Molecular interaction network of plant-herbivorous insects

The interactions between plants and herbivorous insects are complex and involve multiple factors,driving species formation and leading to the beginning of co-evolution and diversification of plant and insect molecules.Various molecular processes regulate the interactions between plants and herbivorous insects.Here,we discuss the molecular patterns of plant perception of herbivorous insect feeding through activation of early signaling components,crosstalk of plant defense network composed of multiple plant hormones,and various adaptive changes in insect responses to plant defenses.Both plant defenses and insect counter-defenses are molecular adaptation processes to each other.Molecular models of plant-herbivorous insect interactions can more intuitively help us to understand the co-evolutionary arms race between plants and herbivorous insects.These results will provide detailed evidence to elucidate and enrich the interaction network of plant-herbivorous insects.

Herbivore and native plant diversity synergistically resist alien plant invasion regardless of nutrient conditions

Alien plant invasion success can be inhibited by two key biotic factors:native herbivores and plant diversity.However,few studies have experimentally tested whether these factors interact to synergistically resist invasion success,especially factoring in changing global environments(e.g.nutrient enrichment).Here we tested how the synergy between native herbivores and plant diversity affects alien plant invasion success in various nutrient conditions.For this purpose,we exposed alien plant species in potmesocosms to different levels of native plant diversity(4 vs.8 species),native generalist herbivores,and high and low soil nutrient levels.We found that generalist herbivores preferred alien plants to native plants,inhibiting invasion success in a native community.This inhibition was amplified by highly diverse native communities.Further,the amplified effect between herbivory and native plant diversity was independent of nutrient conditions.Our results suggest that a higher diversity of native communities can strengthen the resistance of native generalist herbivores to alien plant invasions by enhancing herbivory tolerance.The synergistic effect remains in force in nutrient-enriched habitats that are always invaded by alien plant species.Our results shed light on the effective control of plant invasions using multi-trophic means,even in the face of future global changes.

The Influence of Phlorotannins and Bromophenols on the Feeding Behavior of Marine Herbivorous Gastropod <i>Turbo cornutus</i>

The influence of phlorotannins and bromophenols on the feeding behavior of marine herbivores was determined using bioassay of Turbo cornutus. It was found that phloroglucinol and its oligomers isolated from the brown alga Eisenia bicyclis (eckol, fucofuroeckol A, phlorofucofuroeckol A, dieckol, and 8,8’-bieckol) had a deterrent effect against feeding behavior of T. cornutus in the concentration of algal body, respectively. In the case of the examination of 0.1 mM concentration, although fucofuroeckol A and phlorofucofuroeckol A significantly reduced feeding by T. cornutus, phloroglucinol and 8,8’-bieckol did not show any significant influence on feeding behavior, and eckol and dieckol had stimulating activity. 2,4-Dibromophenol and 2,4,6-tribromophenol, which are major components of extracellular secretions from Eisenia and Ecklonia species, caused the death, the torpidity, and the decreased appetite of T. cornutus at the concentration of 0.1 mM. In addition, 2,4-dibromophenol had strong feeding deterrent activity at the concentration of 1 μM. These results indicate that phlorotannins and bromophenols act as chemical defense agents of brown algae against environmental stresses such as the herbivore attack.

Combined Effects of Temperature and Nutrient Enrichment on Palatability of the Brown Alga Sargassum yezoense (Yamada) Yoshida &T. Konno

Global warming is predicted to strengthen marine plant-herbivore interactions. However, little is known about the effect of temperature on palatability and the associated chemical composition of marine macroalgae. To study the effects of physiological stress caused by the warm water temperatures and nutrient-poor conditions that occur during summer, we cultured the brown alga Sargassum yezoense at three different temperatures (16°C, 22°C, and 28°C) in both nutrient-enriched and non-enriched media. We then compared phlorotannin (i.e., defensive compounds) and nitrogen concentrations of S. yezoense as well as consumption rate by the sea urchin Hemicetrotus pulcherrimus among the treatment groups. No effect of culture temperature on phlorotannin and ni-trogen concentrations or consumption rate was detected. Nutrient enrichment resulted in decreased phlorotannin concentration and increased nitrogen concentration. Although nutrient enrichment did not affect consumption rate, a positive correlation between nitrogen concentration and consumption rate was detected. In contrast, there was no correlation between phlorotannin concentration and consumption rate. These results suggested that palatability of S. yezoense to H. pulcherrimus might not be affected by elevated temperature but that it could increase with nutrient enrichment.

