Constitutive Defense Research Articles

Susceptibility to Phytophthora cinnamomi of six holm oak (Quercus ilex) provenances: are results under controlled vs. natural conditions consistent?

Aim of study: Quercus forests are being affected by severe decline and mortality. The oak decline is associated with the soilborne pathogen Phytophthora cinnamomi (Pc), among others. This work aims to determine if Quercus ilex growing in Pc-infested soils show mortality differences according to their provenance in the field. It also evaluates whether the most tolerant provenances are those with the greatest constitutive chemical defences.
 Area of study: Acorns from six Spanish National Parks with natural presence of Q. ilex were collected for sowing in the greenhouse and later be planted on soils naturally infested by Pc in the surroundings of Plasencia, western Spain.
 Materials and methods: Seedlings were planted in four field plots located in two areas with oak decline: 153, 156, 157 and 155 plants in plot I, II, III and IV, respectively. The presence and infection of Pc was confirmed before their installation and during the experiment. Symptoms, regrowth, mortality and development was recorded for four years.
 Main results: There was a high mortality (56.0-80.5%) with differences among provenances. The most tolerant provenances in the field coincided with those identified under greenhouse conditions in a previous test. Provenances with higher constitutive condensed tannins better tolerate the pathogen under both conditions. In the southern provenances, some families with higher tolerance and, therefore, candidates for use in reforestation programs in areas infected by Pc, were identified.
 Research highlights: The restoration of Pc-affected areas would be possible through the use of Q. ilex plant material with high constitutive defences, more tolerant to the pathogen.

Genetic divergence along a climate gradient shapes chemical plasticity of a foundation tree species to both changing climate and herbivore damage.

Climate change is threatening the persistence of many tree species via independent and interactive effects on abiotic and biotic conditions. In addition, changes in temperature, precipitation, and insect attacks can alter the traits of these trees, disrupting communities and ecosystems. For foundation species such as Populus, phytochemical traits are key mechanisms linking trees with their environment and are likely jointly determined by interactive effects of genetic divergence and variable environments throughout their geographic range. Using reciprocal Fremont cottonwood (Populus fremontii) common gardens along a steep climatic gradient, we explored how environment (garden climate and simulated herbivore damage) and genetics (tree provenance and genotype) affect both foliar chemical traits and the plasticity of these traits. We found that (1) Constitutive and plastic chemical responses to changes in garden climate and damage varied among defense compounds, structural compounds, and leaf nitrogen. (2) For both defense and structural compounds, plastic responses to different garden climates depended on the climate in which a population or genotype originated. Specifically, trees originating from cool provenances showed higher defense plasticity in response to climate changes than trees from warmer provenances. (3) Trees from cool provenances growing in cool garden conditions expressed the lowest constitutive defense levels but the strongest induced (plastic) defenses in response to damage. (4) The combination of hot garden conditions and simulated herbivory switched the strategy used by these genotypes, increasing constitutive defenses but erasing the capacity for induction after damage. Because Fremont cottonwood chemistry plays a major role in shaping riparian communities and ecosystems, the effects of changes in phytochemical traits can be wide reaching. As the southwestern US is confronted with warming temperatures and insect outbreaks, these results improve our capacity to predict ecosystem consequences of climate change and inform selection of tree genotypes for conservation and restoration purposes.

Morphological and Biochemical Factors Associated with Constitutive Defense to Thrips in Alfalfa

