Role of early signalling events in plant-insect interactions

Oviposition-induced plant volatiles prime defences against impending herbivores in neighbouring non-damaged plants

Plants exploit environmental cues about the risks of encountering insect herbivores, often sensitising defensive responses. While herbivore-induced plant volatiles (HIPVs) are reported to enhance plant defences against incoming herbivores, responses to oviposition-induced plant volatiles (OIPVs) are massively under-explored. We studied whether OIPV emissions from Brassica napus enhance defences in non-damaged neighbouring B. napus when subsequently infested with Pieris brassicae larvae. We collected and analysed the emission rates of plant volatile organic compounds under different treatments and measured P. brassicae larvae biomass as a proxy for defence. We show that oviposition triggers the release of specific volatiles, i.e. α-pinene, dimethyl-trisulfide, and limonene, potentially serving as herbivore early warning cues for neighbouring non-damaged plants. Initially, after three days of herbivory, OIPV-receivers emitted lower levels of volatiles compared to control receivers; however, following seven days of herbivory, both control and OIPV-receivers emitted similar amounts of volatiles. We suggest a potential trade-off between direct and indirect defences, with sensitised plants investing metabolic resources initially towards direct and later enhancing indirect defences. We show that OIPVs mediate plant-plant communication, a natural potential for Brassicaceae crop protection.

Spider mite tetranins elicit different defense responses in different host habitats

Spider mites (Tetranychus urticae) are a major threat to economically important crops. Here, we investigated the potential of tetranins, in particular Tet3 and Tet4, as T. urticae protein-type elicitors that stimulate plant defense. Truncated Tet3 and Tet4 proteins showed efficacy in activating the defense gene pathogenesis-related 1 (PR1) and inducing phytohormone production in leaves of Phaseolus vulgaris. In particular, Tet3 caused a drastically higher Ca2+ influx in leaves, but a lower reactive oxygen species (ROS) generation compared to other tetranins, whereas Tet4 caused a low Ca2+ influx and a high ROS generation in the host plants. Such specific and non-specific elicitor activities were examined by knockdown of Tet3 and Tet4 expressions in mites, confirming their respective activities and in particular showing that they function additively or synergistically to induce defense responses. Of great interest is the fact that Tet3 and Tet4 expression levels were higher in mites on their preferred host, P. vulgaris, compared to the levels in mites on the less-preferred host, Cucumis sativus, whereas Tet1 and Tet2 were constitutively expressed regardless of their host. Furthermore, mites that had been hosted on C. sativus induced lower levels of PR1 expression, Ca2+ influx and ROS generation, i.e., Tet3- and Tet4-responsive defense responses, in both P. vulgaris and C. sativus leaves compared to the levels induced by mites that had been hosted on P. vulgaris. Taken together, these findings show that selected tetranins respond to variable host cues that may optimize herbivore fitness by altering the anti-mite response of the host plant.

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

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

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.

Volatiles of the Predator Xylocoris flavipes Recognized by Its Prey Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (Linne) as Escape Signals

The olfactory sensory system plays vital roles in daily activities, such as locating mate partners, foraging, and risk avoidance. Natural enemies can locate their prey through characteristic volatiles. However, little is known about whether prey can recognize the volatiles of their predators and if this recognition can increase the efficiency of prey escaping from predators. Xylocoris flavipes is a predator of Tribolium castaneum (Herbst) and Oryzaephilus surinamensis (Linne) that has been widely used in stored pest control. Herein, we analyze the volatile components of Xylocoris flavipes and their impacts on the olfactory behavior of T. castaneum and O. surinamensis. We found that T. castaneum and O. surinamensis preferred blank air rather than odors of X. flavipes and X. flavipes emissions, which significantly decreased the orientation preference of T. castaneum and O. surinamensis to wheat. X. flavipes emits three major volatiles, including linalool, α-terpineol, and geraniol. Y-tube bioassays showed that T. castaneum and O. surinamensis can recognize linalool and geraniol at certain concentrations, especially at 200 μg/mL. EAG recordings verified that linalool and geraniol elicit higher olfactory responses in the two pests, but very small EAG responses were observed in the insects to α-terpineol. A further repellency evaluation also proved that linalool and geraniol are repellent to the two pests, and this repellency can be slightly enhanced by mixing them together. T. castaneum and O. surinamensis can recognize the predator X. flavipes by perceiving its volatiles and using them as signals for escaping. The two most potent volatiles, linalool and geraniol, may have potential values as repellents in controlling pests in these two stored products.

Glutathione Involvement in Potato Response to French Marigold Volatile Organic Compounds

To elucidate the involvement of glutathione in the mitigation of induced oxidative changes and the sequestration of perceived volatiles in cells, we exposed potato plants to French marigold essential oil. The formation of short-lived radicals, the determination of scavenging activity towards ascorbyl and DPPH radicals, and the assessment of the potato plants' overall intra/extracellular reduction status were performed using electron paramagnetic resonance spectroscopy (EPR). The results showed the presence of hydroxyl radicals in potatoes, with significantly reduced accumulation in exposed plants compared to the control group after 8 h. However, the kinetics of EPR signal intensity change for the pyrrolidine spin probe (3CP) in these plants showed very low reducing potential, suggesting that the antioxidant system acts lethargically and/or the probe has been reoxidized. Total glutathione and its reduced/oxidized form ratio, determined spectrophotometrically, showed that the exposed plants initially had lower glutathione levels with diminutive, reduced form compared to the control. Still, after 8 h, both characteristics were similar to those of the control. RT-qPCR analysis revealed that the volatiles altered the expression of glutathione metabolism-involved genes, especially that of glutathione-S-transferase, after 8 h. Glutathione metabolism was affected by volatiles in the initial response of potato plants exposed to French marigold essential oil, and glutathione molecules were involved in the mitigation of induced oxidative burst.

Molecular Interactions Between Plants and Aphids: Recent Advances and Future Perspectives

Aphids are small, notorious insect pests that negatively impact plant health and agricultural productivity through direct damage, such as sap-sucking, and indirectly as vectors of plant viruses. Plants respond to aphid feeding with a variety of molecular mechanisms to mitigate damage. These responses are diverse and highly dynamic, functioning either independently or in combination. Understanding plant-aphid interactions is crucial for revealing the full range of plant defenses against aphids. When aphids infest, plants detect the damage via specific receptor proteins, initiating a signaling cascade that activates defense mechanisms. These defenses include a complex interaction of phytohormones that trigger defense pathways, secondary metabolites that deter aphid feeding and reproduction, lectins and protease inhibitors that disrupt aphid physiology, and elicitors that activate further defense responses. Meanwhile, aphids counteract plant defenses with salivary effectors and proteins that suppress plant defenses, aiding in their successful colonization. This review offers a detailed overview of the molecular mechanisms involved in plant-aphid interactions, emphasizing both established and emerging plant defense strategies. Its uniqueness lies in synthesizing the recent progress made in plant defense responses to aphids, along with aphids' countermeasures to evade such defenses. By consolidating current knowledge, this review provides key insights for developing sustainable strategies to achieve crop protection and minimize dependence on chemical pesticides.