Formation of time patterns in a diffusive plant-herbivore system with toxin-determined functional response

In this paper, we consider a diffusive plant-herbivore system with the toxin-determined functional response and subject to the homogeneous Neumann boundary conditions on the bounded one-dimensional spatial domain. The impacts of diffusion on the dynamical behaviors are investigated and it is found that although the appearance of diffusion does not affect the stability of constant steady states, it can lead to the occurrence of Hopf bifurcation of spatially inhomogeneous periodic solutions at the constant positive steady state. The conclusions show that the occurrence of spatial diffusion can induce more complex dynamical behaviors.

Trade-offs between the accumulation of cuticular wax and jasmonic acid-mediated herbivory resistance in maize

Plants have evolved complex physical and chemical defense systems that allow them to withstand herbivory infestation.Composed of a complex mixture of very-long-chain fatty acids(VLCFAs)and their derivatives,cuticular wax constitutes the first physical line of defense against herbivores.Here,we report the function of Glossy 8(ZmGL8),which encodes a 3-ketoacyl reductase belonging to the fatty acid elongase complex,in orchestrating wax production and jasmonic acid(JA)-mediated defenses against herbivores in maize(Zea mays).The mutation of GL8 enhanced chemical defenses by activating the JA-dependent pathway.We observed a trade-off between wax accumulation and JA levels across maize glossy mutants and 24 globally collected maize inbred lines.In addition,we demonstrated that mutants defective in cuticular wax biosynthesis in Arabidopsis thaliana and maize exhibit enhanced chemical defenses.Comprehensive transcriptomic and lipidomic analyses indicated that the gl8 mutant confers chemical resistance to herbivores by remodeling VLCFA-related lipid metabolism and subsequent JA biosynthesis and signaling.These results suggest that VLCFA-related lipid metabolism has a critical role in regulating the trade-offs between cuticular wax and JA-mediated chemical defenses.

Mechanisms of Optimal Defense Patterns in Nicotiana attenuata: Flowering Attenuates Herbivory-elicited Ethylene and Jasmonate Signaling

To defend themselves against herbivore attack, plants produce secondary metabolites, which are variously inducible and constitutively deployed, presumably to optimize their fitness benefits in light of their fitness costs. Three phytohormones, jasmonates （JA） and their active forms, the JA-isoleucine （JA-Ile） and ethylene （ET）, are known to play central roles in the elicitation of induced defenses, but little is known about how this mediation changes over ontogeny. The Optimal Defense Theory （ODT） predicts changes in the costs and benefits of the different types of defenses and has been usefully extrapolated to their modes of deployment. Here we studied whether the herbivore-induced accumulation of JA, JA-Ile and ET changed over ontogeny in Nicotiana attenuata, a native tobacco in which inducible defenses are particularly well studied. Herbivore-elicited ET production changed dramatically during six developmental stages, from rosette through flowering, decreasing with the elongation of the first corollas during flower development. This decrease was largely recovered within a day after flower removal by decapitation. A similar pattern was found for the herbivore-induced accumulation of JA and JA-Ile. These results are consistent with ODT predictions and suggest that the last steps in floral development control the inducibility of at least three plant hormones, optimizing defense-growth tradeoffs.

Is there a latitudinal gradient in the proportion of species with spinescence?

Aims We aimed to test the hypothesis that plants that grow at lower lati-tudes will be better structurally defended than plants from higher latitudes.Methods We collated binary spinescence data for 5145 species across Australia and New Zealand.Our dataset spanned 35°of latitude,and included over 1 million observations,making it the larg-est empirical study ever conducted for a single physical defence trait.A weighted logistic regression was applied first within Australia and New Zealand separately,and then across the com-bined dataset.Important Findings There was no significant latitudinal gradient in the proportion of spe-cies with spinescence in Australia or New Zealand,or in the overall dataset.That is,plant species are no more likely to be defended by spines at low latitudes than at high latitudes.This finding is counter to the idea that plant defences increase with latitude due to increased selective pressure from higher levels of herbivory.We suggest that future studies should investigate the relationship between herbivory and defence directly,without using latitude as a proxy.

