Host plants alter their volatiles to help a solitary egg parasitoid distinguish habitats with parasitized hosts from those without

The oviposition of cotton bollworms stimulates the defense against its eggs and larvae in tomato plants

BACKGROUND

Herbivorous insects sustain their populations by oviposition. To reduce the damage caused by herbivores, the host plant triggers a defensive response upon detection of egg deposition. However, the specific impact of the egg deposition time of the cotton bollworm Helicoverpa armigera (Lepidoptera: Noctuidae), on the tomato plant defense remains obscure.

RESULTS

This study investigated the effects of tomato plant defenses on cotton bollworm eggs and larvae at different time intervals following egg deposition. The study revealed that tomato plant defense triggered by egg deposition did not directly affect the hatchability of the eggs. Nevertheless, it attracted Trichogramma chilonis 48 h after the egg deposition. Gas chromatography-mass spectrometry analysis of the oviposition-induced plant volatiles (OIPVs) revealed a considerable increase in the amount of α-pinene released by tomato plants 48 h after egg deposition. The olfactory results from Y-tube experiments showed that α-pinene exhibited a substantial attraction towards T. chilonis. In addition, it was found that the defense response induced by egg deposition for 24 and 48 h significantly inhibited the growth and development of the larvae. Metabolomics analysis revealed that the egg deposition of cotton bollworm altered the metabolite composition and caused significant modifications in the metabolic pathways of tomato plants.

CONCLUSION

These findings provide novel insights into pest management by using egg-induced plant defenses to reduce egg hatching, and impede larval growth and development in herbivorous insects. © 2024 Society of Chemical Industry.

Identification and knockout of a herbivore susceptibility gene enhances planthopper resistance and increases rice yield

Brown planthoppers (Nilaparvata lugens) and white-backed planthoppers (Sogatella furcifera) are among the most destructive pests on rice. However, plant susceptibility genes have not yet been exploited for crop protection. Here we identified a leucine-rich repeat protein, OsLRR2, from susceptible rice varieties that facilitates infestation by brown planthopper N. lugens. Field trials showed that knockout of OsLRR2 significantly reduced BPH infestation and enhanced natural biological control by attracting natural enemies. Yield of a susceptible variety was increased by 18% in insecticide-treated plots that eliminated planthoppers and by 25% in untreated plots. These findings underscore the pivotal role of OsLRR2, offering a promising pathway for pest population suppression and rice yield increase.

Engineering DMNT emission in cotton enhances direct and indirect defense against mirid bugs

INTRODUCTION

As an important herbivore-induced plant volatile, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT) is known for its defensive role against multiple insect pests, including attracting natural enemies. A terpene synthase (GhTPS14) and two cytochrome P450 (GhCYP82L1, GhCYP82L2) enzymes are involved in the de novo synthesis of DMNT in cotton. We conducted a study to test the potential of manipulating DMNT-synthesizing enzymes to enhance plant resistance to insects.

OBJECTIVES

To manipulate DMNT emissions in cotton and generate cotton lines with increased resistance to mirid bug Apolygus lucorum.

METHODS

Biosynthesis and emission of DMNT by cotton plants were altered using CRISPR/Cas9 and overexpression approaches. Dynamic headspace sampling and GC-MS analysis were used to collect, identify and quantify volatiles. The attractiveness and suitability of cotton lines against mirid bug and its parasitoid Peristenus spretus were evaluated through various assays.

RESULTS

No DMNT emission was detected in knockout CAS-L1L2 line, where both GhCYP82L1 and GhCYP82L2 were knocked out. In contrast, gene-overexpressed lines released higher amounts of DMNT when infested by A. lucorum. At the flowering stage, L114 (co-overexpressing GhCYP82L1 and GhTPS14) emitted 10-15-fold higher amounts than controls. DMNT emission in overexpressed transgenic lines could be triggered by methyl jasmonate (MeJA) treatment. Apolygus lucorum and its parasitoid were far less attracted to the double edited CAS-L1L2 plants, however, co-overexpressed line L114 significantly attracted bugs and female wasps. A high dose of DMNT, comparable to the emission of L114, significantly inhibited the growth of A. lucorum, and further resulted in higher mortalities.

CONCLUSION

Turning down DMNT emission attenuated the behavioral preferences of A. lucorum to cotton. Genetically modified cotton plants with elevated DMNT emission not only recruited parasitoids to enhance indirect defense, but also formed an ecological trap to kill the bugs. Therefore, manipulation of DMNT biosynthesis and emission in plants presents a promising strategy for controlling mirid bugs.

