The Aphis gossypii is a major threat of cotton worldwide due to its short life cycle and rapid reproduction. Chemical control is the primary method used to manage the cotton aphid, which has significant environmental impacts. Therefore, prioritizing eco-friendly alternatives is essential for managing the cotton aphid. The ladybird, Hippodamia variegata, is a predominant predator of the cotton aphid. Its performance in cotton plantation is directly linked to chemical communication, where volatile compounds emitted from aphid-infested plants play important roles in successful predation. Here, we comprehensively studied the chemical interaction between the pest, natural enemy and host plants by analyzing the volatile profiles of aphid-infested cotton plants using gas chromatography-mass spectrometry (GC-MS). We then utilized the identified volatile compounds in electrophysiological recording (EAG) and behavioral assays. Through behavioral tests, we initially demonstrated the clear preference of both larvae and adults of H. variegata for aphid-infested plants. Subsequently, 13 compounds, namely α-pinene, cis-3-hexenyl acetate, 4-ethyl-1-octyn-3-ol, β-ocimene, dodecane, E-β-farnesene, decanal, methyl salicylate, β-caryophyllene, α-humulene, farnesol, DMNT, and TMTT were identified from aphid-infested plants. All these compounds were electrophysiologically active and induced detectable EAG responses in larvae and adults. Y-tube olfactometer assays indicated that, with few exceptions for larvae, all identified chemicals were attractive to H. variegata, particularly at the highest tested concentration (100 mg/ml). The outcomes of this study establish a practical foundation for developing attractants for H. variegata and open avenues for potential advancements in aphid management strategies by understanding the details of chemical communication at a tritrophic level.

Volatiles from cotton aphid (Aphis gossypii) infested plants attract the natural enemy Hippodamia variegata

(E)-β-ocimene, a ubiquitous monoterpene volatile in plants, is emitted from flowers to attract pollinators and/or from vegetative tissues as part of inducible defenses mediated by complex signaling networks when plants are attacked by insect herbivores. Wild pear species Pyrus betuleafolia used worldwide as rootstock generally displays valuable pest-resistant traits and is a promising genetic resource for pear breeding. In the current study, transcriptional changes in this wild pear species infested with a polyphagous herbivore Spodoptera litura and the underlying molecular mechanisms were fully investigated. A total of 3,118 differentially expressed genes (DEGs) were identified in damaged pear leaf samples. Spodoptera litura larvae infestation activated complex phytohormonal signaling networks in which jasmonic acid, ethylene, brassinosteroids, cytokinin, gibberellic acid and auxin pathways were induced, whereas salicylic acid and abscisic acid pathways were suppressed. All DEGs associated with growth-related photosynthesis were significantly downregulated, whereas most DEGs involved in defense-related early signaling events, transcription factors, green leaf volatiles and volatile terpenes were significantly upregulated. The PbeOCS (GWHGAAYT028729), a putative (E)-β-ocimene synthase gene, was newly identified in P. betuleafolia transcriptome. The upregulation of PbeOCS in S. litura-infested pear leaves supports a potential role for PbeOCS in herbivore-induced plant defenses. In enzyme-catalyzed reaction, recombinant PbeOCS utilized only geranyl pyrophosphate but not neryl diphosphate, farnesyl pyrophosphate or geranylgeranyl diphosphate as a substrate, producing (E)-β-ocimene as the major product and a trace amount of (Z)-β-ocimene. Moreover, as a catalytic product of PbeOCS, (E)-β-ocimene showed repellent effects on larvae of S. litura in dual-choice bioassays. What is more, (E)-β-ocimene increased mortalities of larvae in no-choice bioassays. These findings provide an overview of transcriptomic changes in wild pears in response to chewing herbivores and insights into (E)-β-ocimene biosynthesis in pear plants, which will help elucidate the molecular mechanisms underlying pear-insect interactions.

/pdf/functional-characterization-of-a-terpene-synthase-kmfynutv.pdf

Functional characterization of a terpene synthase responsible for (E)-β-ocimene biosynthesis identified in Pyrus betuleafolia transcriptome after herbivory

The tricyclic-aromadendrene-type sesquiterpenes are widely distributed and exhibit a range of biological activities, including anti-inflammatory, analgesic, antioxidant, antibacterial, insecticidal and cytotoxic properties. Several key sesquiterpene synthases (STSs) of this type have been identified, of which, viridiflorol synthase has been engineered for efficiently biosynthesizing viridiflorol in an Escherichia coli strain. This paper comprehensively summarizes the distribution and biological activity of aromadendrene-type sesquiterpenes in plant essential oils and microorganisms. The progress in aromadendrene-type sesquiterpene biosynthesis research, including the modifications of key STSs and the optimization of synthetic pathways, is reviewed. Finally, the prospects and associated challenges for the application and biosynthesis of these natural products are also discussed. 

