Inducible Defense Research Articles

New molecules in plant defence against pathogens.

Plants host a multipart immune signalling network to ward off pathogens. Pathogen attack upon plant tissues can often lead to an amplified state of (induced) defence against subsequent infections in distal tissues; this is known as systemic acquired resistance (SAR). The interaction of plants with beneficial microbes of the rhizosphere microbiome can also lead to an induced resistance in above-ground plant tissues, known as induced systemic resistance. Second messengers such as calcium (Ca2+), reactive oxygen species (ROS), and nitric oxide (NO) are necessary for cell-to-cell signal propagation during SAR and show emergent roles in the mediation of other SAR metabolites. These include the lysine-derived signals pipecolic acid (Pip) and N-hydroxypipecolic acid (NHP), which are key signalling metabolites in SAR. Emerging evidence additionally pinpoints plant volatiles as modulators of defence signalling within and between plants. Plant volatile organic compounds (VOCs) such as monoterpenes can promote SAR by functioning through ROS. Furthermore, plant-derived and additionally also microbial VOCs can target both salicylic acid and jasmonic acid signalling pathways in plants and modulate defence against pathogens. In this review, an overview of recent findings in induced defence signalling, with a particular focus on newer signalling molecules and how they integrate into these networks is discussed.

Effects of Nitrogen Supply on Induced Defense in Maize (Zea mays) against Fall Armyworm (Spodoptera frugiperda).

How nitrogen (N) supply affects the induced defense of plants remains poorly understood. Here, we investigated the impacts of N supply on the defense induced in maize (Zea mays) against the fall armyworm (Spodoptera frugiperda). In the absence of herbivore attack or exogenous jasmonic acid (JA) application, N supply increased plant biomass and enhanced maize nutrient (soluble sugar and amino acid) contents and leaf area fed by S. frugiperda (the feeding leaf area of S. frugiperda larvae in maize supplemented with 52.2 and 156.6 mg/kg of N was 4.08 and 3.83 times that of the control, respectively). When coupled with herbivore attack or JA application, maize supplemented with 52.2 mg/kg of N showed an increased susceptibility to pests, while the maize supplemented with 156.6 mg/kg of N showed an improved defense against pests. The changes in the levels of nutrients, and the emissions of volatile organic compounds (VOCs) caused by N supply could explain the above opposite induced defense in maize. Compared with herbivore attack treatment, JA application enhanced the insect resistance in maize supplemented with 156.6 mg/kg of N more intensely, mainly reflecting a smaller feeding leaf area, which was due to indole emission and two upregulated defensive genes, MPI (maize proteinase inhibitor) and PAL (phenylalanine ammonia-lyase). Hence, the optimal N level and appropriate JA application can enhance plant-induced defense against pests.

Jasmonate mediated inducible accumulation of indole glucosinolates confers resistance against Alternaria blight disease in cruciferous wild species Diplotaxis erucoides

The productivity of Indian mustard Brassica juncea is heavily constrained due to damage inflicted by Alternaria blight disease. Genetic resistance against this disease is obscure among the cultivated germplasms. Crop wild relatives (CWR) offer potential source of resistance genes against pathogen and insect-pests. A cruciferous wild relative Diplotaxis erucoides demonstrated high level of resistance against A. brassicae, the causative agent of Alternaria blight. In plants of the Brassicaceae family, sulfur containing secondary metabolites glucosinolates (GSLs) play a significant role in plant immunity and inducible defense against pathogens. Here, we have studied the transcriptional activation of the GSL biosynthetic genes by qRT-PCR and analysed the metabolite profile based on LC-MS in Alternaria resistant D. erucoides and susceptible species B. juncea. A comparative assessment of the gene-expression data demonstrated more efficient transcriptional activation of the key GSL biosynthetic genes by jasmonate mediated defense signaling in D. erucoides compared to B. juncea. The LC-MS analysis empirically established concomitant and inducible higher accumulation of the defense related GSL compounds in D. erucoides compared to B. juncea when challenged with the A. brassicae pathogen. The study also highlighted the two probable candidate genes for engineering resistance to Alternaria blight disease in susceptible genotypes of B. juncea.

Transcriptome profiling of Toona ciliata young stems in response to Hypsipyla robusta Moore.

