisic acid (ABA)- and microbe-associated molecular pattern (MAMP)-induced stomatal closure. SCREWs sensed by NUT function as immunomodulatory phytocytokines and recruit SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE (SERK) co-receptors to relay immune signalling. SCREWs trigger the NUT-dependent phosphorylation of ABA INSENSITIVE 1 (ABI1) and ABI2, which leads to an increase in the activity of ABI phosphatases towards OPEN STOMATA 1 (OST1)-a key kinase that mediates ABA- and MAMP-induced stomatal closure5,6-and a reduction in the activity of S-type anion channels. After induction by dehydration and pathogen infection, SCREW-NUT signalling promotes apoplastic water loss and disrupts microorganism-rich aqueous habitats to limit pathogen colonization. The SCREW-NUT system is widely distributed across land plants, which suggests that it has an important role in preventing uncontrolled stomatal closure caused by abiotic and biotic stresses to optimize plant fitness.

Salivary carbonic anhydrase II in winged aphid morph facilitates plant infection by viruses.

Aphids are the most common insect vector transmitting hundreds of plant viruses. Aphid wing dimorphism (winged vs. wingless) not only showcases the phenotypic plasticity but also impacts virus transmission; however, the superiority of winged aphids in virus transmission over the wingless morph is not well understood. Here, we show that plant viruses were efficiently transmitted and highly infectious when associated with the winged morph of Myzus persicae and that a salivary protein contributed to this difference. The carbonic anhydrase II (CA-II) gene was identified by RNA-seq of salivary glands to have higher expression in the winged morph. Aphids secreted CA-II into the apoplastic region of plant cells, leading to elevated accumulation of H+. Apoplastic acidification further increased the activities of polygalacturonases, the cell wall homogalacturonan (HG)-modifying enzymes, promoting degradation of demethylesterified HGs. In response to apoplastic acidification, plants accelerated vesicle trafficking to enhance pectin transport and strengthen the cell wall, which also facilitated virus translocation from the endomembrane system to the apoplast. Secretion of a higher quantity of salivary CA-II by winged aphids promoted intercellular vesicle transport in the plant. The higher vesicle trafficking induced by winged aphids enhanced dispersal of virus particles from infected cells to neighboring cells, thus resulting in higher virus infection in plants relative to the wingless morph. These findings imply that the difference in the expression of salivary CA-II between winged and wingless morphs is correlated with the vector role of aphids during the posttransmission infection process, which influences the outcome of plant endurance of virus infection.

Overexpression of maize ZmLOX6 in Arabidopsis thaliana enhances damage-induced pentyl leaf volatile emissions that affect plant growth and interaction with aphids.

Pentyl leafy volatiles (PLV) are C5 volatiles produced from polyunsaturated fatty acids by plant 13-lipoxygenases (13-LOX) in concert with other lipid metabolizing enzymes. Unlike related C6 volatiles (GLV, green leafy volatiles), little is known about the biosynthesis and physiological function of PLV in plants. Zea mays LOX6 (ZmLOX6) is an unusual plant LOX that lacks lipid oxygenation activity but acts as a hydroperoxide lyase hypothesized to be specifically involved in PLV synthesis. We overexpressed ZmLOX6 in Arabidopsis thaliana and established that it indeed produces PLVs. Overexpression of ZmLOX6 caused a mild chlorotic phenotype, and induced a similar phenotype in untransformed Col-0 plants grown in close proximity, suggesting that airborne signals, such as PLVs, are responsible for the phenotype. PLV production, dependency on the substrate from endogenous 13-LOX(s), and likely competition with endogenous 13-oxylipin pathway were consistent with the model that ZmLOX6 functions as a hydroperoxide lyase. The abundance of individual PLVs was differentially affected by ZmLOX6 overexpression, and the new profile indicated that ZmLOX6 had reaction products distinct from endogenous PLV-producing activities in the Arabidopsis host plants. ZmLOX6 overexpression also induced a new hormonal status, which is likely responsible for increased attraction and propagation of aphids, nonetheless improving host plant tolerance to aphid infestation.

CRISPR/Cas9-mediated methoprene-tolerant 1 knockout results in precocious metamorphosis of beet armyworm (Spodoptera exigua) only at the late larval stage.

