How do plants sense volatiles sent by other plants?

WRKY1-Mediated Interconversion of MeSA and SA in Neighbouring Apple Plants Enhances Defence Against Powdery Mildew

Powdery mildew (PM), caused by the biotrophic fungus Podospharea leucotricha, is a major threat to apple production. Plant-plant communication (PPC) is a crucial strategy for plant communities to enhance their defence against pathogens. The interconversion of methyl salicylate (MeSA) and salicylic acid (SA) is critical for PPC regulation, but the mechanism of MeSA-mediated PPC is not fully understood. This study reveals a significant increase in SA and MeSA levels in neighbouring plants (receivers) following PM attack on emitter plants, activating defence responses in receivers. Notably, the expression of WRKY1, a previously characterized transcription factor, was upregulated in receivers, implicating its role in defence response modulation. WRKY1 was found to promote SA accumulation and enhance PM resistance in receivers. Importantly, WRKY1 positively regulates the expression of SABP2a, which catalysers MeSA to SA conversion, and negatively regulates SAMT1a, which functions in the reverse reaction. Consequently, WRKY1 facilitates the conversion of MeSA to SA in receivers, preventing its reversion and sustaining elevated SA levels. Collectively, our findings clarify the role of WRKY1 in enhancing the defence response to PM in receivers.

Structure and release function of fragrance glands

Volatile compounds serve physiological, signaling, and defensive purposes in plants and have beneficial effects on the growth, reproduction, resistance, and yield of horticultural plants. They are released through fragrance glands and become gasses by passing through the plasma membrane, cell walls that contain water, and cuticle. Transporter proteins facilitate their transport and reduce the resistance of these barriers. They also regulate the rate of release and concentration of volatiles inside and outside of the membrane. However, there has been no summary of the structure and function of the fragrance glands of horticultural plants, as well as an introduction to the latest research progress on the mechanism of the transport of volatiles. This review focuses on the structure and function of the release of aromas in horticultural plants and explores the mechanism of the release of volatiles through a transporter model. Additionally, it considers the factors that affect their release and ecological functions and suggests directions for future research.

Structural, mechanical, antioxidant and antibacterial properties of double cross-linked chitosan cryogels as hosts for thymol

The practical applications of essential oils (EOs) are limited by their hydrophobicity, volatility and instability. To overcome these drawbacks, the incorporation of EOs into porous materials is recommended. Chitosan (CS)-based composite cryogels as hosts for thymol as a volatile model terpenoid were developed using a double cross-linking of CS with glutaraldehyde (GA) and monochlorotriazinyl-β-cyclodextrin (MCT-β-CD), either in one-pot synthesis or through sequential cross-linking, first with GA and then with MCT-β-CD, resulting in CSCAV composites. Cross-linking with GA occurred under cryogelation conditions, while cross-linking with MCT-β-CD took place by heating at 60-80 °C. The composite cryogels were characterized by FTIR, 13C NMR, SEM, EDX, swelling kinetics, and uniaxial compressive tests. The mechanical, antioxidant, and antibacterial properties of composites were optimized by adjusting the concentrations of CS and GA, the initial CS to MCT-β-CD ratio, and the temperature regime. The novel CS-based biocomposites demonstrated sustained compression over 74 %, characteristic of porous materials obtained through cryogelation process. The antioxidant activity of the CSCAV composites revealed almost all composites exhibited over 85 % 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity. The thymol-loaded composites displayed strong antibacterial effectiveness (up to 100 %) towards both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria, with greater inhibition activity observed against S. aureus.

Plant volatiles-loaded core-shell micro-nano fibers to achieve efficient and sustained bisexual attraction to pests

BACKGROUND

Chemical pesticides face significant challenges regarding their efficacy and environmental impact. Plant-based food attractants have emerged as a promising green alternative for pest control. However, their field application is limited by the short duration of effectiveness, necessitating improved carrier systems for sustained release. Electrospinning is a promising technology in this field, with core-shell fibers offering superior performance in efficient loading and sustained release compared to uniaxial fibers, highlighting their potential for further development.

RESULTS

In this study, core-shell micro-nano fiber mats were prepared via coaxial electrospinning using multiple environmentally friendly polymers. These mats were firstly and successfully loaded with food attractants bisexually attractive to Loxostege sticticalis adults, including 1-octen-3-ol, trans-2-hexenal, linalool, and anethole, enabling sustained release and effective trapping. The components in the core-shell spinning solution were chemically compatible, and after spinning, the poly(3-hydroxybutyrate-co-4-hydroxybutyrate)/polycaprolactone (PHB/PCL) in the shell layer and polyethylene oxide (PEO) in the core layer formed core-shell fibers with clear boundaries. The mats achieved an average encapsulation efficiency of 78% for active ingredients, with a sustained release profile that delivered over 60% of the attractants within 80 days while mitigating early burst release. Electroantennogram and behavioral studies revealed that the mats retained electrophysiological activity for at least 90 days, effectively attracting male and female adult insects even after 75 days. Field trials demonstrated that the mats significantly outperformed commercial slow-release carriers, attracting a higher number of L. sticticalis adults. Additionally, the mats exhibited strong stress resistance, biodegradability, and environmental compatibility, effectively protecting active molecules while minimizing ecological impact.

CONCLUSIONS

The developed fiber mats provide a highly efficient, eco-friendly carrier for plant-based food attractants, offering prolonged efficacy and improved insect trapping performance. This study highlights their potential for sustainable agriculture and pest management, paving the way for greener alternatives to chemical pesticides.

The airborne herbivore-induced plant volatile indole is converted to benzoxazinoid defense compounds in maize plants

Herbivore-induced plant volatiles act as danger signals to prime defense responses in neighboring plants, yet in many cases the mechanism behind this priming is not known. Volatile signals may be recognized directly by receptors and/or converted into other active compounds. Here we investigate the metabolic fate of volatile indole, a known priming signal in maize (Zea mays), to determine if its conversion to other compounds could play a role in its priming of defenses. We identified benzoxazinoids as major products from volatile indole using heavy isotope-labeled volatile indole and Pathway of Origin Determination in Untargeted Metabolomics (PODIUM) analysis. We then used benzoxazinoid biosynthesis maize mutants to investigate their role in indole-mediated priming. Labeled volatile indole was converted into DIMBOA-glucoside in a bx2 (benzoxazinone synthesis2)-dependent manner. The bx2 mutant plants showed elevated green leaf volatile (GLV) production in response to wounding and Spodoptera frugiperda regurgitant irrespective of indole exposure. Thus, volatile indole is converted into benzoxazinoids, and part of its priming mechanism may be due to the enhanced production of these phytoanticipins. However, indole-mediated enhanced GLV production does not rely on the conversion of indole to benzoxazinoids, so indole also has other signaling functions.