Unprecedented oviposition tactics avoid plant defences and reduce attack by parasitic wasps

Female insects oviposit in sites suitable for the development of their offspring. The Oriental armyworm, Mythimna separata is a serious pest of various crops including wheat and prefers to oviposit on withered leaves rather than on fresh plant material, which is surprisingly different from other insects. Studies here showed that this oviposition tactic enables avoidance of wheat defence against eggs and emerged larvae. Intact plants responded to M. separata egg deposition by releasing oviposition-induced plant volatiles including acetophenone, tetradecene and pentadecane after 24 h. Acetophenone was identified as quantitatively accounting for the attraction of the egg parasitoid wasp (Trichogramma chilonis). Leaf jasmonic acid levels significantly increased after M. separata laid eggs, and primed the plant against emerging larvae. In addition, newly emerged M. separata larvae adopted a fast crawling behaviour and starvation tolerance compared with other noctuid larvae, which enhanced the survival of larvae on the withered leaves. The elucidation of this complex and surprising plant-insect interaction provides the first explanation for a herbivore laying eggs on withered leaves to avoid natural enemies and live-plant defence against emerging larvae.

Genomic survey of MYB gene family in six pearl millet (Pennisetum glaucum) varieties and their response to abiotic stresses

In addition to their roles in developmental and metabolic processes, MYB transcription factors play crucial roles in plant defense mechanisms and stress responses. A comprehensive analysis of six pearl millet genomes revealed the presence of 1133 MYB genes, which can be classified into four phylogenetically distinct subgroups. The duplication pattern of MYB genes across the pearl millet genomes demonstrates their conserved and similar evolutionary history. Overall, MYB genes were observed to be involved in drought and heat stress responses, with stronger differential expressed observed in root tissues. Multiple analyses indicated that MYB genes mediate abiotic stress responses by modulating abscisic acid-related pathways, circadian rhythms, and histone modification processes. A substantial number of duplicated genes were determined to exhibit differential expression under abiotic stress. The consistent positive expression trend observed in duplicated gene pairs, such as PMA5G04432.1 and PMA2G00728.1, across various abiotic stresses suggests that duplicated MYB genes plays a key role in the evolution of adaptive responses of pearl millet to abiotic stresses.

Plant-soil-microbe interactions in maintaining ecosystem stability and coordinated turnover under changing environmental conditions

Ecosystem functions directly depend upon biophysical as well as biogeochemical reactions occurring at the soil-microbe-plant interface. Environment is considered as a major driver of any ecosystem and for the distributions of living organisms. Any changes in climate may potentially alter the composition of communities i.e., plants, soil microbes and the interactions between them. Since the impacts of global climate change are not short-term, it is indispensable to appraise its effects on different life forms including soil-microbe-plant interactions. This article highlights the crucial role that microbial communities play in interacting with plants under environmental disturbances, especially thermal and water stress. We reviewed that in response to the environmental changes, actions and reactions of plants and microbes vary markedly within an ecosystem. Changes in environment and climate like warming, CO₂ elevation, and moisture deficiency impact plant and microbial performance, their diversity and ultimately community structure. Plant and soil feedbacks also affect interacting species and modify community composition. The interactive relationship between plants and soil microbes is critically important for structuring terrestrial ecosystems. The anticipated climate change is aggravating the living conditions for soil microbes and plants. The environmental insecurity and complications are not short-term and limited to any particular type of organism. We have appraised effects of climate change on the soil inhabiting microbes and plants in a broader prospect. This article highlights the unique qualities of tripartite interaction between plant-soil-microbe under climate change.

Finding an egg in a haystack: variation in chemical cue use by egg parasitoids of herbivorous insects

Egg parasitoids of herbivorous insects use an interplay of short- and long-range chemical cues emitted by hosts and host plants to find eggs to parasitize. Volatile compounds that attract egg parasitoids can be identified via behavioral assays and used to manipulate parasitoid behavior in the field for biological control of herbivorous pests. However, how and when a particular cue will be used varies over the life of an individual, as well as at and below species level. Future research should expand taxonomic coverage to explore variation in chemical cue use in more natural, dynamic settings. More nuanced understanding of the variability of egg parasitoid host-finding strategies will aid in disentangling the underlying genetics and further enhancing biological control.