Plants have evolved a series of inducible or constitutive defense mechanisms in response to herbivore attack. Constitutive plant defenses are morphological and biochemical traits of the plants themselves, regardless of the presence of herbivores. We bred an alfalfa variety (Caoyuan No.4) with high thrips resistance, but the mechanisms underlying Caoyuan No.4 resistance to thrips are not well understood. To explore the constitutive defense of Caoyuan No.4, the morphological and biochemical traits associated with constitutive defense to thrips in alfalfa were analyzed using a thrips-susceptible alfalfa accession (Caoyuan No.2) as a control. The results showed that Caoyuan No.4 had thicker palisade tissue and parenchyma tissue, wider collenchyma, phloem, cambium and lignin layer, and smaller epidermal cells and stomatal aperture compared to Caoyuan No.2. Moreover, Caoyuan No.4 showed more non-glandular trichomes in both leaves and stems, but less glandular trichomes and more wax in stems. In addition, the results of the widely targeted metabolomics analysis showed that metabolites related to flavonoid, isoflavonoid, flavone and flavonol biosynthesis, as well as cysteine and methionine metabolism, differed between CaoyuanNo.2 and Caoyuan No.4. These findings shed new light on the constitutive insect defense of plants associated with physical or biochemical traits and may provide convenient markers for breeding thrips-resistant alfalfa cultivars.

Bark Beetle Attack History Does Not Influence the Induction of Terpene and Phenolic Defenses in Mature Norway Spruce (Picea abies) Trees by the Bark Beetle-Associated Fungus Endoconidiophora polonica.

Terpenes and phenolics are important constitutive and inducible conifer defenses against bark beetles and their associated fungi. In this study, the inducible defenses of mature Norway spruce (Picea abies) trees with different histories of attack by the spruce bark beetle, Ips typographus were tested by inoculation with the I. typographus-associated fungus Endoconidiophora polonica. We compared trees that had been under previous attack with those under current attack and those that had no record of attack. After fungal inoculation, the concentrations of mono-, sesqui-, and diterpenes in bark increased 3- to 9-fold. For the phenolics, the flavan-3-ols, catechin, and gallocatechin, increased significantly by 2- and 5-fold, respectively, while other flavonoids and stilbenes did not. The magnitudes of these inductions were not influenced by prior bark beetle attack history for all the major compounds and compound classes measured. Before fungal inoculation, the total amounts of monoterpenes, diterpenes, and phenolics (constitutive defenses) were greater in trees that had been previously attacked compared to those under current attack, possibly a result of previous induction. The transcript levels of many genes involved in terpene formation (isoprenyl diphosphate synthases and terpene synthases) and phenolic formation (chalcone synthases) were significantly enhanced by fungal inoculation suggesting de novo biosynthesis. Similar inductions were found for the enzymatic activity of isoprenyl diphosphate synthases and the concentration of their prenyl diphosphate products after fungal inoculation. Quantification of defense hormones revealed a significant induction of the jasmonate pathway, but not the salicylic acid pathway after fungal inoculation. Our data highlight the coordinated induction of terpenes and phenolics in spruce upon infection by E. polonica, a fungal associate of the bark beetle I. typographus, but provide no evidence for the priming of these defense responses by prior beetle attack.

Meta‐analysis of induced anti‐herbivore defence traits in plants from 647 manipulative experiments with natural and simulated herbivory

Abstract Induced anti‐herbivore defences in plants can shape ecosystem structure and functions. Since these are known to be highly variable, quantifying their sources of variation remains important to understand their eco‐evolutionary roles. We conducted meta‐analysis of 647 experiments (paired control and treatment) from 192 studies to address sources of variation in induced anti‐herbivore defensive traits. This covered different agents of herbivory (insect, mammal and clipping), studies in greenhouse and in field settings, and covered 24 types of defence traits in 163 species from 50 families across 24 angiosperm orders. We used meta‐regression models—multi‐level random‐effects (MLREs) and robust variance estimators (RVEs)—to quantify variation due to study setting, herbivore type, chemical identity, angiosperm order, volatility, fertilization, and publication year as moderator variables. There were strong indications for publication bias in favour of large effect sizes, and studies with adequate sample size and precision were rare. Strength of induction was distributed uniformly over the phylogeny of 24 angiosperm orders. Stronger effects were reported from greenhouses than in field conditions, and induction was uninfluenced by herbivore type. Volatiles showed stronger response than non‐volatiles in greenhouses for insects. Biosynthetic precursors (e.g. jasmonates) and many defensive chemicals were induced in the greenhouse, but when measured in field conditions, they were unresponsive to herbivory and appear to be constitutive. Similar to constitutive response, induced responses were also unaffected by fertilization. Direction and magnitude of induction differ greatly from previous assessments as these have also changed over time, representing natural epistemological growth. A third of the variability was explained by moderators (marginal R2: chemical identity, angiosperm order, study setting, herbivore type and publication year); another third (conditional R2) was attributed to the identity of individual studies and observations. Synthesis. Manipulative experiments reveal many intrinsic differences among defensive chemicals and traits. They suggest plants in greenhouses may respond very differently to herbivores from those in field conditions. Although biosynthetic pathways of chemical responses, their modes of action and their effects on herbivores are well‐understood, studies with greater statistical power under ecologically relevant settings are needed to discern induced and constitutive defences in how plants respond to their natural enemies