Plant volatile organic compounds: Emission and perception in a changing world

Volatile organic compounds (VOCs) are produced by all kingdoms of life and play crucial roles in mediating the communication between organisms and their environment through emission and perception. Plants, in particular, produce and emit an exceptional variety of VOCs that together serve as a complex chemical language facilitating intra-plant, inter-plant, plant-animal, and plant-microbe interactions. VOC signals are perceived and decrypted by receiver plants; however, the emission, composition, distribution and effective range, as well as uptake of these infochemicals depend on temperature and atmospheric chemistry in addition to their physicochemical properties. Since both emission and perception are directly affected by ongoing climate change, research into these processes is urgently needed to develop mitigation strategies against this threat to plant communication networks. In this brief review, we highlight the recent advances about plant VOC emission and perception, emphasizing the effect of the current climate crisis on these processes. Despite some progress in understanding VOC emission and perception, significant gaps remain in elucidating their molecular mechanisms in plants.

Chemical application improves stress resilience in plants

In recent years, abiotic stresses, including droughts, floods, high temperatures, and salinity, have become increasingly frequent and severe. These stresses significantly hinder crop yields and product quality, posing substantial challenges to sustainable agriculture and global food security. Simultaneously, the rapidly growing global population exacerbates the need to enhance crop production under worsening environmental conditions. Consequently, the development of effective strategies to strengthen the resilience of crop plants against high temperatures, water scarcity, and extreme environmental conditions is critical for mitigating the impacts of abiotic stress. Plants respond to these environmental challenges by reprogramming their transcriptome and metabolome. Common strategies for developing stress-tolerant plants include screening germplasm, generating transgenic crop plants, and employing genome editing techniques. Recently, chemical treatment has emerged as a promising approach to enhance abiotic stress tolerance in crops. This technique involves the application of exogenous chemical compounds that induce molecular and physiological changes, thereby providing a protective shield against abiotic stress. Forward and reverse genetic approaches have facilitated the identification of chemicals capable of modulating plant responses to abiotic stresses. These priming agents function as epigenetic regulators, agonists, or antagonists, playing essential roles in regulating stomatal closure to conserve water, managing cellular signaling through reactive oxygen species and metabolites to sustain plant growth, and activating gluconeogenesis to enhance cellular metabolism. This review summarizes recent advancements in the field of chemical priming and explores strategies to improve stress tolerance and crop productivity, thereby contributing to the enhancement of global food security.

Structure-Function Analysis of Volatile (Z)-3-Fatty Alcohols in Tomato

Plants emit green leaf volatiles (GLVs) in response to biotic and abiotic stress. Receiver plants perceive GLVs as alarm cues resulting in activation of defensive or protective mechanisms. While this is well documented, it is not known how GLVs are perceived by receiver cells and what the structural determinants are for GLV activity. We tested whether the carbon chain length in (Z)-3-fatty alcohols with four to nine carbons and the double bonds in six-carbon alcohols contribute to bioactivity. In Solanum peruvianum suspension-cultured cells we found that (Z)-3-fatty alcohols, except (Z)-3-butenol, induce medium alkalinization and MAP kinase phosphorylation, two signaling responses often tied to the perception of molecular patterns that function in plant immunity and resistance to herbivores. In tomato (S. lycopersicum) seedlings, we found that (Z)-3-fatty alcohols induce inhibition of root growth. In both signaling and physiological responses, (Z)-3-octenol and (Z)-3-nonenol had a higher bioactivity than (Z)-3-heptenol and (Z)-3-hexenol, with (Z)-3-butenol only being active in root growth assays. Bioactivity correlated not only with chain length but also with lipophilicity of the fatty alcohols. The natural GLVs (E)-2-hexenol and the saturated 1-hexanol exhibited a higher bioactivity in pH assays than (Z)-3-hexenol, indicating that the presence and position of a double bond also contributes to bioactivity. Our results indicate that perceiving mechanisms for (Z)-3-fatty alcohols show a preference for longer chain fatty alcohols or that longer chain fatty alcohols are more accessible to receptors.

Chemical Conversations

Among living organisms, higher animals primarily use a combination of vocal and non-verbal cues for communication. In other species, however, chemical signaling holds a central role. The chemical and biological activity of the molecules produced by the organisms themselves and the existence of receptors/targeting sites that allow recognition of such molecules leads to various forms of responses by the producer and recipient organisms and is a fundamental principle of such communication. Chemical language can be used to coordinate processes within one species or between species. Chemical signals are thus information for other organisms, potentially inducing modification of their behavior. Additionally, this conversation is influenced by the external environment in which organisms are found. This review presents examples of chemical communication among microorganisms, between microorganisms and plants, and between microorganisms and animals. The mechanisms and physiological importance of this communication are described. Chemical interactions can be both cooperative and antagonistic. Microbial chemical signals usually ensure the formation of the most advantageous population phenotype or the disadvantage of a competitive species in the environment. Between microorganisms and plants, we find symbiotic (e.g., in the root system) and parasitic relationships. Similarly, mutually beneficial relationships are established between microorganisms and animals (e.g., gastrointestinal tract), but microorganisms also invade and disrupt the immune and nervous systems of animals.

Cracking the plant VOC sensing code and its practical applications

Volatile organic compounds (VOCs) are essential airborne mediators of interactions between plants. These plant-plant interactions require sophisticated VOC-sensing mechanisms that enable plants to regulate their defenses against pests. However, these interactions are not limited to specific plants or even conspecifics, and can function in very flexible interactions between plants. Sensing and responding to VOCs in plants is finely controlled by their uptake and transport systems as well as by cellular signaling via, for example, chromatin remodeling system-based transcriptional regulation for defense gene activation. Based on the accumulated knowledge about the interactions between plants and their major VOCs, companion plants and biostimulants are being developed for practical applications in agricultural and horticultural pest control, providing a sustainable alternative to harmful chemicals.

Functional Analysis of PsHMGR1 and PsTPS1 Related to Floral Terpenoids Biosynthesis in Tree Peony

Tree peony (Paeonia suffruticosa), as a popular ornamental plant worldwide, has a unique floral fragrance, and it is important in the pollination, ornamental, food, and fragrance product industries. However, the underlying molecular mechanisms for the synthesis of floral fragrance terpenoids in tree peony are not well understood, constraining their exploitation. P. suffruticosa 'Oukan' produces strong floral fragrance terpenoids with high ornamental value and excellent stress resistance and is considered a valuable model for studying tree peony floral fragrance formation. Based on transcriptome data analysis, the PsHMGR1 and PsTPS1 genes associated with floral terpene synthesis were cloned. Then, PsHMGR1 and PsTPS1 were functionally characterized by amino acid sequence analysis, multiple sequence alignment, phylogenetic tree construction, qRT-PCR, and transgenic assay. PsHMGR1 contains two transmembrane structures and a conserved HMG-CoA_reductase_class I domain, and PsTPS1 belongs to TPS-a subfamily. The qRT-PCR analysis showed that the expression levels of PsHMGR1 and PsTPS1 increased and then decreased at different flower development stages, and both were significantly higher in flowers than in roots, stems, and leaves. In addition, the linalool content in PsHMGR1 transgenic lines was significantly higher than that of WT. Germacrene D, which was not found in WT, was detected in the flowers of PsTPS1 transgenic lines. These results indicate that PsHMGR1 and PsTPS1 promote terpene synthesis in plants and provide ideas for the molecular mechanism of enhancing terpene synthesis in tree peony floral fragrance.

