Anja David

Bio: Anja David is an academic researcher from Max Planck Society. The author has contributed to research in topics: Jasmonic acid & Aphid. The author has an hindex of 15, co-authored 23 publications receiving 969 citations.

Whiteflies interfere with indirect plant defense against spider mites in Lima bean

Abstract: Plants under herbivore attack are able to initiate indirect defense by synthesizing and releasing complex blends of volatiles that attract natural enemies of the herbivore. However, little is known about how plants respond to infestation by multiple herbivores, particularly if these belong to different feeding guilds. Here, we report the interference by a phloem-feeding insect, the whitefly Bemisia tabaci, with indirect plant defenses induced by spider mites (Tetranychus urticae) in Lima bean (Phaseolus lunatus) plants. Additional whitefly infestation of spider-mite infested plants resulted in a reduced attraction of predatory mites (Phytoseiulus persimilis) compared to attraction to plants infested by spider mites only. This interference is shown to result from the reduction in (E)-β-ocimene emission from plants infested by both spider mites and whiteflies. When using exogenous salicylic acid (SA) application to mimic B. tabaci infestation, we observed similar results in behavioral and chemical analyses. Phytohormone and gene-expression analyses revealed that B. tabaci infestation, as well as SA application, inhibited spider mite-induced jasmonic acid (JA) production and reduced the expression of two JA-regulated genes, one of which encodes for the P. lunatus enzyme β-ocimene synthase that catalyzes the synthesis of (E)-β-ocimene. Remarkably, B. tabaci infestation concurrently inhibited SA production induced by spider mites. We therefore conclude that in dual-infested Lima bean plants the suppression of the JA signaling pathway by whitefly feeding is not due to enhanced SA levels.

Effects of Feeding Spodoptera littoralis on Lima Bean Leaves: IV. Diurnal and Nocturnal Damage Differentially Initiate Plant Volatile Emission

Abstract: Continuous mechanical damage initiates the rhythmic emission of volatiles in lima bean (Phaseolus lunatus) leaves; the emission resembles that induced by herbivore damage. The effect of diurnal versus nocturnal damage on the initiation of plant defense responses was investigated using MecWorm, a robotic device designed to reproduce tissue damage caused by herbivore attack. Lima bean leaves that were damaged by MecWorm during the photophase emitted maximal levels of β-ocimene and (Z)-3-hexenyl acetate in the late photophase. Leaves damaged during the dark phase responded with the nocturnal emission of (Z)-3-hexenyl acetate, but with only low amounts of β-ocimene; this emission was followed by an emission burst directly after the onset of light. In the presence of 13CO2, this light-dependent synthesis of β-ocimene resulted in incorporation of 75% to 85% of 13C, demonstrating that biosynthesis of β-ocimene is almost exclusively fueled by the photosynthetic fixation of CO2 along the plastidial 2-C-methyl-d-erythritol 4-P pathway. Jasmonic acid (JA) accumulated locally in direct response to the damage and led to immediate up-regulation of the P. lunatus β-ocimene synthase gene (PlOS) independent of the phase, that is, light or dark. Nocturnal damage caused significantly higher concentrations of JA (approximately 2–3 times) along with enhanced expression levels of PlOS. Transgenic Arabidopsis thaliana transformed with PlOS promoter∷β-glucuronidase fusion constructs confirmed expression of the enzyme at the wounded sites. In summary, damage-dependent JA levels directly control the expression level of PlOS, regardless of light or dark conditions, and photosynthesis is the major source for the early precursors of the 2-C-methyl-d-erythritol 4-P pathway.

Plant-mediated facilitation between a leaf-feeding and a phloem-feeding insect in a brassicaceous plant: from insect performance to gene transcription

