Transcriptome analysis of aphids exposed to glandular trichomes in tomato reveals stress and starvation related responses

Abstract

Understanding the responses of insect herbivores to plant chemical defences is pivotal for the management of crops and pests. However, the mechanisms of interaction are not entirely understood. In this study, we compared the whole transcriptome gene expression of the aphid Macrosiphum euphorbiae grown on two different varieties of tomato that differ in their inducible chemical defences. We used two isogenic lines of tomato with a shared genetic background that only differ in the presence of type IV glandular trichomes and their associated acylsucrose excretions. This works also reports a de novo transcriptome of the aphid M. euphorbiae. Subsequently, we identified a unique and distinct gene expression profile for the first time corresponding to aphid´s exposure to type IV glandular trichomes and acylsugars. The analysis of the aphid transcriptome shows that tomato glandular trichomes and their associated secretions are highly efficient in triggering stress-related responses in the aphid, and demonstrating that their role in plant defence goes beyond the physical impediment of herbivore activity. Some of the differentially expressed genes were associated with carbohydrate, lipid and xenobiotic metabolisms, immune system, oxidative stress response and hormone biosynthesis pathways. Also, the observed responses are compatible with a starvation syndrome. The transcriptome analysis puts forward a wide range of genes involved in the synthesis and regulation of detoxification enzymes that reveal important underlying mechanisms in the interaction of the aphid with its host plant and provides a valuable genomic resource for future study of biological processes at the molecular level using this aphid.

Figure 1

Workflow followed in the present study.

Figure 2

Gene Ontology (GO) classification of transcripts of M. euphorbiae. Bar chart describes the distribution of M. euphorbiae transcripts into GO categories. Transcripts were annotated in three domains: (a) molecular function, (b) cellular component, and (c) biological process. The y-axis indicates the number of sequences in a given category.

Figure 3

Hierarchical clustering graph of DEGs found between ABL10-4–MM samples. Heat map (performed by Macrogen, with in-house scripts) shows the significant differentially expressed Macrosiphum euphorbiae genes when are exposed to Moneymaker and ABL10-4 tomato plants. Each row represents a gene and column represents different aphid samples (3 samples per condition).

Figure 4

Up-regulated pathways in aphids reared on ABL10-4 comparing to MM. Illustration of superclusters of overrepresented GO-terms visualised in semantic similarity-based treemap views from REVIGO program, for (a) molecular functions (b) cellular component and (c) biological process. Rectangles in the treemaps are size-adjusted to reflect the corrected P-value (i.e. larger rectangles represent the most significant GO-terms). Each rectangle in the treemap view has a single cluster for representation. These representatives are further joined together to build superclusters that are related terms and displayed in different colours.

Figure 5

Down-regulated pathways in aphids reared on ABL10-4 comparing to MM. Illustration of superclusters of overrepresented GO-terms visualised in semantic similarity-based treemap views from REVIGO program, for (a) molecular functions (b) cellular component and (c) biological process. Rectangles in the treemaps are size-adjusted to reflect the corrected P-value (i.e. larger rectangles represent the most significant GO-terms). Each rectangle in the treemap view has a single cluster for representation. These representatives are further joined together to build superclusters that are related terms and displayed in different colours.

Figure 6

(a) Detoxification and oxidative stress proteins identified from de novo transcriptome of M. euphorbiae. GenBank Accession numbers are indicated in Supplementary Table 6. Diagram of the protein of M. euphorbiae identified as putative mRNAs and their conserved domains. Diagram designed with DOG V.2 software. (b) Transcriptional activity of Cyp4g15, Cyp6a13-like, Cyp6k1-like, Cyp4c1, GPx, GST, Cu–Zn SOD-like in M. euphorbiae. Box and whisker plots represent the expression patterns of Cyp4g15, Cyp6a13-like, Cyp6k1-like, Cyp4c1, GPx, GST, Cu–Zn SOD-like measured by real-time RT-qPCR. Box and whiskers represent the 25–75 percentile and the minimum/maximum measured values; mean is represented by a dot; horizontal line separating the lower (dark) and the upper (light) area represents the median. (*) Asterisks indicate significant differences between MM and ABL10-4 aphids, P < 0.05.