Scavenging H2O2 of plant host by saliva catalase of leafhopper vector benefits viral transmission

Catalase (CAT) is the main reactive oxygen species (ROS)-scavenging enzyme in plants and insects. However, it remains elusive whether and how insect saliva CAT suppresses ROS-mediated plant defense, thereby promoting initial virus transmission by insect vectors. Here, we investigated how leafhopper Recilia dorsalis catalase (RdCAT) was secreted from insect salivary glands into rice phloem, and how it was perceived by rice chaperone NO CATALASE ACTIVITY1 (OsNCA1) to scavenge excessive H2O2 during insect-to-plant virus transmission. We found that the interaction of OsNCA1 with RdCAT activated its enzymatic activity to decompose H2O2 in rice plants during leafhopper feeding. However, initial insect feeding did not significantly change rice CATs transcripts. Knockout of OsNCA1 in transgenic lines decreased leafhopper feeding-activated CAT activity and caused higher H2O2 accumulation. A devastating rice reovirus activated RdCAT expression and promoted the cosecretion of virions and RdCAT into leafhopper salivary cavities and ultimately into the phloem. Virus-mediated increase of RdCAT secretion suppressed excessive H2O2, thereby promoting host attractiveness to insect vectors and initial virus transmission. Our findings provide insights into how insect saliva CAT is secreted and perceived by plant chaperones to suppress the early H2O2 burst during insect feeding, thereby facilitating viral transmission.

Pine Response to Sawfly Pheromones: Effects on Sawfly's Oviposition and Larval Growth

Insect pheromones have been intensively studied with respect to their role in insect communication. However, scarce knowledge is available on the impact of pheromones on plant responses, and how these in turn affect herbivorous insects. A previous study showed that exposure of pine (Pinus sylvestris) to the sex pheromones of the pine sawfly Diprion pini results in enhanced defenses against the eggs of this sawfly; the egg survival rate on pheromone-exposed pine needles was lower than that on unexposed pine. The long-lasting common evolutionary history of D. pini and P. sylvestris suggests that D. pini has developed counter-adaptations to these pine responses. Here, we investigated by behavioral assays how D. pini copes with the defenses of pheromone-exposed pine. The sawfly females did not discriminate between the odor of pheromone-exposed and unexposed pine. However, when they had the chance to contact the trees, more unexposed than pheromone-exposed trees received eggs. The exposure of pine to the pheromones did not affect the performance of larvae and their pupation success. Our findings indicate that the effects that responses of pine to D. pini sex pheromones exert on the sawfly eggs and sawfly oviposition behavior do not extend to effects on the larvae.

Facilitation of Sclerotinia sclerotiorum infestation by aphid feeding behaviour is not affected by aphid resistance in oilseed rape

The relation between aphids and Sclerotinia stem rot (SSR) in oilseed rape is rarely examined because they are often studied alone. We have observed a significant correlation between the number of aphids and the occurrence of SSR in our field studies. Electropenetrography (EPG) was used to evaluate the effects of Brevicoryne brassicae (Linnaeus) on two oilseed rape cultivars while acquiring, vectoring and inoculating of Sclerotinia sclerotiorum Lib. (de Bary) ascospores. The results demonstrated that aphid feeding followed by the application of an ascospore suspension significantly increased S. sclerotiorum incidence. Aphids were capable of adhering to ascospores and carrying them to healthy plants, thereby causing diseases. The results of the EPG analysis indicated that aphid feeding behaviour was significantly altered in all leaf tissue levels following infection with S. sclerotiorum. Aphids initiated their first puncture significantly sooner than the control group, began probing mesophyll cells earlier, significantly increased the frequency of both short probes and intracellular punctures and had a significantly shorter pathway duration. On infected aphid-susceptible cultivars, aphids secreted more saliva but had reduced ingestion compared with aphids feeding on non-infected oilseed rape. In addition, ascospores can affect aphid feeding behaviour by adhering to aphids. Aphids carrying ascospores punctured cells earlier, with a significant increase in the frequency and duration of short probes and cell punctures, shortened pathway durations, increased salivation and reduced ingestion compared with aphids not carrying ascospores. On aphid-susceptible cultivars, aphids carrying ascospores delayed puncture onset, but on resistant cultivars, puncture onset was shortened. There is a correlation between aphids and S. sclerotiorum. The impact of S. sclerotiorum on aphid feeding behaviour is directional, favouring the spread of the fungus. This promotion does not appear to be altered by the aphid resistance of the cultivar.

Ethylene: A Modulator of the Phytohormone-Mediated Insect Herbivory Network in Plants

Plants have evolved to establish insect herbivory defences by modulating their metabolism, growth, and development. Precise networks of phytohormones are essential to induce those herbivory defences. Gaseous phytohormone ET plays an important role in forming herbivory defences. Its role in insect herbivory is not fully understood, but previous studies have shown that it can both positively and negatively regulate herbivory. This review presents recent findings on crosstalk between ET and other phytohormones in herbivory responses. Additionally, the use of exogenous ETH treatment to induce ET in response to herbivory is discussed.

Genetic underpinnings of arthropod community distributions in Populus trichocarpa

Community genetics seeks to understand the mechanisms by which natural genetic variation in heritable host phenotypes can encompass assemblages of organisms such as bacteria, fungi, and many animals including arthropods. Prior studies that focused on plant genotypes have been unable to identify genes controlling community composition, a necessary step to predict ecosystem structure and function as underlying genes shift within plant populations. We surveyed arthropods within an association population of Populus trichocarpa in three common gardens to discover plant genes that contributed to arthropod community composition. We analyzed our surveys with traditional single-trait genome-wide association analysis (GWAS), multitrait GWAS, and functional networks built from a diverse set of plant phenotypes. Plant genotype was influential in structuring arthropod community composition among several garden sites. Candidate genes important for higher level organization of arthropod communities had broadly applicable functions, such as terpenoid biosynthesis and production of dsRNA binding proteins and protein kinases, which may be capable of targeting multiple arthropod species. We have demonstrated the ability to detect, in an uncontrolled environment, individual genes that are associated with the community assemblage of arthropods on a host plant, further enhancing our understanding of genetic mechanisms that impact ecosystem structure.

The MYC2-PUB22-JAZ4 module plays a crucial role in jasmonate signaling in tomato

Jasmonates (JAs), a class of lipid-derived stress hormones, play a crucial role across an array of plant physiological processes and stress responses. Although JA signaling is thought to rely predominantly on the degradation of specific JAZ proteins by SCFCOI1, it remains unclear whether other pathways are involved in the regulation of JAZ protein stability. Here, we report that PUB22, a plant U-box type E3 ubiquitin ligase, plays a critical role in the regulation of plant resistance against Helicoverpa armigera and other JA responses in tomato. Whereas COI1 physically interacts with JAZ1/2/5/7, PUB22 physically interacts with JAZ1/3/4/6. PUB22 ubiquitinates JAZ4 to promote its degradation via the 26S proteasome pathway. Importantly, we observed that pub22 mutants showreduced resistance to H. armigera, whereas jaz4 single mutants and jaz1 jaz3 jaz4 jaz6 quadruple mutants have enhanced resistance. The hypersensitivity of pub22 mutants to herbivores could be partially rescued by JAZ4 mutation. Moreover, we found that expression of PUB22 can be transcriptionally activated by MYC2, thus forming a positive feedback circuit in JA signaling. We noticed that the PUB22-JAZ4 module also regulates other JA responses, including defense against B. cinerea, inhibition of root elongation, and anthocyanin accumulation. Taken together, these results indicate that PUB22 plays a crucial role in plant growth and defense responses, together with COI1-regulated JA signaling, by targeting specific JAZs.