Juvenile hormone (JH) controls almost every aspect of an insect, especially metamorphosis. Since RNA interference works on transcripts and is often insufficient in Lepidoptera, how JH affects larval development in these insects is not well studied. Using the CRISPR/Cas9 technique, we knocked out Spodoptera exigua methoprene-tolerant 1 (SeMet1) gene of beet armyworm by modifying two sites in the coding region. However, SeMet1 knockout did not affect egg hatch rate or larval development at L1-L3 stages. In contrast to the consistent five larval instars of the control group, L4 SeMet1 mutants began to show signs of precocious metamorphosis, that is, small patches of pupal cuticle. Most L4 and all L5 SeMet1 mutants died for failing to shed their mosaic cuticles. RNA-seq indicated that most genes encoding pupal cuticle proteins and chitinase genes were altered in SeMet1 mutant L4 larvae. SeKr-h1, a key transcription factor in JH action was significantly down-regulated in L3-L5 larvae, while SeBR-C, a pupal indicator was only upregulated in L4-L5 larvae. These results suggested that S. exigua larvae may initially develop independently of JH, and involve SeMet1 in transducing JH signalling, leading to controlled larval metamorphosis at the late larval stage. We believe our findings will enhance better understanding of JH regulation of larval development.

An oral dsRNA delivery system based on chitosan induces G protein-coupled receptor kinase 2 gene silencing for Apolygus lucorum control.

RNA interference (RNAi) is recognized as a new and environmentally friendly pest control strategy due to its high specificity. However, the RNAi efficiency is relatively low in many sucking insect pests, such as Apolygus lucorum. Therefore, there is an urgent need to develop new and effective ways of dsRNA delivery. Bacterially expressed or T7 synthesized dsRNA targeting a G Protein-Coupled Receptor Kinase 2 gene was mixed with chitosan in a 1:2 ratio by mass. The size of the chitosan/dsRNA nanoparticles was 69 ± 12 nm, and the TEM and AFM images showed typical spherical or ellipsoidal structures. The chitosan nanoparticles protected the dsRNA from nuclease activity, and pH and temperature-dependent degradation, and the fluorescently-tagged nanoparticles were found to be stable on the surface of green bean plants (48 h) (Phaseolus vulgaris) and were absorbed by midgut epithelial cells and transported to hemolymph. Once fed to the A. lucorum nymph, chitosan/dsRNA could effectively inhibit the expression of the G protein-coupled receptor kinase 2 gene (70%), and led to significantly increase mortality (50%), reduced weight (26.54%) and a prolonged developmental period (8.04%). The feeding-based and chitosan-mediated dsRNA delivery method could be a new strategy for A. lucorum management, providing an effective tool for gene silencing of piercing-sucking insects.

Vitellogenin from planthopper oral secretion acts as a novel effector to impair plant defenses.

Vitellogenin (Vg) is a well-known nutritious protein involved in reproduction in nearly all oviparous animals, including insects. Recently, Vg has been detected in saliva proteomes of several piercing-sucking herbivorous arthropods, including the small brown planthopper (Laodelphax striatellus, SBPH). Its function, however, remains unexplored. We investigated the molecular mechanism underlying SBPH orally secreted Vg-mediated manipulation of plant-insect interaction by RNA interference, phytohormone and H2 O2 profiling, protein-protein interaction studies and herbivore bioassays. A C-terminal polypeptide of Vg (VgC) in SBPH, when secreted into rice plants, acted as a novel effector to attenuate host rice defenses, which in turn improved insect feeding performance. Silencing Vg reduced insect feeding and survival on rice. Vg-silenced SBPH nymphs consistently elicited higher H2 O2 production, a well-established defense mechanism in rice, whereas expression of VgC in planta significantly hindered hydrogen peroxide (H2 O2 ) accumulation and promoted insect performance. VgC interacted directly with the rice transcription factor OsWRKY71, a protein which is involved in induction of H2 O2 accumulation and plant resistance to SBPH. These findings indicate a novel effector function of Vg: when secreted into host rice plants, this protein effectively weakened H2 O2 -mediated plant defense through its association with a plant immunity regulator.

Serratia symbiotica Enhances Fatty Acid Metabolism of Pea Aphid to Promote Host Development.