Test of Specificity in Signalling between Potato Plants in Response to Infection by Fusarium Solani and Phytophthora Infestans

Plant-plant signalling via volatile organic compounds (VOCs) in response to insect herbivory has been widely studied, but its occurrence and specificity in response to pathogen attack has received much less attention. To fill this gap, we carried out a greenhouse experiment using two fungal pathogens (Fusarium solani and Phytophthora infestans) to test for specificity in VOC induction and signalling between potato plants (Solanum tuberosum). We paired potato plants in plastic cages, one acting as VOC emitter and the other as receiver, and subjected emitters to one of the following treatments: no infection (control), infected by F. solani, or infected by P. infestans. We measured total emission and composition of VOCs released by emitter plants to test for pathogen-specificity in VOC induction, and then conducted a pathogen infection bioassay to assess resistance levels on receiver plants by subjecting half of the receivers of each emitter treatment to F. solani infection and the other half to P. infestans infection. This allowed us to test for specificity in plant VOC signalling by comparing its effects on conspecific and heterospecific sequential infections. Results showed that infection by neither F. solani or P. infestans produced quantitative (total emissions) or qualitative (compositional) changes in VOC emissions. Mirroring these patterns, emitter infection treatment (control vs. pathogen infection) did not produce a significant change in pathogen infection levels on receiver plants in any case (i.e., either for conspecific or heterospecific sequential infections), indicating a lack of signalling effects which precluded pathogen-based specificity in signalling. We discuss possible mechanisms for lack of pathogen effects on VOC emissions and call for future work testing for pathogen specificity in plant-plant signalling and its implications for plant-pathogen interactions under ecologically relevant scenarios involving infections by multiple pathogens.

Flowering Ocimum gratissimum intercropped in tea plantations attracts and reduces Apolygus lucorum populations

BACKGROUND

Apolygus lucorum is one of the most important piercing-sucking insect pests of the tea plant In this study, we assessed the attractiveness of basil plants to A. lucorum and the effectiveness of Ocimum gratissimum L. in the control of A. lucorum. The control efficiency of main volatile chemicals emitted from O. gratissimum flowers was also evaluated.

RESULTS

Among seven basil varieties, O. gratissimum was more attractive to A. lucorum adults and was selected as a trap plant to assess its attractiveness to A. lucorum and effects on natural enemies in tea plantations. The population density of A. lucorum on trap strips of O. gratissimum in tea plantations was significantly higher than that on tea at 10-20 m away from the trap strips. Intercropping O. gratissimum with tea plants, at high-density significantly reduced A. lucorum population levels. Eucalyptol, limonene, β-ocimene, and linalool were the four dominant components in the O. gratissimum flower volatiles, and their emissions showed a gradual upward trend over the sampling period. Olfactometer assays indicated that eucalyptol and dodecane showed attraction to A. lucorum. High numbers of A. lucorum were recorded on limonene, eucalyptol, and myrcene-baited yellow sticky traps in field trials in which 11 dominant volatiles emitted by O. gratissimum flowers were evaluated.

CONCLUSION

Our research indicated that the aromatic plant O. gratissimum and its volatiles could attract A. lucorum and planting O. gratissimum has the potential as a pest biocontrol method to manipulate A. lucorum populations in tea plantations. © 2024 Society of Chemical Industry.

Biogenic secondary organic aerosol participates in plant interactions and herbivory defense

Biogenic secondary organic aerosols (SOAs) can be formed from the oxidation of plant volatiles in the atmosphere. Herbivore-induced plant volatiles (HIPVs) can elicit plant defenses, but whether such ecological functions persist after they form SOAs was previously unknown. Here we show that Scots pine seedlings damaged by large pine weevils feeding on their roots release HIPVs that trigger defenses in neighboring conspecific plants. The biological activity persisted after HIPVs had been oxidized to form SOAs, which was indicated by receivers displaying enhanced photosynthesis, primed volatile defenses, and reduced weevil damage. The elemental composition and quantity of SOAs likely determines their biological functions. This work demonstrates that plant-derived SOAs can mediate interactions between plants, highlighting their ecological significance in ecosystems.

Functional characterization of sesquiterpene synthase in Mongolian medicine Syringa oblata in heartwood formation

Lilac (Syringa oblata) is a well-known horticultural plant, and its aromatic heartwood is widely utilized in Traditional Mongolian Medicine for treating angina. However, limited research on the dynamic changes and mechanisms of aromatic substance formation during heartwood development hinders the analysis and utilization of its medicinal components. In this study, volatile metabolome analysis revealed that sesquiterpenes are the primary metabolites responsible for the aroma in heartwood, with cadinane and eremophilane types being the most prevalent. Among the identified sesquiterpene synthases, SoSTPS1-5 exhibited significantly increased expression in heartwood formation and was selected for further investigation. Molecular docking simulations predicted multiple amino acid binding sites and confirmed its ability to catalyze the formation of eremophilane, copaene, cadinane, germacrane, and elemane-type sesquiterpenes from FPP (farnesyl pyrophosphate). Co-expression and promoter analysis suggested a transcriptional regulatory network primarily involving WRKY transcription factors. Additionally, aiotic and biotic stress inducers, such as Ag+, Fusarium oxysporum, and especially MeJA, were found to activate the expression of SoSTPS1-5 and promote sesquiterpene accumulation. This study provides insights into the basis of medicinal substance formation and the potential mechanisms of sesquiterpene accumulation in lilac heartwood, laying a foundation for future research on the biosynthesis and utilization of its medicinal components.