Contrasting plant transcriptome responses between a pierce-sucking and a chewing herbivore go beyond the infestation site

BACKGROUND

Plants have acquired a repertoire of mechanisms to combat biotic stressors, which may vary depending on the feeding strategies of herbivores and the plant species. Hormonal regulation crucially modulates this malleable defense response. Jasmonic acid (JA) and salicylic acid (SA) stand out as pivotal regulators of defense, while other hormones like abscisic acid (ABA), ethylene (ET), gibberellic acid (GA) or auxin also play a role in modulating plant-pest interactions. The plant defense response has been described to elicit effects in distal tissues, whereby aboveground herbivory can influence belowground response, and vice versa. This impact on distal tissues may be contingent upon the feeding guild, even affecting both the recovery of infested tissues and those that have not suffered active infestation.

RESULTS

To study how phytophagous with distinct feeding strategies may differently trigger the plant defense response during and after infestation in both infested and distal tissues, Arabidopsis thaliana L. rosettes were infested separately with the chewing herbivore Pieris brassicae L. and the piercing-sucker Tetranychus urticae Koch. Moderate infestation conditions were selected for both pests, though no quantitative control of damage levels was carried out. Feeding mode did distinctly influence the transcriptomic response of the plant under these conditions. Though overall affected processes were similar under either infestation, their magnitude differed significantly. Plants infested with P. brassicae exhibited a short-term response, involving stress-related genes, JA and ABA regulation and suppressing growth-related genes. In contrast, T. urticae elicited a longer transcriptomic response in plants, albeit with a lower degree of differential expression, in particular influencing SA regulation. These distinct defense responses transcended beyond infestation and through the roots, where hormonal response, flavonoid regulation or cell wall reorganization were differentially affected.

CONCLUSION

These outcomes confirm that the existent divergent transcriptomic responses elicited by herbivores employing distinct feeding strategies possess the capacity to extend beyond infestation and even affect tissues that have not been directly infested. This remarks the importance of considering the entire plant's response to localized biotic stresses.

The WRKY46-MYC2 module plays a critical role in E-2-hexenal-induced anti-herbivore responses by promoting flavonoid accumulation

Volatile organic compounds (VOCs) play key roles in plant-plant communication, especially in response to pest attack. E-2-hexenal is an important component of VOCs, but it is unclear whether it can induce endogenous plant resistance to insects. Here, we show that E-2-hexenal activates early signaling events in Arabidopsis (Arabidopsis thaliana) mesophyll cells, including an H2O2 burst at the plasma membrane, the directed flow of calcium ions, and an increase in cytosolic calcium concentration. Treatment of wild-type Arabidopsis plants with E-2-hexenal increases their resistance when challenged with the diamondback moth Plutella xylostella L., and this phenomenon is largely lost in the wrky46 mutant. Mechanistically, E-2-hexenal induces the expression of WRKY46 and MYC2, and the physical interaction of their encoded proteins was verified by yeast two-hybrid, firefly luciferase complementation imaging, and in vitro pull-down assays. The WRKY46-MYC2 complex directly binds to the promoter of RBOHD to promote its expression, as demonstrated by luciferase reporter, yeast one-hybrid, chromatin immunoprecipitation, and electrophoretic mobility shift assays. This module also positively regulates the expression of E-2-hexenal-induced naringenin biosynthesis genes (TT4 and CHIL) and the accumulation of total flavonoids, thereby modulating plant tolerance to insects. Together, our results highlight an important role for the WRKY46-MYC2 module in the E-2-hexenal-induced defense response of Arabidopsis, providing new insights into the mechanisms by which VOCs trigger plant defense responses.

Electrical signalling and plant response to herbivory: A short review

For a long time, electrical signaling was neglected at the expense of signaling studies in plants being concentrated with chemical and hydraulic signals. Studies conducted in recent years have revealed that plants are capable of emitting, processing, and transmitting bioelectrical signals to regulate a wide variety of physiological functions. Many important biological and physiological phenomena are accompanied by these cellular electrical manifestations, which supports the hypothesis about the importance of bioelectricity as a fundamental 'model' for response the stresses environmental and for activities regeneration of these organisms. Electrical signals have also been characterized and discriminated against in genetically modified plants under stress mediated by sucking insects and/or by the application of systemic insecticides. Such results can guide future studies that aim to elucidate the factors involved in the processes of resistance to stress and plant defense, thus aiding in the development of successful strategies in integrated pest management. Therefore, this mini review includes the results of studies aimed at electrical signaling in response to biotic stress. We also demonstrated how the generation and propagation of electrical signals takes place and included a description of how these electrical potentials are measured.

Defense Strategies of Rice in Response to the Attack of the Herbivorous Insect, Chilo suppressalis

Chilo suppressalis is a notorious pest that attacks rice, feeding throughout the entire growth period of rice and posing a serious threat to rice production worldwide. Due to the boring behavior and overlapping generations of C. suppressalis, the pest is difficult to control. Moreover, no rice variety with high resistance to the striped stem borer (SSB) has been found in the available rice germplasm, which also poses a challenge to controlling the SSB. At present, chemical control is widely used in agricultural production to manage the problem, but its effect is limited and it also pollutes the environment. Therefore, developing genetic resistance is the only way to avoid the use of chemical insecticides. This article primarily focuses on the research status of the induced defense of rice against the SSB from the perspective of immunity, in which plant hormones (such as jasmonic acid and ethylene) and mitogen-activated protein kinases (MAPKs) play an important role in the immune response of rice to the SSB. The article also reviews progress in using transgenic technology to study the relationship between rice and the SSB as well as exploring the resistance genes. Lastly, the article discusses prospects for future research on rice's resistance to the SSB.

Exploring the Application and Prospects of Synthetic Biology in Engineered Living Materials

At the intersection of synthetic biology and materials science, engineered living materials (ELMs) exhibit unprecedented potential. Possessing unique "living" attributes, ELMs represent a significant paradigm shift in material design, showcasing self-organization, self-repair, adaptability, and evolvability, surpassing conventional synthetic materials. This review focuses on reviewing the applications of ELMs derived from bacteria, fungi, and plants in environmental remediation, eco-friendly architecture, and sustainable energy. The review provides a comprehensive overview of the latest research progress and emerging design strategies for ELMs in various application fields from the perspectives of synthetic biology and materials science. In addition, the review provides valuable references for the design of novel ELMs, extending the potential applications of future ELMs. The investigation into the synergistic application possibilities amongst different species of ELMs offers beneficial reference information for researchers and practitioners in this field. Finally, future trends and development challenges of synthetic biology for ELMs in the coming years are discussed in detail.

Repeated mechanical damage enhanced Aquilaria sinensis resistance to Heortia vitessoides through jasmonic acid

Introduction

The leaf-chewing pest Heortia vitessoides severely threatens the growth and development of Aquilaria sinensis. In our previous study, we found that mechanical damage (MD) to stem enhanced A. sinensis sapling resistance to H. vitessoides larvae.

Methods

To reveal the defense mechanisms underlying this observation, we analyzed the types and contents of volatile organic compounds (VOCs), phytohormone contents, and expression of phytohormone-related genes in response to MD and herbivory wounding(HW).

Results

Here, we identified several VOCs, such as the pesticides fenobucarb and 2,4-di-tert-butylphenol, in mature leaf (ML) of MD-treated plants. Compared with salicylic acid (SA) or the ethylene (ET) pathway, jasmonic acid (JA) content and JA-related genes were more strongly upregulated. Interestingly, we found a dramatic difference between JA-related upstream and downstream genes expression in YL and ML, which confirmed that JA-Ile accumulation in MD-ML and HW-ML could be derived from local damaged site.