Evaluation of the Parasitism Capacity of a Thelytoky Egg Parasitoid on a Serious Rice Pest, Nilaparvata lugens (Stål)

Pseudoligosita yasumatsui and Anagrus nilaparvatae are both egg parasitoids of the brown planthopper, Nilaparvata lugens (Stål) (BPH). In this study, we obtained a stable strain of P. yasumatsui reproduced via thelytoky through indoor rearing and screening. We assessed the parasitism capacity of this strain on eggs of N. lugens by comparing the parasitism preference and circadian rhythm of this strain to that of A. nilaparvatae, which is proved as the dominant egg parasitoid species of BPH in rice fields. The findings indicated that both egg parasitoids could parasitize fertilized and unfertilized BPH eggs, however, with a significant preference for fertilized eggs. The daily parasitization volume of P. yasumatsui was slightly higher than that of A. nilaparvatae. Both egg parasitoids preferred parasitizing 1-3-day-old BPH eggs, but the parasitism amount of 5-6-day-old BPH eggs by P. yasumatsui is higher than that by A. nilaparvatae. The parasitism events of both species of egg parasitoid wasps occurred primarily from 7:00-15:00 and the parasitism amount at night accounted for less than 15% of the total amount. The results indicate that this strain of P. yasumatsui reproduced via thelytoky could be valuable for rice planthopper control.

The lipoxygenase gene OsRCI-1 is involved in the biosynthesis of herbivore-induced JAs and regulates plant defense and growth in rice

The pathway mediated by jasmonic acid (JA), biosynthesized via 13-lipoxygenases (LOX), plays a central role in both plant development and defense. In rice, there are at least fourteen 13-LOXs. Yet, only two 13-LOXs have been known to be involved in the biosynthesis of JA and plant defenses in rice. Here we cloned a chloroplast-localized 13-LOX gene from rice, OsRCI-1, whose transcripts were upregulated following infestation by brown planthopper (BPH, Nilaparvata lugens), one of the most important pests in rice. Overexpression of OsRCI-1 (oeRCI lines) increased levels of BPH-induced JA, jasmonate-isoleucine, trypsin protease inhibitors and three volatile compounds, 2-heptanone, 2-heptanol and α-thujene. BPHs showed a decreased colonization, fecundity and mass, and developed slowly on oeRCI plants compared with wild-type (WT) plants. Moreover, BPH-infested oeRCI plants were more attractive to the egg parasitoid of BPH, Anagrus nilaparvatae than equally treated WT plants. The decreased attractiveness to BPH and enhanced attractiveness to the parasitoid of oeRCI plants correlated with higher levels of BPH-induced 2-heptanone and 2-heptanol, and 2-heptanone, respectively. Compared with oeRCI plants, WT plants had higher plant height and 1000-grain weight. These results indicate that OsRCI-1 is involved in herbivore-induced JA bursts and plays a role in plant defense and growth.

AlepPBP2, but not AlepPBP3, may involve in the recognition of sex pheromones and maize volatiles in Athetis lepigone

Athetis lepigone Möschler (Lepidoptera, Noctuidae) is a common maize pest in Europe and Asia. However, there is no long-term effective management strategy is available yet to suppress its population. Adults rely heavily on olfactory cues to locate their optimal host plants and oviposition sites. Pheromone-binding proteins (PBPs) are believed to be responsible for recognizing and transporting different odorant molecules to interact with receptor membrane proteins. In this study, the ligand-binding specificities of two AlepPBPs (AlepPBP2 and AlepPBP3) for sex pheromone components and host plant (maize) volatiles were measured by fluorescence ligand-binding assay. The results demonstrated that AlepPBP2 had a high affinity with two pheromones [(Z)-7-dodecenyl acetate, Ki = 1.11 ± 0.1 μM, (Z)-9-tetradecenyl acetate, Ki = 1.32 ± 0.15 μM] and ten plant volatiles, including (-)-limonene, α-pinene, myrcene, linalool, benzaldehyde, nonanal, 2-hexanone, 3-hexanone, 2-heptanone and 6-methyl-5-hepten-2-one. In contrast, we found that none of these chemicals could bind to AlepPBP3. Our results clearly show no significant differences in the functional characterization of the binding properties between AlepPBP2 and AlepPBP3 to sex pheromones and host plant volatiles. Furthermore, molecular docking was employed for further detail on some crucial amino acid residues involved in the ligand-binding of AlepPBP2. These findings will provide valuable information about the potential protein binding sites necessary for protein-ligand interactions which appear as attractive targets for the development of novel technologies and management strategies for insect pests.

The genome of the rice planthopper egg parasitoid wasps Anagrus nilaparvatae casts light on the chemo- and mechanosensation in parasitism

BACKGROUND

Mymaridae is an ancient insect group and is a basal lineage of the superfamily Chalcidoidea. Species of Mymaridae have great potential for biological control. Anagrus nilaparvatae, a representative species of Mymaridae, is ideal for controlling rice planthopper due to its high rate of parasitism and ability to find hosts efficiently in paddy ridges and fields.