Abstract: Summary 1 Plants face threats from a variety of herbivorous insects and can use induced responses to defend themselves against these attackers Induced responses are mediated by signal transduction involving phytohormones, such as jasmonic acid (JA) and salicylic acid (SA) Cross-talk between signal transduction pathways triggered by attackers with contrasting feeding styles allows plants to fine-tune defences A central question in this emerging field is to understand how responses to single attackers interfere with responses to other attackers, especially by integratively addressing molecular and ecological aspects 2 We examined the plant-mediated interactions between the leaf-chewing Pieris brassicae and the phloem-sucking Brevicoryne brassicae, and their respective parasitoids Cotesia glomerata and Diaeretiella rapae, when feeding simultaneously, sequentially or in isolation on the brassicaceous ecological model plant Brassica oleracea We analysed the underlying defence mechanisms in the plant Levels of the phytohormones JA and SA transcriptional responses of a number of selected defence-related genes and secondary plant compounds were quantified at different time points during the single and multiple infestations 3 The caterpillars developed faster and reached a larger body mass on plants previously attacked by aphids Aphids initially developed faster on plants with caterpillars, although the moment of moulting to adults was independent of the presence of caterpillars Both parasitoid species performed better under multiple-infestation scenarios than in single-herbivore situations 4 On plants attacked by aphids, the JA levels were tenfold lower than on undamaged plants or plants with caterpillars Additionally, the low transcript levels of LOX and MYC, genes coding for a JA biosynthesis-related enzyme and a transcription factor, respectively, in aphid-infested plants, suggest that the facilitation of the caterpillar performance was mediated by interference in signal transduction Levels of carbon and nitrogen and secondary plant compounds (glucosinolates) did not differ significantly between treatments, suggesting that these compounds did not mediate the facilitation 5 Our data show that the leaf chewer and phloem feeder asymmetrically interact not via competition as would be expected from interspecific herbivores but instead via facilitation; the phloem feeder attenuated JA-related plant defences, thus facilitating the growth and development of the leaf chewers In linear bitrophic systems, interactions between JA and SA signalling pathways have been proposed to allow plants to fine-tune their defences, but if facilitation frequently occurs in interspecific interguild interactions among herbivores this may represent an important constraint for plant defences Such a constraint might be reduced if, as in our model system, parasitoids also benefit from interactions between interguild hosts and nonhosts, but parasitoids are rarely considered in model molecular systems to assess the impact of herbivore-induced plant defences

Evidence for behavioral attractiveness of methoxylated aromatics in a dynastid scarab beetle-pollinated Araceae

Abstract: Many plants attract their pollinators with floral scents, and these olfactory signals are especially important at night, when visual signals become inefficient. Dynastid scarab beetles are a speciose group of night-active pollinators, and several plants pollinated by these insects have methoxylated aromatic compounds in their scents. However, there is a large gap in our knowledge regarding the compounds responsible for beetle attraction. We used chemical analytical analyses to determine temporal patterns of scent emission and the composition of scent released from inflorescences of Philodendron selloum. The attractiveness of the main components in the scent to the dynastid scarab beetle Erioscelis emarginata, the exclusive pollinator of this plant, was assessed in field biotests. The amount of scent increased rapidly in the evening, and large amounts of scent were released during the activity time of the beetle pollinators. Inflorescences emitted a high number of compounds of different biosynthetic origin, among them both uncommon and also widespread flower scents. Methoxylated aromatic compounds dominated the scent, and 4-methoxystyrene, the most abundant compound, attracted E. emarginata beetles. Other compounds, such as (Z)-jasmone and possibly also the methoxylated aromatic compound 3,4-dimethoxystyrene increased the attractiveness of 4-methoxystyrene. Methoxylated aromatics, which are known from other dynastid pollinated plants as well, are important signals in many scarab beetles in a different context (e.g., pheromones), thus suggesting that these plants exploit pre-existing preferences of the beetles for attracting this group of insects as pollinators.

Hormonal Modulation of Plant Immunity

Abstract: Plant hormones have pivotal roles in the regulation of plant growth, development, and reproduction. Additionally, they emerged as cellular signal molecules with key functions in the regulation of immune responses to microbial pathogens, insect herbivores, and beneficial microbes. Their signaling pathways are interconnected in a complex network, which provides plants with an enormous regulatory potential to rapidly adapt to their biotic environment and to utilize their limited resources for growth and survival in a cost-efficient manner. Plants activate their immune system to counteract attack by pathogens or herbivorous insects. Intriguingly, successful plant enemies evolved ingenious mechanisms to rewire the plant’s hormone signaling circuitry to suppress or evade host immunity. Evidence is emerging that beneficial root-inhabiting microbes also hijack the hormone-regulated immune signaling network to establish a prolonged mutualistic association, highlighting the central role of plant hormones in the regulation of plant growth and survival.

