Volatile signaling in plant-plant-herbivore interactions: what is real?

Phenylalanine treatment induces tomato resistance to Tuta absoluta via increased accumulation of benzenoid/phenylpropanoid volatiles serving as defense signals

Tuta absoluta ("leafminer"), is a major pest of tomato crops worldwide. Controlling this insect is difficult due to its efficient infestation, rapid proliferation, and resilience to changing weather conditions. Furthermore, chemical pesticides have only a short-term effect due to rapid development of T. absoluta strains. Here, we show that a variety of tomato cultivars, treated with external phenylalanine solutions exhibit high resistance to T. absoluta, under both greenhouse and open field conditions, at different locations. A large-scale metabolomic study revealed that tomato leaves absorb and metabolize externally given Phe efficiently, resulting in a change in their volatile profile, and repellence of T. absoluta moths. The change in the volatile profile is due to an increase in three phenylalanine-derived benzenoid phenylpropanoid volatiles (BPVs), benzaldehyde, phenylacetaldehyde, and 2-phenylethanol. This treatment had no effect on terpenes and green leaf volatiles, known to contribute to the fight against insects. Phe-treated plants also increased the resistance of neighboring non-treated plants. RNAseq analysis of the neighboring non-treated plants revealed an exclusive upregulation of genes, with enrichment of genes related to the plant immune response system. Exposure of tomato plants to either benzaldehyde, phenylacetaldehyde, or 2-phenylethanol, resulted in induction of genes related to the plant immune system that were also induced due to neighboring Phe-treated plants. We suggest a novel role of phenylalanine-derived BPVs as mediators of plant-insect interactions, acting as inducers of the plant defense mechanisms.

Metabolic crosstalk between hydroxylated monoterpenes and salicylic acid in tomato defense response against bacteria

Hydroxylated monoterpenes (HMTPs) are differentially emitted by tomato (Solanum lycopersicum) plants resisting bacterial infection. We have studied the defensive role of these volatiles in the tomato response to bacteria, whose main entrance is through stomatal apertures. Treatments with some HMTPs resulted in stomatal closure and pathogenesis-related protein 1 (PR1) induction. Particularly, α-terpineol induced stomatal closure in a salicylic acid (SA) and abscisic acid-independent manner and conferred resistance to bacteria. Interestingly, transgenic tomato plants overexpressing or silencing the monoterpene synthase MTS1, which displayed alterations in the emission of HMTPs, exhibited changes in the stomatal aperture but not in plant resistance. Measures of both 2-C-methyl-D-erythritol-2,4-cyclopyrophosphate (MEcPP) and SA levels revealed competition for MEcPP by the methylerythritol phosphate (MEP) pathway and SA biosynthesis activation, thus explaining the absence of resistance in transgenic plants. These results were confirmed by chemical inhibition of the MEP pathway, which alters MEcPP levels. Treatments with benzothiadiazole (BTH), a SA functional analog, conferred enhanced resistance to transgenic tomato plants overexpressing MTS1. Additionally, these MTS1 overexpressors induced PR1 gene expression and stomatal closure in neighboring plants. Our results confirm the role of HMTPs in both intra- and interplant immune signaling and reveal a metabolic crosstalk between the MEP and SA pathways in tomato plants.

Plant-plant communication in Camellia japonica and C. rusticana via volatiles

Plants emit volatile compounds when they are subjected to herbivorous, pathogenic, or artificial damages. Both the damaged plant and the neighboring intact plants induce resistance when they receive these volatiles, a phenomenon known as plant-plant communication. However, field observations of this phenomenon are limited. To understand the nature of plant-plant communication, we collected information about intra- and inter-plant signaling via volatiles in Camellia japonica and C. rusticana under natural conditions. We exposed intact branches of damaged plant (intra-plant) or neighboring plant (inter-plant) to artificially damaged plant volatiles (ADPVs). Leaf damage reduced in ADPVs-exposed branches in the neighboring plants compared to branches that were exposed to volatiles from intact leaves, thus, indicating that inter-plant signaling occur by the emission of volatiles from damaged leaves. We also conducted an air-transfer experiment wherein the headspace air of the damaged branch was transferred to the headspace of intact branches. Leaf damage reduced on the ADPVs-transferred branch compared to the control branch. The effect of volatiles on damage reduction lasted for three months. Our results indicate that ADPVs in Camellia species contain cues that induce resistance in neighboring plants. Our findings improve understanding of plant defense strategies that may be used in horticulture and agriculture.

Screening herbal extracts as biostimulant to increase germination, plant growth and secondary metabolite production in wheatgrass

Recently it has been recognized that herbal plants contain endogenous molecules with biostimulant properties, capable of inducing morphological and biochemical changes in crop plants. Therefore, the present experiment was conducted to screen herbal samples for their plant growth promoting properties. Twenty-five herbal extracts were tested for their biostimulating activity on wheat crop (Triticum aestivum) through seed priming. Morphological parameters chosen for evaluation include: percent seed germination, length and weight of seedling, wheat grass length and biomass. Biochemical parameters include: total phenolic and flavonoid, enzymatic activity of catalase and phenylalanine ammonium lyase and antioxidant activity. Results indicated an increase in the tested parameters by the extracts, however the biostimulant property varied between the selected herbal samples. Some of the samples, such as Phyllanthus emblica, Plumbago zeylanica, Catharanthus roseus and Baccopa monnieri, were highly effective in inducing plant growth promoting parameters. Principal component analysis was performed and herbal samples were grouped into categories based on their activity.

How plant traits respond to and affect vertebrate and invertebrate herbivores-Are measurements comparable across herbivore types?

Despite plants realistically being affected by vertebrate and invertebrate herbivores simultaneously, fundamental differences in the ecology and evolution of these two herbivore guilds often means their impacts on plants are studied separately. A synthesis of the literature is needed to understand the types of plant traits examined and their response to, and effect on (in terms of forage selection) vertebrate and invertebrate herbivory, and to identify associated knowledge gaps. Focusing on grassland systems and species, we found 138 articles that met our criteria: 39 invertebrate, 97 vertebrate and 2 focussed on both vertebrate and invertebrate herbivores. Our study identified invertebrate focussed research, research conducted in the Southern Hemisphere and research on nondomesticated herbivores was significantly underrepresented based on our search and should be a focus of future research. Differences in study focus (trait response or trait effect), along with differences in the types of traits examined, led to limited opportunity for comparison between the two herbivore guilds. This review therefore predominantly discusses the response and effect of plant traits to each herbivore guild separately. In future studies, we suggest this review be used as a guide for trait selection, to improve comparability and the broader significance of results.

Genome-wide identification and expression of BAHD acyltransferase gene family shed novel insights into the regulation of linalyl acetate and lavandulyl acetate in lavender

The BAHD acyltransferase superfamily has a variety of biological functions, especially in catalyzing the synthesis of ester compounds and improving plant stress resistance. Linalyl acetate and lavandulyl acetate, the most important volatile esters in lavender, are generated by LaBAHDs. However, the systematic identification, expression characteristics of LaBAHD genes and their correlations with ester formation remain elusive. Here, 166 LaBAHD genes were identified from the lavender genome. Based on detailed phylogenetic analysis, the LaBAHD family genes were divided into five groups, among which the LaBAHDs involved in volatile ester biosynthesis belong to the IIIa and Va clades. Whole-genome duplications (WGDs) and tandem duplications (TDs) jointly drive the expansion of LaBAHD superfamily. The promoter regions of LaBAHDs contained a variety of stress- and hormone-related motifs, as well as binding sites with five types of transcription factors (TFs). Then, linalyl acetate- and lavandulyl acetate-regulated coexpression modules were established and some candidate TFs that may function in inducing ester formation were identified. Based on the correlation analysis between the ester contents and expression profiles of BAHD genes in different tissues, five candidate genes were screened for further examination. Drought, salt and MeJA treatments increased the accumulation of linalyl acetate and lavandulyl acetate, and induced the expression of LaBAHDs. Our results indicated that LaBAHD57, LaBAHD63, LaBAHD104, LaBAHD105 and LaBAHD119 are crucial candidate genes involved in linalyl acetate and lavandulyl acetate biosynthesis. Our findings offer a theoretical foundation for further studying the specific biological functions of LaBAHD family and improving the quality of lavender essential oil.