Toona ciliata is a traditional woody plant that can be used as a medicinal material in China. The extracts of its roots, stems, leaves, and flowers all have a wide range of bioactive compounds. However, T. ciliata has been facing an unresolved pest problem caused by Hypsipyla robusta Moore (HRM), which seriously affects its growth and development. In this study, the expression level of TcMYB3 gene reached the maximum (28-fold) at 12 h and transcriptome sequencing of young stems eaten by HRM for 0, 3, 12, and 21 h were performed. A large number of differentially expressed genes (DEGs) were identified including jointly up-regulated genes (263) and down-regulated genes (378). JA synthesis and signaling transduction, terpene biosynthesis, and MAPKs signaling pathway were analyzed in depth and found that TcOPR3, TcJAR1, TcJAZs, and TcTPS9 genes possessed anti-insect potential. Moreover, MYB and ERF transcription factor (TF) families were significantly strengthened to the point that they may participate in induced defense mechanisms in T. ciliata. These data not only provide insights into the molecular mechanisms in resistance of T. ciliata to HRM but also helps to explore the new biocontrol strategies against insects in eco-friendly woody plants.

Pollen beetle offspring is more parasitized under moderate nitrogen fertilization of oilseed rape due to more attractive volatile signal

Biocontrol providing parasitoids can orientate according to volatile organic compounds (VOCs) of their host’s plants, the emission of which is potentially dependent on the availability of soil nitrogen (N). This paper aimed at finding the optimal N fertilization rate for oilseed rape (Brassica napus L.) to favor parasitism of pollen beetles (Brassicogethes aeneus Fab. syn. Meligethes aeneus Fab.) in a controlled environment. Pollen beetles preferred to oviposit into buds of plants growing under higher N fertilization, whereas their parasitoids favored moderate N fertilization. As a part of induced defense, the proportion of volatile products of glucosinolate pathway in the total oilseed rape VOC emission blend was increased. Our results suggest that the natural biological control of pollen beetle herbivory is best supported by moderate N fertilization rates.

Elicitation of Roots and AC-DC with PEP-13 Peptide Shows Differential Defense Responses in Multi-Omics.

The root extracellular trap (RET) has emerged as a specialized compartment consisting of root AC-DC and mucilage. However, the RET’s contribution to plant defense is still poorly understood. While the roles of polysaccharides and glycoproteins secreted by root AC-DC have started to be elucidated, how the low-molecular-weight exudates of the RET contribute to root defense is poorly known. In order to better understand the RET and its defense response, the transcriptomes, proteomes and metabolomes of roots, root AC-DC and mucilage of soybean (Glycine max (L.) Merr, var. Castetis) upon elicitation with the peptide PEP-13 were investigated. This peptide is derived from the pathogenic oomycete Phytophthora sojae. In this study, the root and the RET responses to elicitation were dissected and sequenced using transcriptional, proteomic and metabolomic approaches. The major finding is increased synthesis and secretion of specialized metabolites upon induced defense activation following PEP-13 peptide elicitation. This study provides novel findings related to the pivotal role of the root extracellular trap in root defense.

The stress effect of atrazine on the inducible defense traits of Daphnia pulex in response to fish predation risk: Evidences from morphology, life history traits, and expression of the defense-related genes

Herbicide pollution is persistent, which not only has a negative impact on individual organisms, but also may endanger the interspecific relationship between predators and prey. Cladocerans, i.e. zooplankton that plays an important role in the energy flow and material circulation in freshwater ecosystem, usually develop induced defense in response to predation risk. We used atrazine, one of the most used herbicides in the world, and Daphnia pulex, a representative cladocerans, to test the possible interference effect of herbicides on the induced defensive traits of cladocerans in response to predator fish (Rhodeus ocellatus) kairomone, including morphological defense, life history strategies, and the expression of defense-related genes. Atrazine reduced the body size, spine size, growth rate, total offspring, and the relative reproductive output of D. pulex, which further affected the response strength of the morphological and life history defenses, i.e., atrazine significantly reduced the spine size, relative spine size, and fecundity of D. pulex in response to R. ocellatus kairomone. Exposure to atrazine affected the expression of defense-related genes, and we speculated that atrazine affected the signaling process in the induced anti-predation defense of cladocerans. Specially, fish kairomone attenuated the negative effects of high concentrations of atrazine on the life history traits of D. pulex. Our results will help to accurately assess the potential risk of artificial compounds in freshwater ecosystems from the perspective of interspecific relationships, and help to understand the impact of environmental changes on the inducible anti-predator defense of prey in aquatic ecosystems.