Bacterial symbionts associated with insects are often involved in host development and ecological adaptation. Serratia symbiotica, a common facultative endosymbiont harbored in pea aphids, improves host fitness and heat tolerance, but studies concerning the nutritional metabolism and impact on the aphid host associated with carrying Serratia are limited. In the current study, we showed that Serratia-infected aphids had a shorter nymphal developmental time and higher body weight than Serratia-free aphids when fed on detached leaves. Genes connecting to fatty acid biosynthesis and elongation were up-regulated in Serratia-infected aphids. Specifically, elevated expression of fatty acid synthase 1 (FASN1) and diacylglycerol-o-acyltransferase 2 (DGAT2) could result in accumulation of myristic acid, palmitic acid, linoleic acid, and arachidic acid in fat bodies. Impairing fatty acid synthesis in Serratia-infected pea aphids either by a pharmacological inhibitor or through silencing FASN1 and DGAT2 expression prolonged the nymphal growth period and decreased the aphid body weight. Conversely, supplementation of myristic acid (C14:0) to these aphids restored their normal development and weight gain. Our results indicated that Serratia promoted development and growth of its aphid host through enhancing fatty acid biosynthesis. Our discovery has shed more light on nutritional effects underlying the symbiosis between aphids and facultative endosymbionts.

The H3K4 demethylase Jar1 orchestrates ROS production and expression of pathogenesis-related genes to facilitate Botrytis cinerea virulence.

Histone 3 Lysine 4 (H3K4) demethylation is ubiquitous in organisms, however the roles of H3K4 demethylase JARID1(Jar1)/KDM5 in fungal development and pathogenesis remain largely unexplored. Here, we demonstrate that Jar1/KDM5 in Botrytis cinerea, the grey mould fungus, plays a crucial role in these processes. The BcJAR1 gene was deleted and its roles in fungal development and pathogenesis were investigated using approaches including genetics, molecular/cell biology, pathogenicity and transcriptomic profiling. BcJar1 regulates H3K4me3 and both H3K4me2 and H3K4me3 methylation levels during vegetative and pathogenic development, respectively. Loss of BcJAR1 impairs conidiation, appressorium formation and stress adaptation; abolishes infection cushion (IC) formation and virulence, but promotes sclerotium production in the ΔBcjar1 mutants. BcJar1 controls reactive oxygen species (ROS) production and proper assembly of Sep4, a core septin protein and virulence determinant, to initiate infection structure (IFS) formation and host penetration. Exogenous cAMP partially restored the mutant appressorium, but not IC, formation. BcJar1 orchestrates global expression of genes for ROS production, stress response, carbohydrate transmembrane transport, secondary metabolites, etc., which may be required for conidiation, IFS formation, host penetration and virulence of the pathogen. Our work systematically elucidates BcJar1 functions and provides novel insights into Jar1/KDM5-mediated H3K4 demethylation in regulating fungal development and pathogenesis.

CIRCADIAN CLOCK-ASSOCIATED1 Controls Resistance to Aphids by Altering Indole Glucosinolate Production.

CIRCADIAN CLOCK-ASSOCIATED1 (CCA1), a well-known central circadian clock regulator, coordinates plant responses to environmental challenges. Its daily rhythmic expression in Arabidopsis (Arabidopsis thaliana) confers host resistance to the caterpillar Trichoplusia ni However, it is unclear whether CCA1 plays a role in defense against phloem sap-feeding aphids. In this study, we showed that green peach aphid (Myzus persicae) displayed an intrinsic circadian feeding rhythm. Under constant light, wild-type Columbia-0 (Col-0) Arabidopsis plants coentrained with aphids in the same light/dark cycles exhibited greater antixenotic activity than plants preentrained in the opposite cycle from the aphids. Consistently, circadian mutants cca1-1, cca1-11, lhy-21, ztl-1, ztl-4, and lux-2 suffered more severe damage than Col-0 plants when infested by aphids, suggesting that the Arabidopsis circadian clock plays a defensive role. However, the arrhythmic CCA1 overexpression line (CCA1-OX) displayed strong antixenotic and antibiotic activities despite its loss of circadian regulation. Aphids feeding on CCA1-OX plants exhibited lower reproduction and smaller body size and weight than those on Col-0. Apparently, CCA1 regulates both clock-dependent and -independent defense responses. Systematic investigation based on bioinformatics analyses indicated that resistance to aphids in CCA1-OX plants was due primarily to heightened basal indole glucosinolate levels. Interestingly, aphid feeding induced alternatively spliced intron-retaining CCA1a/b transcripts, which are normally expressed at low levels, whereas expression of the major fully spliced CCA1 transcript remained largely unchanged. We hypothesize that posttranscriptional modulation of CCA1 expression upon aphid infestation maximizes the potential of circadian-mediated defense and stress tolerance while ensuring normal plant development.