Discussion

Taken together, we provide evidence that the JA pathway plays a dominant role in the A. sinensis response to MD and HW.

Monocot crop-aphid interactions: plant resilience and aphid adaptation

Globally, aphids cause immense economic damage to several crop plants. In addition, aphids vector several plant viral diseases that accelerate crop yield losses. While feeding, aphids release saliva that contains effectors, which modulate plant defense responses. Although there are many studies that describe the mechanisms that contribute to dicot plant-aphid interactions, our understanding of monocot crop defense mechanisms against aphids is limited. In this review, we focus on the interactions between monocot crops and aphids and report the recently characterized aphid effectors and their functions in aphid adaptation to plant immunity. Recent studies on plant defense against aphids in monocot-resistant and -tolerant crop lines have exploited various 'omic' approaches to understand the roles of early signaling molecules, phytohormones, and secondary metabolites in plant response to aphid herbivory. Unraveling key regulatory mechanisms underlying monocot crop resistance to aphids will lead to deeper understanding of sap-feeding insect management strategies for increased food security and sustainable agriculture.

Glutamate receptor like channels: Emerging players in calcium mediated signaling in plants

Glutamate receptors like channels (GLRs) are ligand gated non-selective cation channels and are multigenic in nature. They are homologs of mammalian ionic glutamate receptors (iGLRs) that play an important role in neurotransmission. It has been more than 25 years of discovery of plant GLRs, since then, significant progress has been made to unravel their structure and function in plants. Recently, the first crystal structure of plant GLR has been resolved that suggests that, though, plant GLRs contain the conserved signature domains of iGLRs, their unique features enable agonist/antagonist-dependent change in their activity. GLRs exhibit diverse subcellular localization and undergo dynamic expression variation in response to developmental and environmental stress conditions in plants. The combined use of genetic, electrophysiology and calcium imaging using different genetically encoded calcium indicators has revealed that GLRs are involved in generating calcium (Ca²⁺) influx across the plasma membrane and are involved in shaping the Ca²⁺ signature in response to different developmental and environmental stimuli. These findings indicate that GLRs influence cytosolic Ca²⁺ dynamics, thus, highlighting "GLR-Ca²⁺-crosstalk (GCC)" in developmental and stress-responsive signaling pathways. With this background, the present review summarises the recent developments pertaining to GLR function, in the broader context of regulation of stress tolerance in plants.

Bacterial Volatiles (mVOC) Emitted by the Phytopathogen Erwinia amylovora Promote Arabidopsis thaliana Growth and Oxidative Stress

Phytopathogens are well known for their devastating activity that causes worldwide significant crop losses. However, their exploitation for crop welfare is relatively unknown. Here, we show that the microbial volatile organic compound (mVOC) profile of the bacterial phytopathogen, Erwinia amylovora, enhances Arabidopsis thaliana shoot and root growth. GC-MS head-space analyses revealed the presence of typical microbial volatiles, including 1-nonanol and 1-dodecanol. E. amylovora mVOCs triggered early signaling events including plasma transmembrane potential Vm depolarization, cytosolic Ca2+ fluctuation, K+-gated channel activity, and reactive oxygen species (ROS) and nitric oxide (NO) burst from few minutes to 16 h upon exposure. These early events were followed by the modulation of the expression of genes involved in plant growth and defense responses and responsive to phytohormones, including abscisic acid, gibberellin, and auxin (including the efflux carriers PIN1 and PIN3). When tested, synthetic 1-nonanol and 1-dodecanol induced root growth and modulated genes coding for ROS. Our results show that E. amylovora mVOCs affect A. thaliana growth through a cascade of early and late signaling events that involve phytohormones and ROS.

Integrative biology of injury in animals

Mechanical injury is a prevalent challenge in the lives of animals with myriad potential consequences for organisms, including reduced fitness and death. Research on animal injury has focused on many aspects, including the frequency and severity of wounding in wild populations, the short- and long-term consequences of injury at different biological scales, and the variation in the response to injury within or among individuals, species, ontogenies, and environmental contexts. However, relevant research is scattered across diverse biological subdisciplines, and the study of the effects of injury has lacked synthesis and coherence. Furthermore, the depth of knowledge across injury biology is highly uneven in terms of scope and taxonomic coverage: much injury research is biomedical in focus, using mammalian model systems and investigating cellular and molecular processes, while research at organismal and higher scales, research that is explicitly comparative, and research on invertebrate and non-mammalian vertebrate species is less common and often less well integrated into the core body of knowledge about injury. The current state of injury research presents an opportunity to unify conceptually work focusing on a range of relevant questions, to synthesize progress to date, and to identify fruitful avenues for future research. The central aim of this review is to synthesize research concerning the broad range of effects of mechanical injury in animals. We organize reviewed work by four broad and loosely defined levels of biological organization: molecular and cellular effects, physiological and organismal effects, behavioural effects, and ecological and evolutionary effects of injury. Throughout, we highlight the diversity of injury consequences within and among taxonomic groups while emphasizing the gaps in taxonomic coverage, causal understanding, and biological endpoints considered. We additionally discuss the importance of integrating knowledge within and across biological levels, including how initial, localized responses to injury can lead to long-term consequences at the scale of the individual animal and beyond. We also suggest important avenues for future injury biology research, including distinguishing better between related yet distinct injury phenomena, expanding the subjects of injury research to include a greater variety of species, and testing how intrinsic and extrinsic conditions affect the scope and sensitivity of injury responses. It is our hope that this review will not only strengthen understanding of animal injury but will contribute to building a foundation for a more cohesive field of 'injury biology'.

Genome-wide analysis of the CML gene family and its response to melatonin in common bean (Phaseolus vulgaris L.)

Calmodulin-like proteins (CML) are important calcium signal transduction proteins in plants. CML genes have been analyzed in several plants. However, little information on CML in Phaseolus vulgare is available. In this study, we identified 111 PvCMLs distributed on eleven chromosomes. Phylogenetic analysis classified them into seven subfamilies. Cis-acting element prediction showed that PvCML contained elements related to growth and development, response to abiotic stress and hormones. Moreover, the majority of PvCMLs showed different expression patterns in most of the nine tissues and developmental stages which indicated the role of PvCML in the growth and development of common bean. Additionally, the common bean was treated with melatonin by seed soaking, and root transcriptome at the 5th day and qRT-PCR of different tissue at several stages were performed to reveal the response of PvCML to the hormone. Interestingly, 9 PvCML genes of subfamily VI were detected responsive to exogenous melatonin, and the expression dynamics of nine melatonin response PvCML genes after seed soaking with melatonin were revealed. Finally, the protein interaction network analysis of nine melatonin responsive PvCMLs was constructed. The systematic analysis of the PvCML gene family provides theoretical support for the further elucidation of their functions, and melatonin response molecular mechanism of the CML family in P. vulgaris.