Constitutive and Induced Defenses in Long-lived Pines Do Not Trade Off but Are Influenced by Climate.

Plants resist herbivores and pathogens by using constitutive (baseline) and inducible (change in defense after an attack) defenses. Inducibility has long been predicted to trade off with constitutive defense, reflecting the economic use of resources. However, empirical evidence for such tradeoffs is variable, and we still lack understanding about when and where defense trade-offs occur. We tested for tradeoffs between constitutive and induced defenses in natural populations of three species of long-lived pines (Pinus balfouriana, P. flexilis, P. longaeva) that differ greatly in constitutive defense and resistance to mountain pine beetle (MPB, Dendroctonus ponderosae). We also assessed how climate influenced constitutive and inducible defenses. At seven high-elevation sites in the western U.S., we simulated MPB attack to induce defenses and measured concentrations of terpene-based phloem defenses on days 0, 15, and 30. Constitutive and induced defenses did not trade off among or within species. Simulated MPB attack induced large increases in defense concentrations in all species independent of constitutive levels. MPB and its symbiotic fungi typically kill trees and thus could be selective forces maintaining strong inducibility within and among species. The contrasting constitutive concentrations in these species could be driven by the adaptation for specializing in harsh, high-elevation environments (e.g., P. balfouriana and P. longaeva) or by competition (e.g., P. flexilis), though these hypotheses have not been empirically examined. Climate influenced defenses, with the greatest concentrations of constitutive and induced defenses occurring at the coldest and driest sites. The interactions between climate and defenses have implications for these species under climate change.

Control of leaf spot in yam with leaf extracts of bitter melon

The use of plant extracts to induce resistance against pathogens has shown to be a promising alternative in the management of plant diseases. The objective was to evaluate the potential of ethanolic extract of Mormodica charantia on management of the Curvularia eragrostidis and enzyme activation involved on defense responses in yam (Dioscorea alata). The isolate of C. eragrostidis was obtained from leaves of yam with symptoms. Mycelial growth and sporulation were evaluated. The treatments were: extract of Momordica charantia 10, 100, 500 and 1000 ppm, acibenzolar-S-methyl (200 mg.L-1), fungicide (200 g.ha-1) and control. The evaluations were done daily, until the 15th day of the application of the treatments. The severity of the disease was evaluated at the end of the experiment, by the size of lesions in each plant. For determination of β-1,3-glucanase and phenylalanine ammonia lyase, leaves were collected in periods of 192 h after treatments application. Fungitoxic action of the treatments in the control of C. eragrostidis in vitro was verified. The M. charantia extract conferred significative levels of protection in yam plants against C. eragrostidis reducing incidence and disease severity. Thus, it was promoted increase in enzymatic activity, preconditioning yam in induced defense mechanisms.

The future of plant volatile organic compounds (pVOCs) research: Advances and applications for sustainable agriculture

Volatile organic compounds emitted by plants (pVOCs) protect themselves from abiotic and biotic stresses. Plants are under constant threats from biotic stress especially herbivores which facilitate plants to emit herbivore-induced plant volatiles (HIPVs), an inducible defense in plants against herbivores by communicating to herbivores’ natural enemies and neighboring plants. HIPVs are reported to act as feeding and/or oviposition deterrents to herbivores, belonging to four major groups including terpene/terpenoids, benzenoids and phenylpropanoids, the volatile fatty acid derivatives, and the volatile aminoacid derivatives. However, the plant volatile profiles induced by herbivores have been reported to be altered by silicon (Si)-fertilization, priming of plants with chemical elicitors and climate change which can induce plants to produce and emit novel plant volatiles that are not expressed by plants in response to damage by herbivory. Transgenic crops and/or sentinel crops with enhanced pVOCs emission profiles have been proposed to improve plant resistance, health and yields. Currently several technological advances in devices including field-portable electronic devices (e-Nose) and hand-held smartphone-based biosensors for in situ early detection of pVOCs profiles which are now available and supported by artificial intelligence (AI), to increase detection accuracy of these systems. The present review highlights the multi-dimension approaches emerging in pVOCs research for early and rapid detection of specific VOCs indicators as markers with associated plant biotic stressors.