An aphid facultative symbiont suppresses plant defence by manipulating aphid gene expression in salivary glands.

Aphids often carry facultative symbionts to achieve diverse advantages. Serratia symbiotica, one of facultative endosymbionts, increases aphid tolerance to heat. However, whether it benefits aphid colonization on host plants is yet to be determined. In the current study, we found that Acyrthosiphon pisum harbouring S. symbiotica had longer feeding duration on Medicago truncatula than Serratia-free aphids. Contrastingly, Serratia-free aphids triggered higher accumulation of reactive oxygen species (ROS), jasmonic acid and salicylic acid responsive genes and cytosolic Ca2+ elevations than Serratia-infected aphids. Transcriptomic analysis of salivary glands indicated that a histidine-rich Ca2+ -binding protein-like gene (ApHRC) was expressed more highly in the salivary gland of Serratia-infected aphids than that of Serratia-free aphids. Once ApHRC was silenced, Serratia-infected aphids also displayed shorter phloem-feeding duration and caused Ca2+ elevation and ROS accumulation in plants. Our results suggest that ApHRC, a potential effector up-regulated by S. symbiotica in the salivary glands, impairs plant defence response by suppressing Ca2+ elevation and ROS accumulation, allowing colonization of aphids. This study has provided an insight into how facultative symbionts facilitate aphid colonization and adaptation to host plants.

Noninvasive and Nondestructive Detection of Cowpea Bruchid within Cowpea Seeds with a Hand-Held Raman Spectrometer.

Insect damage to crops is a serious issue, in particular when the pest dwells within its host. The cowpea bruchid ( Callosobruchus maculatus) is an herbivore of legumes including beans and peas. The bruchid lays its eggs on the seeds themselves; after hatching, the larvae burrow into and develop inside the seed, complicating detection and treatment. Left unchecked, two insects could destroy up to 50% of 1 ton of harvest cowpea ( Vigna unguiculata) after several months of storage. In this study, we investigated the possibility of using a hand-held Raman spectrometer to detect the pest during its development within intact cowpeas. Our results show that Raman spectroscopy can detect chemical signatures of bruchid larvae as well as their excrements inside the intact seeds. Additionally, using chemometric methods, we distinguished between healthy and infested seeds as well as among seeds hosting developmentally early or late-stage larvae with high accuracy. This study demonstrates Raman spectroscopy's efficacy in not only detection of pathogens and pests present on the surface of plant leaves and the grain but also inside the seeds. This Raman-based method may prove useful as a rapid means of screening crops for internal pests.

Priming of jasmonate-mediated antiherbivore defense responses in rice by silicon.

Although the function of silicon (Si) in plant physiology has long been debated, its beneficial effects on plant resistance against abiotic and biotic stresses, including insect herbivory, have been well documented. In addition, the jasmonate (JA) signaling pathway plays a crucial role in mediating antiherbivore defense responses in plants. However, potential interactions between JA and Si in response to insect attack have not been examined directly. To explore the role JA may play in Si-enhanced resistance, we silenced the expression of allene oxide synthase (OsAOS; active in JA biosynthesis) and CORONATINE INSENSITIVE1 (OsCOI1; active in JA perception) genes in transgenic rice plants via RNAi and examined resulting changes in Si accumulation and defense responses against caterpillar Cnaphalocrocis medinalis (rice leaffolder, LF) infestation. Si pretreatment increased rice resistance against LF larvae in wild-type plants but not in OsAOS and OsCOI1 RNAi lines. Upon LF attack, wild-type plants subjected to Si pretreatment exhibited enhanced defense responses relative to untreated controls, including higher levels of JA accumulation; increased levels of transcripts encoding defense marker genes; and elevated activities of peroxidase, polyphenol oxidase, and trypsin protease inhibitor. Additionally, reduced Si deposition and Si cell expansion were observed in leaves of OsAOS and OsCOI1 RNAi plants in comparison with wild-type plants, and reduced steady-state transcript levels of the Si transporters OsLsi1, OsLsi2, and OsLsi6 were observed in Si-pretreated plants after LF attack. These results suggest a strong interaction between Si and JA in defense against insect herbivores involving priming of JA-mediated defense responses by Si and the promotion of Si accumulation by JA.