Integrated Analysis of Metabolome and Transcriptome of Bambusa emeiensis Shoots in Response to Bamboo Snout Beetle Cyrtotrachelus buqueti (Coleoptera: Curculionidae)

Plants have evolved constitutive and inductive defense mechanisms to protect themselves from herbivorous insects. Metabolites in plants are thought to be involved in response to herbivores. Bambusa emeiensis is an important bamboo species widely distributed in Southwest China. It is easy to attract herbivores such as Cyrtotrachelus buqueti. Through the detection and analysis of metabolites in B. emeiensis metabolomic data, 35 differential metabolites (biomarkers) were finally identified from 206 detection peaks, mainly primary metabolites. Subsequently, we conducted an association analysis between 35 biomarkers that annotated to be involved in 71 metabolic pathways in the metabolome and 324 differentially expressed genes (DEGs) in 207 gene expression pathways distributed in the transcriptome of B. emeiensis after feeding by C. buqueti. We also discussed the relationship between the changes in gene expression levels and metabolite content variation. A total of 47 integrated pathways containing the corresponding DEGs and biomarkers were screened out, with the amino acid synthesis pathway (ko01230) containing the most DEGs and biomarkers. In these integrated pathways, the changes in biomarkers content and the expression levels of the corresponding genes were generally consistent. For example, the increase in tryptophan content was accompanied by an increase in the expression of the corresponding catalase in the tryptophan synthesis pathway. Similar to this was glucose and trehalose in carbohydrate metabolism. Therefore, this study further deepened our understanding of the defense mechanism of B. emeiensis against bamboo pests and provided new insights for the prevention and control of bamboo diseases and pests.

Interactive effects of biotic stressors and provenance on chemical defence induction by holm oak (Quercus ilex)

Key MessageThe patterns of induced chemical defences in Quercus ilex leaves are specific to the biotic stress factor that causes them. Interactive effects between stressors depend on provenance.Quercus forests are suffering serious decline worldwide, closely linked to the consequences of climate change. The increase of biotic stressors threatens the survival of the holm oak (Quercus ilex), a dominant tree species in the Mediterranean Basin. A better understanding of its resistance mechanisms is urgently required to enable a better control of its decline. In this work, the ability of holm oaks from six Iberian provenances to respond to multiple biotic damage is studied through an analysis of their induced chemical defence patterns. Using 2016 seedlings established in a common garden trial (6 regions × 12 families/region × 7 seedlings/family × 4 treatments), biotic damage was induced at the root level (by infection with the widespread pathogen Phytophthora cinnamomi) and at the above-ground level (by mechanical defoliation). The levels of constitutive and induced total phenols, total tannins and condensed tannins were measured. Results showed that (1) the defensive chemical patterns present significant local and geographical variation, (2) survival to stress is more related to constitutive defences than induced ones, (3) the induced response is stressor-specific, and (4) there is an interactive effect amongst stressors whose sign (induction/inhibition) depends on the provenance. These findings on biotic stressor effects on the chemical defences and survival of holm oak can contribute to the development of genetic material selection programs in the integrated control of the widespread decline of Quercus.

