Benefits of photosynthesis for insects in galls

Hemiptera-induced galls of Sapium glandulosum have histological and cytological compartmentalization created with a large amount of carbohydrate

Gall formation impacts the development of plant species by altering the structure and mobilization of reserves, and the functional and physiological patterns of the host organ. The current study aimed to evaluate the impact generated by the Neolithus fasciatus galling insect (Hemiptera: Triozidae) in Sapium glandulosum leaves (Euphorbiaceae) at the cytological, histological, histochemical, and biochemical levels. Non-galled leaves and galls in the young, mature, and senescent stages were evaluated. The non-galled leaf has a uniseriate epidermis, stomata only on the abaxial side, a dorsiventral mesophyll, and parenchyma cells with thin primary walls containing chloroplasts with plastoglobules. The gall has a parenchymatous compartmentalized cortex. The young and mature galls already have a dense cytoplasm, especially in the inner cells of the cortex, with chloroplasts, mitochondria, Golgi complex, and large and evident nuclei. In senescent galls, there are signs of organelle degradation and cell digestion. Carbohydrates occur in greater amounts in the mature gall, mainly in the starch grain form, while proteins and lipids predominate in non-galled leaves. Secondary metabolites occur mainly in the young gall and may be related to its protection and to the signaling of its development. Sapium glandulosum galls have histological and cytological compartmentalization of the cortex with a large amount of carbohydrates, which supply energy to maintain the development of the structure.

Feeding-induced plant metabolite responses to a phoretic gall mite, its carrier psyllid and both, after detachment

Phoresy is one of the most distinctive relationships between mites and insects, and the off-host interaction between phoretic mites and their carriers is the most critical factor sustaining the phoretic association. As phoretic associations commonly occur in temporary habitats, little is known about off-host interactions between phoronts and carriers. However, an off-host interaction has been reported, in which the plant-mediated competition between a phoretic gall mite, Aceria pallida, and its psyllid vector, Bactericera gobica, after detachment decreases leaf abscission caused by B. gobica and then directly facilitates their phoretic association. In this obligate phoresy, A. pallida seasonally attaches to B. gobica for overwinter survival and they share the same host plant, Lycium barbarum, during the growing season. It is unknown how the host plant responds to these two herbivores and what plant metabolites are involved in their interspecific interaction. Here, effects of A. pallida and B. gobica on the host plant's transcriptome and metabolome, and on enzymes involved in plant defence, at various infestation stages were studied by inoculating A. pallida and B. gobica either separately or simultaneously on leaves of L. barbarum. Our results showed that (a) A. pallida significantly promoted primary and secondary metabolite accumulation, (b) B. gobica markedly inhibited primary and secondary metabolite accumulation and had little influence on defence enzyme activity, and (c) under simultaneous A. pallida and B. gobica infestation, an intermediate response was predicted. These findings indicate that A. pallida and B. gobica have different effects on host plants, A. pallida inhibits B. gobica mainly by increasing the secondary metabolism of L. barbarum, whereas B. gobica inhibits A. pallida mainly by decreasing the primary metabolism of L. barbarum. In conjunction with our previous research, we speculate that this trade-off in host plant metabolite response between A. pallida and B. gobica after detachment promotes a stable phoretic association.

Extreme acidity in a cynipid gall: a potential new defensive strategy against natural enemies

The morphology of insect-induced galls contributes to defences of the gall-inducing insect species against its natural enemies. In terms of gall chemistry, the only defensive compounds thus far identified in galls are tannins that accumulate in many galls, preventing damage by herbivores. Intrigued by the fruit-like appearance of the translucent oak gall (TOG; Amphibolips nubilipennis, Cynipidae, Hymenoptera) induced on red oak (Quercus rubra), we hypothesized that its chemical composition may deviate from other galls. We found that the pH of the gall is between 2 and 3, making it among the lowest pH levels found in plant tissues. We examined the organic acid content of TOG and compared it to fruits and other galls using high-performance liquid chromatography and gas chromatography-mass spectrometry. Malic acid, an acid with particularly high abundance in apples, represents 66% of the organic acid detected in TOGs. The concentration of malic acid was two times higher than in other galls and in apples. Gall histology showed that the acid-containing cells were enlarged and vacuolized just like fruits mesocarp cells. Accumulation of organic acid in gall tissues is convergent with fruit morphology and may constitute a new defensive strategy against predators and parasitoids.