RESULTS

Using both PacBio single-molecule real-time and Illumina sequencing, we sequenced and assembled the whole genome of A. nilaparvatae, a first for the family Mymaridae. The assembly consists of 394 scaffolds, totaling 488.8 Mb. The assembly is of high continuity and completeness, indicated by the N50 value of 25.4 Mb and 98.2% mapping rate of Benchmarking Universal Single-Copy Orthologs. In total, 16,894 protein-coding genes in the genome were annotated. A phylogenomic tree constructed for A. nilaparvatae and other 12 species of Hymenoptera confirmed that the family Mymaridae is sister to all remaining chalcidoids. The divergence time between A. nilaparvatae and the other seven Chalcidoidea species was dated at ~ 126.9 Mya. Chemoreceptor and mechanoreceptor genes are important in explaining parasitic behavior. We identified 17 odorant binding proteins, 11 chemosensory proteins, four Niemann-Pick type C2 proteins, 88 olfactory receptors, 12 gustatory receptors, 22 ionotropic receptors and 13 sensory neuron membrane proteins in the genome of A. nilaparvatae, which are associated with the chemosensory functions. Strikingly, there is only one pickpocket receptors and nine transient receptor potential genes in the genome that have a mechanosensory function.

CONCLUSIONS

We obtained a high-quality genome assembly for A. nilaparvatae using PacBio single-molecule real-time sequencing, which provides phylogenomic insights for its evolutionary history. The small numbers of chemo- and mechanosensory genes in A. nilaparvatae indicate the species-specific host detection and oviposition behavior of A. nilaparvatae might be regulated by relatively simple molecular pathways.

Elevated CO2 Altered Rice VOCs Aggravate Population Occurrence of Brown Planthoppers by Improving Host Selection Ability

Simple Summary

In recent years, the atmospheric CO₂ concentration was increasing continuously, which has led to the change in the photosynthesis and chemical composition of rice plants. The growth and development of brown planthopper (BPH) Nilaparvata lugens are further affected. Plants release volatile organic compounds (VOCs) to mediate intra- and inter-specific interactions with other organisms in the surrounding environment. Therefore, here we aim to explore the effect of rice VOCs on the host selection ability of BPH under elevated CO₂. Among the identified thirty-six rice VOCs, the contents of heptadecane, linalool and limonene from rice plants were significantly decreased under elevated CO₂. Moreover, we found that the VOCs of rice damaged by BPH were also changed. Undecane, hexadecane, nonanal and 2,6-diphenylphenol from BPH-damaged rice plants under elevated CO₂ were all significantly higher than those from healthy rice plants, which might lead to enhancement of the host selection ability of BPH, eventually aggravating the damage caused by BPH. However, the role of these VOCs in host selection ability of BPH is not clear, and more experiments are needed to verify their function.

Abstract

It is predicted that plant volatile organic compounds (VOCs) are affected by the atmospheric CO₂ levels rising globally, which further affects the interaction between plants and herbivorous insects, especially the host selection behavior of herbivorous insects. In this study, the effects of elevated CO₂ on the host-selection behavior of the brown planthopper (BPH) Nilaparvata lugens, and the emission of VOCs from the healthy and BPH-damaged rice plants were studied simultaneously to make clear the population occurrence of BPH under global climate change. Compared with ambient CO₂, elevated CO₂ significantly increased the host selection percent of BPH for the healthy (CK) and BPH-damaged rice plants, and the host selection percent of BPH for the BPH-damaged rice plants was significantly higher than that for the healthy rice plants under elevated CO₂, which might be regulated by the transcription levels of OBP1, OBP2 and CSP8 in BPH due to the upregulated transcriptional levels of these three genes of BPH under elevated CO₂. In addition, we analyzed and quantified the emission of VOCs in rice plants grown under ambient CO₂ and elevated CO₂ by GS-MS. A total of 36 VOCs from rice plants were identified into eight categories, including alkanes, alkenes, alcohols, aldehydes, ketones, esters, phenols and aromatic hydrocarbons. Elevated CO₂ significantly decreased the contents of heptadecane, linalool and limonene from rice plants compared with ambient CO₂. Besides, the contents of linalool, phytol, decanal, 1-methyldecalin and 2,6-diphenylphenol from BPH-damaged rice plants under ambient CO₂, and undecane, hexadecane, nonanal and 2,6-diphenylphenol from BPH-damaged rice plants under elevated CO₂ were all significantly higher than those from healthy rice plants. The percentage composition of phenols was positively correlated with the host selection rate of BPH. Our study indicates that elevated CO₂ is beneficial to promote the host selection ability of BPH for rice plants damaged by BPHs due to the changed plant VOCs.