Photoperiod Stress in Arabidopsis thaliana Induces a Transcriptional Response Resembling That of Pathogen Infection

Plants are exposed to regular diurnal rhythms of light and dark. Changes in the photoperiod by the prolongation of the light period cause photoperiod stress in short day-adapted Arabidopsis thaliana. Here, we report on the transcriptional response to photoperiod stress of wild-type A. thaliana and photoperiod stress-sensitive cytokinin signaling and clock mutants and identify a core set of photoperiod stress-responsive genes. Photoperiod stress caused altered expression of numerous reactive oxygen species (ROS)-related genes. Photoperiod stress-sensitive mutants displayed similar, but stronger transcriptomic changes than wild-type plants. The alterations showed a strong overlap with those occurring in response to ozone stress, pathogen attack and flagellin peptide (flg22)-induced PAMP triggered immunity (PTI), which have in common the induction of an apoplastic oxidative burst. Interestingly, photoperiod stress triggers transcriptional changes in jasmonic acid (JA) and salicylic acid (SA) biosynthesis and signaling and results in increased JA, SA and camalexin levels. These responses are typically observed after pathogen infections. Consequently, photoperiod stress increased the resistance of Arabidopsis plants to a subsequent infection by Pseudomonas syringae pv. tomato DC3000. In summary, we show that photoperiod stress causes transcriptional reprogramming resembling plant pathogen defense responses and induces systemic acquired resistance (SAR) in the absence of a pathogen

Comparison of Solanum dulcamara transcriptome after real and simulated herbivory

Plants are attacked by diverse herbivores and respond with manifold defense responses. To study transcriptional and other early regulation events of these plant responses, herbivory is often mimicked to standardize the temporal and spatial dynamics that vary tremendously for natural herbivory. Yet to what extent such mimics of herbivory are able to elicit the same plant response as real herbivory remains largely undetermined. We examined the transcriptional response of a new model plant to herbivory by a lepidopteran larva and to a commonly used herbivory mimic by applying the larvae’s oral secretions to standardized wounds. We designed a microarray for Solanum dulcamara and showed that the transcriptional response to real and to simulated herbivory by Spodoptera exigua overlapped moderately by about 40%. Interestingly, certain responses were mimicked better than others; 60% of the genes up-regulated but not even a quarter of the genes down-regulated by herbivory were similarly affected by application of oral secretions to wounds. While the regulation of genes involved in signaling, defense and water stress were mirrored well by the herbivory mimic, most of the genes related to photosynthesis, carbohydrate- and lipid metabolism were exclusively regulated by real herbivory. Thus, wounding and elicitor application decently mimics herbivory-induced defense responses but likely not the re-allocation of primary metabolites induced by real herbivory. Overall design Four treatment groups were analyzed in S. dulcamara clones from different locations (Siethen, Erkner, Grunewald, and Mehrow, all in the vicinity of Berlin, Germany). Leaves were either undamaged controls (control), fed upon by S. exigua (spodo) caterpillars for 24 h or damaged with a pattern wheel and treated with S. exigua oral secretions (w+os) and harvested either after 1 h or 24 h

Slug feeding triggers dynamic metabolomic and transcriptomic responses leading to induced resistance in Solanum dulcamara

Induced plant responses to insect herbivores are well studied, but we know very little about responses to gastropod feeding. We aim to identify the temporal dynamics of signalling- and defence-related plant responses after slug feeding in relation to induced resistance. We exposed Solanum dulcamara plants to feeding by the grey field slug (GFS; Deroceras reticulatum) for different periods and tested discs of local and systemic leaves in preference assays. Induced responses were analysed using metabolomics and transcriptomics. GFS feeding induced local and systemic responses. Slug feeding for 72h more strongly affected the plant metabolome than 24h feeding. It increased the levels of a glycoalkaloid (solasonine), phenolamides, anthocyanins, and trypsin protease inhibitors as well as polyphenol oxidase activity. Phytohormone and transcriptome analyses revealed that jasmonic acid, abscisic acid and salicylic acid signalling were activated. GFS feeding upregulated more genes than that it downregulated. The response directly after feeding was more than five times higher than after an additional 24h without feeding. Our research showed that GFS, like most chewing insects, triggers anti-herbivore defences by activating defence signalling pathways, resulting in increased resistance to further slug feeding. Slug herbivory may therefore impact other herbivores in the community. Overall design Four seed batches were selected from S. dulcamara populations in the Netherlands (Goeree and Friesland) and Germany (Erkner and Siethen). Plants were randomly assigned to one of four treatments (n = 16 plants / population / treatment). Leaf number 10 from the apex was exposed to feeding by GFS for 24h or fitted with an empty clip cage for the same time period (undamaged control). Harvest took place directly (0h) after removing the slugs or after an additional 24h without exposure to GFS. RNA from four plants of a single plant population at each time point were pooled, resulting in four total RNA samples per treatment (control or induced) for both time points

Extrafloral nectar secretion from wounds of Solanum dulcamara

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Interactive responses of Solanum dulcamara to drought and insect feeding are herbivore species specific

In nature, plants are frequently subjected to multiple biotic and abiotic stresses, resulting in a convergence of adaptive responses. We hypothesized that hormonal signalling regulating defences to different herbivores may interact with drought response, causing distinct resistance phenotypes. To test this, we studied hormonal and transcriptomic responses of Solanum dulcamara subjected to drought and herbivory by the generalist Spodoptera exigua (BAW) or the specialist Leptinotarsa decemlineata (CPB). Bioassays showed that plants under drought became more resistant to BAW, but not to CPB. While drought did not alter BAW-induced hormonal responses, it enhanced CPB-induced accumulation of jasmonic acid and salicylic acid (SA) as well as supressed ethylene (ET) emission. Microarray analyses showed that under drought BAW herbivory enhanced several herbivore-induced responses, including cell-wall remodelling and metabolism of carbohydrates, lipids and secondary metabolites. In contrast, CPB herbivory enhanced several photosynthesis-related and pathogen responses in drought-stressed plants. This may divert resources away from the production of effective defences and increase tissue nutritive value. In conclusion, while BAW suffers from the drought-enhanced defences, CPB may benefit from effects of the enhanced SA and reduced ET signalling. This suggests that the fine-tuned interaction between the plant and its specialist herbivore is sustained under drought. Overall design 24 samples for 8 treatment groups (3 replicate each) were analysed. Leaves of plants under control watering regime (CON) or drought treatment (DRY) were either undamaged (NO) or fed upon by Spodoptera exigua (BAW2) or Leptinotarsa decemlineata (CPB2) for 48 h. Samples from plants under control watering regime that were fed by S. exigua (BAW1) and L. decemlineata (CPB1) for 24h were also included