Morphology, Ultrastructure and Possible Functions of Antennal Sensilla of Sitodiplosis mosellana Géhin (Diptera: Cecidomyiidae).

To better understand the olfactory receptive mechanisms involved in host selection and courtship behavior of Sitodiplosis mosellana (Diptera: Cecidomyiidae), one of the most important pests of wheat, scanning and transmission electron microscopy were used to examine the external morphology and ultrastructure of the antennal sensilla. The moniliform antennae exhibit obvious sexual dimorphism: antennae of the males are markedly longer than those of the females. Furthermore, each male flagellomere consists of two globular nodes, whereas each female flagellomere is cylindrical. Seven types of sensilla were identified in both sexes. Two types of s. chaetica have a lumen without dendrites and thick walls, suggesting that they are mechanoreceptors. S. trichodea and s. circumfila are typical chemoreceptors, possessing thin multiporous walls encircling a lumen with multiple dendrites. There are significantly more s. trichodea in female than in male, which may be related to host plant localization. In contrast, male s. circumfila are highly elongated compared to those of females, perhaps for pheromone detection. Peg-shaped s. coeloconica are innervated with unbranched dendrites extending from the base to the distal tip. Type 1 s. coeloconica, which have deep longitudinal grooves and finger-like projections on the surface, may serve as olfactory or humidity receptors, whereas type 2 s. coeloconica, smooth with a terminal pore, may be contact chemoreceptors. Also, this is the first report of Böhm' bristles at proximal scape on antennae of Cecidomyiid species potentially functioning as mechanoreceptors.

Insect response to plant defensive protease inhibitors.

Plant protease inhibitors (PIs) are natural plant defense proteins that inhibit proteases of invading insect herbivores. However, their anti-insect efficacy is determined not only by their potency toward a vulnerable insect system but also by the response of the insect to such a challenge. Through the long history of coevolution with their host plants, insects have developed sophisticated mechanisms to circumvent antinutritional effects of dietary challenges. Their response takes the form of changes in gene expression and the protein repertoire in cells lining the alimentary tract, the first line of defense. Research in insect digestive proteases has revealed the crucial roles they play in insect adaptation to plant PIs and has brought about a new appreciation of how phytophagous insects employ this group of molecules in both protein digestion and counterdefense. This review provides researchers in related fields an up-to-date summary of recent advances.

BOTRYTIS-INDUCED KINASE1 Modulates Arabidopsis Resistance to Green Peach Aphids via PHYTOALEXIN DEFICIENT4.

BOTRYTIS-INDUCED KINASE1 (BIK1) plays important roles in induced defense against fungal and bacterial pathogens in Arabidopsis (Arabidopsis thaliana). Its tomato (Solanum lycopersicum) homolog is required for host plant resistance to a chewing insect herbivore. However, it remains unknown whether BIK1 functions in plant defense against aphids, a group of insects with a specialized phloem sap-feeding style. In this study, the potential role of BIK1 was investigated in Arabidopsis infested with the green peach aphid (Myzus persicae). In contrast to the previously reported positive role of intact BIK1 in defense response, loss of BIK1 function adversely impacted aphid settling, feeding, and reproduction. Relative to wild-type plants, bik1 displayed higher aphid-induced hydrogen peroxide accumulation and more severe lesions, resembling a hypersensitive response (HR) against pathogens. These symptoms were limited to the infested leaves. The bik1 mutant showed elevated basal as well as induced salicylic acid and ethylene accumulation. Intriguingly, elevated salicylic acid levels did not contribute to the HR-like symptoms or to the heightened aphid resistance associated with the bik1 mutant. Elevated ethylene levels in bik1 accounted for an initial, short-term repellence. Introducing a loss-of-function mutation in the aphid resistance and senescence-promoting gene PHYTOALEXIN DEFICIENT4 (PAD4) into the bik1 background blocked both aphid resistance and HR-like symptoms, indicating bik1-mediated resistance to aphids is PAD4 dependent. Taken together, Arabidopsis BIK1 confers susceptibility to aphid infestation through its suppression of PAD4 expression. Furthermore, the results underscore the role of reactive oxygen species and cell death in plant defense against phloem sap-feeding insects.