Activation of mycelial defense mechanisms in the oyster mushroom Pleurotus ostreatus induced by Tyrophagus putrescentiae

Fungal chemicals are vital in processes recognizing damage- and microbe-associated molecules (DAMPs/MAMPs) that trigger defense responses in fungi. Pleurotus ostreatus is a widely cultivated edible fungus that is prone to attack from fungivorous insects and mites. Yet P. ostreatus has evolved an elegant defense system against fungivore attacks. In this study, we investigated how the oyster mushroom responds to the fungivory and mechanical wounding by conducting transcriptome, proteome, and secondary metabolic analyses. The profiling analysis revealed a total of 11,495 transcripts and 866 proteins, 4416 differentially expressed genes (DEGs), and 62 differentially expressed proteins (DEPs) were identified in response to the mite Tyrophagus putrescentiae feeding and mechanical wounding. In comparing the responses induced by mechanical wounding, some genes, proteins, and metabolites were uniquely induced or repressed by the mite. At the transcript level, nine pathways were activated by the mite feeding, including those of “MAPK signaling pathway–yeast”, “Phenylalanine metabolism”, and “Biotin metabolism”, among others, while both enrichment of “Ribosome”, “Ribosome biogenesis in eukaryotes”, and “Regulation of Mitophagy in Yeast” demonstrated the common effects upon fungal secretory protein synthesis and processing induced by fungivory and mechanical wounding. Fungivory also stimulated the synthesis of C8-aryl compounds and sesquiterpenes (especially1-octen-3-ol and α-/β-bisabolene), and these compounds repellent to T. putrescentiae. Both jasmonic acid (JA) and jasmonic acid methyl ester (MeJA) were specifically regulated by mite feeding and mechanical wounding. The terpene synthase gene transcription was significantly increased induced by the exogenous addition of MeJA, resulting in defensive sesquiterpene production against the mite. These findings are the first to demonstrate that the reactive oxygen species (ROS)/MAPK signaling pathway, JA regulation, specific gene expression, and protein synthesis, and anti-mite substance metabolism are all involved in coordinated inducible chemical-based defense responses in P. ostreatus, which could be especially effective the mite T. putrescentiae.

Pathophysiology and transcriptomic analysis of Picea koraiensis inoculated by bark beetle-vectored fungus Ophiostoma bicolor.

Ophiostomatoid fungi exhibit a complex relationship with bark beetles; exhausting of host tree defenses is traditionally regarded as one of the key benefits provided to beetle vectors. Ophiostoma bicolor is one of the dominant species of the mycobiota associated with Ips genus bark beetles which infect the spruce trees across the Eurasian continent. Host spruce trees resist fungal invasion through structural and inducible defenses, but the underlying mechanisms at the molecular level, particularly with respect to the interaction between bark beetle-associated fungi and host trees, remain unclear. The aim of this study was to observe the pathological physiology and molecular changes in Picea koraiensis seedlings after artificial inoculation with O. bicolor strains (TS, BH, QH, MX, and LWQ). This study showed that O. bicolor was a weakly virulent pathogen of spruce, and that the virulent of the five O. bicolor strains showed differentiation. All O. bicolor strains could induce monoterpenoid release. A positive correlation between fungal virulence and release of monoterpenoids was observed. Furthermore, the release rate of monoterpenoids peaked at 4 days post-inoculation (dpi) and then decreased from 4 to 90 dpi. Transcriptomic analysis at 4 dpi showed that many plant-pathogen interaction processes and mitogen-activated protein kinase (MAPK) metabolic processes were activated. The expression of monoterpenoid precursor synthesis genes and diterpenoid synthesis genes was upregulated, indicating that gene expression regulated the release rate of monoterpenoids at 4 dpi. The enriched pathways may reveal the immune response mechanism of spruce to ophiostomatoid fungi. The dominant O. bicolor possibly induces the host defense rather than defense depletion, which is likely the pattern conducted by the pioneers of beetle-associated mycobiota, such as Endoconidiophora spp.. Overall, these results facilitate a better understanding of the interaction mechanism between the dominant association of beetles and the host at the molecular level.