Strategies of plants to overcome abiotic and biotic stresses

In their environment, plants are exposed to a multitude of abiotic and biotic stresses that differ in intensity, duration and severity. As sessile organisms, they cannot escape these stresses, but instead have developed strategies to overcome them or to compensate for the consequences of stress exposure. Defence can take place at different levels and the mechanisms involved are thought to differ in efficiency across these levels. To minimise metabolic constraints and to reduce the costs of stress defence, plants prioritise first-line defence strategies in the apoplastic space, involving ascorbate, defensins and small peptides, as well as secondary metabolites, before cellular processes are affected. In addition, a large number of different symplastic mechanisms also provide efficient stress defence, including chemical antioxidants, antioxidative enzymes, secondary metabolites, defensins and other peptides as well as proteins. At both the symplastic and the apoplastic level of stress defence and compensation, a number of specialised transporters are thought to be involved in exchange across membranes that still have not been identified, and information on the regeneration of different defence compounds remains ambiguous. In addition, strategies to overcome and compensate for stress exposure operate not only at the cellular, but also at the organ and whole-plant levels, including stomatal regulation, and hypersensitive and systemic responses to prevent or reduce the spread of stress impacts within the plant. Defence can also take place at the ecosystem level by root exudation of signalling molecules and the emission of volatile organic compounds, either directly or indirectly into the rhizosphere and/or the aboveground atmosphere. The mechanisms by which plants control the production of these compounds and that mediate perception of stressful conditions are still not fully understood. Here we summarise plant defence strategies from the cellular to ecosystem level, discuss their advantages and disadvantages for plant growth and development, elucidate the current state of research on the transport and regeneration capacity of defence metabolites, and outline insufficiently explored questions for further investigation.

Nanoparticle-mediated defense priming: A review of strategies for enhancing plant resilience against biotic and abiotic stresses

Nanotechnology has emerged as a promising field with the potential to revolutionize agriculture, particularly in enhancing plant defense mechanisms. Nanoparticles (NPs) are instrumental in plant defense priming, where plants are pre-exposed to controlled levels of stress to heighten their alertness and responsiveness to subsequent stressors. This process improves overall plant performance by enabling quicker and more effective responses to secondary stimuli. This review explores the application of NPs as priming agents, utilizing their unique physicochemical properties to bolster plants' innate defense mechanisms. It discusses key findings in NP-based plant defense priming, including various NP types such as metallic, metal oxide, and carbon-based NPs. The review also investigates the intricate mechanisms by which NPs interact with plants, including uptake, translocation, and their effects on plant physiology, morphology, and molecular processes. Additionally, the review examines how NPs can enhance plant responses to a range of stressors, from pathogen attacks and herbivore infestations to environmental stresses. It also discusses NPs' ability to improve plants' tolerance to abiotic stresses like drought, salinity, and heavy metals. Safety and regulatory aspects of NP use in agriculture are thoroughly addressed, emphasizing responsible and ethical deployment for environmental and human health safety. By harnessing the potential of NPs, this approach shows promise in reducing crop losses, increasing yields, and enhancing global food security while minimizing the environmental impact of traditional agricultural practices. The review concludes by emphasizing the importance of ongoing research to optimize NP formulations, dosages, and delivery methods for practical application in diverse agricultural settings.

Plant Molecular Phenology and Climate Feedbacks Mediated by BVOCs

Climate change profoundly affects the timing of seasonal activities of organisms, known as phenology. The impact of climate change is not unidirectional; it is also influenced by plant phenology as plants modify atmospheric composition and climatic processes. One important aspect of this interaction is the emission of biogenic volatile organic compounds (BVOCs), which link the Earth's surface, atmosphere, and climate. BVOC emissions exhibit significant diurnal and seasonal variations and are therefore considered essential phenological traits. To understand the dynamic equilibrium arising from the interplay between plant phenology and climate, this review presents recent advances in comprehending the molecular mechanisms underpinning plant phenology and its interaction with climate. We provide an overview of studies investigating molecular phenology, genome-wide gene expression analyses conducted in natural environments, and how these studies revolutionize the concept of phenology, shifting it from observable traits to dynamic molecular responses driven by gene-environment interactions. We explain how this knowledge can be scaled up to encompass plant populations, regions, and even the globe by establishing connections between molecular phenology, changes in plant distribution, species composition, and climate.

Chemical diversity in angiosperms - monoterpene synthases control complex reactions that provide the precursors for ecologically and commercially important monoterpenoids

Monoterpene synthases (MTSs) catalyze the first committed step in the biosynthesis of monoterpenoids, a class of specialized metabolites with particularly high chemical diversity in angiosperms. In addition to accomplishing a rate enhancement, these enzymes manage the formation and turnover of highly reactive carbocation intermediates formed from a prenyl diphosphate substrate. At each step along the reaction path, a cationic intermediate can be subject to cyclization, migration of a proton, hydride, or alkyl group, or quenching to terminate the sequence. However, enzymatic control of ligand folding, stabilization of specific intermediates, and defined quenching chemistry can maintain the specificity for forming a signature product. This review article will discuss our current understanding of how angiosperm MTSs control the reaction environment. Such knowledge allows inferences about the origin and regulation of chemical diversity, which is pertinent for appreciating the role of monoterpenoids in plant ecology but also for aiding commercial efforts that harness the accumulation of these specialized metabolites for the food, cosmetic, and pharmaceutical industries.

Aphid alarm pheromone mimicry in transgenic Chrysanthemum morifolium: insights into the potential of (E)-β-farnesene for aphid resistance

(E)-β-Farnesene (EBF) serves as the primary component of the alarm pheromone used by most aphid pest species. Pyrethrum (Tanacetum cinerariifolium) exhibits tissue-specific regulation of EBF accumulation and release, effectively mimicking the aphid alarm signal, deterring aphid attacks while attracting aphid predators. However, cultivated chrysanthemum (Chrysanthemum morifolium), a popular and economically significant flower, is highly vulnerable to aphid infestations. In this study, we investigated the high expression of the pyrethrum EBF synthase (TcEbFS) gene promoter in the flower head and stem, particularly in the parenchyma cells. Subsequently, we introduced the TcEbFS gene, under the control of its native promoter, into cultivated chrysanthemum. This genetic modification led to increased EBF accumulation in the flower stem and young flower bud, which are the most susceptible tissues to aphid attacks. Analysis revealed that aphids feeding on transgenic chrysanthemum exhibited prolonged probing times and extended salivation durations during the phloem phase, indicating that EBF in the cortex cells hindered their host-location behavior. Interestingly, the heightened emission of EBF was only observed in transgenic chrysanthemum flowers after mechanical damage. Furthermore, we explored the potential of this transgenic chrysanthemum for aphid resistance by comparing the spatial distribution and storage of terpene volatiles in different organs and tissues of pyrethrum and chrysanthemum. This study provides valuable insights into future trials aiming for a more accurate replication of alarm pheromone release in plants. It highlights the complexities of utilizing EBF for aphid resistance in cultivated chrysanthemum and calls for further investigations to enhance our understanding of this defense mechanism.