GT Factor ZmGT-3b Is Associated With Regulation of Photosynthesis and Defense Response to Fusarium graminearum Infection in Maize Seedling.

It is of critical importance for plants to correctly and efficiently allocate their resources between growth and defense to optimize fitness. Transcription factors (TFs) play crucial roles in the regulation of plant growth and defense response. Trihelix TFs display multifaceted functions in plant growth, development, and responses to various biotic and abiotic stresses. In our previous investigation of maize stalk rot disease resistance mechanism, we found a trihelix TF gene, ZmGT-3b, which is primed for its response to Fusarium graminearum challenge by implementing a rapid and significant reduction of its expression to suppress seedling growth and enhance disease resistance. The disease resistance to F. graminearum was consistently increased and drought tolerance was improved, while seedling growth was suppressed and photosynthesis activity was significantly reduced in the ZmGT-3b knockdown seedlings. Thus, the seedlings finally led to show a kind of growth–defense trade-off phenotype. Moreover, photosynthesis-related genes were specifically downregulated, especially ZmHY5, which encodes a conserved central regulator of seedling development and light responses; ZmGT-3b was confirmed to be a novel interacting partner of ZmHY5 in yeast and in planta. Constitutive defense responses were synchronically activated in the ZmGT-3b knockdown seedlings as many defense-related genes were significantly upregulated, and the contents of major cell wall components, such as lignin, were increased in the ZmGT-3b knockdown seedlings. These suggest that ZmGT-3b is involved in the coordination of the metabolism during growth–defense trade-off by optimizing the temporal and spatial expression of photosynthesis- and defense-related genes.

Reduction of the canonical function of a glycolytic enzyme enolase triggers immune responses that further affect metabolism and growth in Arabidopsis.

Primary metabolism provides energy for growth and development as well as secondary metabolites for diverse environmental responses. Here we describe an unexpected consequence of disruption of a glycolytic enzyme enolase named LOW EXPRESSION OF OSMOTICALLY RESPONSIVE GENE 2 (LOS2) in causing constitutive defense responses or autoimmunity in Arabidopsis thaliana. The autoimmunity in the los2 mutant is accompanied by a higher expression of about one-quarter of intracellular immune receptor nucleotide-binding leucine-rich repeat (NLR) genes in the genome and is partially dependent on one of these NLR genes. The LOS2 gene was hypothesized to produce an alternatively translated protein c-Myc Binding Protein (MBP-1) that functions as a transcriptional repressor. Complementation tests show that LOS2 executes its function in growth and immunity regulation through the canonical enolase activity but not the production of MBP-1. In addition, the autoimmunity in the los2 mutants leads to a higher accumulation of sugars and organic acids and a depletion of glycolytic metabolites. These findings indicate that LOS2 does not exert its function in immune responses through an alternatively translated protein MBP-1. Rather, they show that a perturbation of glycolysis from the reduction of the enolase activity results in activation of NLR-involved immune responses which further influences primary metabolism and plant growth, highlighting the complex interaction between primary metabolism and plant immunity.

Between-population differences in constitutive and infection-induced gene expression in threespine stickleback.

Vertebrate immunity is a complex system consisting of a mix of constitutive and inducible defences. Furthermore, host immunity is subject to selective pressure from a range of parasites and pathogens which can produce variation in these defences across populations. As populations evolve immune responses to parasites, they may adapt via a combination of (1) constitutive differences, (2) shared inducible responses, or (3) divergent inducible responses. Here, we leverage a powerful natural host‐parasite model system (Gasterosteus aculeatus and Schistochephalus solidus) to tease apart the relative contributions of these three types of adaptations to among‐population divergence in response to parasites. Gene expression analyses revealed limited evidence of significant divergence in constitutive expression of immune defence, and strong signatures of conserved inducible responses to the parasite. Furthermore, our results highlight a handful of immune‐related genes which show divergent inducible responses which may contribute disproportionately to functional differences in infection success or failure. In addition to investigating variation in evolutionary adaptation to parasite selection, we also leverage this unique data set to improve understanding of cellular mechanisms underlying a putative resistance phenotype (fibrosis). Combined, our results provide a case study in evolutionary immunology showing that a very small number of genes may contribute to genotype differences in infection response.