Plagiodera versicolora feeding induces systemic and sexually differential defense responses in poplars

Dioecious plants have evolved effective defense strategies to deal with various biotic and abiotic stresses. However, little is known regarding sexual differences in their defense against herbivores. In this study, we investigated the mechanism of systemic defense responses in male and female Populus cathayana attacked by Plagiodera versicolora Laicharting. The results revealed that P. cathayana exhibits sexually differential responses to a defoliator. The percentage of damaged leaf area was greater in males than in females. Furthermore, the observed saccharide changes imply that males and females exhibit different response times to defoliators. The contents of flavonoids and anthocyanins were significantly increased in both sexes but were higher in females. Specifically, the jasmonic acid (JA) pathway plays an important role. Expression of pest-related genes further revealed that hormones induce changes in downstream genes and metabolites, and upregulation of JA ZIM-domain (JAZ) and CORONATINE INSENSITIVE 1 (COI1) was more significant in females. In the undamaged adjacent leaves, metabolite and gene changes displayed similar patterns to the damaged local leaves, but levels of JA, JAZ1, and COI1 were higher in females. Therefore, our data confirmed that plants initiate the JA pathway to defend against herbivores, that there is systematic signal transduction, and that this ability is stronger in females than in males. This study provides new insights into the resistance of dioecious plants to herbivory and adds a new theoretical basis for the systemic signal transduction of plants in response to biotic stress.

Calcium Signaling in Plant-Insect Interactions

In plant-insect interactions, calcium (Ca²⁺) variations are among the earliest events associated with the plant perception of biotic stress. Upon herbivory, Ca²⁺ waves travel long distances to transmit and convert the local signal to a systemic defense program. Reactive oxygen species (ROS), Ca²⁺ and electrical signaling are interlinked to form a network supporting rapid signal transmission, whereas the Ca²⁺ message is decoded and relayed by Ca²⁺-binding proteins (including calmodulin, Ca²⁺-dependent protein kinases, annexins and calcineurin B-like proteins). Monitoring the generation of Ca²⁺ signals at the whole plant or cell level and their long-distance propagation during biotic interactions requires innovative imaging techniques based on sensitive sensors and using genetically encoded indicators. This review summarizes the recent advances in Ca²⁺ signaling upon herbivory and reviews the most recent Ca²⁺ imaging techniques and methods.

Rapid systemic responses to herbivory

Rapid systemic signals travel within the first seconds and minutes after herbivore infestation to mount defense responses in distal tissues. Recent studies have revealed that wound-induced hydraulic pressure changes play an important role in systemic electrical signaling and subsequent calcium and reactive oxygen species waves. These insights raise new questions about signal specificity, the role of insect feeding guild and feeding style and the impact on longer term plant defenses. Here, we integrate the current molecular understanding of wound-induced rapid systemic signaling in the framework of insect-plant interactions.

Plant Responses to Herbivory, Wounding, and Infection

Plants have various self-defense mechanisms against biotic attacks, involving both physical and chemical barriers. Physical barriers include spines, trichomes, and cuticle layers, whereas chemical barriers include secondary metabolites (SMs) and volatile organic compounds (VOCs). Complex interactions between plants and herbivores occur. Plant responses to insect herbivory begin with the perception of physical stimuli, chemical compounds (orally secreted by insects and herbivore-induced VOCs) during feeding. Plant cell membranes then generate ion fluxes that create differences in plasma membrane potential (Vm), which provokes the initiation of signal transduction, the activation of various hormones (e.g., jasmonic acid, salicylic acid, and ethylene), and the release of VOCs and SMs. This review of recent studies of plant–herbivore–infection interactions focuses on early and late plant responses, including physical barriers, signal transduction, SM production as well as epigenetic regulation, and phytohormone responses.

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.

Effector-mediated plant-virus-vector interactions

Hemipterans (such as aphids, whiteflies, and leafhoppers) are some of the most devastating insect pests due to the numerous plant pathogens they transmit as vectors, which are primarily viral. Over the past decade, tremendous progress has been made in broadening our understanding of plant-virus-vector interactions, yet on the molecular level, viruses and vectors have typically been studied in isolation of each other until recently. From that work, it is clear that both hemipteran vectors and viruses use effectors to manipulate host physiology and successfully colonize a plant and that co-evolutionary dynamics have resulted in effective host immune responses, as well as diverse mechanisms of counterattack by both challengers. In this review, we focus on advances in effector-mediated plant-virus-vector interactions and the underlying mechanisms. We propose that molecular synergisms in vector-virus interactions occur in cases where both the virus and vector benefit from the interaction (mutualism). To support this view, we show that mutualisms are common in virus-vector interactions and that virus and vector effectors target conserved mechanisms of plant immunity, including plant transcription factors, and plant protein degradation pathways. Finally, we outline ways to identify true effector synergisms in the future and propose future research directions concerning the roles effectors play in plant-virus-vector interactions.

Volatile-mediated plant-plant interactions: volatile organic compounds as modulators of receiver plant defence, growth, and reproduction

It is firmly established that plants respond to biotic and abiotic stimuli by emitting volatile organic compounds (VOCs). These VOCs provide information on the physiological status of the emitter plant and are available for detection by the whole community. In the context of plant-plant interactions, research has focused mostly on the defence-related responses of receiver plants. However, responses may span hormone signalling and both primary and secondary metabolism, and ultimately affect plant fitness. Here we present a synthesis of plant-plant interactions, focusing on the effects of VOC exposure on receiver plants. An overview of the important chemical cues, the uptake and conversion of VOCs, and the adsorption of VOCs to plant surfaces is presented. This is followed by a review of the substantial VOC-induced changes to receiver plants affecting both primary and secondary metabolism and influencing plant growth and reproduction. Further research should consider whole-plant responses for the effective evaluation of the mechanisms and fitness consequences of exposure of the receiver plant to VOCs.

Characterized constituents of insect herbivore oral secretions and their influence on the regulation of plant defenses

For more than 350 million years, there have been ongoing dynamic interactions between plants and insects. In several cases, insects cause-specific feeding damage with ensuing herbivore-associated molecular patterns that invoke characteristic defense responses. During feeding on plant tissue, insects release oral secretions (OSs) containing a repertoire of molecules affecting plant defense (effectors). Some of these OS components might elicit a defense response to combat insect attacks (elicitors), while some might curb the plant defenses (suppressors). Few reports suggest that the synthesis and function of OS components might depend on the host plant and associated microorganisms. We review these intricate plant-insect interactions, during which there is a continuous exchange of molecules between plants and feeding insects along with the associated microorganisms. We further provide a list of commonly identified inducible plant produced defensive molecules released upon insect attack as well as in response to OS treatments of the plants. Thus, we describe how plants specialized and defense-related metabolism is modulated at innumerable phases by OS during plant-insect interactions. A molecular understanding of these complex interactions will provide a means to design eco-friendly crop protection strategies.

RNA-Seq and Electrical Penetration Graph Revealed the Role of Grh1-Mediated Activation of Defense Mechanisms towards Green Rice Leafhopper (Nephotettix cincticeps Uhler) Resistance in Rice (Oryza sativa L.)

