Systemic acquired resistance (SAR) is a plant immune response to pathogen attack. Recent evidence suggests that plant immunity involves regulation by chromatin remodeling and DNA methylation. We ...investigated whether SAR can be inherited epigenetically following disease pressure by Pseudomonas syringae pv tomato DC3000 (PstDC3000). Compared to progeny from control-treated Arabidopsis (Arabidopsis thaliana; C₁), progeny from PstDV3000-inoculated Arabidopsis (P₁) were primed to activate salicylic acid (SA)-inducible defense genes and were more resistant to the (hemi) biotrophic pathogens Hyaloperonospora arabidopsidis and PstDC3000. This transgenerational SAR was sustained over one stress-free generation, indicating an epigenetic basis of the phenomenon. Furthermore, P₁ progeny displayed reduced responsiveness of jasmonic acid (JA)-inducible genes and enhanced susceptibility to the necrotrophic fungus Alternaria brassicicola. This shift in SA-and JA-dependent gene responsiveness was not associated with changes in corresponding hormone levels. Instead, chromatin immunoprecipitation analyses revealed that SA-inducible promoters of PATHOGENESIS-RELATED GENE1, WRKY6, and WRKY53 in P₁ plants are enriched with acetylated histone H3 at lysine 9, a chromatin mark associated with a permissive state of transcription. Conversely, the JA-inducible promoter of PLANT DEFENSIN1.2 showed increased H3 triple methylation at lysine 27, a mark related to repressed gene transcription. P₁ progeny from the defense regulatory mutant non expressor of PR1 (npr1)-1 failed to develop transgenerational defense phenotypes, demonstrating a critical role for NPR1 in expression of transgenerational SAR. Furthermore, the drm1drm2cmt3 mutant that is affected in non-CpG DNA methylation mimicked the transgenerational SAR phenotype. Since PstDC3000 induces DNA hypomethylation in Arabidopsis, our results suggest that transgenerational SAR is transmitted by hypomethylated genes that direct priming of SA-dependent decfenses in the following generations.
Lepidopteran stemborers and parasitic weeds in the genus Striga are major constraints to efficient production of cereals, the most important staple food crops in Africa. Smallholder farmers are ...resource constrained and unable to afford expensive chemicals for crop protection. Development of a push-pull approach for integrated pest and weed management is reviewed here. Appropriate plants were discovered that naturally emit signalling chemicals (semiochemicals). Plants highly attractive for egg laying by stemborer pests were selected and employed as trap crops (pull), to draw pests away from the main crop. Of these, Napier grass, Pennisetum purpureum (Schumach), despite its attractiveness, supported minimal survival of the pests' immature stages. Plants that repelled stemborer pests, notably molasses grass, Melinis minutiflora P. Beauv., and forage legumes in the genus Desmodium, were selected as intercrops (push). Desmodium intercrops suppress Striga hermonthica (Del.) Benth. through an allelopathic mechanism. Their root exudates contain novel flavonoid compounds, which stimulate suicidal germination of S. hermonthica seeds and dramatically inhibit its attachment to host roots. The companion crops provide valuable forage for farm animals while the leguminous intercrops also improve soil fertility and moisture retention. The system is appropriate as it is based on locally available plants, not expensive external inputs, and fits well with traditional mixed cropping systems in Africa. To date it has been adopted by more than 30 000 smallholder farmers in East Africa where maize yields have increased from ~1 t ha⁻¹ to 3.5 t ha⁻¹. Future directions for semiochemical delivery by plants including biotechnological opportunities are discussed.