Elevated CO2 alters the feeding behaviour of the pea aphid by modifying the physical and chemical resistance of Medicago truncatula.

Elevated CO(2) compromises the resistance of leguminous plants against chewing insects, but little is known about whether elevated CO(2) modifies the resistance against phloem-sucking insects or whether it has contrasting effects on the resistance of legumes that differ in biological nitrogen fixation. We tested the hypothesis that the physical and chemical resistance against aphids would be increased in Jemalong (a wild type of Medicago truncatula) but would be decreased in dnf1 (a mutant without biological nitrogen fixation) by elevated CO(2). The non-glandular and glandular trichome density of Jemalong plants increased under elevated CO(2), resulting in prolonged aphid probing. In contrast, dnf1 plants tended to decrease foliar trichome density under elevated CO(2), resulting in less surface and epidermal resistance to aphids. Elevated CO(2) enhanced the ineffective salicylic acid-dependent defence pathway but decreased the effective jasmonic acid/ethylene-dependent defence pathway in aphid-infested Jemalong plants. Therefore, aphid probing time decreased and the duration of phloem sap ingestion increased on Jemalong under elevated CO(2), which, in turn, increased aphid growth rate. Overall, our results suggest that elevated CO(2) decreases the chemical resistance of wild-type M. truncatula against aphids, and that the host's biological nitrogen fixation ability is central to this effect.

A color morph-specific salivary carotenoid desaturase enhances plant photosynthesis and facilitates phloem feeding of Myzus persicae (Sulzer).

BACKGROUND: Body-color polymorphisms in insects are often explained by environmental selective advantages. Differential fitness related to body coloration has been demonstrated in Myzus persicae (Sulzer): performance of the red morph is in general better than that of the green morph on tobacco plants. However, the molecular mechanism involved is largely unclear. RESULTS: Here we showed that the red morph of M. persicae had higher expression of a carotenoid desaturase CarD763 in the whole body, salivary gland and saliva relative to the green morph. Also, 18% individuals displayed faded red body color 5 days post dsCarD763 treatment. Furthermore, knockdown of CarD763 in the red morph significantly prolonged the time needed to locate phloem and shortened the duration of phloem feeding. Honeydew production and survival rate decreased as well. In contrast, overexpression of CarD763 in tobacco leaves facilitated aphid feeding, enhanced honeydew production and improved the survival rate of aphids. Compared with those fed by dsGFP aphids, plants infested by dsCarD763-treated aphids had higher ROS accumulation, lower lycopene content and photosynthetic rate, and maximum photon quantum yield. The reverse was true when plants overexpressed CarD763. CONCLUSION: These findings demonstrated that CarD763, a red morph-specific salivary protein, could enhance aphid feeding and early colonization by promoting plant photosynthesis. © 2024 Society of Chemical Industry.

Characterization of three glutathione S-transferases potentially associated with adaptation of the wheat blossom midge Sitodiplosis mosellana to host plant defense.