Antennal Transcriptome Evaluation and Analysis for Odorant-Binding Proteins, Chemosensory Proteins, and Suitable Reference Genes in the Leaf Beetle Pest Diorhabda rybakowi Weise (Coleoptera: Chrysomelidae)

Diorhabda rybakowi Weise is one of the dominant pests feeding on Nitraria spp., a pioneer plant used for windbreaking and sand fixation purposes, and poses a threat to local livestock and ecosystems. To clarify the key olfactory genes of D. rybakowi and provide a theoretical basis for attractant and repellent development, the optimal reference genes under two different conditions (tissue and sex) were identified, and the bioinformatics and characterization of the tissue expression profiles of two categories of soluble olfactory proteins (OBPs and CSPs) were investigated. The results showed that the best reference genes were RPL13a and RPS18 for comparison among tissues, and RPL19 and RPS18 for comparison between sexes. Strong expressions of DrybOBP3, DrybOBP6, DrybOBP7, DrybOBP10, DrybOBP11, DrybCSP2, and DrybCSP5 were found in antennae, the most important olfactory organ for D. rybakowi. These findings not only provide a basis for further in-depth research on the olfactory molecular mechanisms of host-specialized pests but also provide a theoretical basis for the future development of new chemical attractants or repellents using volatiles to control D. rybakowi.

Methyl-salicylate (MeSA)-mediated airborne defence

Stressed plants emit a variety of chemicals into the environment, leading to increased pest resistance in neighbouring plants but the genetic and molecular mechanisms of the emissions remain obscure. Recently, Gong et al. identified novel methyl salicylate (MeSA)-mediated airborne defence that confers resistance to neighbouring plants against aphids and viruses.

Green leaf volatiles co-opt proteins involved in molecular pattern signalling in plant cells

The green leaf volatiles (GLVs) Z-3-hexen-1-ol (Z3-HOL) and Z-3-hexenyl acetate (Z3-HAC) are airborne infochemicals released from damaged plant tissues that induce defenses and developmental responses in receiver plants, but little is known about their mechanism of action. We found that Z3-HOL and Z3-HAC induce similar but distinctive physiological and signaling responses in tomato seedlings and cell cultures. In seedlings, Z3-HAC showed a stronger root growth inhibition effect than Z3-HOL. In cell cultures, the two GLVs induced distinct changes in MAP kinase (MAPK) activity and proton fluxes as well as rapid and massive changes in the phosphorylation status of proteins within 5 min. Many of these phosphoproteins are involved in reprogramming the proteome from cellular homoeostasis to stress and include pattern recognition receptors, a receptor-like cytoplasmic kinase, MAPK cascade components, calcium signaling proteins and transcriptional regulators. These are well-known components of damage-associated molecular pattern (DAMP) signaling pathways. These rapid changes in the phosphoproteome may underly the activation of defense and developmental responses to GLVs. Our data provide further evidence that GLVs function like DAMPs and indicate that GLVs coopt DAMP signaling pathways.

Plant airborne defense against insects, viruses, and beyond

Plants emit volatiles as signals to trigger broad physiological responses, including airborne defense (AD). Gong et al. (Nature 2023; 622: 139-145) recently reported the genetic framework of how plants use AD to combat aphids and viruses. The study elucidates the mutualistic relationships between aphids and the viruses they transmit, revealing the broad biological and ecological significance of AD.

Feedback regulation of plant secondary metabolism: Applications and challenges

Plant secondary metabolites offer resistance to invasion by herbivorous organisms, and are also useful in the chemical, pharmaceutical, cosmetic, and fragrance industries. There are numerous approaches to enhancing secondary metabolite yields. However, a growing number of studies has indicated that feedback regulation may be critical in regulating secondary metabolite biosynthesis. Here, we review examples of feedback regulation in secondary metabolite biosynthesis pathways, phytohormone signal transduction, and complex deposition sites associated with secondary metabolite biosynthesis. We propose a new strategy to enhance secondary metabolite production based on plant feedback regulation. We also discuss challenges in feedback regulation that must be overcome before its application to enhancing secondary metabolite yields. This review discusses recent advances in the field and highlights a strategy to overcome feedback regulation-related obstacles and obtain high secondary metabolite yields.

Chemically Mediated Plant-Plant Interactions: Allelopathy and Allelobiosis

Plant-plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant-plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant-plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant-plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant-plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root-soil interactions and plant-soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant-plant interactions.

Molecular basis of methyl-salicylate-mediated plant airborne defence

Aphids transmit viruses and are destructive crop pests1. Plants that have been attacked by aphids release volatile compounds to elicit airborne defence (AD) in neighbouring plants2-5. However, the mechanism underlying AD is unclear. Here we reveal that methyl-salicylate (MeSA), salicylic acid-binding protein-2 (SABP2), the transcription factor NAC2 and salicylic acid-carboxylmethyltransferase-1 (SAMT1) form a signalling circuit to mediate AD against aphids and viruses. Airborne MeSA is perceived and converted into salicylic acid by SABP2 in neighbouring plants. Salicylic acid then causes a signal transduction cascade to activate the NAC2-SAMT1 module for MeSA biosynthesis to induce plant anti-aphid immunity and reduce virus transmission. To counteract this, some aphid-transmitted viruses encode helicase-containing proteins to suppress AD by interacting with NAC2 to subcellularly relocalize and destabilize NAC2. As a consequence, plants become less repellent to aphids, and more suitable for aphid survival, infestation and viral transmission. Our findings uncover the mechanistic basis of AD and an aphid-virus co-evolutionary mutualism, demonstrating AD as a potential bioinspired strategy to control aphids and viruses.

Fungal volatile organic compounds: mechanisms involved in their sensing and dynamic communication with plants

Microbial volatile organic compounds (MVOCs) are mixtures of gas-phase hydrophobic carbon-based molecules produced by microorganisms such as bacteria and fungi. They can act as airborne signals sensed by plants being crucial players in triggering signaling cascades influencing their secondary metabolism, development, and growth. The role of fungal volatile organic compounds (FVOCs) from beneficial or detrimental species to influence the physiology and priming effect of plants has been well studied. However, the plants mechanisms to discern between FVOCs from friend or foe remains significantly understudied. Under this outlook, we present an overview of the VOCs produced by plant-associate fungal species, with a particular focus on the challenges faced in VOCs research: i) understanding how plants could perceive FVOCs, ii) investigating the differential responses of plants to VOCs from beneficial or detrimental fungal strains, and finally, iii) exploring practical aspects related to the collection of VOCs and their eco-friendly application in agriculture.

Jasmonates Coordinate Secondary with Primary Metabolism

Jasmonates (JAs), including jasmonic acid (JA), its precursor 12-oxo-phytodienoic acid (OPDA) and its derivatives jasmonoyl-isoleucine (JA-Ile), methyl jasmonate (MeJA), cis-jasmone (CJ) and other oxylipins, are important in the regulation of a range of ecological interactions of plants with their abiotic and particularly their biotic environments. Plant secondary/specialized metabolites play critical roles in implementing these ecological functions of JAs. Pathway and transcriptional regulation analyses have established a central role of JA-Ile-mediated core signaling in promoting the biosynthesis of a great diversity of secondary metabolites. Here, we summarized the advances in JAs-induced secondary metabolites, particularly in secondary metabolites induced by OPDA and volatile organic compounds (VOCs) induced by CJ through signaling independent of JA-Ile. The roles of JAs in integrating and coordinating the primary and secondary metabolism, thereby orchestrating plant growth-defense tradeoffs, were highlighted and discussed. Finally, we provided perspectives on the improvement of the adaptability and resilience of plants to changing environments and the production of valuable phytochemicals by exploiting JAs-regulated secondary metabolites.

