Project description:In this experiment we measured the transcriptional response of tomato plants (cv “Money maker”) when attacked belowground by the nematode M. inognita and, subsequently, aboveground by different (and common for this crop) biotic agents. Three weeks-old plants were exposed to nematodes for 5 days. At the fifth day the terminal leaflet of one of the first two true leaves was infected with the Cauliflower Mosaic Virus, or with the pathogen, or with the potato aphid Macrosiphum euphorbiae, or with the CMV-infected M. euphorbiae. For each belowground/aboveground combination treatment a set of control plants that received only the aboveground treatment was prepared. The infected leaflets of 5 biological replicates, each consisting of 1 plant, were collected 1, 2, 3, 4, 5 and 6 days after the onset of the aboveground treatment and flash frozen in liquid nitrogen. A different set of plants was used for every time point. Corresponding leaves from plants that did not receive any aboveground treatment (control) were selected and sampled as described above. Three biological replicates were selected among the five for RNA isolation. Total RNA was sent for sequencing to BGI Hong Kong.
Project description:Tomato produces a number of terpenes in their glandular trichomes that contribute to host plant resistance against pests. While glandular trichomes of cultivated tomato Solanum lycopersicum primarily accumulate a blend of monoterpenes, those of the wild tomato species Solanum habrochaites produce various sesquiterpenes. Recently, we have identified two groups of sesquiterpenes in S. habrochaites accessions that negatively affect the performance and choice behavior of the potato aphid (Macrosiphum euphorbiae). Aphids are piercing-sucking herbivores that use their mouthpart to penetrate and probe plant tissues in order to ultimately access vascular tissue and ingest phloem sap. Because secondary metabolites produced in glandular trichomes can affect the initial steps of the aphid feeding behavior, introducing the formation of defensive terpenes into additional plant tissues via metabolic engineering has the potential to reduce tissue penetration by aphids and in consequence virus transmission. Here, we have developed two multicistronic expression constructs based on the two sesquiterpene traits with activity toward M. euphorbiae previously identified in S. habrochaites. Both constructs are composed of sequences encoding a prenyl transferase and a respective S. habrochaites terpene synthase, as well as enhanced green fluorescent protein as a visible marker. All three coding sequences were linked by short nucleotide sequences encoding the foot-and-mouth disease virus 2A self-processing oligopeptide which allows their co-expression under the control of one promoter. Transient expression of both constructs under the epidermis-specific Arabidopsis CER5-promoter in tomato leaves demonstrated that formation of the two sets of defensive sesquiterpenes, β-caryophyllene/α-humulene and (-)-endo-α-bergamotene/(+)-α-santalene/(+)-endo-β-bergamotene, can be introduced into new tissues in tomato. The epidermis-specific transgene expression and terpene formation were verified by fluorescence microscopy and tissue fractionation with subsequent analysis of terpene profiles, respectively. In addition, the longevity and fecundity of M. euphorbiae feeding on these engineered tomato leaves were significantly reduced, demonstrating the efficacy of this novel aphid control strategy.
Project description:Aphids deliver saliva into plants and acquire plant sap for their nourishment using a specialized mouthpart or stylets. Aphid saliva is of great importance as it contains effectors that are involved in modulating host defense and metabolism. Although profiling aphid salivary glands and identifying secreted proteins have been successfully used, success in direct profiling of aphid saliva have been limited due to scarcity of saliva collected in artificial diets. Here we present the use of a neurostimulant, resorcinol, for inducing aphid salivation. Saliva of potato aphids (Macrosiphum euphorbiae), maintained on tomato, was collected in resorcinol diet, used in mass spectrometry and compared to the salivary proteome collected in water. Great majority of the proteins identified in the resorcinol diet were also present in the water diet and represented proteins with plethora of functions in addition to a large number of unknowns. About half of the salivary proteins were not predicted for secretion or had canonical secretion signal peptides. To further characterize M. euphorbiae saliva and identify effectors, salivary phosphoproteins were detected. Among these phosphorylated proteins were three known aphid effectors, Me_WB01635 /Mp1, Me10/Mp58 and Me23. In addition to insect proteins, tomato host proteins were also identified in aphid saliva. Our results indicate that aphid saliva is complex and provides a rich resource for functional characterization of effectors.