Mechanisms of plant defense against insect herbivores

Abstract: Plants respond to herbivory through various morphological, biochemicals, and molecular mechanisms to counter/offset the effects of herbivore attack. The biochemical mechanisms of defense against the herbivores are wide-ranging, highly dynamic, and are mediated both by direct and indirect defenses. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. In addition, plants also release volatile organic compounds that attract the natural enemies of the herbivores. These strategies either act independently or in conjunction with each other. However, our understanding of these defensive mechanisms is still limited. Induced resistance could be exploited as an important tool for the pest management to minimize the amounts of insecticides used for pest control. Host plant resistance to insects, particularly, induced resistance, can also be manipulated with the use of chemical elicitors of secondary metabolites, which confer resistance to insects. By understanding the mechanisms of induced resistance, we can predict the herbivores that are likely to be affected by induced responses. The elicitors of induced responses can be sprayed on crop plants to build up the natural defense system against damage caused by herbivores. The induced responses can also be engineered genetically, so that the defensive compounds are constitutively produced in plants against are challenged by the herbivory. Induced resistance can be exploited for developing crop cultivars, which readily produce the inducible response upon mild infestation, and can act as one of components of integrated pest management for sustainable crop production.

Plant–soil feedbacks: the past, the present and future challenges

Abstract: Summary Plant–soil feedbacks is becoming an important concept for explaining vegetation dynamics, the invasiveness of introduced exotic species in new habitats and how terrestrial ecosystems respond to global land use and climate change. Using a new conceptual model, we show how critical alterations in plant–soil feedback interactions can change the assemblage of plant communities. We highlight recent advances, define terms and identify future challenges in this area of research and discuss how variations in strengths and directions of plant–soil feedbacks can explain succession, invasion, response to climate warming and diversity-productivity relationships. While there has been a rapid increase in understanding the biological, chemical and physical mechanisms and their interdependencies underlying plant–soil feedback interactions, further progress is to be expected from applying new experimental techniques and technologies, linking empirical studies to modelling and field-based studies that can include plant–soil feedback interactions on longer time scales that also include long-term processes such as litter decomposition and mineralization. Significant progress has also been made in analysing consequences of plant–soil feedbacks for biodiversity-functioning relationships, plant fitness and selection. To further integrate plant–soil feedbacks into ecological theory, it will be important to determine where and how observed patterns may be generalized, and how they may influence evolution. Synthesis. Gaining a greater understanding of plant–soil feedbacks and underlying mechanisms is improving our ability to predict consequences of these interactions for plant community composition and productivity under a variety of conditions. Future research will enable better prediction and mitigation of the consequences of human-induced global changes, improve efforts of restoration and conservation and promote sustainable provision of ecosystem services in a rapidly changing world.

PLANT-SOIL FEEDBACKS IN A CHANGING WORLD Plant-soil feedbacks: the past, the present and future challenges

Abstract: Summary 1. Plant–soil feedbacks is becoming an important concept for explaining vegetation dynamics, the invasiveness of introduced exotic species in new habitats and how terrestrial ecosystems respond to global land use and climate change. Using a new conceptual model, we show how critical alterations in plant–soil feedback interactions can change the assemblage of plant communities. We highlight recent advances, define terms and identify future challenges in this area of research and discuss how variations in strengths and directions of plant–soil feedbacks can explain succession, invasion, response to climate warming and diversity-productivity relationships. 2. While there has been a rapid increase in understanding the biological, chemical and physical mechanisms and their interdependencies underlying plant–soil feedback interactions, further progress is to be expected from applying new experimental techniques and technologies, linking empirical studies to modelling and field-based studies that can include plant–soil feedback interactions on longer time scales that also include long-term processes such as litter decomposition and mineralization. 3. Significant progress has also been made in analysing consequences of plant–soil feedbacks for biodiversity-functioning relationships, plant fitness and selection. 4. To further integrate plant–soil feedbacks into ecological theory, it will be important to determine where and how observed patterns may be generalized, and how they may influence evolution. 5. Synthesis. Gaining a greater understanding of plant–soil feedbacks and underlying mechanisms is improving our ability to predict consequences of these interactions for plant community composition and productivity under a variety of conditions. Future research will enable better prediction and mitigation of the consequences of human-induced global changes, improve efforts of restoration and conservation and promote sustainable provision of ecosystem services in a rapidly changing world.