Main flavor compounds and molecular regulation mechanisms in fruits and vegetables

Fruits and vegetables (F&V) are an indispensable part of a healthy diet. The volatile and nonvolatile compounds present in F&V constitute unique flavor substances. This paper reviews the main flavor substances present in F&V, as well as the biosynthetic pathways and molecular regulation mechanisms of these compounds. A series of compounds introduced include aromatic substances, soluble sugars and organic acids, which constitute the key flavor substances of F&V. Esters, phenols, alcohols, amino acids and terpenes are the main volatile aromatic substances, and nonvolatile substances are represented by amino acids, fatty acids and carbohydrates; The combination of these ingredients is the cause of the sour, sweet, bitter, astringent and spicy taste of these foods. This provides a theoretical basis for the study of the interaction between volatile and nonvolatile substances in F&V, and also provides a research direction for the healthy development of food in the future.

Two jasmonic acid carboxyl methyltransferases in Gossypium hirsutum involved in MeJA biosynthesis may contribute to plant defense

Jasmonic acid (JA) and methyl jasmonate (MeJA), the crucial plant hormones, can induce the emission of plant volatiles and regulate the behavioral responses of insect pests or their natural enemies. In this study, two jasmonic acid carboxyl methyltransferases (JMTs), GhJMT1 and GhJMT2, involved in MeJA biosynthesis in Gossypium. hirsutum were identified and further functionally confirmed. In vitro, recombinant GhJMT1 and GhJMT2 were both responsible for the conversion of JA to MeJA. Quantitative real-time PCR (qPCR) measurement indicated that GhJMT1 and GhJMT2 were obviously up-regulated in leaves and stems of G. hirsutum after being treated with MeJA. In gas chromatography-mass spectrometry (GC-MS) analysis, MeJA treatment significantly induced plant volatiles emission such as (E)-β-ocimene, (Z)-3-hexenyl acetate, linalool and (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), which play vital roles in direct and indirect plant defenses. Moreover, antennae of parasitoid wasps Microplitis mediator showed electrophysiological responses to MeJA, β-ocimene, (Z)-3-hexenyl acetate and linalool at a dose dependent manner, while our previous research revealed that DMNT excites electrophysiological responses and behavioral tendencies. These findings provide a better understanding of MeJA biosynthesis and defense regulation in upland cotton, which lay a foundation to JA and MeJA employment in agricultural pest control.

Inter-laboratory comparison of plant volatile analyses in the light of intra-specific chemodiversity

INTRODUCTION

Assessing intraspecific variation in plant volatile organic compounds (VOCs) involves pitfalls that may bias biological interpretation, particularly when several laboratories collaborate on joint projects. Comparative, inter-laboratory ring trials can inform on the reproducibility of such analyses.

OBJECTIVES

In a ring trial involving five laboratories, we investigated the reproducibility of VOC collections with polydimethylsiloxane (PDMS) and analyses by thermal desorption-gas chromatography-mass spectrometry (TD-GC-MS). As model plant we used Tanacetum vulgare, which shows a remarkable diversity in terpenoids, forming so-called chemotypes. We performed our ring-trial with two chemotypes to examine the sources of technical variation in plant VOC measurements during pre-analytical, analytical, and post-analytical steps.

METHODS

Monoclonal root cuttings were generated in one laboratory and distributed to five laboratories, in which plants were grown under laboratory-specific conditions. VOCs were collected on PDMS tubes from all plants before and after a jasmonic acid (JA) treatment. Thereafter, each laboratory (donors) sent a subset of tubes to four of the other laboratories (recipients), which performed TD-GC-MS with their own established procedures.

RESULTS

Chemotype-specific differences in VOC profiles were detected but with an overall high variation both across donor and recipient laboratories. JA-induced changes in VOC profiles were not reproducible. Laboratory-specific growth conditions led to phenotypic variation that affected the resulting VOC profiles.

CONCLUSION

Our ring trial shows that despite large efforts to standardise each VOC measurement step, the outcomes differed both qualitatively and quantitatively. Our results reveal sources of variation in plant VOC research and may help to avoid systematic errors in similar experiments.

Plant-herbivore interactions: Experimental demonstration of genetic variability in plant-plant signalling

Plant-herbivore interactions mediated by plant-plant signalling have been documented in different species but its within-species variability has hardly been quantified. Here, we tested if herbivore foraging activity on plants was influenced by a prior contact with a damaged plant and if the effect of such plant-plant signalling was variable across 113 natural genotypes of Arabidopsis thaliana. We filmed the activity of the generalist herbivore Cornu aspersum during 1 h on two plants differing only in a prior contact with a damaged plant or not. We recorded each snails' first choice, and measured its first duration on a plant, the proportion of time spent on both plants and leaf consumption. Overall, plant-plant signalling modified the foraging activity of herbivores in A. thaliana. On average, snails spent more time and consumed more of plants that experienced a prior contact with a damaged plant. However, the effects of plant-plant signalling on snail behaviour was variable: depending on genotype identity, plant-plant signalling made undamaged plants more repellant or attractive to snails. Genome-wide associations revealed that genes related to stress coping ability and jasmonate pathway were associated to this variation. Together, our findings highlight the adaptive significance of plant-plant signalling for plant-herbivore interactions.

Stemborer-induced rice plant volatiles boost direct and indirect resistance in neighboring plants

Herbivore-induced plant volatiles (HIPVs) are known to be perceived by neighboring plants, resulting in induction or priming of chemical defenses. There is little information on the defense responses that are triggered by these plant-plant interactions, and the phenomenon has rarely been studied in rice. Using chemical and molecular analyses in combination with insect behavioral and performance experiments, we studied how volatiles emitted by rice plants infested by the striped stemborer (SSB) Chilo suppressalis affect defenses against this pest in conspecific plants. Compared with rice plants exposed to the volatiles from uninfested plants, plants exposed to SSB-induced volatiles showed enhanced direct and indirect resistance to SSB. When subjected to caterpillar damage, the HIPV-exposed plants showed increased expression of jasmonic acid (JA) signaling genes, resulting in JA accumulation and higher levels of defensive proteinase inhibitors. Moreover, plants exposed to SSB-induced volatiles emitted larger amounts of inducible volatiles and were more attractive to the parasitoid Cotesia chilonis. By unraveling the factors involved in HIPV-mediated defense priming in rice, we reveal a key defensive role for proteinase inhibitors. These findings pave the way for novel rice management strategies to enhance the plant's resistance to one of its most devastating pests.

Volatile organic compounds shape belowground plant-fungi interactions

Volatile organic compounds (VOCs), a bouquet of chemical compounds released by all life forms, play essential roles in trophic interactions. VOCs can facilitate a large number of interactions with different organisms belowground. VOCs-regulated plant-plant or plant-insect interaction both below and aboveground has been reported extensively. Nevertheless, there is little information about the role of VOCs derived from soilborne pathogenic fungi and beneficial fungi, particularly mycorrhizae, in influencing plant performance. In this review, we show how plant VOCs regulate plant-soilborne pathogenic fungi and beneficial fungi (mycorrhizae) interactions. How fungal VOCs mediate plant-soilborne pathogenic and beneficial fungi interactions are presented and the most common methods to collect and analyze belowground volatiles are evaluated. Furthermore, we suggest a promising method for future research on belowground VOCs.