Siliceous and non‐nutritious: Nitrogen limitation increases anti‐herbivore silicon defences in a model grass

Abstract Silicon (Si) accumulation alleviates a diverse array of environmental stresses in many plants, including conferring physical resistance against insect herbivores. It has been hypothesised that grasses, in particular, utilise ‘low metabolic cost’ Si for structural and defensive roles under nutrient limitation. While carbon (C) concentrations often negatively correlate with Si concentrations, the relationship between nitrogen (N) status and Si is more variable. Moreover, the impacts of N limitation on constitutive physical Si defences (e.g. silica and prickle cells) against herbivores are unknown. We determined how N limitation affected Si deposition in the model grass Brachypodium distachyon and how changes in these constitutive defences impacted insect herbivore Helicoverpa armigera growth rates. We used scanning electron microscopy (SEM) and energy dispersive X‐ray spectrometry in conjunction with X‐ray mapping (XRM) to quantify physical structures on leaves and determine Si deposition patterns. We also determined how N limitation and Si supply impacted the jasmonic acid (JA) pathway, the master regulator of induced defences against arthropod herbivores. N limitation reduced shoot growth by over 40%, but increased root mass (+21%), leaf Si concentrations (+50%) and the density of silica (+28%) and flattened prickle (+76%) cells. Energy‐dispersive X‐ray spectroscopy and XRM established that Si was being deposited in these structures, together with hooked prickle cells and macro‐hairs. Herbivore relative growth rates (RGR) were more than 115% lower in Si‐supplied plants compared to plants without Si supply and negatively correlated with leaf Si concentration and silica cell density. RGR was further reduced by N limitation and positively correlated with leaf N concentrations. Increases in JA concentrations following induction of the JA pathway were at least doubled by N limitation. Synthesis. Si accumulation and deposition were highly regulated by N availability, with N limitation promoting both constitutive Si physical defences and induction of the JA defensive pathway, in line with the resource availability hypothesis. These results indicate that grasses use ‘low‐cost Si’ when resources are limited and suggest that plant productivity may benefit from optimising conventional fertilisers and Si fertilisation.

Adaptive defence and sensing responses of host plant roots to fungal pathogen attack revealed by transcriptome and metabolome analyses

Plant root-produced constitutive and inducible defences inhibit pathogenic microorganisms within roots and in the rhizosphere. However, regulatory mechanisms underlying host responses during root-pathogen interactions are largely unexplored. Using the model species Brachypodium distachyon (Bd), we studied transcriptional and metabolic responses altered in Bd roots following challenge with Fusarium graminearum (Fg), a fungal pathogen that causes diseases in diverse organs of cereal crops. Shared gene expression patterns were found between Bd roots and spikes during Fg infection associated with the mycotoxin deoxynivalenol (DON). Overexpression of BdMYB78, an up-regulated transcription factor, significantly increased root resistance during Fg infection. We show that Bd roots recognize encroaching Fg prior to physical contact by altering transcription of genes associated with multiple cellular processes such as reactive oxygen species and cell development. These changes coincide with altered levels of secreted host metabolites detected by an untargeted metabolomic approach. The secretion of Bd metabolites was suppressed by Fg as enhanced levels of defence-associated metabolites were found in roots during pre-contact with a Fg mutant defective in host perception and the ability to cause disease. Our results help to understand root defence strategies employed by plants, with potential implications for improving the resistance of cereal crops to soil pathogens.

Different Polyphenolic Parenchyma Cell and Phloem Axial Resin Duct-Like Structure Formation Rates in Cupressus sempervirens Clones Infected with Seiridium cardinale.