Immature leaves are the dominant volatile-sensing organs of maize

Plants perceive herbivory-induced volatiles and respond to them by upregulating their defenses. To date, the organs responsible for volatile perception remain poorly described. Here, we show that responsiveness to the herbivory-induced green leaf volatile (Z)-3-hexenyl acetate (HAC) in terms of volatile emission, transcriptional regulation, and jasmonate defense hormone activation is largely constrained to younger maize leaves. Older leaves are much less sensitive to HAC. In a given leaf, responsiveness to HAC is high at immature developmental stages and drops off rapidly during maturation. Responsiveness to the non-volatile elicitor ZmPep3 shows an opposite pattern, demonstrating that this form of hyposmia (i.e., decreased sense of smell) is not due to a general defect in jasmonate defense signaling in mature leaves. Neither stomatal conductance nor leaf cuticle composition explains the unresponsiveness of older leaves to HAC, suggesting perception mechanisms upstream of jasmonate signaling as driving factors. Finally, we show that hyposmia in older leaves is not restricted to HAC and extends to the full blend of herbivory-induced volatiles. In conclusion, our work identifies immature maize leaves as dominant stress volatile-sensing organs. The tight spatiotemporal control of volatile perception may facilitate within plant defense signaling to protect young leaves and may allow plants with complex architectures to explore the dynamic odor landscapes at the outer periphery of their shoots.

Identification and characterization of TMV-induced volatile signals in Nicotiana benthamiana: evidence for JA/ET defense pathway priming in congeneric neighbors via airborne (E)-2-octenal

Plants release a mixture of volatile compounds when subjects to environmental stress, allowing them to transmit information to neighboring plants. Here, we find that Nicotiana benthamiana plants infected with tobacco mosaic virus (TMV) induces defense responses in neighboring congeners. Analytical screening of volatiles from N. benthamiana at 7 days post inoculation (dpi) using an optimized SPME-GC-MS method showed that TMV triggers the release of several volatiles, such as (E)-2-octenal, 6-methyl-5-hepten-2-one, and geranylacetone. Exposure to (E)-2-octenal enhances the resistance of N. benthamiana plants to TMV and triggers the immune system with upregulation of pathogenesis-related genes, such as NbPR1a, NbPR1b, NbPR2, and NbNPR1, which are related to TMV resistance. Furthermore, (E)-2-octenal upregulates jasmonic acid (JA) that levels up to 400-fold in recipient N. benthamiana plants and significantly affects the expression pattern of key genes in the JA/ET signaling pathway, such as NbMYC2, NbERF1, and NbPDF1.2, while the salicylic acid (SA) level is not significantly affected. Our results show for the first time that the volatile (E)-2-octenal primes the JA/ET pathway and then activates immune responses, ultimately leading to enhanced TMV resistance in adjacent N. benthamiana plants. These findings provide new insights into the role of airborne compounds in virus-induced interplant interactions.

Aroma profiling of Shine Muscat grape provides detailed insights into the regulatory effect of gibberellic acid and N-(2-chloro-4-pyridinyl)-N-phenylurea applications on aroma quality

As plant growth regulators, gibberellic acid (GA₃) and CPPU [forchlorfenuron, N-(2-chloro-4-pyridinyl)-N-phenylurea] are widely used in the production of table grapes. However, how these compounds regulate the aroma quality remains unclear. By measuring free and bound aroma compounds in Shine Muscat grapes from eight groups during whole growth period, GA₃ and CPPU were both found to significantly promote the synthesis of acyclic monoterpenes and (E)-2-hexenal, and double applications were found to further increase the aroma compound contents. On the other hand, GA₃ and CPPU obviously promoted the expansion of berries, and the effect of promoting the synthesis of aroma compounds was largely diminished. In conclusion, free compound concentrations in berry were almost unaffected by GA₃ and CPPU. From the perspective of aroma compounds, a highly concerted interplay was observed for terpenes, and bound compounds exhibited higher correlations than those of free compounds. In addition, 17 compounds could be used as markers that indicated the developmental timing of berries.

Volatile-mediated plant-plant communication and higher-level ecological dynamics

Volatile organic compounds (VOCs) in general and herbivory-induced plant volatiles (HIPVs) in particular are increasingly understood as major mediators of information transfer between plant tissues. Recent findings have moved the field of plant communication closer to a detailed understanding of how plants emit and perceive VOCs and seem to converge on a model that juxtaposes perception and emission mechanisms. These new mechanistic insights help to explain how plants can integrate different types of information and how environmental noise can affect the transmission of information. At the same time, ever-new functions of VOC-mediated plant-plant interactions are being revealed. Chemical information transfer between plants is now known to fundamentally affect plant organismal interactions and, additionally, population, community, and ecosystem dynamics. One of the most exciting new developments places plant-plant interactions along a behavioral continuum with an eavesdropping strategy at one end and mutually beneficial information-sharing among plants within a population at the other. Most importantly and based on recent findings as well as theoretical models, plant populations can be predicted to evolve different communication strategies depending on their interaction environment. We use recent studies from ecological model systems to illustrate this context dependency of plant communication. Moreover, we review recent key findings about the mechanisms and functions of HIPV-mediated information transfer and suggest conceptual links, such as to information theory and behavioral game theory, as valuable tools for a deeper understanding of how plant-plant communication affects ecological and evolutionary dynamics.

(-)-Loliolide is a general signal of plant stress that activates jasmonate-related responses

The production of defensive metabolites in plants can be induced by signaling chemicals released by neighboring plants. Induction is mainly known from volatile aboveground signals, with belowground signals and their underlying mechanisms largely unknown. We demonstrate that (-)-loliolide triggers defensive metabolite responses to competitors, herbivores, and pathogens in seven plant species. We further explore the transcriptional responses of defensive pathways to verify the signaling role of (-)-loliolide in wheat and rice models with well-known defensive metabolites and gene systems. In response to biotic and abiotic stressors, (-)-loliolide is produced and secreted by roots. This, in turn, induces the production of defensive compounds including phenolic acids, flavonoids, terpenoids, alkaloids, benzoxazinoids, and cyanogenic glycosides, regardless of plant species. (-)-Loliolide also triggers the expression of defense-related genes, accompanied by an increase in the concentration of jasmonic acid and hydrogen peroxide (H₂ O₂ ). Transcriptome profiling and inhibitor incubation indicate that (-)-loliolide-induced defense responses are regulated through pathways mediated by jasmonic acid, H₂ O₂ , and Ca ²⁺ . These findings argue that (-)-loliolide functions as a common belowground signal mediating chemical defense in plants. Such perception-dependent plant chemical defenses will yield critical insights into belowground signaling interactions.