Stress-Induced Volatile Emissions and Signalling in Inter-Plant Communication

The sessile plant has developed mechanisms to survive the "rough and tumble" of its natural surroundings, aided by its evolved innate immune system. Precise perception and rapid response to stress stimuli confer a fitness edge to the plant against its competitors, guaranteeing greater chances of survival and productivity. Plants can "eavesdrop" on volatile chemical cues from their stressed neighbours and have adapted to use these airborne signals to prepare for impending danger without having to experience the actual stress themselves. The role of volatile organic compounds (VOCs) in plant-plant communication has gained significant attention over the past decade, particularly with regard to the potential of VOCs to prime non-stressed plants for more robust defence responses to future stress challenges. The ecological relevance of such interactions under various environmental stresses has been much debated, and there is a nascent understanding of the mechanisms involved. This review discusses the significance of VOC-mediated inter-plant interactions under both biotic and abiotic stresses and highlights the potential to manipulate outcomes in agricultural systems for sustainable crop protection via enhanced defence. The need to integrate physiological, biochemical, and molecular approaches in understanding the underlying mechanisms and signalling pathways involved in volatile signalling is emphasised.

On the qualitative study of a two-trophic plant-herbivore model

The coexistence of plant-herbivore populations in an ecological system is a fundamental topic of research in mathematical ecology. Plant-herbivore interactions are often described by using discrete-time models in the case of non-overlapping generations: such generations have some specific time interval of life and their old generations are replaced by new generations after some regular interval of time. Keeping in mind the dynamical reliability of continuous-time models we presented two discrete-time plant-herbivore models. Mainly, by applying Euler's forward method a discrete-time plant-herbivore model is obtained from a continuous-time plant-herbivore model. In addition, a dynamically consistent discrete-time plant-herbivore model is obtained by applying a nonstandard difference scheme. Moreover, local stability is discussed and the existence of bifurcation about positive equilibrium is shown under some mathematical conditions. To control bifurcation and chaos, a modified hybrid technique is developed. Finally, to support our theocratical results and to show the dynamical reliability of the nonstandard difference scheme some numerical examples are provided.

Characterization of honey peach (Prunus persica (L.) Batsch) aroma variation and unraveling the potential aroma metabolism mechanism through proteomics analysis under abiotic stress

Honey peach (Prunus persica (L.) Batsch) is a climacteric fruit with short storage period. Generally, the low temperature storage (LTS) technology is implemented to lessen aroma loss and keep the quality. However, the LTS procedure brings about cold stress issues and affects the aroma metabolism. It is essential to unravel the primary aroma and the corresponding metabolism mechanism through key proteins under abiotic stress. In this study, the primary components were characterized under LTS at 1 °C during 0 to 40 days. Furthermore, the proteomics analysis was performed to acquire differentially expressed proteins to clarify the underlying metabolism mechanisms of the primary aroma and potential proteins. As a result, four proteins were considered as potential key proteins that associated with fatty acid and amino acid metabolism under cold stress. Additionally, this study provides theoretical cornerstones for regulating and improving the quality of honey peach.

Insect Herbivory Caused Plant Stress Emissions Increases the Negative Radiative Forcing of Aerosols

Plant stress in a changing climate is predicted to increase plant volatile organic compound (VOC) emissions and thus can affect the formed secondary organic aerosol (SOA) concentrations, which in turn affect the radiative properties of clouds and aerosol. However, global aerosol-climate models do not usually consider plant stress induced VOCs in their emission schemes. In this study, we modified the monoterpene emission factors in biogenic emission model to simulate biotic stress caused by insect herbivory on needleleaf evergreen boreal and broadleaf deciduous boreal trees and studied the consequent effects on SOA formation, aerosol-cloud interactions as well as direct radiative effects of formed SOA. Simulations were done altering the fraction of stressed and healthy trees in the latest version of ECHAM-HAMMOZ (ECHAM6.3-HAM2.3-MOZ1.0) global aerosol-climate model. Our simulations showed that increasing the extent of stress to the aforementioned tree types, substantially increased the SOA burden especially over the areas where these trees are located. This indicates that increased VOC emissions due to increasing stress enhance the SOA formation via oxidation of VOCs to low VOCs. In addition, cloud droplet number concentration at the cloud top increased with increasing extent of biotic stress. This indicates that as SOA formation increases, it further enhances the number of particles acting as cloud condensation nuclei. The increase in SOA formation also decreased both all-sky and clear-sky radiative forcing. This was due to a shift in particle size distributions that enhanced aerosol reflecting and scattering of incoming solar radiation.

Fingerprints and changes analysis of volatile compounds in fresh-cut yam during yellowing process by using HS-GC-IMS

The purpose of this study was to investigate the dynamic change in volatile components during the yellowing process. The volatile components were analyzed by headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) and the critical enzyme activities were determined by commercial kits. The results revealed that 29 signal peaks for 20 compounds were identified, which were quantified in all samples: 1 furan, 1 ester, 15 aldehydes, 3 ketones, and 9 alcohols. The contents of most of these compounds increased first and then decreased at 36 h, which were basically consistent with the enzyme activities of LOX, HPL, ADH and AAT. Subsequently, principal component analysis (PCA) results clearly showed that the fresh-cut yams for different yellowing processes were well distinguished by the volatile compounds. These results showed that the potential of HS-GC-IMS-based approaches to evaluate the volatile compound profiles of fresh-cut yam at different stages in the yellowing period.

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.

Attraction of the Biocontrol Agent, Galerucella placida Towards Volatile Blends of Two Polygonaceae Weeds, Rumex dentatus and Polygonum glabrum

The Polygonaceae weed, Rumex dentatus L. grows in association with wheat, mustard and potato, while Polygonum glabrum Willd. grows in association with rice in India. Both larvae and adults of Galerucella placida Baly (Coleoptera: Chrysomelidae) voraciously consume these weeds. Applications of synthetic herbicides to control weeds are harmful to the environment including beneficial organisms. We propose to find volatile organic compounds (VOCs) from both weeds causing attraction of the biocontrol agent, G. placida, in order to attempt to use the insect as a biological weed control. Behavioral responses of G. placida towards volatile blends characteristic of undamaged (UD), insect-damaged (ID), jasmonic acid-treated (JA) or mechanically-damaged (MD) plants were conducted by Y-tube olfactometer bioassays. Cuminaldehyde was predominant in VOCs of UD R. dentatus, ID P. glabrum, and both JA and MD R. dentatus and P. glabrum. Geraniol was predominant in VOCs of UD P. glabrum, while 1,3-diethylbenzene predominated in VOCs of ID R. dentatus. Females were more attracted towards volatile blends of ID plants compared to UD or JA plants. Females did not show attraction towards volatile blends of JA plants. We identified two bioactive synthetics blends, one comprised of seven compounds - 16.65 µg 1,3-diethylbenzene, 10.72 µg acetophenone, 6.52 µg 2,6-(E,Z)-nonadienal, 2.46 µg 1-nonanol, 4.19 µg decanal, 9.86 µg 4-ethylacetophenone and 3.34 µg 1-hexadecene dissolved in 25 µl CH₂Cl₂ and the other containing five compounds - 2.50 µg 2-octanol, 6.84 µg limonene, 0.64 µg dodecane, 6.63 µg 4-ethylacetophenone and 0.24 µg geranyl acetone dissolved in 25 µl CH₂Cl₂. These two blends of volatile compounds could be used to attract the biocontrol agent during early vegetative period of these two weeds, which could lead to eradication of weeds from crop fields.