The green rice leafhopper (GRH, Nephotettix cincticeps Uhler) is one of the most important insect pests causing serious damage to rice production and yield loss in East Asia. Prior to performing RNA-Seq analysis, we conducted an electrical penetration graph (EPG) test to investigate the feeding behavior of GRH on Ilpum (recurrent parent, GRH-susceptible cultivar), a near-isogenic line (NIL carrying Grh1) compared to the Grh1 donor parent (Shingwang). Then, we conducted a transcriptome-wide analysis of GRH-responsive genes in Ilpum and NIL, which was followed by the validation of RNA-Seq data by qPCR. On the one hand, EPG results showed differential feeding behaviors of GRH between Ilpum and NIL. The phloem-like feeding pattern was detected in Ilpum, whereas the EPG test indicated a xylem-like feeding habit of GRH on NIL. In addition, we observed a high death rate of GRH on NIL (92%) compared to Ilpum (28%) 72 h post infestation, attributed to GRH failure to suck the phloem sap of NIL. On the other hand, RNA-Seq data revealed that Ilpum and NIL GRH-treated plants generated 1,766,347 and 3,676,765 counts per million mapped (CPM) reads, respectively. The alignment of reads indicated that more than 75% of reads were mapped to the reference genome, and 8859 genes and 15,815,400 transcripts were obtained. Of this number, 3424 differentially expressed genes (DEGs, 1605 upregulated in Ilpum and downregulated in NIL; 1819 genes upregulated in NIL and downregulated in Ilpum) were identified. According to the quantile normalization of the fragments per kilobase of transcript per million mapped reads (FPKM) values, followed by the Student’s t-test (p < 0.05), we identified 3283 DEGs in Ilpum (1935 upregulated and 1348 downregulated) and 2599 DEGs in NIL (1621 upregulated and 978 downregulated) with at least a log₂ (logarithm base 2) twofold change (Log₂FC ≥2) in the expression level upon GRH infestation. Upregulated genes in NIL exceeded by 13.3% those recorded in Ilpum. The majority of genes associated with the metabolism of carbohydrates, amino acids, lipids, nucleotides, the activity of coenzymes, the action of phytohormones, protein modification, homeostasis, the transport of solutes, and the uptake of nutrients, among others, were abundantly upregulated in NIL (carrying Grh1). However, a high number of upregulated genes involved in photosynthesis, cellular respiration, secondary metabolism, redox homeostasis, protein biosynthesis, protein translocation, and external stimuli response related genes were found in Ilpum. Therefore, all data suggest that Grh1-mediated resistance against GRH in rice would involve a transcriptome-wide reprogramming, resulting in the activation of bZIP, MYB, NAC, bHLH, WRKY, and GRAS transcription factors, coupled with the induction of the pathogen-pattern triggered immunity (PTI), systemic acquired resistance (SAR), symbiotic signaling pathway, and the activation of genes associated with the response mechanisms against viruses. This comprehensive transcriptome profile of GRH-responsive genes gives new insights into the molecular response mechanisms underlying GRH (insect pest)–rice (plant) interaction.

Seed priming with calcium chloride enhances wheat resistance against wheat aphid Schizaphis graminum Rondani

BACKGROUND

Calcium is an essential macronutrient for plant growth. Although it has been shown that exogenous Ca application can increase plant resistance to abiotic stress, little is known about its potential to enhance plant tolerance to biotic stress. Here, we investigated whether pretreatment of wheat (Triticum aestivum L.) seeds with calcium chloride (CaCl₂ ) improves plant resistance against wheat aphid (Schizaphis graminum Rondani). The developmental time, population size, feeding behavior of aphids on plants grown from CaCl₂ - and water-pretreated seeds, and plant defense responses to aphid attack were investigated.

RESULTS

Seed pretreatment with CaCl₂ extended aphid development time and reduced aphid population size and feeding efficiency. In addition, the pretreatment significantly increased the concentration of Ca²⁺ in wheat leaves, and upregulated expression levels of TaCaM genes and callose synthase genes (TaGSL2, TaGSL8, TaGSL10, TaGSL12, TaGSL19, TaGSL22 and TaGSL23). Callose concentration in the leaves of plants grown from CaCl₂ -pretreated seeds increased significantly upon aphid attack. Further, callose deposition was observed mainly in the phloem.

CONCLUSION

These results suggest that seed pretreatment with CaCl₂ primes the plant response against wheat aphid attack, leading to modulation of callose deposition in the phloem in response to aphid attack. © 2021 Society of Chemical Industry.

Deciphering the Role of Ion Channels in Early Defense Signaling against Herbivorous Insects

Plants and insect herbivores are in a relentless battle to outwit each other. Plants have evolved various strategies to detect herbivores and mount an effective defense system against them. These defenses include physical and structural barriers such as spines, trichomes, cuticle, or chemical compounds, including secondary metabolites such as phenolics and terpenes. Plants perceive herbivory by both mechanical and chemical means. Mechanical sensing can occur through the perception of insect biting, piercing, or chewing, while chemical signaling occurs through the perception of various herbivore-derived compounds such as oral secretions (OS) or regurgitant, insect excreta (frass), or oviposition fluids. Interestingly, ion channels or transporters are the first responders for the perception of these mechanical and chemical cues. These transmembrane pore proteins can play an important role in plant defense through the induction of early signaling components such as plasma transmembrane potential (V_m) fluctuation, intracellular calcium (Ca²⁺), and reactive oxygen species (ROS) generation, followed by defense gene expression, and, ultimately, plant defense responses. In recent years, studies on early plant defense signaling in response to herbivory have been gaining momentum with the application of genetically encoded GFP-based sensors for real-time monitoring of early signaling events and genetic tools to manipulate ion channels involved in plant-herbivore interactions. In this review, we provide an update on recent developments and advances on early signaling events in plant-herbivore interactions, with an emphasis on the role of ion channels in early plant defense signaling.

Exposure to (Z)-11-hexadecenal [(Z)-11-16:Ald] increases Brassica nigra susceptibility to subsequent herbivory

It is well established that plants emit, detect and respond to volatile organic compounds; however, knowledge on the ability of plants to detect and respond to volatiles emitted by non-plant organisms is limited. Recent studies indicated that plants detect insect-emitted volatiles that induce defence responses; however, the mechanisms underlying this detection and defence priming is unknown. Therefore, we explored if exposure to a main component of Plutella xylostella female sex pheromone namely (Z)-11-hexadecenal [(Z)-11-16:Ald] induced detectable early and late stage defence-related plant responses in Brassica nigra. Exposure to biologically relevant levels of vapourised (Z)-11-16:Ald released from a loaded septum induced a change in volatile emissions of receiver plants after herbivore attack and increased the leaf area consumed by P. xylostella larvae. Further experiments examining the effects of the (Z)-11-16:Ald on several stages of plant defence-related responses showed that exposure to 100 ppm of (Z)-11-16:Ald in liquid state induced depolarisation of the transmembrane potential (Vm), an increase in cytosolic calcium concentration [Ca²⁺]_cyt, production of H₂O₂ and an increase in expression of reactive oxygen species (ROS)-mediated genes and ROS-scavenging enzyme activity. The results suggest that exposure to volatile (Z)-11-16:Ald increases the susceptibility of B. nigra to subsequent herbivory. This unexpected finding, suggest alternative ecological effects of detecting insect pheromone to those reported earlier. Experiments conducted in vitro showed that high doses of (Z)-11-16:Ald induced defence-related responses, but further experiments should assess how specific the response is to this particular aldehyde.

Current progress of PM-localized protein functions in jasmonate pathway

Jasmonate (JA), a class of lipid-derived phytohormone, regulates diverse developmental processes and responses to abiotic or biotic stresses. The biosynthesis and signaling of JA mainly occur in various organelles, except for the plasma membrane (PM). Recently, several PM proteins have been reported to be associated with the JA pathway. This mini-review summarized the recent progress on the functional role of PM-localized proteins involved in JA transportation, JA-related defense responses, and JA-regulated endocytosis.

Plant electrical signals: A multidisciplinary challenge

Plant electrical signals, an early event in the plant-stimulus interaction, rapidly transmit information generated by the stimulus to other organs, and even the whole plant, to promote the corresponding response and trigger a regulatory cascade. In recent years, many promising state-of-the-art technologies applicable to study plant electrophysiology have emerged. Research focused on expression of genes associated with electrical signals has also proliferated. We propose that it is appropriate for plant electrical signals to be considered in the form of a "plant electrophysiological phenotype". This review synthesizes research on plant electrical signals from a novel, interdisciplinary perspective, which is needed to improve the efficient aggregation and use of plant electrical signal data and to expedite interpretation of plant electrical signals.

