Transcriptomic response of female adult moths to host and non-host plants in two closely related species.

BACKGROUND: Divergent selection has been shown to promote speciation in many taxa and especially in phytophagous insects. In the Ostrinia species complex, the European corn borer (ECB) and adzuki bean borer (ABB) are two sibling species specialized to different host plants. The first is a well-known maize pest, whereas the second is a polyphagous species associated with various dicotyledons. Their specialization to host plants is driven by morphological, behavioral and physiological adaptations. In particular, previous studies have shown that ECB and ABB display marked behavior with regard to plant choice during oviposition, involving specific preference and avoidance mechanisms. In this study, our goal was to identify the mechanisms underlying this host-plant specialization in adult females through an analysis of their gene expression. We assembled and annotated a de novo reference transcriptome and measured differences in gene expression between ECB and ABB females, and between environments. We related differentially expressed genes to host preference behavior, and highlighted the functional categories involved. We also conducted a specific analysis of chemosensory genes, which are considered to be good candidates for host recognition before oviposition. RESULTS: We recorded more differentially expressed genes in ECB than in ABB samples, and noticed that the majority of genes potentially involved in the host preference were different between the two species. At the functional level, the response to plant environment in adult females involved many processes, including the metabolism of carbohydrates, lipids, proteins, and amino acids; detoxification mechanisms and immunity; and the chemosensory repertoire (as expected). Until now, most of the olfactory receptors described in Ostrinia spp. had been tested for their putative role in pheromone recognition by males. Here we observed that one specific olfactory receptor was clearly associated with ECB's discrimination between maize and mugwort conditions, highlighting a potential new candidate involved in plant odor discrimination in adult females. CONCLUSIONS: Our results are a first step toward the identification of candidate genes and functions involved in chemosensory processes, carbohydrate metabolism, and virus and retrovirus dynamics. These candidates provide new avenues for research into understanding the role of divergent selection between different environments in species diversification.

Draft genome and reference transcriptomic resources for the urticating pine defoliator Thaumetopoea pityocampa (Lepidoptera: Notodontidae).

The pine processionary moth Thaumetopoea pityocampa (Lepidoptera: Notodontidae) is the main pine defoliator in the Mediterranean region. Its urticating larvae cause severe human and animal health concerns in the invaded areas. This species shows a high phenotypic variability for various traits, such as phenology, fecundity and tolerance to extreme temperatures. This study presents the construction and analysis of extensive genomic and transcriptomic resources, which are an obligate prerequisite to understand their underlying genetic architecture. Using a well-studied population from Portugal with peculiar phenological characteristics, the karyotype was first determined and a first draft genome of 537 Mb total length was assembled into 68,292 scaffolds (N50 = 164 kb). From this genome assembly, 29,415 coding genes were predicted. To circumvent some limitations for fine-scale physical mapping of genomic regions of interest, a 3X coverage BAC library was also developed. In particular, 11 BACs from this library were individually sequenced to assess the assembly quality. Additionally, de novo transcriptomic resources were generated from various developmental stages sequenced with HiSeq and MiSeq Illumina technologies. The reads were de novo assembled into 62,376 and 63,175 transcripts, respectively. Then, a robust subset of the genome-predicted coding genes, the de novo transcriptome assemblies and previously published 454/Sanger data were clustered to obtain a high-quality and comprehensive reference transcriptome consisting of 29,701 bona fide unigenes. These sequences covered 99% of the cegma and 88% of the busco highly conserved eukaryotic genes and 84% of the busco arthropod gene set. Moreover, 90% of these transcripts could be localized on the draft genome. The described information is available via a genome annotation portal (http://bipaa.genouest.org/sp/thaumetopoea_pityocampa/).

Proteome Analysis of Urticating Setae From Thaumetopoea pityocampa (Lepidoptera: Notodontidae).

Thaumetopoea pityocampa (Denis & Schiffermüller) (Lepidoptera: Notodontidae) is harmful to conifer trees because of defoliation and to public health because of the release of urticating setae from the caterpillars. Contact with setae by humans and domestic animals induces dermatitis, usually localized to the exposed areas. Recent studies demonstrated the presence of a complex urticating mechanism where proteins present in the setae may play a role as activators of immune responses. Yet, limited information is available at present about the proteins occurring in the setae of T. pityocampa. Using a refined method for protein extraction from the setae, and a combination of liquid chromatography tandem-mass spectrometry (LC-MS/MS), de novo assembly of transcriptomic data, and sequence similarity searches, an extensive data set of 353 proteins was obtained. These were further categorized by molecular function, biological process, and cellular location. All the 353 proteins identified were found to match through BLAST search with at least one Lepidoptera sequence available in databases. We found the previously known allergens Tha p 1 and Tha p 2 described from T. pityocampa, as well as enzymes involved in chitin biosynthesis, one of the principal components of the setae, and serine proteases that were responsible for inflammatory and allergic reactions in other urticating Lepidoptera. This new proteomic database may allow for a better understanding of the complexity of allergenic reactions due to T. pityocampa and to other Lepidoptera sharing similar defense systems.