The roots of most land plants are colonised by mycorrhizal fungi that provide mineral nutrients in exchange for carbon. Here, we show that mycorrhizal mycelia can also act as a conduit for signalling ...between plants, acting as an early warning system for herbivore attack. Insect herbivory causes systemic changes in the production of plant volatiles, particularly methyl salicylate, making bean plants, Vicia faba, repellent to aphids but attractive to aphid enemies such as parasitoids. We demonstrate that these effects can also occur in aphid‐free plants but only when they are connected to aphid‐infested plants via a common mycorrhizal mycelial network. This underground messaging system allows neighbouring plants to invoke herbivore defences before attack. Our findings demonstrate that common mycorrhizal mycelial networks can determine the outcome of multitrophic interactions by communicating information on herbivore attack between plants, thereby influencing the behaviour of both herbivores and their natural enemies.
This review summarizes and discusses the current knowledge on (1) phytochemicals of brassicaceous plants important for plant protection and human health, (2) factors that influence the content of ...these compounds, (3) plant protection strategies that exploit secondary metabolites of Brassicaceae to minimize crop damage.
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► We reviewed phytochemicals of Brassicaceae in plant protection and human health. ► We summarize the biotic and abiotic factors influencing Brassicaceae phytochemicals. ► Multi-factorial approaches that simulate effects on phytochemicals are promising. ► Plant protection strategies exploiting phytochemicals of Brassicaceae are promising.
In this review, we provide an overview of the role of glucosinolates and other phytochemical compounds present in the Brassicaceae in relation to plant protection and human health. Current knowledge of the factors that influence phytochemical content and profile in the Brassicaceae is also summarized and multi-factorial approaches are briefly discussed. Variation in agronomic conditions (plant species, cultivar, developmental stage, plant organ, plant competition, fertilization, pH), season, climatic factors, water availability, light (intensity, quality, duration) and CO
2 are known to significantly affect content and profile of phytochemicals. Phytochemicals such as the glucosinolates and leaf surface waxes play an important role in interactions with pests and pathogens. Factors that affect production of phytochemicals are important when designing plant protection strategies that exploit these compounds to minimize crop damage caused by plant pests and pathogens. Brassicaceous plants are consumed increasingly for possible health benefits, for example, glucosinolate-derived effects on degenerative diseases such as cancer, cardiovascular and neurodegenerative diseases. Thus, factors influencing phytochemical content and profile in the production of brassicaceous plants are worth considering both for plant and human health. Even though it is known that factors that influence phytochemical content and profile may interact, studies of plant compounds were, until recently, restricted by methods allowing only a reductionistic approach. It is now possible to design multi-factorial experiments that simulate their combined effects. This will provide important information to ecologists, plant breeders and agronomists.
In an environment with changing availability and quality of host plants, phytophagous insects are under selection pressure to find quality hosts. They need to maximize their fitness by locating ...suitable plants and avoiding unsuitable ones. Thus, they have evolved a finely tuned sensory system, for detection of host cues, and a nervous system, capable of integrating inputs from sensory neurons with a high level of spatio-temporal resolution. Insect responses to cues are not fixed but depend on the context in which they are perceived, the physiological state of the insect, and prior learning experiences. However, there are examples of insects making ‘mistakes’ and being attracted to poor quality hosts. While insects have evolved ways of finding hosts, plants have been under selection pressure to do precisely the opposite and evade detection or defend themselves when attacked. Once on the plant, insect-associated molecules may trigger or suppress defence depending on whether the plant or the insect is ahead in evolutionary terms. Plant volatile emission is influenced by defence responses induced by insect feeding or oviposition which can attract natural enemies but repel herbivores. Conversely, plant reproductive fitness is increased by attraction of pollinators. Interactions can be altered by other organisms associated with the plant such as other insects, plant pathogens, or mycorrhizal fungi. Plant phenotype is plastic and can be changed by epigenetic factors in adaptation to periods of biotic stress. Space and time play crucial roles in influencing the outcome of interactions between insects and plants.
Combinations of volatile phytochemicals are perceived by insects as having a different quality from individual compounds as they can elicit different behavioural responses.
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► Plant ...volatiles provide host recognition cues to insects. ► The olfactory system gives fine scale spatio-temporal resolution of these signals. ► Olfactory receptor neurons have high sensitivity and specificity to volatiles at physiologically relevant concentrations. ► Behavioural activity depends on perception of blends. ► Blends can elicit different behavioural responses compared to individual compounds.