Insects-plants-pathogens: Toxicity, dependence and defense dynamics

In a natural ecosystem, the pathogen-plant-insect relationship has diverse implications for each other. The pathogens as well as insect-pests consume plant tissues as their feed that mostly results in damage. In turn, plant species have evolved specialized defense system to not only protect themselves but reduce the damage also. Such tripartite interactions involve toxicity, metabolic modulations, resistance etc. among all participants of interaction. These attributes result in selection pressure among participants. Coevolution of such traits reveals need to focus and unravel multiple hidden aspects of insect-plant-pathogen interactions. The definite modulations during plant responses to biotic stress and the operating defense network against herbivores are vital to research areas. Different types of plant pathogens and herbivores are tackled with various changes in plants, e.g. changes in genes expression, glucosinolate metabolism detoxification, signal transduction, cell wall modifications, Ca²⁺dependent signaling. It is essential to clarify which chemical in plants can work as a defense signal or weapon in plant-pathogen-herbivore interactions. In spite of increased knowledge regarding signal transduction pathways regulating growth-defense balance, much more is needed to unveil the coordination of growth rate with metabolic modulations in bi-trophic interactions. Here, we addressed plant-pathogen-insect interaction for toxicity as well as dependnce along with plant defense dynamics against pathogens and insects with broad range effects at the physio-biochemical and molecular level. We have reviewed interfaces in plant-pathogen-insect research to show pulsating regulation of plant immunity for attuning survival and ecological equilibrium. An improved understanding of the systematic foundation of growth-defense stability has vital repercussions for enhancing crop yield, including insights into uncoupling of host-parasite tradeoffs for ecological and environmental sustainability.

Electrical signalling on Bt and non-Bt cotton plants under stress by Aphis gossypii

Plants have developed various mechanisms to respond specifically to each biotrophic attack. It has been shown that the electrical signals emitted by plants are associated with herbivory stress responses and can lead to the activation of multiple defences. Bt cotton is a genetically modified pest-resistant plant that produces an insecticide from Bacillus thuringiensis (Bt) to control Lepidopteran species. Surprisingly, there is no study-yet, that characterizes the signalling mechanisms in transgenic cotton plants attacked by non-target insects, such as aphids. In this study, we characterized the production of electrical signals on Bt and non-Bt cotton plants infested with Aphis gossypii and, in addition, we characterized the dispersal behaviour of aphids to correlate this behaviour to plant signalling responses. Electrical signalling of the plants was recorded with an extracellular measurement technique. Impressively, our results showed that both Bt and non-Bt cotton varieties, when attacked by A. gossypii, emitted potential variation-type electrical signals and clearly showed the presence of distinct responses regarding their perception and the behaviour of aphids, with evidence of delay, in terms of signal amount, and almost twice the amount of Cry1F protein was observed on Bt cotton plants at the highest density of insects/plant. We present in our article some hypotheses that are based on plant physiology and insect behaviour to explain the responses found on Bt cotton plants under aphid stress.

Plant Allelochemicals as Sources of Insecticides

In this review, we describe the role of plant-derived biochemicals that are toxic to insect pests. Biotic stress in plants caused by insect pests is one of the most significant problems, leading to yield losses. Synthetic pesticides still play a significant role in crop protection. However, the environmental side effects and health issues caused by the overuse or inappropriate application of synthetic pesticides forced authorities to ban some problematic ones. Consequently, there is a strong necessity for novel and alternative insect pest control methods. An interesting source of ecological pesticides are biocidal compounds, naturally occurring in plants as allelochemicals (secondary metabolites), helping plants to resist, tolerate or compensate the stress caused by insect pests. The abovementioned bioactive natural products are the first line of defense in plants against insect herbivores. The large group of secondary plant metabolites, including alkaloids, saponins, phenols and terpenes, are the most promising compounds in the management of insect pests. Secondary metabolites offer sustainable pest control, therefore we can conclude that certain plant species provide numerous promising possibilities for discovering novel and ecologically friendly methods for the control of numerous insect pests.

Interactions between calcium and ABA signaling pathways in the regulation of fruit ripening

Fruit ripening and senescence are finely controlled by plant hormones such as ethylene and abscisic acid (ABA) but also by calcium ions and by calcium-dependent signaling pathways. Although there are extensive data supporting an interaction between ethylene and calcium in fruit ripening, the regulatory mechanisms resulting from the interaction between ABA and calcium have not yet been fully clarified. In this article, we have reviewed the full roles of calcium and its sensors (CaM, CMLs, CDPKs, CBLs) as well as ABA and the interactions between the two signaling pathways in the regulation of stress responses and in fruit ripening. To illustrate the possible interaction between calcium sensors and ABA signaling components in the control of fruit ripening, we propose an interaction model between the calcium and ABA signaling pathways.

Extracellular Fragmented Self-DNA Is Involved in Plant Responses to Biotic Stress

A growing body of evidence indicates that extracellular fragmented self-DNA (eDNA), by acting as a signaling molecule, triggers inhibitory effects on conspecific plants and functions as a damage-associated molecular pattern (DAMP). To evaluate early and late events in DAMP-dependent responses to eDNA, we extracted, fragmented, and applied the tomato (Solanum lycopersicum) eDNA to tomato leaves. Non-sonicated, intact self-DNA (intact DNA) was used as control. Early event analyses included the evaluation of plasma transmembrane potentials (Vm), cytosolic calcium variations (Ca²⁺ _{cy t}), the activity and subcellular localization of both voltage-gated and ligand-gated rectified K⁺ channels, and the reactive oxygen species (ROS) subcellular localization and quantification. Late events included RNA-Seq transcriptomic analysis and qPCR validation of gene expression of tomato leaves exposed to tomato eDNA. Application of eDNA induced a concentration-dependent Vm depolarization which was correlated to an increase in (Ca²⁺)_cyt; this event was associated to the opening of K⁺ channels, with particular action on ligand-gated rectified K⁺ channels. Both eDNA-dependent (Ca²⁺)_cyt and K⁺ increases were correlated to ROS production. In contrast, application of intact DNA produced no effects. The plant response to eDNA was the modulation of the expression of genes involved in plant-biotic interactions including pathogenesis-related proteins (PRPs), calcium-dependent protein kinases (CPK1), heat shock transcription factors (Hsf), heat shock proteins (Hsp), receptor-like kinases (RLKs), and ethylene-responsive factors (ERFs). Several genes involved in calcium signaling, ROS scavenging and ion homeostasis were also modulated by application of eDNA. Shared elements among the transcriptional response to eDNA and to biotic stress indicate that eDNA might be a common DAMP that triggers plant responses to pathogens and herbivores, particularly to those that intensive plant cell disruption or cell death. Our results suggest the intriguing hypothesis that some of the plant reactions to pathogens and herbivores might be due to DNA degradation, especially when associated to the plant cell disruption. Fragmented DNA would then become an important and powerful elicitor able to trigger early and late responses to biotic stress.