Eliciting Plant Defenses Through Herbivore-Induced Plant Volatiles’ Exposure in Sweet Peppers

Insect herbivory activates plant defense mechanisms and releases a blend of herbivore-induced plant volatiles (HIPVs). These volatile compounds may be involved in plant-plant communication and induce defense response in undamaged plants. In this work, we investigated whether the exposure of sweet pepper plants to HIPVs [(Z)-3-hexenol, (Z)-3-hexenyl acetate, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, hexyl butanoate, methyl salicylate and methyl jasmonate] activates the sweet pepper immune defense system. For this, healthy sweet pepper plants were individually exposed to the each of the above mentioned HIPVs over 48 h. The expression of jasmonic acid and salicylic acid related genes was quantified. Here, we show that all the tested volatiles induced plant defenses by upregulating the jasmonic acid and salicylic acid signaling pathway. Additionally, the response of Frankliniella occidentalis, a key sweet pepper pest, and Orius laevigatus, the main natural enemy of F. occidentalis, to HIPV-exposed sweet pepper plants were studied in a Y-tube olfactometer. Only plants exposed to (Z)-3-hexenyl propanoate and methyl salicylate repelled F. occidentalis whereas O. laevigatus showed a strong preference to plants exposed to (Z)-3-hexenol, (Z)-3-hexenyl propanoate, (Z)-3-hexenyl butanoate, methyl salicylate and methyl jasmonate. Our results show that HIPVs act as elicitors to sweet pepper plant defenses by enhancing defensive signaling pathways. We anticipate our results to be a starting point for integrating HIPVs-based approaches in sweet pepper pest management systems which may provide a sustainable strategy to manage insect pests in horticultural plants.

How do plants sense volatiles sent by other plants?

Plants communicate via the emission of volatile organic compounds (VOCs) with many animals as well as other plants. We still know little about how VOCs are perceived by receiving (eavesdropping) plants. Here we propose a multiple system of VOC perception, where stress-induced VOCs dock on odorant-binding proteins (OBPs) like in animals and are transported to as-yet-unknown receptors mediating downstream metabolic and/or behavioral changes. Constitutive VOCs that are broadly and lifelong emitted by plants do not bind OBPs but may directly change the metabolism of eavesdropping plants. Deciphering how plants listen to their talking neighbors could empower VOCs as a tool for bioinspired strategies of plant defense when challenged by abiotic and biotic stresses.

Endophytic bacterial communities are associated with leaf mimicry in the vine Boquila trifoliolata

The mechanisms behind the unique capacity of the vine Boquila trifoliolata to mimic the leaves of several tree species remain unknown. A hypothesis in the original leaf mimicry report considered that microbial vectors from trees could carry genes or epigenetic factors that would alter the expression of leaf traits in Boquila. Here we evaluated whether leaf endophytic bacterial communities are associated with the mimicry pattern. Using 16S rRNA gene sequencing, we compared the endophytic bacterial communities in three groups of leaves collected in a temperate rainforest: (1) leaves from the model tree Rhaphithamnus spinosus (RS), (2) Boquila leaves mimicking the tree leaves (BR), and (3) Boquila leaves from the same individual vine but not mimicking the tree leaves (BT). We hypothesized that bacterial communities would be more similar in the BR-RS comparison than in the BT-RS comparison. We found significant differences in the endophytic bacterial communities among the three groups, verifying the hypothesis. Whereas non-mimetic Boquila leaves and tree leaves (BT-RS) showed clearly different bacterial communities, mimetic Boquila leaves and tree leaves (BR-RS) showed an overlap concerning their bacterial communities. The role of bacteria in this unique case of leaf mimicry should be studied further.

Qualitative analysis of a discrete-time phytoplankton-zooplankton model with Holling type-II response and toxicity

The interaction among phytoplankton and zooplankton is one of the most important processes in ecology. Discrete-time mathematical models are commonly used for describing the dynamical properties of phytoplankton and zooplankton interaction with nonoverlapping generations. In such type of generations a new age group swaps the older group after regular intervals of time. Keeping in observation the dynamical reliability for continuous-time mathematical models, we convert a continuous-time phytoplankton-zooplankton model into its discrete-time counterpart by applying a dynamically consistent nonstandard difference scheme. Moreover, we discuss boundedness conditions for every solution and prove the existence of a unique positive equilibrium point. We discuss the local stability of obtained system about all its equilibrium points and show the existence of Neimark-Sacker bifurcation about unique positive equilibrium under some mathematical conditions. To control the Neimark-Sacker bifurcation, we apply a generalized hybrid control technique. For explanation of our theoretical results and to compare the dynamics of obtained discrete-time model with its continuous counterpart, we provide some motivating numerical examples. Moreover, from numerical study we can see that the obtained system and its continuous-time counterpart are stable for the same values of parameters, and they are unstable for the same parametric values. Hence the dynamical consistency of our obtained system can be seen from numerical study. Finally, we compare the modified hybrid method with old hybrid method at the end of the paper.

Identification of a wild carrot as carrot psylla (Bactericera trigonica) attractant and host plant chemistry

Carrot psylla is one of the devastating pests of carrot throughout northern Europe and the Mediterranean basin. Here we characterized the behavioral response of psylla females towards different carrot germplasm and identified the chemical cues involved in the host selection of psylla females by oviposition choice experiments and metabolic profiling of leaf volatiles. In choice assays, carrot psylla displayed differential responses to tested 14 germplasm. Among germplasm, wild accessions 21793 and 20465 were highly preferred by carrot psylla, while wild accessions 20465 and the orange cultivar Nairobi were less. In non-choice experiments conducted only with this four-germplasm revealed that the carrot psylla females gave higher preference to the Nairobi and wild accession 20465, indicating the vicinity to other host plants in the same area might affect female preference. Moreover, the nymph development and survival experiments showed the lowest nymphs survival rate on the wild accessions 21793 and 20497. Furthermore, the volatile emissions among different carrot cultivars infested with psylla showed qualitative and quantitative differences versus intact plants. Among these volatiles, apiol, β-asarone, myristicin, and sabinene showed a relationship with psyllas growth and survival. We also showed that myristicin and sabinene exogenous applications caused a dramatic reduction in the number of eggs laid by psylla and subsequent nymph survival. This is an initial study of the volatiles that mediate attraction and oviposition preference of carrot psylla in response to its host plant. The results from this study provide baseline information for the development of new control strategies against carrot psylla.

A hypothesis on the capacity of plant odorant-binding proteins to bind volatile isoprenoids based on in silico evidences

Volatile organic compounds (VOCs) from 'emitting' plants inform the 'receiving' (listening) plants of impending stresses or simply of their presence. However, the receptors that allow receivers to detect the volatile cue are elusive. Most likely, plants (as animals) have odorant-binding proteins (OBPs), and in fact, a few OBPs are known to bind 'stress-induced' plant VOCs. We investigated whether these and other putative OBPs may bind volatile constitutive and stress-induced isoprenoids, the most emitted plant VOCs, with well-established roles in plant communication and defense. Molecular docking simulation experiments suggest that structural features of a few plant proteins screened in databases could allow VOC binding. In particular, our results show that monoterpenes may bind the same plant proteins that were described to bind other stress-induced VOCs, while the constitutive hemiterpene isoprene is unlikely to bind any investigated putative OBP and may not have an info-chemical role. We conclude that, as for animal, there may be plant OBPs that bind multiple VOCs. Plant OBPs may play an important role in allowing plants to eavesdrop messages by neighboring plants, triggering defensive responses and communication with other organisms.