The Recent Progress of Tricyclic Aromadendrene-Type Sesquiterpenoids: Biological Activities and Biosynthesis

The tea leafhopper (Empoasca (Matsumurasca) onukii Matsuda, 1952) is the predominant pest infesting tea and causes significant losses in yield. Plants have evolved multiple defense responses to protect themselves from insect herbivores. Camellia tetracocca, a kind of ancient tea with local popularity, is unique to southwest China. This ancient tea is often attacked by the tea leafhopper. However, there are no relevant reports on changes in volatile components and defense signaling pathways after Camellia tetracocca has been attacked by E. onukii. To reveal changes in the responses of the volatile components of C. tetracocca to E. onukii, the headspace sampling technique and GC-MS were adopted to determine and analyze the volatiles. Furthermore, to unveil the defense mechanisms of C. tetracocca in response to E. onukii, transcriptome analysis was applied to damaged tea leaves and healthy leaves. The GC-MS analysis showed significant increases in the linalool and (E)-2-hexenal contents. The transcriptome analysis revealed a set of core pest-responsive genes (3074 upregulated and 5098 downregulated). Most of the enriched pest-responsive genes are mainly involved in plant hormone signal transduction photosynthesis, terpenoid backbone biosynthesis, alpha-linolenic acid metabolism, and the NF-κB signaling pathway. A conjoint analysis of the transcriptome and metabolome indicated that N2-acetylornithine, D-malic acid, theogallin, fucosyllactose, 5-caffeoylquinic acid, fumarprotocetraric acid, and arabinogalactose have a significant correlation with LOC114279735, LOC114317534, LOC114282078, LOC114317768, and LOC114263181. This study lays a foundation for further research on the breeding and cultivation of insect-resistant germplasm resources for C. tetracocca and on the promotion and development of the plant.

HS-SPEM-GC-MS Analyses of Volatiles and Transcriptome Analysis of Camellia tetracocca in Response to Feeding by Empoasca onukii Matsuda

Abstract To investigate the molecular mechanism of the defense response of “Cabernet Sauvignon” grapes to feeding by Apolygus lucorum, high‐throughput sequencing technology was used to analyze the transcriptome of grape leaves under three different treatments: feeding by A. lucorum , puncture injury, and an untreated control. The research findings indicated that the differentially expressed genes were primarily enriched in three aspects: cellular composition, molecular function, and biological process. These genes were found to be involved in 42 metabolic pathways, particularly in plant hormone signaling metabolism, plant‐pathogen interaction, MAPK signaling pathway, and other metabolic pathways associated with plant‐induced insect resistance. Feeding by A. lucorum stimulated and upregulated a significant number of genes related to jasmonic acid and calcium ion pathways, suggesting their crucial role in the defense molecular mechanism of “Cabernet Sauvignon” grapes. The consistency between the gene expression and transcriptome sequencing results further supports these findings. This study provides a reference for the further exploration of the defense response in “Cabernet Sauvignon” grapes by elucidating the expression of relevant genes during feeding by A. lucorum .

Transcriptomic analysis of the defense response in “Cabernet Sauvignon” grape leaf induced by Apolygus lucorum feeding

When attacked by insect herbivores, plants initiate sophisticated defenses mediated by complex signaling networks and usually release a blend of functional volatiles such as terpenes against infestation. The extra-long staple cotton Gossypium barbadense cultivated worldwide as natural textile fiber crop is frequently exposed to a variety of herbivores, such as cotton bollworm Helicoverpa armigera. However, little is known about insect-induced transcriptional changes and molecular mechanisms underlying subsequent defense responses in G. barbadense. In the current study, transcriptome changes in G. barbadense infested with chewing H. armigera larvae were investigated, and we identified 5,629 differentially expressed genes (DEGs) in the infested cotton leaves compared with non-infested controls. H. armigera feeding triggered complex signaling networks in which almost all (88 out of 90) DEGs associated with the jasmonic acid (JA) pathway were upregulated, highlighting a central role for JA in the defense responses of G. barbadense against target insects. All DEGs involved in growth-related photosynthesis were downregulated, whereas most DEGs associated with defense-related transcript factors and volatile secondary metabolism were upregulated. It was noteworthy that a terpene synthase gene in the transcriptome data, GbTPS1, was strongly expressed in H. armigera-infested G. barbadense leaves. The upregulation of GbTPS1 in qPCR analysis also suggested an important role for GbTPS1 in herbivore-induced cotton defense. In vitro assays showed that recombinant GbTPS1 catalyzed farnesyl pyrophosphate and neryl diphosphate to produce three sesquiterpenes (selinene, α-gurjunene, and β-elemene) and one monoterpene (limonene), respectively. Moreover, these catalytic products of GbTPS1 were significantly elevated in G. barbadense leaves after H. armigera infestation, and elemene and limonene had repellent effects on H. armigera larvae in a dual-choice bioassay and increased larval mortality in a no-choice bioassay. These findings provide a valuable insight into understanding the transcriptional changes reprogramming herbivore-induced sesquiterpene biosynthesis in G. barbadense infested by H. armigera, which help elucidate the molecular mechanisms underlying plant defense against insect pests.

https://www.frontiersin.org/articles/10.3389/fpls.2022.898541/pdf

Characterization of a Novel Insect-Induced Sesquiterpene Synthase GbTPS1 Based on the Transcriptome of Gossypium barbadense Feeding by Cotton Bollworm

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Characterization of a Novel Insect-Induced Sesquiterpene Synthase GbTPS1 Based on the Transcriptome of Gossypium barbadense Feeding by Cotton Bollworm