Gall- and erineum-forming Eriophyes mites alter photosynthesis and volatile emissions in an infection severity-dependent manner in broad-leaved trees Alnus glutinosa and Tilia cordata

Highly host-specific eriophyoid gall- and erineum-forming mites infest a limited range of broadleaf species, with the mites from the genus Eriophyes particularly widespread on Alnus spp. and Tilia spp. Once infected, the infections can be massive, covering a large part of leaf area and spreading through the plant canopy, but the effects of Eriophyes mite gall formation on the performance of host leaves are poorly understood. We studied the influence of three frequent Eriophyes infections, E. inangulis gall-forming mites on Alnus glutinosa, and E. tiliae gall-forming and E. exilis erineum-forming mites on Tilia cordata, on foliage morphology, chemistry, photosynthetic characteristics, and constitutive and induced volatile emissions. For all types of infections, leaf dry mass per unit area, net assimilation rate per area and stomatal conductance strongly decreased with increasing severity of infection. Mite infections resulted in enhancement or elicitation of emissions of fatty acid-derived volatiles, isoprene, benzenoids and carotenoid breakdown products in an infection severity-dependent manner for all different infections. Monoterpene emissions were strongly elicited in T. cordata mite infections, but these emissions were suppressed in E. inangulis-infected A. glutinosa. Although the overall level of mite-induced emissions was surprisingly low, these results highlight the uniqueness of the volatile profiles and offer opportunities for using volatile fingerprints and overall emission rates to diagnose infections by Eriophyes gall- and erineum-forming mites on temperate trees and assess their impact on the physiology of the affected trees.

The Diversity and Dynamics of Fungi in Dryocosmus kuriphilus Community

Simple Summary

Dryocosmus kuriphilus is an invasive pest species which is native to China and is widely distributed in Asia, Europe and North America. D. kuriphilus induces insect galls on chestnut trees, and fungi can cause the necrosis of chestnut trees and the death of D. kuriphilus. The aim of this research was to investigate the potential role of D. kuriphilus in the transmission of fungi. We provide the first evidence that D. kuriphilus adults shared most fungal species with associated insect galls and the galled twigs of Castanea mollissima, and were dominated by Botryosphaeria sp., Aspergillus sp. and Diaporthe sp. Furthermore, we suggest that D. kuriphilus adults may be potential vectors of plant pathogens and mediate the transmission of fungi between chestnut trees.

Abstract

Dryocosmus kuriphilus (Hymenoptera: Cynipidae) is a gall wasp that induces insect galls on chestnut trees and results in massive yield losses worldwide. Fungi can cause the necrosis of chestnut trees and the death of gall wasps. The aim of this research was to investigate the potential role of D. kuriphilus in the transmission of fungi. We sequenced the ribosomal RNA internal transcribed spacer region 1 of fungi in D. kuriphilus adults, associated insect galls and the galled twigs of Castanea mollissima, using high-throughput sequencing. We compared the species richness, α-diversity and community structure of fungi in D. kuriphilus adults, insect galls and the galled twigs. We provide the first evidence that D. kuriphilus adults shared most fungal species with associated insect galls and the galled twigs, and were dominated by Botryosphaeria sp., Aspergillus sp. and Diaporthe sp. We suggest D. kuriphilus adults may be potential vectors of plant pathogens and may facilitate the transmission of fungi between chestnut trees. Furthermore, the fungi may horizontally transmit among D. kuriphilus adults, associated insect galls and the galled twigs.

Photosymbiosis for Biomedical Applications

Without the sustained provision of adequate levels of oxygen by the cardiovascular system, the tissues of higher animals are incapable of maintaining normal metabolic activity, and hence cannot survive. The consequence of this evolutionarily suboptimal design is that humans are dependent on cardiovascular perfusion, and therefore highly susceptible to alterations in its normal function. However, hope may be at hand. “Photosynthetic strategies,” based on the recognition that photosynthesis is the source of all oxygen, offer a revolutionary and promising solution to pathologies related to tissue hypoxia. These approaches, which have been under development over the past 20 years, seek to harness photosynthetic microorganisms as a local and controllable source of oxygen to circumvent the need for blood perfusion to sustain tissue survival. To date, their applications extend from the in vitro creation of artificial human tissues to the photosynthetic maintenance of oxygen-deprived organs both in vivo and ex vivo, while their potential use in other medical approaches has just begun to be explored. This review provides an overview of the state of the art of photosynthetic technologies and its innovative applications, as well as an expert assessment of the major challenges and how they can be addressed.