Proteomic changes associated with predator‐induced morphological defences in oysters

Inducible prey defences occur when organisms undergo plastic changes in phenotype to reduce predation risk. When predation pressure varies persistently over space or time, such as when predator and prey co-occur over only part of their biogeographic ranges, prey populations can become locally adapted in their inducible defences. In California estuaries, native Olympia oyster (Ostrea lurida) populations have evolved disparate phenotypic responses to an invasive predator, the Atlantic oyster drill (Urosalpinx cinerea). In this study, oysters from an estuary with drills, and oysters from an estuary without drills, were reared for two generations in a laboratory common garden, and subsequently exposed to cues from Atlantic drills. Comparative proteomics was then used to investigate molecular mechanisms underlying conserved and divergent aspects of their inducible defences. Both populations developed smaller, thicker, and harder shells after drill exposure, and these changes in shell phenotype were associated with upregulation of calcium transport proteins that could influence biomineralization. Inducible defences evolve in part because defended phenotypes incur fitness costs when predation risk is low. Immune proteins were downregulated by both oyster populations after exposure to drills, implying a trade-off between biomineralization and immune function. Following drill exposure, oysters from the population that co-occurs with drills grew smaller shells than oysters inhabiting the estuary not yet invaded by the predator. Variation in the response to drills between populations was associated with isoform-specific protein expression. This trend suggests that a stronger inducible defence response evolved in oysters that co-occur with drills through modification of an existing mechanism.

Marine gastropods at higher trophic level show stronger tolerance to ocean acidification

Climate change and anthropogenic activities are producing a range of new selection pressures, both abiotic and biotic, on marine organisms. Although it is known that climate change can differentially affect fitness‐related traits at different trophic levels of the food web, it is not clear if different trophic levels will respond via phenotypic plasticity in the form of maintenance of phenotypes in the face of abiotic and biotic environmental stress similarly. To answer this question, we combined a mesocosm experiment (120 days) using a food web comprising three gastropod species from two trophic levels (grazers and meso‐predators) and a meta‐analysis including 38 studies to address whether different trophic levels exhibit similar phenotypic responses to abiotic and biotic variables. Abiotic (ocean acidification) and biotic (predation) stress significantly influenced body mass, shell mass, shell thickness and shell strength in both grazers and meso‐predators in the mesocosm experiment, with the magnitude of OA effects greater on the meso‐predator than the grazers; a result supported by the meta‐analysis. In contrast, both mesocosm experiment and meta‐analysis found that predation risk induced stronger responses in shell morphology for grazers compared to meso‐predators. Together, our findings indicate that higher trophic level species are better able to maintain aspects of their phenotype under OA, suggesting that they may show greater tolerance to climate change effects in general, while lower trophic levels express higher levels of plastic inducible defences to maintain function when under threat of predation. By using marine snails as a model, our study provides new knowledge for understanding how changing environmental conditions may alter biological interactions, and increases our understanding of how climate change may affect ecological communities in which gastropods play a key role.

Differing Responses to Phytophthora cinnamomi Infection in Susceptible and Partially Resistant Persea americana (Mill.) Rootstocks: A Case for the Role of Receptor-Like Kinases and Apoplastic Proteases.