The aim of this study was the characterization of constitutive and induced defense mechanisms in the bark tissues of Cupressus sempervirens before and after infection with the bark fungus Seiridium cardinale, which is responsible for cypress canker disease. The time-course development of polyphenolic parenchyma (PP) cells and phloem axial resin duct (PARD)-like structures in the phloem was investigated in two C. sempervirens clones, one resistant and one susceptible to the disease, through anatomical and histological observations carried out by light microscope during a 19-day trial. PP cells were constitutively more abundant in the canker-resistant clone (R clone) compared with the susceptible clone (S clone), whereas PARD-like structures were not present in the bark of untreated plants of both clones. PP cells increased in both clones as a response to infection, but in the R clone, they were more abundant 5 and 12 days after inoculation. After inoculation, PARD-like structures appeared in the phloem after 5 days in the R clone and only after 12 days in the S clone. Even the number of cells surrounding the PARD-like structures was higher in the R clone 5 and 12 days after inoculation compared with the S clone. These observations demonstrate a faster phloem response of the R clone in the early phase of the infection. This may slow down initial growth of the fungus, contributing to the resistance mechanism.

Maize biochemistry in response to root herbivory was mediated by domestication, spread, and breeding

With domestication, northward spread, and breeding, maize defence against root-herbivores relied on induced defences, decreasing levels of phytohormones involved in resistance, and increasing levels of a phytohormone involved in tolerance. We addressed whether a suite of maize (Zea mays mays) phytohormones and metabolites involved in herbivore defence were mediated by three successive processes: domestication, spread to North America, and modern breeding. With those processes, and following theoretical predictions, we expected to find: a change in defence strategy from reliance on induced defences to reliance on constitutive defences; decreasing levels of phytohormones involved in herbivore resistance, and; increasing levels of a phytohormone involved in herbivore tolerance. We tested those predictions by comparing phytohormone levels in seedlings exposed to root herbivory by Diabrotica virgifera virgifera among four plant types encompassing those processes: the maize ancestor Balsas teosinte (Zea mays parviglumis), Mexican maize landraces, USA maize landraces, and USA inbred maize cultivars. With domestication, maize transitioned from reliance on induced defences in teosinte to reliance on constitutive defences in maize, as predicted. One subset of metabolites putatively involved in herbivory defence (13-oxylipins) was suppressed with domestication, as predicted, though another was enhanced (9-oxylipins), and both were variably affected by spread and breeding. A phytohormone (indole-3-acetic acid) involved in tolerance was enhanced with domestication, and with spread and breeding, as predicted. These changes are consistent with documented changes in herbivory resistance and tolerance, and occurred coincidentally with cultivation in increasingly resource-rich environments, i.e., from wild to highly enriched agricultural environments. We concluded that herbivore defence evolution in crops may be mediated by processes spanning thousands of generations, e.g., domestication and spread, as well as by processes spanning tens of generations, e.g., breeding and agricultural intensification.

Ecometabolomics of plant–herbivore and plant–fungi interactions: a synthesis study