Effect of Neuroterus quercusbaccarum (L.) galls on physiological and biochemical response of Quercus robur leaves

Gall formation is associated with multiple changes in plant cells, which still requires a better understanding. In this study, galls caused by sexual generation (♀♂) of Neuroterus quercusbaccarum (L.) (Hymenoptera: Cynipidae) on pedunculate oak trees (Quercus robur L.) were used as a model. Cytoplasmic membrane condition, concentration of hydrogen peroxide (H2O2), the activity of antioxidant enzymes and amino acid decarboxylase as well as chlorophyll fluorescence parameters were determined. Changes in physiological and biochemical parameters were analyzed in foliar tissues with galls and gall tissues themselves and compared to control. The presence of galls on oak leaves caused an increase of lipid peroxidation level. A significant decline in H2O2 and TBARS content with the reduction of guaiacol peroxidase (GPX) and ascorbate peroxidase (APX) activity were observed in gall tissues. The activity amino acid decarboxylase, i.e., LDC, ODC and TyDC varied between samples, which may affect the content of amino acids. The presence of N. quercusbaccarum galls caused an insignificant increase of the chlorophylls, carotenoids and anthocyanin contents, while the content of pigments and their ratios in gall tissues was extremely low. Moreover, photosynthetic parameters (F0, Fm, Fv/Fm, Y, qP) were significantly decreased. Data generated in this study indicate that the development of N. quercusbaccarum galls on pedunculate oak leaves has a negative effect on host plant related to the disruption of cell membrane integrity, disturbance of photosynthesis and reduction of the antioxidant potential of the host plant.

Oak gall wasp infections of Quercus robur leaves lead to profound modifications in foliage photosynthetic and volatile emission characteristics

Oak trees (Quercus) are hosts of diverse gall-inducing parasites, but the effects of gall formation on the physiology and biochemistry on host oak leaves is poorly understood. The influence of infection by four species from two widespread gall wasp genera, Neuroterus (N. anthracinus and N. albipes) and Cynips (C. divisa and C. quercusfolii), on foliage morphology, chemistry, photosynthetic characteristics, constitutive isoprene, and induced volatile emissions in Q. robur was investigated. Leaf dry mass per unit area (M_A ), net assimilation rate per area (A_A ), stomatal conductance (g_s ), and constitutive isoprene emissions decreased with the severity of infection by all gall wasp species. The reduction in A_A was mainly determined by reduced M_A and to a lower extent by lower content of leaf nitrogen and phosphorus in gall-infected leaves. The emissions of lipoxygenase pathway volatiles increased strongly with increasing infection severity for all 4 species with the strongest emissions in major vein associated species, N. anthracinus. Monoterpene and sesquiterpene emissions were strongly elicited in N. albipes and Cynips species, but not in N. anthracinus. These results provide valuable information for diagnosing oak infections using ambient air volatile fingerprints and for predicting the impacts of infections on photosynthetic productivity and whole tree performance.

Reacquisition of New Meristematic Sites Determines the Development of a New Organ, the Cecidomyiidae Gall on Copaifera langsdorffii Desf. (Fabaceae)

The development of gall shapes has been attributed to the feeding behavior of the galling insects and how the host tissues react to galling stimuli, which ultimately culminate in a variable set of structural responses. A superhost of galling herbivores, Copaifera langsdorffii, hosts a bizarre "horn-shaped" leaflet gall morphotype induced by an unidentified species of Diptera: Cecidomyiidae. By studying the development of this gall morphotype under the anatomical and physiological perspectives, we demonstrate the symptoms of the Cecidomyiidae manipulation over plant tissues, toward the cell redifferentiation and tissue neoformation. The most prominent feature of this gall is the shifting in shape from growth and development phase toward maturation, which imply in metabolites accumulation detected by histochemical tests in meristem-like group of cells within gall structure. We hypothesize that the development of complex galls, such as the horn-shaped demands the reacquisition of cell meristematic competence. Also, as mature galls are green, their photosynthetic activity should be sufficient for their oxygenation, thus compensating the low gas diffusion through the compacted gall parenchyma. We currently conclude that the galling Cecidomyiidae triggers the establishment of new sites of meristematic tissues, which are ultimately responsible for shifting from the young conical to the mature horn-shaped gall morphotype. Accordingly, the conservative photosynthesis activity in gall site maintains tissue homeostasis by avoiding hypoxia and hipercarbia in the highly compacted gall tissues.