Identification of Lathyrus sativus plant volatiles causing behavioral preference of Aphis craccivora

BACKGROUND

The viviparous aphid Aphis craccivora Koch (Hemiptera: Aphididae) is a serious threat to the crop yield of Lathyrus sativus L. (Fabaceae), commonly known as grass pea. The synthetic insecticides applied to control this insect pest are not safe for the environment. Hence, it is necessary to find volatile organic compounds (VOCs) from two cultivars [BIO L 212 Ratan (BIO) and Nirmal B-1 (NIR)] of L. sativus plants causing behavioral preference of A. craccivora.

RESULTS

The VOCs from undamaged (UD), insect-damaged (ID) [plants on which 50 or 100 adults of A. craccivora were fed for 4 h (ID 50 or ID 100)], and mechanically damaged (MD) plants were identified and quantified by gas chromatography-mass spectrometry and gas chromatography-flame ionization detection analyses, respectively. Total VOCs were higher in ID plants compared to UD plants of each cultivar. However, total VOCs were higher in NIR cultivar compared to BIO cultivar for both UD and ID plants. Benzyl alcohol was predominant in volatile extracts of all treatments. In Y-tube olfactometer bioassays, females showed preference towards volatile extracts of UD, ID, and MD plants of each cultivar compared to the control solvent (CH₂ Cl₂ ). Insects preferred certain synthetic blends comparable to volatile extracts of UD, ID, and MD plants of each L. sativus cultivar against the control solvent.

CONCLUSION

Females preferred a synthetic blend of benzyl alcohol, 1,3-diethylbenzene, thymol, and 1-hexadecene at ratios of 142.49: 62.03:1.18:1 dissolved in 25 μL of CH₂ Cl₂ in olfactometer bioassays, which could be used in developing lures to control this insect pest.

Proteomic analysis of "Oriental Beauty" oolong tea leaves with different degrees of leafhopper infestation

RATIONALE

Oriental Beauty, a type of oolong tea native to Taiwan, is highly prized by connoisseurs for its unique fruity aroma and sweet taste. Leaves of Oriental Beauty vary in appearance, aroma, and taste, depending on the degree of tea green leafhopper (Jacobiasca formosana) infestation. In this study, the aim is to investigate the differential expression of proteins in leaves with low, medium, and high degrees of leafhopper infestation.

METHODS

Proteomic techniques 2DE (two-dimensional electrophoresis) and nanoscale liquid chromatography/tandem mass spectrometry (LC/MS/MS) were used to investigate the differential expression of proteins in tea leaves with different degrees of leafhopper infestation.

RESULTS

A total of 89 proteins were found to exhibit significant differences in expression. In a gene ontology analysis, most of these proteins participated in biosynthesis, carbohydrate metabolism, transport, responses to stress, and amino acid metabolism.

CONCLUSIONS

These results indicated that the unique aroma and taste of the leaves might be influenced by their protein expression profiles, as well as related factors such as defensive responses to tea green leafhopper saliva.

Low temperature synergistically promotes wounding-induced indole accumulation by INDUCER OF CBF EXPRESSION-mediated alterations of jasmonic acid signaling in Camellia sinensis

Plants have to cope with various environmental stress factors which significantly impact plant physiology and secondary metabolism. Individual stresses, such as low temperature, are known to activate plant volatile compounds as a defense. However, less is known about the effect of multiple stresses on plant volatile formation. Here, the effect of dual stresses (wounding and low temperature) on volatile compounds in tea (Camellia sinensis) plants and the underlying signalling mechanisms were investigated. Indole, an insect resistance volatile, was maintained at a higher content and for a longer time under dual stresses compared with wounding alone. CsMYC2a, a jasmonate (JA)-responsive transcription factor, was the major regulator of CsTSB2, a gene encoding a tryptophan synthase β-subunit essential for indole synthesis. During the recovery phase after tea wounding, low temperature helped to maintain a higher JA level. Further study showed that CsICE2 interacted directly with CsJAZ2 to relieve inhibition of CsMYC2a, thereby promoting JA biosynthesis and downstream expression of the responsive gene CsTSB2 ultimately enhancing indole biosynthesis. These findings shed light on the role of low temperature in promoting plant damage responses and advance knowledge of the molecular mechanisms by which multiple stresses coordinately regulate plant responses to the biotic and abiotic environment.

Molecular Insights into Host and Vector Manipulation by Plant Viruses

Plant viruses rely on both host plant and vectors for a successful infection. Essentially to simplify studies, transmission has been considered for decades as an interaction between two partners, virus and vector. This interaction has gained a third partner, the host plant, to establish a tripartite pathosystem in which the players can react with each other directly or indirectly through changes induced in/by the third partner. For instance, viruses can alter the plant metabolism or plant immune defence pathways to modify vector’s attraction, settling or feeding, in a way that can be conducive for virus propagation. Such changes in the plant physiology can also become favourable to the vector, establishing a mutualistic relationship. This review focuses on the recent molecular data on the interplay between viral and plant factors that provide some important clues to understand how viruses manipulate both the host plants and vectors in order to improve transmission conditions and thus ensuring their survival.

Fruit Volatiles of Creeping Cucumber (Solena amplexicaulis) Attract a Generalist Insect Herbivore

Herbivorous insects employ host plant volatile blends as cue for host recognition. Adults of Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) feed on leaves, flowers, and fruits of Solena amplexicaulis (Lam.) Gandhi (syn: Melothria heterophylla) (Cucurbitaceae), commonly known as creeping cucumber. Currently, this pest is controlled by insecticides application. Hence, it is necessary to find out volatile components from fruits attracting the insect, which might be used for eco-friendly pest management program. behavioral responses of females were measured by Y-tube olfactometer bioassays towards volatile blends from undamaged (UD), insect-damaged (ID), and mechanically damaged (MD) fruits with the aim to identify the compounds responsible for host fruit location. Volatile organic compounds were identified and quantified by GC-MS and GC-FID analyses, respectively. Nonanal was predominant in volatile blends of UD, ID, and MD fruits. 1-Octen-3-ol, 3-octanone, 2-octanol, heptadienal (2E,4E), 1-pentadecanol, and 1-hexadecanol were present in volatile blends of ID and MD fruits, but females did not show response to these six compounds. 1-Octanol and 1-heptadecanol were unique in volatile blends of UD fruits after 4 hr of damage, but females did not show response to these compounds. Females were more attracted to volatile blends from UD fruits after 4 hr of damage in comparison to volatile blends released by UD fruits, due to increased emissions of (E,Z)-2,6-nonadienal and 2E-nonenal. A synthetic blend of 3.35 μg (E,Z)-2,6-nonadienal and 1.72 μg 2E-nonenal dissolved in 25 μl CH₂Cl₂ could be used for the development of baited traps to control this insect pest in integrated pest management strategies.

Plant-Plant Communication: Is There a Role for Volatile Damage-Associated Molecular Patterns?

Damage-associated molecular patterns (DAMPs) are an ancient form of tissue-derived danger or alarm signals that initiate cellular signaling cascades, which often initiate defined defense responses. A DAMP can be any molecule that is usually not exposed to cells such as cell wall components, peptides, nucleic acid fragments, eATP and other compounds. DAMPs might be revealed upon tissue damage or during attack. Typically, DAMPs are derived from the injured organism. Almost all eukaryotes can generate and respond to DAMPs, including plants. Besides the molecules mentioned, certain volatile organic compounds (VOCs) can be considered as DAMPs. Due to their chemical nature, VOCs are supposed to act not only locally and systemically in the same plant but also between plants. Here, we focus on damage-induced volatiles (DIVs) that might be regarded as DAMPs; we will review their origin, chemical nature, physiochemical properties, biological relevance and putative function in plant-plant communications. Moreover, we discuss the possibility to use such airborne DAMPs as eco-friendly compounds to stimulate natural defenses in agriculture in order to avoid pesticides.