AbstractThe functional adaptive responses of higher plants to biotic interactions with herbivores and fungi have long been topics of research. One constraint to obtaining a comprehensive understanding of the most general plant responses, however, has been the difficulty of studying all plant functional shifts simultaneously due to analytical limitations. Now this is possible with the advent of metabolomics. Using 151 records from the WEB of SCIENCE database, we have analyzed the development and application of metabolomic profiles to ecological studies in the last two decades. We have used meta‐analysis and pathway enrichment analyses to assess the whole set of constitutive and inducible defenses. Constitutive defenses against herbivores were mainly based on a significant high level of the metabolism of several amino acids with parallel increases in the concentrations of flavones (phenolics) and saponins (glycosides). Inducible defenses, though, were mainly based on the increases in concentration of methyl‐ketone, pantothenate, and Coenzyme A. Butyrate metabolism and the mitochondrial electron‐transport chain were upregulated, in agreement with previous reports that herbivory‐activated plant chemical defenses were mainly based on jasmonic acid, salicylic acid, and ethylene‐associated pathways. The metabolic responses/acclimations to pathogenic fungi were mainly linked with increases in aspartate and pyruvate metabolism, the transfer of acetyl groups within mitochondria, and the upregulation of branched‐chain amino acids degradation pathways. These responses/acclimations were accompanied by higher concentrations of the most important groups of secondary metabolites such as phenolics (anthocyanins, flavonoids), quinones, alkaloids, terpenoids, and polyamines and other compounds related to antistress mechanisms such as proline. The leaves of mycorrhized plants accumulated nucleotide sugars, sphingolipids, and methylhistidine. These responses were associated with maintaining the integrity of plant cell membranes under fungal hypha penetration. The responses were accompanied by increases in the concentrations of phenolics, blumenols, and alkaloids and decreases in the concentrations of polyamines, consistent with the mycorrhizal inhibition of polyamines. This summary provides a clear synthesis of the most successful plant strategies selected after millions of years of evolution and will be a very promising tool for the management of crops and ecosystems and for selecting the main lines in breeding studies for future research.

European oak chemical diversity - from ecotypes to herbivore resistance.

Climate change is increasing insect pressure and forcing plants to adapt. Although chemotypic differentiation and phenotypic plasticity in spatially separated tree populations are known for decades, understanding their importance in herbivory resistance across forests remains challenging. We studied four oak forest stands in Germany using nontarget metabolomics, elemental analysis, and chemometrics and mapped the leaf metabolome of herbivore-resistant (T-) and herbivore-susceptible (S-) European oaks (Quercus robur) to Tortrix viridana, an oak pest that causes severe forest defoliation. Among the detected metabolites, we identified reliable metabolic biomarkers to distinguish S- and T-oak trees. Chemotypic differentiation resulted in metabolic shifts of primary and secondary leaf metabolism. Across forests, T-oaks allocate resources towards constitutive chemical defense enriched of polyphenolic compounds, e.g. the flavonoids kaempferol, kaempferol and quercetin glucosides, while S-oaks towards growth-promoting substances such as carbohydrates and amino-acid derivatives. This extensive work across natural forests shows that oaks' resistance and susceptibility to herbivory are linked to growth-defense trade-offs of leaf metabolism. The discovery of biomarkers and the developed predictive model pave the way to understand Quercus robur's susceptibility to herbivore attack and to support forest management, contributing to the preservation of oak forests in Europe.

Tomato transcriptomic response to Tuta absoluta infestation

BackgroundThe South America pinworm, Tuta absoluta, is a destructive pest of tomato that causes important losses worldwide. Breeding of resistant/tolerant tomato cultivars could be an effective strategy for T. absoluta management but, despite the economic importance of tomato, very limited information is available about its response to this treat. To elucidate the defense mechanisms to herbivore feeding a comparative analysis was performed between a tolerant and susceptible cultivated tomato at both morphological and transcriptome level to highlight constitutive leaf barriers, molecular and biochemical mechanisms to counter the effect of T. absoluta attack.ResultsThe tolerant genotype showed an enhanced constitutive barrier possibly as result of the higher density of trichomes and increased inducible reactions upon mild infestation thanks to the activation/repression of key transcription factors regulating genes involved in cuticle formation and cell wall strength as well as of antinutritive enzymes, and genes involved in the production of chemical toxins and bioactive secondary metabolites.ConclusionsOverall, our findings suggest that tomato resilience to the South America pinworm is achieved by a combined strategy between constitutive and induced defense system. A well-orchestrated modulation of plant transcription regulation could ensure a trade-off between defense needs and fitness costs. Our finding can be further exploited for developing T. absoluta tolerant cultivars, acting as important component of integrated pest management strategy for more sustainable production.