Herbivore performance and plant defense after sequential attacks by inducing and suppressing herbivores

It is well known that herbivore-induced plant defenses alter host plant quality and can affect the behavior and performance of later arriving herbivores.Effects of sequential attacks by herbivores that either suppress or induce plant defenses are less well studied.We sequentially infested leaves of tomato plants with a strain of the phytophagous spider mite Tetranychus urticae that induces plant defenses and the closely related Tetranychus evansi, which suppresses plant defenses.Plant quality was quantified through oviposifion of both spider mite species and by measuring proteinase inhibitor activity using plant material that had been sequentially attacked by both herbivore species.Spider-mite oviposifion data show that T.evansi could suppress an earlier induction of plant defenses by T.urticae,and T.urticae could induce defenses in plants previously attacked by T.evansi in 1 day.Longer attacks by the second species did not result in further changes in oviposifion.Proteinase inhibitor activity levels showed that T.evansi suppressed the high activity levels induced by T.urticae to constitutive levels in 1 day,and further suppressed activity to levels similar to those in plants attacked by T.evansi alone.Attacks by T.urticae induced proteinase inhibitor activity in plants previously attacked by T.evansi,eventually to similar levels as induced by T.urticae alone.Hence,plant quality and plant defenses were significantly affected by sequential attacks and the order of attack does not affect subsequent performance,but does affect proteinase inhibitor activity levels.Based on our results,we discuss the evolution of suppression of plant defenses.

Shifting Nicotiana attenuata's diurnal rhythm does not alter its resistance to the specialist herbivore Manduca sexta

Arabidopsis thaliana plants are less resistant to attack by the generalist lepidopteran herbivore Trichoplusia ni when plants and herbivores are entrained to opposite, versus identical diurnal cycles and tested under constant conditions. This effect is associated with circadian fluctuations in levels of jasmonic acid, the transcription factor MYC2, and glucosinolate contents in leaves. We tested whether a similar effect could be observed in a different plant-herbivore system： the wild tobacco Nicotiana attenuata and its co-evolved specialist herbivore, Manduca sexta. We measured larval growth on plants under both constant and diurnal conditions following identical or opposite entrainment, profiled the metabolome of attacked leaf tissue, quantified specific metabolites known to reduce M. sexta growth, and monitored A/I. sexta feeding activity under all experimental conditions. Entrainment did not consistently affect NI. sexta growth or plant defense induction. However, both were reduced under constant dark conditions,as was M. sexta feeding activity. Our data indicate that the response induced by NI. sexta in N. attenuata is robust to diurnal cues and independent of plant or herbivore entrain- ment. We propose that while the patterns of constitutive or general damage-induced defense may undergo circadian fluctuation, the orchestration of specific induced responses is more complex.

An intercontinental comparison of insect seed predation between introduced and native oaks

Novel interactions between introduced oaks and their natural enemies across different continents provide an opportunity to test the enemy release hypothesis(ERH)at local and global scales.Based on the ERH,we assessed the impacts of native seed-feeding insects on introduced and native oaks within and among continents.We combined a common-garden experiment in China and biogeographic literature surveys to measure seed predation by insects and the proportion of acorn embryos surviving after insect infestation among 4 oak species with different geographical origins:Quercus mongolica origin from China,Q.robur and Q.petraea from Europe,and Q.rubra from North America.Mostly supporting the ERH,oaks in introduced continents escaped seed predation compared to those in native continents and compared to other native oaks in introduced continents.Common-garden comparisons showed that total acorn infestation rate of introduced Q.rubra(section Lobatae)was considerably lower than that of native oaks(section Quercus)in China and Europe,likely because of the differences in seed traits associated with different oak sections.Literature surveys showed that seed predation of introduced oaks was lower in the introduced continent than in the native continent.Embryo survival was higher in introduced Q.rubra than native oaks in China and Poland.However,insect seed predation of recently introduced Q.rubra in China was similar to that in Europe,which is not consistent with the ERH.Our results suggest that reduced acorn attack by native insects and higher embryo survival after acorn damage could increase the establishment success or invasion risk of introduced oaks in non-native continents.