The hemibiotrophic plant pathogen Phytophthora cinnamomi Rands is the most devastating pathogen of avocado (Persea americana Mill.) and, as such, causes significant annual losses in the industry. Although the molecular basis of P. cinnamomi resistance in avocado and P. cinnamomi virulence determinants have been the subject of recent research, none have yet attempted to compare the transcriptomic responses of both pathogen and host during their interaction. In the current study, the transcriptomes of both avocado and P. cinnamomi were explored by dual RNA sequencing. The basis for partial resistance was sought by the inclusion of both susceptible (R0.12) and partially resistant (Dusa®) rootstocks sampled at early (6, 12 and 24 hours post-inoculation, hpi) and late time-points (120 hpi). Substantial differences were noted in the number of differentially expressed genes found in Dusa® and R0.12, specifically at 12 and 24 hpi. Here, the partially resistant rootstock perpetuated defense responses initiated at 6 hpi, while the susceptible rootstock abruptly reversed course. Instead, gene ontology enrichment confirmed that R0.12 activated pathways related to growth and development, essentially rendering its response at 12 and 24 hpi no different from that of the mock-inoculated controls. As expected, several classes of P. cinnamomi effector genes were differentially expressed in both Dusa® and R0.12. However, their expression differed between rootstocks, indicating that P. cinnamomi might alter the expression of its effector arsenal based on the rootstock. Based on some of the observed differences, several P. cinnamomi effectors were highlighted as potential candidates for further research. Similarly, the receptor-like kinase (RLK) and apoplastic protease coding genes in avocado were investigated, focusing on their potential role in differing rootstock responses. This study suggests that the basis of partial resistance in Dusa® is predicated on its ability to respond appropriately during the early stages following P. cinnamomi inoculation, and that important components of the first line of inducible defense, apoplastic proteases and RLKs, are likely to be important to the observed outcome.

The double-edged sword of inducible defences: costs and benefits of maladaptive switching from the individual to the community level

Phenotypic plasticity can increase individual fitness when environmental conditions change over time. Inducible defences are a striking example, allowing species to react to fluctuating predation pressure by only expressing their costly defended phenotype under high predation risk. Previous theoretical investigations have focused on how this affects predator–prey dynamics, but the impact on competitive outcomes and broader community dynamics has received less attention. Here we use a small food web model, consisting of two competing plastic autotrophic species exploited by a shared consumer, to study how the speed of inducible defences across three trade-off constellations affects autotroph coexistence, biomasses across trophic levels, and temporal variability. Contrary to the intuitive idea that faster adaptation increases autotroph fitness, we found that higher switching rates reduced individual fitness as it consistently provoked more maladaptive switching towards undefended phenotypes under high predation pressure. This had an unexpected positive impact on the consumer, increasing consumer biomass and lowering total autotroph biomass. Additionally, maladaptive switching strongly reduced autotroph coexistence through an emerging source-sink dynamic between defended and undefended phenotypes. The striking impact of maladaptive switching on species and food web dynamics indicates that this mechanism may be of more critical importance than previously recognized.

Coping with antagonistic predation risks: Predator-dependent unique responses are dominant in Ceriodaphnia cornuta.

Inducible defences of prey are evolved under diverse and variable predation risks. However, during the co-evolution of prey and multiple predators, the responses of prey to antagonistic predation risks, which may put the prey into a dilemma of responding to predators, remain unclear. Based on antagonistic predation pressure from an invertebrate (Chaoborus larvae) and a vertebrate (Rhodeus ocellatus) predator, we studied the responses of multiple traits and transcriptomes of the freshwater crustacean Ceriodaphnia cornuta under multiple predation risks. Chaoborus predation risk altered the expression of genes encoding cuticle proteins and modulated the biosynthesis of steroid hormones, cutin, suberine, and wax, leading to the development of horns and increase in size at the late developmental stage. Meanwhile, fish predation risk primarily triggered genes encoding ribosomes and those involved in unsaturated fatty acid biosynthesis and cysteine and methionine metabolism, resulting in smaller individual size and earlier reproduction. Inducible responses of both transcriptome and individual traits revealed that predator-dependent unique responses were dominant and the dilemma of antagonistic responses was relatively limited. However, the unique individual traits in response to invertebrate predation could be significantly impaired by vertebrate predation risk, even though the unique responses to different predators were extremely weakly correlated and could be elicited simultaneously. These results indicate that diverse predator-dependent unique responses are favoured by Ceriodaphnia during its co-evolution with multiple predators. Nonetheless, Ceriodaphnia is not a generalist that can fully adopt all predator-dependent unique responses simultaneously under multiple predation risks.