Shelter-Building Insects and Their Role as Ecosystem Engineers

Amelioration of harsh conditions, manipulation of host plant quality, and protection from natural enemies have all been suggested as potential forces in the evolution and maintenance of concealed feeding in insects. The construction of shelters--either in the form of mines, galls, and leaf rolls--are expected to increase larval survivorship and might influence other organisms of the community through non-trophic direct and indirect effects when shelters are co-occupied or occupied after abandonment, placing leaf and stem shelter-builders within the context of ecosystem engineering. In this review, we evaluate the potential of shelter built by insects to reduce pressure exerted by natural enemies, increase tissue quality, and provide shelter against abiotic conditions experienced during insect development. Through a quantitative analysis, we also examined the effects of insect shelters on patterns of richness and abundance of local communities, reviewing the data published in the last 15 years. We demonstrate strong effects of shelters on several arthropods, with increased richness and abundance when shelters are present in the host plants. These results reinforce the importance of the physical structures created by insects that although subtle, might have important roles in facilitative interactions.

Hypoxia and hypercarbia in endophagous insects: Larval position in the plant gas exchange network is key

Gas composition is an important component of any micro-environment. Insects, as the vast majority of living organisms, depend on O2 and CO2 concentrations in the air they breathe. Low O2 (hypoxia), and high CO2 (hypercarbia) levels can have a dramatic effect. For phytophagous insects that live within plant tissues (endophagous lifestyle), gas is exchanged between ambient air and the atmosphere within the insect habitat. The insect larva contributes to the modification of this environment by expiring CO2. Yet, knowledge on the gas exchange network in endophagous insects remains sparse. Our study identified mechanisms that modulate gas composition in the habitat of endophagous insects. Our aim was to show that the mere position of the insect larva within plant tissues could be used as a proxy for estimating risk of occurrence of hypoxia and hypercarbia, despite the widely diverse life history traits of these organisms. We developed a conceptual framework for a gas diffusion network determining gas composition in endophagous insect habitats. We applied this framework to mines, galls and insect tunnels (borers) by integrating the numerous obstacles along O2 and CO2 pathways. The nature and the direction of gas transfers depended on the physical structure of the insect habitat, the photosynthesis activity as well as stomatal behavior in plant tissues. We identified the insect larva position within the gas diffusion network as a predictor of risk exposure to hypoxia and hypercarbia. We ranked endophagous insect habitats in terms of risk of exposure to hypoxia and/or hypercarbia, from the more to the less risky as cambium mines>borer tunnels≫galls>bark mines>mines in aquatic plants>upper and lower surface mines. Furthermore, we showed that the photosynthetically active tissues likely assimilate larval CO2 produced. In addition, temperature of the microhabitat and atmospheric CO2 alter gas composition in the insect habitat. We predict that (i) hypoxia indirectly favors the evolution of cold-tolerant gallers, which do not perform well at high temperatures, and (ii) normoxia (ambient O2 level) in mines allows miners to develop at high temperatures. Little is known, however, about physiological and morphological adaptations to hypoxia and hypercarbia in endophagous insects. Endophagy strongly constrains the diffusion processes with cascading consequences on the evolutionary ecology of endophagous insects.

The imbalance of redox homeostasis in arthropod-induced plant galls: Mechanisms of stress generation and dissipation

BACKGROUND

Galls have specialized tissues for the protection and nutrition of the inducers, and these tissues have been studied from the developmental and histochemical perspectives. Recently, the role of oxidative stress in galls has been tested histochemically through detection of H2O2 in gall tissues.

SCOPE OF REVIEW

Developmental processes and cytological events are revisited from the perspective of the redox-potential balance in both the apoplast and symplast, especially concerning the accumulation of reactive oxygen species (ROS).

MAJOR CONCLUSIONS

The redox potential is imbalanced differently in the apoplast and symplast at gall sites, with the apoplast having lower antioxidant-buffering capacity than the symplast. The strategies to recover redox-potential homeostasis involve the dissipation of ROS by scavenging molecules, such as phenolics, flavonoid derivatives, tocopherol, and enzyme systems.

GENERAL SIGNIFICANCE

Insect galls are good models to test developmental hypotheses. Although the exact mechanisms of gall induction and development have not been elucidated at the biochemical and biophysical levels, modulation of the redox potential is involved in the crucial steps of gall initiation and establishment. This article is part of a Special Issue entitled Redox regulation of differentiation and de-differentiation.