Tobacco Hornworm (Manduca sexta) Oral Secretion Elicits Reactive Oxygen Species in Isolated Tomato Protoplasts

Plants are under constant attack by a suite of insect herbivores. Over millions of years of coexistence, plants have evolved the ability to sense insect feeding via herbivore-associated elicitors in oral secretions, which can mobilize defense responses. However, herbivore-associated elicitors and the intrinsic downstream modulator of such interactions remain less understood. In this study, we show that tobacco hornworm caterpillar (Manduca sexta) oral secretion (OS) induces reactive oxygen species (ROS) in tomato (Solanum lycopersicum) protoplasts. By using a dye-based ROS imaging approach, our study shows that application of plant-fed (PF) M. sexta OS generates significantly higher ROS while artificial diet-fed (DF) caterpillar OS failed to induce ROS in isolated tomato protoplasts. Elevation in ROS generation was saturated after ~140 s of PF OS application. ROS production was also suppressed in the presence of an antioxidant NAC (N-acetyl-L-cysteine). Interestingly, PF OS-induced ROS increase was abolished in the presence of a Ca²⁺ chelator, BAPTA-AM (1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid). These results indicate a potential signaling cascade involving herbivore-associated elicitors, Ca²⁺, and ROS in plants during insect feeding. In summary, our results demonstrate that plants incorporate a variety of independent signals connected with their herbivores to regulate and mount their defense responses.

Role of reactive oxygen species and isoflavonoids in soybean resistance to the attack of the southern green stink bug

Southern green stink bugs (Nezara viridula L.) are one of the major pests in many soybean producing areas. They cause a decrease in yield and affect seed quality by reducing viability and vigor. Alterations have been reported in the oxidative response and in the secondary metabolites in different plant species due to insect damage. However, there is little information available on soybean-stink bug interactions. In this study we compare the response of undamaged and damaged seeds by Nezara viridula in two soybean cultivars, IAC-100 (resistant) and Davis (susceptible), grown under greenhouse conditions. Pod hardness, H₂O₂ generation, enzyme activities in guaiacol peroxidase (GPOX), catalase (CAT) and superoxide dismutase (SOD) as well as lipoxygenase expression and isoflavonoid production were quantified. Our results showed a greater resistance of IAC-100 to pod penetration, a decrease in peroxide content after stink bug attack, and higher GPOX, CAT and SOD activities in seeds due to the genotype and to the genotype-interaction with the herbivory treatment. Induction of LOX expression in both cultivars and higher production of isoflavonoids in IAC-100 were also detected. It was then concluded that the herbivory stink bug induces pathways related to oxidative stress and to the secondary metabolites in developing seeds of soybean and that differences between cultivars hold promise for a plant breeding program.

Convergent molecular evolution among ash species resistant to the emerald ash borer

Recent studies show that molecular convergence plays an unexpectedly common role in the evolution of convergent phenotypes. We exploited this phenomenon to find candidate loci underlying resistance to the emerald ash borer (EAB, Agrilus planipennis), the United States' most costly invasive forest insect to date, within the pan-genome of ash trees (the genus Fraxinus). We show that EAB-resistant taxa occur within three independent phylogenetic lineages. In genomes from these resistant lineages, we detect 53 genes with evidence of convergent amino acid evolution. Gene-tree reconstruction indicates that, for 48 of these candidates, the convergent amino acids are more likely to have arisen via independent evolution than by another process such as hybridization or incomplete lineage sorting. Seven of the candidate genes have putative roles connected to the phenylpropanoid biosynthesis pathway and 17 relate to herbivore recognition, defence signalling or programmed cell death. Evidence for loss-of-function mutations among these candidates is more frequent in susceptible species than in resistant ones. Our results on evolutionary relationships, variability in resistance, and candidate genes for defence response within the ash genus could inform breeding for EAB resistance, facilitating ecological restoration in areas invaded by this beetle.

Transcriptome Analysis of Wounding in the Model Grass Lolium temulentum

For forage and turf grasses, wounding is a predominant stress that often results in extensive loss of vegetative tissues followed by rapid regrowth. Currently, little is known concerning the perception, signaling, or molecular responses associated with wound stress in forage- and turf-related grasses. A transcriptome analysis of Lolium temulentum plants subjected to severe wounding revealed 9413 upregulated and 7704 downregulated, distinct, differentially expressed genes (DEGs). Categories related to signaling, transcription, and response to stimuli were enriched in the upregulated DEGs. Specifically, sequences annotated as enzymes involved in hormone biosynthesis/action and cell wall modifications, mitogen-activated protein kinases, WRKY transcription factors, proteinase inhibitors, and pathogen defense-related DEGs were identified. Surprisingly, DEGs related to heat shock and chaperones were more prevalent in the downregulated DEGs when compared with the upregulated DEGs. This wound transcriptome analysis is the first step in identifying the molecular components and pathways used by grasses in response to wounding. The information gained from the analysis will provide a valuable molecular resource that will be used to develop approaches that can improve the recovery, regrowth, and long-term fitness of forage and turf grasses before/after cutting or grazing.

Soy and Arabidopsis receptor-like kinases respond to polysaccharide signals from Spodoptera species and mediate herbivore resistance

Plants respond to herbivory by perceiving herbivore danger signal(s) (HDS(s)), including "elicitors", that are present in herbivores' oral secretions (OS) and act to induce defense responses. However, little is known about HDS-specific molecules and intracellular signaling. Here we explored soybean receptor-like kinases (RLKs) as candidates that might mediate HDS-associated RLKs' (HAKs') actions in leaves in response to OS extracted from larvae of a generalist herbivore, Spodoptera litura. Fractionation of OS yielded Frα, which consisted of polysaccharides. The GmHAKs composed of their respective homomultimers scarcely interacted with Frα. Moreover, Arabidopsis HAK1 homomultimers interacted with cytoplasmic signaling molecule PBL27, resulting in herbivory resistance, in an ethylene-dependent manner. Altogether, our findings suggest that HAKs are herbivore-specific RLKs mediating HDS-transmitting, intracellular signaling through interaction with PBL27 and the subsequent ethylene signaling for plant defense responses in host plants.

Plant Defenses Against Tetranychus urticae: Mind the Gaps

The molecular interactions between a pest and its host plant are the consequence of an evolutionary arms race based on the perception of the phytophagous arthropod by the plant and the different strategies adopted by the pest to overcome plant triggered defenses. The complexity and the different levels of these interactions make it difficult to get a wide knowledge of the whole process. Extensive research in model species is an accurate way to progressively move forward in this direction. The two-spotted spider mite, Tetranychus urticae Koch has become a model species for phytophagous mites due to the development of a great number of genetic tools and a high-quality genome sequence. This review is an update of the current state of the art in the molecular interactions between the generalist pest T. urticae and its host plants. The knowledge of the physical and chemical constitutive defenses of the plant and the mechanisms involved in the induction of plant defenses are summarized. The molecular events produced from plant perception to the synthesis of defense compounds are detailed, with a special focus on the key steps that are little or totally uncovered by previous research.

Research advances in plant-insect molecular interaction

Acute and precise signal perception and transduction are essential for plant defense against insects. Insect elicitors-that is, the biologically active molecules from insects' oral secretion (which contains regurgitant and saliva), frass, ovipositional fluids, and the endosymbionts-are recognized by plants and subsequently induce a local or systematic defense response. On the other hand, insects secrete various types of effectors to interfere with plant defense at multiple levels for better adaptation. Jasmonate is a main regulator involved in plant defense against insects and integrates with multiple pathways to make up the intricate defense network. Jasmonate signaling is strictly regulated in plants to avoid the hypersensitive defense response and seems to be vulnerable to assault by insect effectors at the same time. Here, we summarize recently identified elicitors, effectors, and their target proteins in plants and discuss their underlying molecular mechanisms.