Interspecific variations in the habitats of Reichardia tingitana (L.) Roth leading to changes in its bioactive constituents and allelopathic activity

Reichardia tingitana is an annual plant growing in different habitats of the Egyptian deserts. Little is known about variation among the habitats occupied by this species, its distribution, chemical composition, and allelopathic activity. The present study aimed to (a) assess the vegetation composition of three different habitats (Western Coast, Delta Coast, and Wadi Hagoul) of R. tingitana in Egypt, (b) determine their correlation to soil factors, (c) identify the changes in the bioactive constituents of R. tingitana in the three regions, and (d) evaluate the allelopathic activity regarding the variation in the habitat. Density and cover of all plant species associated with R. tingitana were estimated within 52 plots, representing three regions. Physical and chemical parameters of soil were analyzed in each plot. R. tingitana aboveground biomass was collected from each habitat, and the bioactive composition was analyzed using HPLC. The allelopathic effect against two weeds (Amaranthus lividius and Chenopodium murale) was assessed. The floristic composition showed the presence of 133 species belonging to 27 families. In the Delta Coast habitat of R. tingitana, Zygophyllum aegyptium and Calligonum polygonoides co-dominate, while Lycium shawii dominate the Western Coast habitat and finally the habitat of Wadi Hagoul was dominated by Haloxylon salicornicum. Soil analysis revealed little variations among habitats, especially salinity and organic matter. Fifteen compounds, mainly phenolics (60% of the total identified compounds) were identified from all R. tingitana samples. The major compounds were quercetin, naringenin, ellagic, gallic, chlorogenic, and caffeic acids. These compounds varied in diversity or quantity among different habitats. The Western Coast sample was the richest in species, followed by Delta Coast sample. Our study showed that salinity is the crucial factor that induces the production of bioactive constituents in R. tingitana, especially phenolics and flavonoids. The R. tingitana extracts significantly reduced the germination and growth of Chenopodium and Amaranthus. However, the Western Coast sample showed potent allelopathic activity, where the germination was wholly inhibited at 75 mg L^-1 and 50 mg L^-1, respectively. Thereby, this extract could be used as eco-friendly bioherbicide and may be integrated into weed control strategies.

The Ecology of Salicylic Acid Signaling: Primary, Secondary and Tertiary Effects with Applications in Agriculture

The salicylic acid pathway is one of the primary plant defense pathways, is ubiquitous in vascular plants, and plays a role in rapid adaptions to dynamic abiotic and biotic stress. Its prominence and ubiquity make it uniquely suited for understanding how biochemistry within plants can mediate ecological consequences. Induction of the salicylic acid pathway has primary effects on the plant in which it is induced resulting in genetic, metabolomic, and physiologic changes as the plant adapts to challenges. These primary effects can in turn have secondary consequences for herbivores and pathogens attacking the plant. These secondary effects can both directly influence plant attackers and mediate indirect interactions between herbivores and pathogens. Additionally, stimulation of salicylic acid related defenses can affect natural enemies, predators and parasitoids, which can recruit to plant signals with consequences for herbivore populations and plant herbivory aboveground and belowground. These primary, secondary, and tertiary ecological consequences of salicylic acid signaling hold great promise for application in agricultural systems in developing sustainable high-yielding management practices that adapt to changing abiotic and biotic environments.

Herbivore-induced volatile emission from old-growth black poplar trees under field conditions

Herbivory is well known to trigger increased emission of volatile organic compounds (VOCs) from plants, but we know little about the responses of mature trees. We measured the volatiles emitted by leaves of old-growth black poplar (Populus nigra) trees after experimental damage by gypsy moth (Lymantria dispar) caterpillars in a floodplain forest, and studied the effect of herbivory on the transcript abundance of two genes involved in the biosynthesis of VOCs, and the accumulation of defence phytohormones. Herbivory significantly increased volatile emission from the experimentally damaged foliage, but not from adjacent undamaged leaves in the damaged branches (i.e., no systemic response). Methylbutyraldoximes, 4,8-dimethyl-1,3,7-nonatriene (DMNT), (Z)-3-hexenol and (E)-β-ocimene, amongst other compounds, were found to be important in distinguishing the blend of herbivore-damaged vs. undamaged leaves. Herbivory also increased expression of PnTPS3 (described here for the first time) and PnCYP79D6-v4 genes at the damaged sites, these genes encode for an (E)-β-ocimene synthase and a P450 enzyme involved in aldoxime formation, respectively, demonstrating de novo biosynthesis of the volatiles produced. Herbivore-damaged leaves had significantly higher levels of jasmonic acid and its conjugate (-)-jasmonic acid-isoleucine. This study shows that mature trees in the field have a robust response to herbivory, producing induced volatiles at the damaged sites even after previous natural herbivory and under changing environmental conditions, however, further studies are needed to establish whether the observed absence of systemic responses is typical of mature poplar trees or if specific conditions are required for their induction.

Eavesdropping on gall-plant interactions: the importance of the signaling function of induced volatiles

The galling insect manipulates the host plant tissue to its own benefit, building the gall structure where it spends during most of its life cycle. These specialist herbivore insects can induce and manipulate plant structure and metabolism throughout gall development and may affect plant volatile emission. Consequently, volatile emission from altered metabolism contribute to eavesdropping cueing. Eavesdropping can be part of adaptive strategies used by evolution for both galling insects and the entire-associated community in order to cue some interaction response. This is in contrast to some herbivores associated with delayed induced responses, altering plant metabolites during the short time while they feed. Due to the different lifestyles of the galling organism, which are associated with different plant tissues and organs (e.g leaves, flowers or fruits), a distinct diversity of organisms may eavesdrop on induced volatiles interacting with the galls. Furthermore, the eavesdropping cues may be defined according to the phenological coupling between galling organism and host plant, which results from the development of a gall structure. For instance, when plants release volatile-induced defenses after galling insects' activity, another interactor may perceive these volatiles and change its behavior and interactions with host plants and galls. Thus, natural enemies could be attracted by different volatiles emitted by the gall tissues. Considering the duration of the life cycle of the galling organism and the gall, the temporal extent of gall-induced volatiles may include more persistent volatile cues and eavesdropping effects than the volatiles induced by non-galling herbivores. Accordingly, from chemical ecology perspective we expect that galling herbivore-induced volatiles may exhibit robust effects on neighboring-plant interactions including those ones during different plant developmental or phenological periods. Information about multitrophic interactions between insects and plants supports the additional understanding of direct and indirect effects, and allows insight into new hypotheses.

Classification of different pineapple varieties grown in Malaysia based on volatile fingerprinting and sensory analysis

Background

Pineapple is highly relished for its attractive sweet flavour and it is widely consumed in both fresh and canned forms. Pineapple flavour is a blend of a number of volatile and non-volatile compounds that are present in small amounts and in complex mixtures. The aroma compounds composition may be used for purposes of quality control as well as for authentication and classification of pineapple varieties.

Results

The key volatile compounds and aroma profile of six pineapple varieties grown in Malaysia were investigated by gas chromatography–olfactometry (GC-O), gas-chromatography–mass spectrometry and qualitative descriptive sensory analysis. A total of 59 compounds were determined by GC-O and aroma extract dilution analysis. Among these compounds, methyl-2-methylbutanoate, methyl hexanoate, methyl-3-(methylthiol)-propanoate, methyl octanoate, 2,5-dimethyl-4-methoxy-3(2H)-furanone, δ-octalactone, 2-methoxy-4-vinyl phenol, and δ-undecalactone contributed greatly to the aroma quality of the pineapple varieties, due to their high flavour dilution factor. The aroma of the pineapples was described by seven sensory terms as sweet, floral, fruity, fresh, green, woody and apple-like.