Structural, biochemical, and physiological characterization of photosynthesis in leaf-derived cup-shaped galls on Litsea acuminata

BACKGROUND

The source and sink relationships between insect-induced galls and host plant leaves are interesting. In this research, we collected cup-like galls induced by Bruggmanniella sp. (Diptera: Cecidomyiidae) on host leaves of Litsea acuminata and assessed them to investigate source-sink relationships between galls and host leaves. We characterized several of their photosynthetic characteristics including chlorophyll fluorescence (Fv/Fm), stomatal conductance, and photosynthetic capacity, biochemical components such as total soluble sugar, starches, free amino acids, and soluble proteins. The structural analyses were performed under confocal, light, and scanning electron microscopies.

RESULTS

Compared with host leaves, galls exhibited slightly lower chlorophyll fluorescence; however, stomatal conductance and photosynthetic capacity were not detected at all. Galls accumulated higher total soluble sugars and free amino acids but less soluble proteins than host leaves. No stomata was observed on exterior or interior gall surfaces under light or scanning electron microscopy, but their inner surfaces were covered with fungal hyphae. Confocal imagery showed a gradient of chloroplasts distribution between gall outer and inner surfaces.

CONCLUSIONS

Our results strongly suggest that leaf-derived cecidomyiid galls are a type of chlorophyll-deficient non-leaf green tissue and consists on a novel sink in L. acuminate.

Leaf-derived cecidomyiid galls are sinks in Machilus thunbergii (Lauraceae) leaves

Three relevant hypotheses - nutrition, environment and the enemies hypothesis - often invoked to explore source and sink relationships between galls and their host plants are still under dispute. In this research, chlorophyll fluorescence, gas exchange capacity, stomatal conductance, total carbon and nitrogen, total soluble sugars and starches, and scanning and transmission electron microscopy of two types of galls were used to investigate source-sink relationships. Compared with host leaves, these galls demonstrated slightly lower chlorophyll fluorescence; however, gas exchange capacity and stomatal conductance were not detected at all. Scanning electron micrographs demonstrated that the abaxial epidermis of host leaves contain normal amounts of stomata, whereas no stomata were observed on the exterior and interior surfaces of both types of galls. In addition, gall inner surfaces were covered with many kinds of fungal hyphae. Gall total carbon (C) and nitrogen (N) levels were lower but the C/N ratio was higher in galls than host leaves. Both types of galls accumulated higher total soluble sugars and starches than host leaves. Transmission electron micrographs also revealed that both types of galls contain plastoglobuli and giant starch granules during gall development. Results strongly indicate that leaf-derived cecidomyiid galls are sinks in Machilus thunbergii leaves. However, it is perplexing how larvae cycle and balance CO(2) and O(2) in gall growth chambers without stomata.

Leaf-galling phylloxera on grapes reprograms host metabolism and morphology

Endoparasitism by gall-forming insects dramatically alters the plant phenotype by altering growth patterns and modifying plant organs in ways that appear to directly benefit the gall former. Because these morphological and physiological changes are linked to the presence of the insect, the induced phenotype is said to function as an extension of the parasite, albeit by unknown mechanisms. Here we report the gall-forming aphid-like parasite phylloxera, Daktulosphaira vitifoliae, induces stomata on the adaxial surface of grape leaves where stomata typically do not occur. We characterized the function of the phylloxera-induced stomata by tracing transport of assimilated carbon. Because induction of stomata suggests a significant manipulation of primary metabolism, we also characterized the gall transcriptome to infer the level of global reconfiguration of primary metabolism and the subsequent changes in downstream secondary metabolism. Phylloxera feeding induced stomata formation in proximity to the insect and promoted the assimilation and importation of carbon into the gall. Gene expression related to water, nutrient, and mineral transport; glycolysis; and fermentation increased in leaf-gall tissues. This shift from an autotrophic to a heterotrophic profile occurred concurrently with decreased gene expression for nonmevalonate and terpenoid synthesis and increased gene expression in shikimate and phenylpropanoid biosynthesis, secondary metabolite systems that alter defense status in grapes. These functional insect-induced stomata thus comprise part of an extended phenotype, whereby D. vitifoliae globally reprograms grape leaf development to alter patterns of primary metabolism, nutrient mobilization, and defense investment in favor of the galling habit.