Volatile plant secondary metabolites are detected by the highly sensitive olfactory system employed by insects to locate suitable plants as hosts and to avoid unsuitable hosts. Perception of these compounds depends on olfactory receptor neurones (ORNs) in sensillae, mostly on the insect antennae, which can recognise individual molecular structures. Perception of blends of plant volatiles plays a pivotal role in host recognition, non-host avoidance and ensuing behavioural responses as different responses can occur to a whole blend compared to individual components. There are emergent properties of blend perception because components of the host blend may not be recognised as host when perceived outside the context of that blend. Often there is redundancy in the composition of blends recognised as host because certain compounds can be substituted by others. Fine spatio-temporal resolution of the synchronous firing of ORNs tuned to specific compounds enables insects to pick out relevant host odour cues against high background noise and with ephemeral exposure to the volatiles at varying concentrations. This task is challenging as they usually rely on ubiquitous plant volatiles and not those taxonomically characteristic of host plants. However, such an odour coding system has the advantage of providing flexibility; it allows for adaptation to changing environments by alterations in signal processing while maintaining the same peripheral olfactory receptors.
Plant volatiles play important roles in attraction of certain pollinators and in host location by herbivorous insects. Virus infection induces changes in plant volatile emission profiles, and this ...can make plants more attractive to insect herbivores, such as aphids, that act as viral vectors. However, it is unknown if virus-induced alterations in volatile production affect plant-pollinator interactions. We found that volatiles emitted by cucumber mosaic virus (CMV)-infected tomato (Solanum lycopersicum) and Arabidopsis thaliana plants altered the foraging behaviour of bumblebees (Bombus terrestris). Virus-induced quantitative and qualitative changes in blends of volatile organic compounds emitted by tomato plants were identified by gas chromatography-coupled mass spectrometry. Experiments with a CMV mutant unable to express the 2b RNA silencing suppressor protein and with Arabidopsis silencing mutants implicate microRNAs in regulating emission of pollinator-perceivable volatiles. In tomato, CMV infection made plants emit volatiles attractive to bumblebees. Bumblebees pollinate tomato by 'buzzing' (sonicating) the flowers, which releases pollen and enhances self-fertilization and seed production as well as pollen export. Without buzz-pollination, CMV infection decreased seed yield, but when flowers of mock-inoculated and CMV-infected plants were buzz-pollinated, the increased seed yield for CMV-infected plants was similar to that for mock-inoculated plants. Increased pollinator preference can potentially increase plant reproductive success in two ways: i) as female parents, by increasing the probability that ovules are fertilized; ii) as male parents, by increasing pollen export. Mathematical modeling suggested that over a wide range of conditions in the wild, these increases to the number of offspring of infected susceptible plants resulting from increased pollinator preference could outweigh underlying strong selection pressures favoring pathogen resistance, allowing genes for disease susceptibility to persist in plant populations. We speculate that enhanced pollinator service for infected individuals in wild plant populations might provide mutual benefits to the virus and its susceptible hosts.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Selecting a suitable oviposition site is crucial to the fitness of female insects because it determines the successful development of their offspring. During the oviposition process, an insect must ...use cues from the external environment to make an appropriate choice of where to lay eggs. Generalist insects can detect and react to a plethora of cues, but are under selection pressure to adopt the most reliable ones to override noise and increase efficiency in finding hosts. The oriental fruit fly, Bactrocera dorsalis (Hendel), is a generalist that utilizes a multitude of fruits as oviposition sites. However, the identity and nature of oviposition stimulants for B. dorsalis is not well known. Recently, we identified a volatile compound γ-octalactone that elicits an innate oviposition response in B. dorsalis. We screened 21 EAD-active volatiles, identified from mango, for their oviposition stimulant activity. 1-Octen-3-ol, ethyl tiglate, and benzothiazole instigated oviposition in gravid B. dorsalis females. Flies deposited most of their eggs into pulp discs with oviposition-stimulants, and only a small fraction of eggs were laid into control discs. In a binary choice oviposition assay, 95.1, 93.7, and 65.6 % of eggs were laid in discs treated with 1-octen-3-ol, ethyl tiglate, and benzothiazole, respectively. Single plate two-choice assays proved that oviposition-stimulants were crucial in oviposition site selection by gravid female B. dorsalis. In simulated semi-natural assays, gravid B. dorsalis females accurately differentiated between fruits with and without 1-octen-3-ol, ethyl tiglate, and γ-octalactone by laying more eggs on the treated fruit. However, benzothiazole did not elicit an increase in oviposition when presented in this context. Our results suggest that the identified oviposition-stimulants are ‘key’ compounds, which the flies associate with suitable oviposition sites.