Conclusion

Inter-relationship between the aroma-active compounds and the pineapples revealed that ‘Moris’ and ‘MD2’ covaried majorly with the fruity esters, and the other varieties correlated with lesser numbers of the fruity esters. Hierarchical cluster analysis (HCA) was used to establish similarities among the pineapples and the results revealed three main groups of pineapples.

Multiannual effects of induced plant defenses: Are defended plants good or bad neighbors?

Defenses induced by herbivore feeding or phytohormones such as methyl jasmonate (MeJA) can affect growth, reproduction, and herbivory, not only on the affected individual but also in its neighboring plants. Here, we report multiannual defense, growth, and reproductive responses of MeJA-treated bilberry (Vaccinium myrtillus) and neighboring ramets. In a boreal forest in western Norway, we treated bilberry ramets with MeJA and water (control) and measured responses over three consecutive years. We observed the treatment effects on variables associated with herbivory, growth, and reproduction in the MeJA-treated and untreated ramet and neighboring ramets distanced from 10 to 500 cm. MeJA-treated ramets had fewer grazed leaves and browsed shoots compared to control, with higher effects in 2014 and 2015, respectively. In 2013, growth of control ramets was greater than MeJA-treated ramets. However, MeJA-treated ramets had more flowers and berries than control ramets 2 years after the treatment. The level of insect and mammalian herbivory was also lower in untreated neighboring ramets distanced 10-150 cm and, consistent with responses of MeJA-treated ramets, the stronger effect was also one and 2 years delayed, respectively. The same neighboring ramets had fewer flowers and berries than untreated ramets, indicating a trade-off between defense and reproduction. Although plant-plant effects were observed across all years, the strength varied by the distance between the MeJA-treated ramets and its untreated neighbors. We document that induced defense in bilberry reduces both insect and mammalian herbivory, as well as growth, over multiple seasons. The defense responses occurred in a delayed manner with strongest effects one and 2 years after the induction. Additionally, our results indicate defense signaling between MeJA-treated ramets and untreated neighbors. In summary, this study shows that induced defenses are important ecological strategies not only for the induced individual plant but also for neighboring plants across multiple years in boreal forests.

Characterization and Synergistic Effect of Antifungal Volatile Organic Compounds Emitted by the Geotrichum candidum PF005, an Endophytic Fungus from the Eggplant

Plant-associated endophytes are recognized as sources of novel bioactive molecules having diverse applications. In this study, an endophytic yeast-like fungal strain was isolated from the fruit of eggplant (Solanum melongena) and identified as Geotrichum candidum through phenotypic and genotypic characterizations. This endophytic G. candidum isolate PF005 was found to emit fruity scented volatiles. The compositional profiling of volatile organic compounds (VOCs) revealed the presence of 3-methyl-1-butanol, ethyl 3-methylbutanoate, 2-phenylethanol, isopentyl acetate, naphthalene, and isobutyl acetate in significant proportion when analyzed on a time-course basis. The VOCs from G. candidum exhibited significant mycelial growth inhibition (54%) of phytopathogen Rhizoctonia solani, besides having mild antifungal activity against a few other fungi. The source of carbon as a nutrient was found to be an important factor for the enhanced biosynthesis of antifungal VOCs. The antifungal activity against phytopathogen R. solani was improved up to 91% by feeding the G. candidum with selective precursors of alcohol and ester volatiles. Furthermore, the antifungal activity of VOCs was enhanced synergistically up to 92% upon the exogenous addition of naphthalene (1.0 mg/plate). This is the first report of G. candidum as an endophyte emitting antifungal VOCs, wherein 2-penylethanol, isopentyl acetate, and naphthalene were identified as important contributors to its antifungal activity. Possible utilization of G. candidum PF005 as a mycofumigant has been discussed based upon its antifungal activity and the qualified presumption of safety status.

Alternaria Brassicae Induces Systemic Jasmonate Responses in Arabidopsis Which Travel to Neighboring Plants via a Piriformsopora Indica Hyphal Network and Activate Abscisic Acid Responses

Stress information received by a particular local plant tissue is transferred to other tissues and neighboring plants, but how the information travels is not well understood. Application of Alternaria Brassicae spores to Arabidopsis leaves or roots stimulates local accumulation of jasmonic acid (JA), the expression of JA-responsive genes, as well as of NITRATE TRANSPORTER (NRT)2.5 and REDOX RESPONSIVE TRANSCRIPTION FACTOR1 (RRTF1). Infection information is systemically spread over the entire seedling and propagates radially from infected to non-infected leaves, axially from leaves to roots, and vice versa. The local and systemic NRT2.5 responses are reduced in the jar1 mutant, and the RRTF1 response in the rbohD mutant. Information about A. brassicae infection travels slowly to uninfected neighboring plants via a Piriformospora Indica hyphal network, where NRT2.5 and RRTF1 are up-regulated. The systemic A. brassicae-induced JA response in infected plants is converted to an abscisic acid (ABA) response in the neighboring plant where ABA and ABA-responsive genes are induced. We propose that the local threat information induced by A. brassicae infection is spread over the entire plant and transferred to neighboring plants via a P. indica hyphal network. The JA-specific response is converted to a general ABA-mediated stress response in the neighboring plant.

Exploring genes involved in benzoic acid biosynthesis in the Populus davidiana transcriptome and their transcriptional activity upon methyl jasmonate treatment

Benzoic acids (BAs) are important structural elements in a wide variety of essential compounds and natural products, and play crucial roles in plant fitness. BA is a precursor of diverse benzenoid compounds, including the hormone salicylic acid (SA) and the aglycone moiety of salicin, which is particularly important in the Salicaceae family. The biosynthetic pathways leading to BA formation in plants are largely unknown. Recently, the CoA-dependent β-oxidative BA biosynthesis pathway, which occurs in peroxisomes, has been characterized in petunia. The core of this pathway is cinnamic acid → cinnamoyl-CoA → 3-hydroxy-3-phenylpropanoyl-CoA → 3-oxo-3-phenylpropanoyl-CoA → benzoyl-CoA. Here, we used 454 pyrosequencing to analyze the transcriptome of Populus davidiana and isolate putative genes involved in BA biosynthesis. De novo assembly generated 57,322 unique sequences, including 15,217 contigs and 42,105 singletons. From the unique sequences, we selected six genes exhibiting high similarity to genes encoding L-phenylalanine ammonia lyase, cinnamate:CoA ligase, cinnamoyl-CoA hydratase-dehydrogenase, 3-ketoacyl-CoA thiolase, benzoyl-CoA:benzyl alcohol O-benzoyltransferase, and benzaldehyde dehydrogenase. Each of these enzymes might be involved in BA biosynthesis. Real-time PCR (qPCR) analysis revealed that these six genes were highly transcribed in the aerial organs of P. davidiana, particularly in leaves. Treating the leaves of in vitro cultured plants with methyl jasmonate (MeJA) strongly enhanced the mRNA accumulation of all 6 genes, and this treatment also clearly enhanced the accumulation of BA, SA, salicyl alcohol, benzyl alcohol, benzyl benzoate, and benzaldehyde but not salicin. Our study shows that P. davidiana may possess a CoA-dependent β-oxidative BA synthesis pathway. We also identified a relationship between the transcription of these genes and the accumulation of benzenoids, including BA and SA, which are highly responsive to the defense signaling molecule (MeJA).