Inducibility of chemical defences by exogenous application of methyl jasmonate is long-lasting and conserved among populations in mature Pinus pinaster trees

Induced defences in conifers are an effective strategy that allows individuals to increase resistance against pests and pathogens by optimizing associated costs. Studies exploring inducibility of defences in conifers have usually been conducted in young individuals (i.e., seedlings and saplings) whereby effects were addressed within weeks or months after induction, limiting knowledge and generalization of long-term patterns in mature individuals growing under natural conditions. In addition, few studies have explored how plasticity and genetic differentiation among populations may affect the inducibility of defences in mature trees. We took advantage of two long-term Pinus pinaster common gardens to explore the interactive and independent contribution of genetic differentiation (i.e., variation among populations) and the environment (i.e., plasticity between sites) as drivers of variation in short-term, long-term and systemic inducibility of chemical defences (resin flow, non-volatile resin, phenolics) in response to simulated herbivore damage associated with jasmonate signalling. We provide evidence that the external application of methyl jasmonate increased the production of resin based defences in mature P. pinaster trees for at least two years after its application. We found that inducibility of defences did not differ among populations, but was rather contingent on local environmental conditions. Systemic effects of methyl jasmonate were also observed and suggest that induced responses likely involve complex within-individual reallocation of chemical defences. Our results contribute to better understanding of the ecological and evolutionary relevance of induced defence strategies in conifers and have important implications for integrating forest management practices aiming to improve forest health and resistance to pests and pathogens.

MAMP-elicited changes in amino acid transport activity contribute to restricting bacterial growth.

Plants live under the constant challenge of microbes that probe the environment in search of potential hosts. Plant cells perceive microbe-associated molecular patterns (MAMPs) from incoming microbes and activate defense responses that suppress attempted infections. Despite the substantial progress made in understanding MAMP-triggered signaling pathways, the downstream mechanisms that suppress bacterial growth and disease remain poorly understood. Here, we uncover how MAMP perception in Arabidopsis (Arabidopsis thaliana) elicits dynamic changes in extracellular concentrations of free L-amino acids (AA). Within the first 3 h of MAMP perception, a fast and transient inhibition of AA uptake produces a transient increase in extracellular AA concentrations. Within 4 and 12 h of MAMP perception, a sustained enhanced uptake activity decreases the extracellular concentrations of AA. Gene expression analysis showed that salicylic acid-mediated signaling contributes to inducing the expression of AA/H+ symporters responsible for the MAMP-induced enhanced uptake. A screening of loss-of-function mutants identified the AA/H+ symporter lysin/histidine transporter-1 as an important contributor to MAMP-induced enhanced uptake of AA. Infection assays in lht1-1 seedlings revealed that high concentrations of extracellular AA promote bacterial growth in the absence of induced defense elicitation but contribute to suppressing bacterial growth upon MAMP perception. Overall, the data presented in this study reveal a mechanistic connection between MAMP-induced plant defense and suppression of bacterial growth through the modulation of AA transport activity.

Acute methyl jasmonate exposure results in major bursts of stress volatiles, but in surprisingly low impact on specialized volatile emissions in the fragrant grass Cymbopogon flexuosus

Methyl jasmonate (MeJA) is an airborne hormonal elicitor that induces a fast rise of emissions of characteristic stress marker compounds methanol and green leaf volatiles (GLV), and a longer-term release of volatile terpenoids, but there is limited information of how terpene emissions respond to MeJA in terpene-storing species. East-Indian lemongrass (Cymbopogon flexuosus), an aromatic herb with a large terpenoid storage pool in idioblasts, was used to investigate the short- (0–1 h) and long-term (1–16 h) responses of leaf net assimilation rate (A), stomatal conductance (Gs) and volatile emissions to MeJA concentrations ranging from moderate to lethal. Both A and Gs were increasingly inhibited with increasing MeJA concentration in both short and long term. MeJA exposure resulted in a rapid elicitation, within 1 h after exposure, of methanol and GLV emissions. Subsequently, a secondary rise of GLV emissions was observed, peaking at 2 h after MeJA exposure for the highest and at 8 h for the lowest application concentration. The total amount and maximum emission rate of methanol and the first and second GLV emission bursts were positively correlated with MeJA concentration. Unexpectedly, no de novo elicitation of terpene emissions was observed through the experiment. Although high MeJA application concentrations led to visible lesions and desiccation in extensive leaf regions, this did not result in breakage of terpene-storing idioblasts. The study highlights an overall insensitivity of lemongrass to MeJA and indicates that differently from mechanical wounding, MeJA-driven cellular death does not break terpene-storing cells. Further studies are needed to characterize the sensitivity of induced defense responses in species with strongly developed constitutive defenses.