Arabidopsis thaliana-Spider Mite Interaction: Plant Perception, Signalling, and Response

The two-spotted spider mite, Tetranychus urticae, is a cell-content feeding chelicerate herbivore, feeding on over 1000 plant species, one of which is Arabidopsis thaliana. This research uses microarray data from two A. thaliana accessions that differ in susceptibility to spider mite feeding to identify how the plant defends itself against this herbivore. Mutant analysis of induced plant defense pathways and physiological assays of mite performance indicate that A. thaliana utilizes: a) damage associated molecular pattern receptors, PEPR1 and PEPR2, to aid in perception of attack; b) jasmonic acid as the key phytohormone involved in resistance signalling; and c) indole glucosinolates as effective secondary metabolites affecting mite performance and development. My findings provide insight into how A. thaliana defends itself against this class of arthropod herbivores using defences that have previously been associated with deterrence of insect herbivores, which are distantly related to chelicerates

Tetranychus urticae adaptation to tomato

The arms race between plants and herbivores has resulted in a great diversity of plant compounds to act as defences against attackers. It has concurrently resulted in herbivorous pest adaptations to host defences, including plant-host defence suppression through the action of secreted effectors, and detoxification of phytochemicals ingested during feeding. While these two mechanisms of herbivore adaptation are relatively well studied, they have not been tested for use at the same time. This study uses the model plant species Solanum lycopersicum (tomato), and the model arthropod species Tetranychus urticae (two-spotted spider mite), to characterize the utilization of the above-mentioned mechanisms in an experimental adaptation set-up. Two spider mite strains, non-adapted (ancestral) and tomato-adapted, were used to infest tomato under different experimental conditions to interrogate the adaptation process. Tomato adaptation was validated through plant damage and mite performance assays. Transcriptional analysis of differentially expressed genes demonstrated an attenuation of the response to non-adapted mites by adapted ones, indicating the defence response to be deficient in induced defence programs, such as jasmonic acid biosynthesis and protease inhibitor biosynthesis. This was supported with marker gene and hormone quantification. However, inhibition activity was found to be differentially induced in different tomato cultivars, being highly induced in Moneymaker and attenuated in Heinz samples fed on by adapted mites, suggesting mites still encounter protease inhibitors as a plant defence in certain tomato cultivars despite being adapted to tomato in general. A mite co-infestation experiment was used to demonstrate that any benefit to host-plant modulation occurs only at the feeding site. Characterization of mite protease activity and fecundity post-inhibition by a synthetic inhibitor, E-64, suggest that mites increase their protease activity to overcome tomato protease inhibitors. Detoxification was also found to be involved in tomato adaptation, whereby inhibiting different classes of enzymes (cytochrome P450s, esterases, or glutathione-S-transferases) resulted in decreased fecundity on tomato

Differentially expressed genes of T. urticae in the experimental evolutionary set-up

Different DEG lists, arising from different transcriptomic comparisons, are shown in different tabs of the excel file. The abbreviations are explained in Table 1 of the main text

Data from: Adaptation of a polyphagous herbivore to a novel host plant extensively shapes the transcriptome of herbivore and host

Generalist arthropod herbivores rapidly adapt to a broad range of host plants. However, the extent of transcriptional reprogramming in the herbivore and its hosts associated with adaptation remains poorly understood. Using the spider mite Tetranychus urticae and tomato as models with available genomic resources, we investigated the reciprocal genomewide transcriptional changes in both spider mite and tomato as a consequence of mite's adaptation to tomato. We transferred a genetically diverse mite population from bean to tomato where triplicated populations were allowed to propagate for 30 generations. Evolving populations greatly increased their reproductive performance on tomato relative to their progenitors when reared under identical conditions, indicative of genetic adaptation. Analysis of transcriptional changes associated with mite adaptation to tomato revealed two main components. First, adaptation resulted in a set of mite genes that were constitutively downregulated, independently of the host. These genes were mostly of an unknown function. Second, adapted mites mounted an altered transcriptional response that had greater amplitude of changes when re-exposed to tomato, relative to nonadapted mites. This gene set was enriched in genes encoding detoxifying enzymes and xenobiotic transporters. Besides the direct effects on mite gene expression, adaptation also indirectly affected the tomato transcriptional responses, which were attenuated upon feeding of adapted mites, relative to the induced responses by nonadapted mite feeding. Thus, constitutive downregulation and increased transcriptional plasticity of genes in a herbivore may play a central role in adaptation to host plants, leading to both a higher detoxification potential and reduced production of plant defence compounds

Differentially expressed genes of tomato in the experimental evolutionary set-up

The abbreviations are explained in Table 1 of the main text

Application of two-spotted spider mite Tetranychus urticae for plant-pest interaction studies

The two-spotted spider mite, Tetranychus urticae, is a ubiquitous polyphagous arthropod herbivore that feeds on a remarkably broad array of species, with more than 150 of economic value. It is a major pest of greenhouse crops, especially in Solanaceae and Cucurbitaceae (e.g., tomatoes, eggplants, peppers, cucumbers, zucchini) and greenhouse ornamentals (e.g., roses, chrysanthemum, carnations), annual field crops (such as maize, cotton, soybean, and sugar beet), and in perennial cultures (alfalfa, strawberries, grapes, citruses, and plums)(1,2). In addition to the extreme polyphagy that makes it an important agricultural pest, T. urticae has a tendency to develop resistance to a wide array of insecticides and acaricides that are used for its control(3-7). T. urticae is an excellent experimental organism, as it has a rapid life cycle (7 days at 27 degrees C) and can be easily maintained at high density in the laboratory. Methods to assay gene expression (including in situ hybridization and antibody staining) and to inactivate expression of spider mite endogenous genes using RNA interference have been developed(8-10). Recently, the whole genome sequence of T. urticae has been reported, creating an opportunity to develop this pest herbivore as a model organism with equivalent genomic resources that already exist in some of its host plants (Arabidopsis thaliana and the tomato Solanum lycopersicum)(11). Together, these model organisms could provide insights into molecular bases of plant-pest interactions. Here, an efficient method for quick and easy collection of a large number of adult female mites, their application on an experimental plant host, and the assessment of the plant damage due to spider mite feeding are described. The presented protocol enables fast and efficient collection of hundreds of individuals at any developmental stage (eggs, larvae, nymphs, adult males, and females) that can be used for subsequent experimental applicatio

Spider mite performance on different host plants, before and after tomato adaptation.

Performance was quantified as the total population sizes (including eggs and mobile stages) 10 days after the initial inoculation using 35 female mites. The T. urticae London mite strain and the following plant cultivars were used; bean: Phaseolus vulgaris L. cv ‘Prelude’, cucumber: Cucumis sativus L. cv ‘Tanja’, tomato: Solanum lycopersicum L. cv ‘Moneymaker’ and bell pepper: Capsicum annuum L. cv ‘California Wonder’

Spider mite performance on different host plants, before and after tomato adaptation.

Performance was quantified as the total population sizes (including eggs and mobile stages) 10 days after the initial inoculation using 35 female mites. The T. urticae London mite strain and the following plant cultivars were used; bean: Phaseolus vulgaris L. cv ‘Prelude’, cucumber: Cucumis sativus L. cv ‘Tanja’, tomato: Solanum lycopersicum L. cv ‘Moneymaker’ and bell pepper: Capsicum annuum L. cv ‘California Wonder’

Annotations of tomato genes

ITAG, Blast2GO and EC descriptions for tomato genes are included