Ecology of Fear: Spines, Armor and Noxious Chemicals Deter Predators in Cancer and in Nature

In nature, many multicellular and unicellular organisms use constitutive defenses such as armor, spines, and noxious chemicals to keep predators at bay. These defenses render the prey difficult and/or dangerous to subdue and handle, which confers a strong deterrent for predators. The distinct benefit of this mode of defense is that prey can defend in place and continue activities such as foraging even under imminent threat of predation. The same qualitative types of armor-like, spine-like, and noxious defenses have evolved independently and repeatedly in nature, and we present evidence that cancer is no exception. Cancer cells exist in environments inundated with predator-like immune cells, so the ability of cancer cells to defend in place while foraging and proliferating would clearly be advantageous. We argue that these defenses repeatedly evolve in cancers and may be among the most advanced and important adaptations of cancers. By drawing parallels between several taxa exhibiting armor-like, spine-like, and noxious defenses, we present an overview of different ways these defenses can appear and emphasize how phenotypes that appear vastly different can nevertheless have the same essential functions. This cross-taxa comparison reveals how cancer phenotypes can be interpreted as anti-predator defenses, which can facilitate therapy approaches which aim to give the predators (the immune system) the upper hand. This cross-taxa comparison is also informative for evolutionary ecology. Cancer provides an opportunity to observe how prey evolve in the context of a unique predatory threat (the immune system) and varied environments.

Nitrogen Supply Alters Rice Defense Against the Striped Stem Borer Chilo suppressalis.

Plant nutrition status is closely associated with plant defense against insect herbivores. However, the way nitrogen supply regulates rice anti-herbivore is not clear. This study investigated the effects of low (LN, 0.3 mM) and high (HN, 3 mM) nitrate levels on rice resistance against the striped stem borer Chilo suppressalis (SSB), one of the major destructive rice pests. Seven-day-old rice seedlings were cultured with different nitrate levels for 30 days and then inoculated with third instars of SSB. LN significantly enhanced rice anti-herbivore defense and lowered the total nitrogen content in the plants, but increased the content of free amino acids after SSB infestation. Additionally, LN significantly increased the accumulation of phenolic acids and flavonoids, especially lignin, resulting in enhanced constitutive defense in SSB-infested plants. SSB feeding led to a rapid accumulation of secondary metabolites. HN application led to the accumulation of metabolites derived from cinnamic acid, p-coumaric acid, p-coumaric CoA, feruloyl CoA, and apigenin, while LN led to the accumulation of metabolites derived from 3-dehydroquinic acid, phenylalanine, acetyl CoA, and aspartic acid. Collectively, our finding suggests that nitrogen deficiency enhances rice anti-herbivore defense via constitutive defense by the accumulation of phenolic acids and flavonoids.

Maize Responses Challenged by Drought, Elevated Daytime Temperature and Arthropod Herbivory Stresses: A Physiological, Biochemical and Molecular View.

Maize (Zea mays L.) is one of the main cereals grown around the world. It is used for human and animal nutrition and also as biofuel. However, as a direct consequence of global climate change, increased abiotic and biotic stress events have been reported in different regions of the world, which have become a threat to world maize yields. Drought and heat are environmental stresses that influence the growth, development, and yield processes of maize crops. Plants have developed dynamic responses at the physiological, biochemical, and molecular levels that allow them to escape, avoid and/or tolerate unfavorable environmental conditions. Arthropod herbivory can generate resistance or tolerance responses in plants that are associated with inducible and constitutive defenses. Increases in the frequency and severity of abiotic stress events (drought and heat), as a consequence of climate change, can generate critical variations in plant-insect interactions. However, the behavior of herbivorous arthropods under drought scenarios is not well understood, and this kind of stress may have some positive and negative effects on arthropod populations. The simultaneous appearance of different environmental stresses and biotic factors results in very complex plant responses. In this review, recent information is provided on the physiological, biochemical, and molecular responses of plants to the combination of drought, heat stress, and the effect on some arthropod pests of interest in the maize crop.