Comparative transcriptome analysis of salivary glands of two populations of rice brown planthopper, Nilaparvata lugens, that differ in virulence

Abstract

Background: The brown planthopper (BPH), Nilaparvata lugens (Stål), a destructive rice pest in Asia, can quickly overcome rice resistance by evolving new virulent populations. Herbivore saliva plays an important role in plant-herbivore interactions, including in plant defense and herbivore virulence. However, thus far little is known about BPH saliva at the molecular level, especially its role in virulence and BPH-rice interaction.

Methodology/principal findings: Using cDNA amplification in combination with Illumina short-read sequencing technology, we sequenced the salivary-gland transcriptomes of two BPH populations with different virulence; the populations were derived from rice variety TN1 (TN1 population) and Mudgo (M population). In total, 37,666 and 38,451 unigenes were generated from the salivary glands of these populations, respectively. When combined, a total of 43,312 unigenes were obtained, about 18 times more than the number of expressed sequence tags previously identified from these glands. Gene ontology annotations and KEGG orthology classifications indicated that genes related to metabolism, binding and transport were significantly active in the salivary glands. A total of 352 genes were predicted to encode secretory proteins, and some might play important roles in BPH feeding and BPH-rice interactions. Comparative analysis of the transcriptomes of the two populations revealed that the genes related to 'metabolism,' 'digestion and absorption,' and 'salivary secretion' might be associated with virulence. Moreover, 67 genes encoding putative secreted proteins were differentially expressed between the two populations, suggesting these genes may contribute to the change in virulence.

Conclusions/significance: This study was the first to compare the salivary-gland transcriptomes of two BPH populations having different virulence traits and to find genes that may be related to this difference. Our data provide a rich molecular resource for future functional studies on salivary glands and will be useful for elucidating the molecular mechanisms underlying BPH feeding and virulence differences.

Figure 1. Species distribution of the BLASTX results of brown planthopper salivary-gland genes.

This figure shows the species distribution of unigene BLASTX results against the NCBI nr protein database with a cutoff E-value ≤1.0E^–5 and the proportions of each species, represented by different colors. Species with proportions greater than 1% are shown.

Figure 2. Gene ontology (GO) classifications of salivary-gland genes of TN1 and Mudgo (M) populations.

The results are summarized in three main categories: biological process, molecular function, and cellular component. The y-axis shows the number of matching unigenes in a category.

Figure 3. KEGG pathway distributions of unigenes from salivary glands of TN1 and Mudgo (M) populations.

The top fifteen pathways (excluding human disease-related) with the highest percentages of mapped unigenes are shown.

Figure 4. Bitmap of differentially expressed genes.

The red and green points represent up- and down-regulated genes in the salivary glands of TN1 population, respectively; the blue points represent genes with no differences in expression based on the criteria of the false discovery rate (FDR) ≤0.001 and an absolute value of the log₂ ratio ≥1.

Figure 5. Fold difference distribution of differently expressed genes.

The x-axis shows the fold change (log₂ ratio) in gene expression in TN1 population compared to Mudgo (M) population.

Figure 6. Distribution of significantly differentially expressed transcripts in gene ontology (GO) subclasses.

The y-axis shows the number of the matching differentially expressed genes in that category.