BACKGROUND: Insect glutathione S-transferases (GSTs), a multifunctional protein family, play a crucial role in detoxification of plant defensive compounds. However, they have been rarely investigated in Sitodiplosis mosellana, a destructive pest of wheat worldwide. In this study, we characterized for the first time a delta (SmGSTd1) and two epsilon GST genes (SmGSTe1 and SmGSTe2) and analyzed their expression patterns and functions associated with adaptation to host plant defense in this species. RESULTS: Expression of these SmGST genes greatly increased in S. mosellana larvae feeding on resistant wheat varieties Kenong1006, Shanmai139 and Jinmai47 which contain higher tannin and ferulic acid, the major defensive compounds of wheat against this pest, compared with those feeding on susceptible varieties Xinong822, Xinong88 and Xiaoyan22. Their expression was also tissue-specific, most predominant in larval midgut. Recombinant SmGSTs expressed in Escherichia coli could catalyze the conjugation of 1-chloro-2,4-dinitrobenzene, with activity peak at pH around 7.0 and temperature between 30 and 40 °C. Notably, they could metabolize tannin and ferulic acid, with the strongest metabolic ability by SmGSTe2 against two compounds, followed by SmGSTd1 on tannin, and SmGSTe1 on ferulic acid. CONCLUSION: The results suggest that these SmGSTs are important in metabolizing wheat defensive chemicals during feeding, which may be related to host plant adaptation of S. mosellana. Our study has provided information for future investigation and development of strategies such as host-induced gene silencing of insect-detoxifying genes for managing pest adaptation. © 2023 Society of Chemical Industry.

Gene cloning, protein expression, and enzymatic characterization of a double-stranded RNA degrading enzyme in Apolygus lucorum.

RNA interference (RNAi) is a powerful tool that post-transcriptionally silences target genes in eukaryotic cells. However, silencing efficacy varies greatly among different insect species. Recently, we met with little success when attempting to knock down genes in the mirid bug Apolygus lucorum via dsRNA injection. The disappearance of double-stranded RNA (dsRNA) could be a potential factor that restricts RNAi efficiency. Here, we found that dsRNA can be degraded in midgut fluids, and a dsRNase of A. lucorum (AldsRNase) was identified and characterized. Sequence alignment indicated that its 6 key amino acid residues and the Mg2+ -binding site were similar to those of other insects' dsRNases. The signal peptide and endonuclease non-specific domain shared high sequence identity with the brown-winged green stinkbug Plautia stali dsRNase. AldsRNase showed high salivary gland and midgut expression and was continuously expressed through the whole life cycle, with peaks at the 4th instar ecdysis in the whole body. The purified AldsRNase protein obtained by heterologously expressed can rapidly degrade dsRNA. When comparing the substrate specificity of AldsRNase, 3 specific substrates (dsRNA, small interfering RNA, and dsDNA) were all degraded, and the most efficient degradation is dsRNA. Subsequently, immunofluorescence revealed that AldsRNase was expressed in the cytoplasm of midgut cells. Through cloning and functional study of AldsRNase, the enzyme activity and substrate specificity of the recombinant protein, as well as the subcellular localization of nuclease, the reason for the disappearance of dsRNA was explained, which was useful in improving RNAi efficiency in A. lucorum and related species.

Pea aphid promotes amino acid metabolism both in Medicago truncatula and bacteriocytes to favor aphid population growth under elevated CO2.

Rising atmospheric CO(2) levels can dilute the nitrogen (N) resource in plant tissue, which is disadvantageous to many herbivorous insects. Aphids appear to be an exception that warrants further study. The effects of elevated CO(2) (750 ppm vs. 390 ppm) were evaluated on N assimilation and transamination by two Medicago truncatula genotypes, a N-fixing-deficient mutant (dnf1) and its wild-type control (Jemalong), with and without pea aphid (Acyrthosiphon pisum) infestation. Elevated CO(2) increased population abundance and feeding efficiency of aphids fed on Jemalong, but reduced those on dnf1. Without aphid infestation, elevated CO(2) increased photosynthetic rate, chlorophyll content, nodule number, biomass, and pod number for Jemalong, but only increased pod number and chlorophyll content for dnf1. Furthermore, aphid infested Jemalong plants had enhanced activities of N assimilation-related enzymes (glutamine synthetase, Glutamate synthase) and transamination-related enzymes (glutamate oxalate transaminase, glutamine phenylpyruvate transaminase), which presumably increased amino acid concentration in leaves and phloem sap under elevated CO(2). In contrast, aphid infested dnf1 plants had decreased activities of N assimilation-related enzymes and transmination-related enzymes and amino acid concentrations under elevated CO(2). Furthermore, elevated CO(2) up-regulated expression of genes relevant to amino acid metabolism in bacteriocytes of aphids associated with Jemalong, but down-regulated those associated with dnf1. Our results suggest that pea aphids actively elicit host responses that promote amino acid metabolism in both the host plant and in its bacteriocytes to favor the population growth of the aphid under elevated CO(2).