Dynamic environmental interactions shaped by vegetative plant volatiles

Covering: up to November 2022Plants shape terrestrial ecosystems through physical and chemical interactions. Plant-derived volatile organic compounds in particular influence the behavior and performance of other organisms. In this review, we discuss how vegetative plant volatiles derived from leaves, stems and roots are produced and released into the environment, how their production and release is modified by abiotic and biotic factors, and how they influence other organisms. Vegetative plant volatiles are derived from different biosynthesis and degradation pathways and are released via distinct routes. Both biosynthesis and release are regulated by other organisms as well as abiotic factors. In turn, vegetative plant volatiles modify the physiology and the behavior of a wide range of organisms, from microbes to mammals. Several concepts and frameworks can help to explain and predict the evolution and ecology of vegetative plant volatile emission patterns of specific pathways: multifunctionality of specialized metabolites, chemical communication displays and the information arms race, and volatile physiochemistry. We discuss how these frameworks can be leveraged to understand the evolution and expression patterns of vegetative plant volatiles. The multifaceted roles of vegetative plant volatiles provide fertile grounds to understand ecosystem dynamics and harness their power for sustainable agriculture.

Biosynthesis and the Transcriptional Regulation of Terpenoids in Tea Plants (Camellia sinensis)

Terpenes, especially volatile terpenes, are important components of tea aroma due to their unique scents. They are also widely used in the cosmetic and medical industries. In addition, terpene emission can be induced by herbivory, wounding, light, low temperature, and other stress conditions, leading to plant defense responses and plant-plant interactions. The transcriptional levels of important core genes (including HMGR, DXS, and TPS) involved in terpenoid biosynthesis are up- or downregulated by the MYB, MYC, NAC, ERF, WRKY, and bHLH transcription factors. These regulators can bind to corresponding cis-elements in the promoter regions of the corresponding genes, and some of them interact with other transcription factors to form a complex. Recently, several key terpene synthesis genes and important transcription factors involved in terpene biosynthesis have been isolated and functionally identified from tea plants. In this work, we focus on the research progress on the transcriptional regulation of terpenes in tea plants (Camellia sinensis) and thoroughly detail the biosynthesis of terpene compounds, the terpene biosynthesis-related genes, the transcription factors involved in terpene biosynthesis, and their importance. Furthermore, we review the potential strategies used in studying the specific transcriptional regulation functions of candidate transcription factors that have been discriminated to date.

Aphid-repellent, ladybug-attraction activities, and binding mechanism of methyl salicylate derivatives containing geraniol moiety

BACKGROUND

Aphids have been mainly controlled by traditional chemical insecticides, resulting in unamiable risk to the environment over the last decades. Push-pull strategy is regarded as a promising eco-friendly approach for aphid management through repelling aphid away and attracting their natural enemy. Methyl salicylate (MeSA), one of typical HIPVs (herbivore-induced plant volatiles), can repel aphids and attract ladybugs. Our previous studies discovered a new lead compound 3e, a salicylate-substituted carboxyl (E)-β-farnesene derivative that had effective aphid-repellent activity. However, whether 3e has attractive activity to ladybug like MeSA is unknown. Meanwhile, to discover a new derivative for both deterring aphid and recruiting ladybug is meaningful for green control of aphids.

RESULTS

Through the structural optimization of 3e, 14 new derivatives were designed and synthesized. Among them, compounds 4e and 4i had good aphid (Acyrthosiphon pisum) repellent activity, and compounds 3e, 4e and 4i had significant ladybug (Harmonia axyridis) attractive activity to males. Particularly, 4i exhibited manifest attractive effect on the females as well. Binding mechanism showed that 4i not only bound effectively with the aphid (Acyrthosiphon pisum) target ApisOBP9 thanks to its multiple hydrophobic interactions and hydrogen-bond, but also had strong binding affinity with ladybug target HaxyOBP15 due to the suitable steric space. Additionally, 4i displayed low toxicity to bee Apis mellifera.

CONCLUSION

Compound 3e does exhibit attractive activity to male ladybug as MeSA. However, the new derivative 4i, with both pleasant aphid-repellent and ladybug-attraction activities, can be considered as a novel potential push-pull candidate for aphid control in sustainable agriculture. © 2022 Society of Chemical Industry.

Perspectives in Plant Abiotic Stress Signaling

State-of-the-art collections of strategies, approaches, and methods are immediately useful for ongoing characterizations or for novel discoveries in the scientific field of plant abiotic stress signaling. It must however be kept in mind that, in the future, these strategies, approaches, and methods will be facing a number of increasingly complex issues. The development of the necessary confrontation of laboratory-based knowledge on abiotic stress signaling mechanisms with real-life in natura situations of plant-stress interactions involves at least five levels of complexity: (i) plant biodiversity, (ii) the spatio-temporal heterogeneity of stress-related parameters, (iii) the unknowns of future stress-related constraints, (iv) the influence of biotic interactions, (v) the crosstalk between various signaling pathways and their final integration into physiological responses. These complexities are major bottlenecks for assessing the evolutionary, ecological, and agronomical relevance of abiotic stress signaling studies. All of the presently-described strategies, approaches, and methods will have to be gradually complemented with the development of real-time and in natura tools, with systematic application of mathematical modeling to complex interactions and with further research on the impact of stress memory mechanisms on long-term responses.

Emission of cyanobacterial volatile organic compounds and their roles in blooms

Cyanobacteria are photosynthetic prokaryotes and one of dominant species in eutrophicated waters, which easily burst blooms in summer with high irradiance and temperature conditions. In response to high irradiance, high temperature, and nutrient conditions, cyanobacteria release abundant of volatile organic compounds (VOCs) by up-regulating related gene expression and oxidatively degrading β-carotene. These VOCs not only increase offensive odor in waters, but also transfer allelopathic signals to algae and aquatic plants, resulting in cyanobacteria dominating eutrophicated waters. Among these VOCs, β-cyclocitral, α-ionone, β-ionone, limonene, longifolene, and eucalyptol have been identified as the main allelopathic agents, which even directly kill algae by inducing programmed cell death (PCD). The VOCs released from cyanobacteria, especially the ruptured cells, exhibit repelling effects on the herbivores, which is beneficial to survival of the population. Cyanobacterial VOCs might transfer aggregating information among homogeneous species, so the acceptors initiate aggregation to resist the coming stresses. It can be speculated that the adverse conditions can promote VOC emission from cyanobacteria, which play important roles in cyanobacteria dominating eutrophicated waters and even bursting blooms.