Companion Plants for Aphid Pest Management

A potential strategy for controlling pests is through the use of "companion plants" within a crop system. This strategy has been used in several trials to fight against a major crop insect pest: the aphid. We reviewed the literature to highlight the major mechanisms by which a companion plant may act. Trials carried out under laboratory or field conditions revealed that companion plants operate through several mechanisms. A companion plant may be associated with a target crop for various reasons. Firstly, it can attract aphids and draw them away from their host plants. Secondly, it can alter the recognition of the host plant. This effect is mostly attributed to companion plant volatiles since they disturb the aphid host plant location, and additionally they may react chemically and physiologically with the host plant, making it an unsuitable host for aphids. Thirdly, it can attract natural enemies by providing shelter and food resources. In this review, the feasibility of using companion plants is discussed. We conclude that many factors need to be taken into account for a successful companion plant strategy. For the best long-term results, companion plant strategies have to be combined with other alternative approaches against aphids.

A secreted chitinase-like protein (OsCLP) supports root growth through calcium signaling in Oryza sativa

Chitinases belong to a conserved protein family and play multiple roles in defense, development and growth regulation in plants. Here, we identified a secreted chitinase-like protein, OsCLP, which functions in rice growth. A T-DNA insertion mutant of OsCLP (osclp) showed significant retardation of root and shoot growth. A comparative proteomic analysis was carried out using root tissue of wild-type and the osclp mutant to understand the OsCLP-mediated rice growth retardation. Results obtained revealed that proteins related to glycolysis (phosphoglycerate kinase), stress adaption (chaperonin) and calcium signaling (calreticulin and CDPK1) were differentially regulated in osclp roots. Fura-2 molecular probe staining, which is an intracellular calcium indicator, and inductively coupled plasma-mass spectrometry (ICP-MS) analysis suggested that the intracellular calcium content was significantly lower in roots of osclp as compared with the wild-type. Exogenous application of Ca²⁺ resulted in successful recovery of both primary and lateral root growth in osclp. Moreover, overexpression of OsCLP resulted in improved growth with modified seed shape and starch structure; however, the overall yield remained unaffected. Taken together, our results highlight the involvement of OsCLP in rice growth by regulating the intracellular calcium concentrations.

The Tree Drought Emission MONitor (Tree DEMON), an innovative system for assessing biogenic volatile organic compounds emission from plants

BACKGROUND

Biogenic volatile organic compounds (BVOC) emitted by plants play an important role for ecological and physiological processes, for example as response to stressors. These emitted compounds are involved in chemical processes within the atmosphere and contribute to the formation of aerosols and ozone. Direct measurement of BVOC emissions requires a specialized sample system in order to obtain repeatable and comparable results. These systems need to be constructed carefully since BVOC measurements may be disturbed by several side effects, e.g., due to wrong material selection and lacking system stability.

RESULTS

In order to assess BVOC emission rates, a four plant chamber system was constructed, implemented and throughout evaluated by synthetic tests and in two case studies on 3-year-old sweet chestnut seedlings. Synthetic system test showed a stable sampling with good repeatability and low memory effects. The first case study demonstrated the capability of the system to screen multiple trees within a few days and revealed three different emission patterns of sweet chestnut trees. The second case study comprised an application of drought stress on two seedlings compared to two in parallel assessed seedlings of a control. Here, a clear reduction of BVOC emissions during drought stress was observed.

CONCLUSION

The developed system allows assessing BVOC as well as CO₂ and water vapor gas exchange of four tree specimens automatically and in parallel with repeatable results. A canopy volume of 30 l can be investigated, which constitutes in case of tree seedlings the whole canopy. Longer lasting experiments of e.g., 1-3 weeks can be performed easily without any significant plant interference.

Interplant Aboveground Signaling Prompts Upregulation of Auxin Promoter and Malate Transporter as Part of Defensive Response in the Neighboring Plants

When disrupted by stimuli such as herbivory, pathogenic infection, or mechanical wounding, plants secrete signals such as root exudates and volatile organic compounds (VOCs). The emission of VOCs induces a response in the neighboring plant communities and can improve plant fitness by alerting nearby plants of an impending threat and prompting them to alter their physiology for defensive purposes. In this study, we investigated the role of plant-derived signals, released as a result of mechanical wounding, that may play a role in intraspecific communication between Arabidopsis thaliana communities. Plant-derived signals released by the wounded plant resulted in more elaborate root development in the neighboring, unwounded plants. Such plant-derived signals also upregulated the Aluminum-activated malate transporter (ALMT1) responsible for the secretion of malic acid (MA) and the DR5 promoter, an auxin responsive promoter concentrated in root apex of the neighboring plants. We speculate that plant-derived signal-induced upregulation of root-specific ALMT1 in the undamaged neighboring plants sharing the environment with stressed plants may associate more with the benign microbes belowground. We also observed increased association of beneficial bacterium Bacillus subtilis UD1022 on roots of the neighboring plants sharing environment with the damaged plants. Wounding-induced plant-derived signals therefore induce defense mechanisms in the undamaged, local plants, eliciting a two-pronged preemptive response of more rapid root growth and up-regulation of ALMT1, resulting in increased association with beneficial microbiome.

Olive fruits infested with olive fly larvae respond with an ethylene burst and the emission of specific volatiles

Olive fly (Bactrocera oleae R.) is the most harmful insect pest of olive (Olea europaea L.) which strongly affects fruits and oil production. Despite the expanding economic importance of olive cultivation, up to now, only limited information on plant responses to B. oleae is available. Here, we demonstrate that olive fruits respond to B. oleae attack by producing changes in an array of different defensive compounds including phytohormones, volatile organic compounds (VOCs), and defense proteins. Bactrocera oleae-infested fruits induced a strong ethylene burst and transcript levels of several putative ethylene-responsive transcription factors became significantly upregulated. Moreover, infested fruits induced significant changes in the levels of 12-oxo-phytodienoic acid and C12 derivatives of the hydroperoxide lyase. The emission of VOCs was also changed quantitatively and qualitatively in insect-damaged fruits, indicating that B. oleae larval feeding can specifically affect the volatile blend of fruits. Finally, we show that larval infestation maintained high levels of trypsin protease inhibitors in ripe fruits, probably by affecting post-transcriptional mechanisms. Our results provide novel and important information to understand the response of the olive fruit to B. oleae attack; information that can shed light onto potential new strategies to combat this pest.

Volatiles from Plants Induced by Multiple Aphid Attacks Promote Conidial Performance of Lecanicillium lecanii

Herbivore-induced plant volatiles (HIPVs) are clues that help predatory insects search for food. The hypothesis that entomopathogenic fungi, which protect plants, benefit from the release of HIPVs was tested. The plant Arabidopsis thaliana was used as the source of HIPVs. The insect herbivore Lipaphis erysimi (Kaltenbach) was used as the inducer, and the fungal pathogen of the aphid Lecanicillium lecanii was exposed to HIPVs to test our hypothesis. When exposed to aphid-induced A. thaliana volatiles, the mortality of aphids pre-treated with a conidial suspension of L. lecanii, the conidial germination and the appressorial formation were significantly increased compared with the control. The decan-3-ol and 4-methylpentyl isothiocyanate that were detected in the headspace seemed to have positive and negative affection, respectively. Moreover, HIPVs generated from groups of eight aphids per plant promoted significantly increased conidial germination and appressorial formation compared with HIPVs from groups of one, two and four aphids per plant. Our results demonstrated that the pathogenicity of the entomopathogenic fungus L. lecanii was enhanced when exposed to HIPVs and that the HIPVs were affected by the number of insect herbivores that induced them.