Food insecurity is a chronic problem in Africa and is likely to worsen with climate change and population growth. It is largely due to poor yields of the cereal crops caused by factors including ...stemborer pests, striga weeds and degraded soils. A platform technology, ‘push–pull’, based on locally available companion plants, effectively addresses these constraints resulting in substantial grain yield increases. It involves intercropping cereal crops with a forage legume, desmodium, and planting Napier grass as a border crop. Desmodium repels stemborer moths (push), and attracts their natural enemies, while Napier grass attracts them (pull). Desmodium is very effective in suppressing striga weed while improving soil fertility through nitrogen fixation and improved organic matter content. Both companion plants provide high-value animal fodder, facilitating milk production and diversifying farmers’ income sources. To extend these benefits to drier areas and ensure long-term sustainability of the technology in view of climate change, drought-tolerant trap and intercrop plants are being identified. Studies show that the locally commercial brachiaria cv mulato (trap crop) and greenleaf desmodium (intercrop) can tolerate long droughts. New on-farm field trials show that using these two companion crops in adapted push–pull technology provides effective control of stemborers and striga weeds, resulting in significant grain yield increases. Effective multi-level partnerships have been established with national agricultural research and extension systems, non-governmental organizations and other stakeholders to enhance dissemination of the technology with a goal of reaching one million farm households in the region by 2020. These will be supported by an efficient desmodium seed production and distribution system in eastern Africa, relevant policies and stakeholder training and capacity development.
Multitrophic interactions are likely to be altered by climate change but there is little empirical evidence relating the responses of herbivores and parasitoids to abiotic factors. Here we ...investigated the effects of drought on an above/below-ground system comprising a generalist and a specialist aphid species (foliar herbivores), their parasitoids, and a dipteran species (root herbivore).We tested the hypotheses that: (1) high levels of drought stress and below-ground herbivory interact to reduce the performance of parasitoids developing in aphids; (2) drought stress and root herbivory change the profile of volatile organic chemicals (VOCs) emitted by the host plant; (3) parasitoids avoid ovipositing in aphids feeding on plants under drought stress and root herbivory. We examined the effect of drought, with and without root herbivory, on the olfactory response of parasitoids (preference), plant volatile emissions, parasitism success (performance), and the effect of drought on root herbivory. Under drought, percentage parasitism of aphids was reduced by about 40-55% compared with well watered plants. There was a significant interaction between drought and root herbivory on the efficacy of the two parasitoid species, drought stress partially reversing the negative effect of root herbivory on percent parasitism. In the absence of drought, root herbivory significantly reduced the performance (e.g. fecundity) of both parasitoid species developing in foliar herbivores. Plant emissions of VOCs were reduced by drought and root herbivores, and in olfactometer experiments parasitoids preferred the odour from well-watered plants compared with other treatments. The present work demonstrates that drought stress can change the outcome of interactions between herbivores feeding above- and below-ground and their parasitoids, mediated by changes in the chemical signals from plants to parasitoids. This provides a new insight into how the structure of terrestrial communities may be affected by drought.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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