Exploring plant volatile-mediated interactions between native and introduced plants and insects

In invasion scenarios, native and introduced species co-occur creating new interactions and modifying existing ones. Many plant–plant and plant–insect interactions are mediated by volatile organic compounds (VOCs), however, these have seldom been studied in an invasion context. To fill this knowledge gap, we explored some interactions mediated by VOCs between native and introduced plants and insects in a New Zealand system. We investigated whether a native plant, Leptospermum scoparium (mānuka), changes its volatile profile when grown adjacent to two European introduced plants, Calluna vulgaris (heather) and Cytisus scoparius (Scotch broom), in a semi-field trial using potted plants without above- or below-ground physical contact. We also investigated the influence of plant cues on the host-searching behaviour of two beetles, the native Pyronota festiva (mānuka beetle), and the introduced biocontrol agent Lochmaea suturalis (heather beetle), by offering them their host-plant and non-host volatiles versus clean air, and their combination in a Y-tube olfactometer. As a follow-up, we performed preference/feeding tests in Petri dishes with fresh plant material. Results of the semi-field experiment show a significant reduction in green leaf volatiles, sesquiterpenes and total volatile emissions by mānuka plants neighbouring heather. In the Y-tube assays, the native beetle P. festiva performed poorly in discriminating between host and non-host plants based on plant volatile cues only. However, it performed relatively well in the Petri dish tests, where other cues (i.e., visual, gustatory or tactile) were present. In contrast, the introduced beetle L. suturalis showed high host-specificity in both Y-tube and Petri dish assays. This study illustrates the importance of VOCs in mediating interactions between introduced and native species, suggesting that invasive plants can disrupt native plants’ communication and affect the host-searching behaviour of native insects. It also reinforces the relevance of regular host testing on introduced weed biocontrol agents to avoid unwanted host shifts or host-range expansion.

Volatile uptake, transport, perception, and signaling shape a plant's nose

Herbivore-induced plant volatiles regulate defenses in undamaged neighboring plants. Understanding the mechanisms by which plant volatiles are taken up, perceived, and translated into canonical defense signaling pathways is an important frontier of knowledge. Volatiles can enter plants through stomata and the cuticle. They are likely perceived by membrane-associated receptors as well as intracellular receptors. The latter likely involves metabolization and transport across cell membranes by volatile transporters. Translation of volatiles into defense priming and induction typically involves mitogen-activated protein kinases (MAPKs), WRKY transcription factors, and jasmonates. We propose that the broad range of molecular processes involved in volatile signaling will likely result in substantial spatiotemporal and ontogenetic variation in plant responsiveness to volatiles, with important consequences for plant–environment interactions.

CML8 and GAD4 function in (Z)-3-hexenol-mediated defense by regulating γ-aminobutyric acid accumulation in Arabidopsis

(Z)-3-hexenol, a small gaseous molecule, is produced in plants under biotic stress and induces defense responses in neighboring plants. However, little is known about how (Z)-3-hexenol induces plant defense-related signaling. In this study, we uncovered how (Z)-3-hexenol treatment enhances plant resistance to insect attacks by increasing γ-aminobutyric acid (GABA) contents in Arabidopsis leaves. First, (Z)-3-hexenol increases the intracellular content of calcium as secondary messenger in Arabidopsis leaf mesophyll cells. Both intracellular and extracellular calcium stores regulate changes in calcium content. Then, CML8 and GAD4 transmit calcium signaling to affect (Z)-3-hexenol induced GABA content and plant resistance. Herein, CML8 interaction with GAD4 was examined via yeast two-hybrid assays, firefly luciferase complementation imaging, and GST pull-down assays. These results indicate that (Z)-3-hexenol treatment increased the GABA contents in Arabidopsis leaves based on CML8 and GAD4, thus increasing plant resistance to the insect Plutella xylostella. This study revealed the mechanism of activating plant insect defense induced by (Z)-3-hexenol, which guides the study of volatiles as biological pest control.

Essential Oils as Multicomponent Mixtures and Their Potential for Human Health and Well-Being

Essential oils (EOs) and their individual volatile organic constituents have been an inherent part of our civilization for thousands of years. They are widely used as fragrances in perfumes and cosmetics and contribute to a healthy diet, but also act as active ingredients of pharmaceutical products. Their antibacterial, antiviral, and anti-inflammatory properties have qualified EOs early on for both, the causal and symptomatic therapy of a number of diseases, but also for prevention. Obtained from natural, mostly plant materials, EOs constitute a typical example of a multicomponent mixture (more than one constituent substances, MOCS) with up to several hundreds of individual compounds, which in a sophisticated composition make up the property of a particular complete EO. The integrative use of EOs as MOCS will play a major role in human and veterinary medicine now and in the future and is already widely used in some cases, e.g., in aromatherapy for the treatment of psychosomatic complaints, for inhalation in the treatment of respiratory diseases, or topically administered to manage adverse skin diseases. The diversity of molecules with different functionalities exhibits a broad range of multiple physical and chemical properties, which are the base of their multi-target activity as opposed to single isolated compounds. Whether and how such a broad-spectrum effect is reflected in natural mixtures and which kind of pharmacological potential they provide will be considered in the context of ONE Health in more detail in this review.

Linalool Activates Oxidative and Calcium Burst and CAM3-ACA8 Participates in Calcium Recovery in Arabidopsis Leaves

Plants produce linalool to respond to biotic stress, but the linalool-induced early signal remains unclear. In wild-type Arabidopsis, plant resistance to diamondback moth (Plutella xylostella) increased more strongly in a linalool-treated group than in an untreated control group. H₂O₂ and Ca²⁺, two important early signals that participated in biotic stress, burst after being treated with linalool in Arabidopsis mesophyll cells. Linalool treatment increased H₂O₂ and intracellular calcium concentrations in mesophyll cells, observed using a confocal microscope with laser scanning, and H₂O₂ signaling functions upstream of Ca²⁺ signaling by using inhibitors and mutants. Ca²⁺ efflux was detected using non-invasive micro-test technology (NMT), and Ca²⁺ efflux was also inhibited by NADPH oxidase inhibitor DPI (diphenyleneiodonium chloride) and in cells of the NADPH oxidase mutant rbohd. To restore intracellular calcium levels, Ca²⁺-ATPase was activated, and calmodulin 3 (CAM3) participated in Ca²⁺-ATPase activation. This result is consistent with the interaction between CAM7 and Ca²⁺-ATPase isoform 8 (ACA8). In addition, a yeast two-hybrid assay, firefly luciferase complementation imaging assay, and an in vitro pulldown assay showed that CAM3 interacts with the N-terminus of ACA8, and qRT-PCR showed that some JA-related genes and defense genes expressions were enhanced when treated with linalool in Arabidopsis leaves. This study reveals that linalool enhances H₂O₂ and intracellular calcium concentrations in Arabidopsis mesophyll cells; CAM3-ACA8 reduces intracellular calcium concentrations, allowing cells to resume their resting state. Additionally, JA-related genes and defense genes' expression may enhance plants' defense when treated with linalool.