male Bombyx mori

Functional Genomics of Moth Chemoreception

     The silkworm (Bombyx mori) genome remains the first and only lepidopteran genome currently available. Chemoreceptor genes are highly divergent and their expression levels can be very low.

      Indeed, significant progress in this field only resulted after the advent of whole genome sequencing. We are using the silkworm genome (Chinese project  / Japanese project) as a model to address basic and applied research questions in the order Lepidoptera.

Moths and caterpillars use their sense of olfaction to locate and orient to potential host plants. Contact chemoreptors (gustation) on the front tarsi and ovipositor of female moths, and on the caterpillar mouthparts, largely arbitrate host plant selection for feeding and oviposition. We are annotating and functionally characterizing silkworm odorant and gustatory receptors that mediate these behaviors. We have identified several odorant receptors that are expressed at higher levels in female moth antennae that may be involved in detecting key host plant volatiles or male produced sex pheromones (Wanner et al., 2007). In collaboration with Richard Newcomb (HortReseach, New Zealand) we are characterizing the ligand binding specificity of these female-biased receptors expressed in Sf9 cells (activation is measured by calcium imaging).

We have also identified a silkworm odorant receptor lineage that is predominantly expressed in the larval antennae, which may be involved in host selection. Using olfactory bioassays we have found that neonate silkworms prefer the smell of (and crawl towards) new mulberry leaves (QuickTime Movie Clip 1-large file!) or mature leaves with feeding damage (QuickTime Movie Clip 2-large file!). The last half of Clip 2 shows neonate larvae crawling towards a mature mulberry leaf with feeding damage even though the damage is hardly visible in the video. Allison Mooney is working on this topic as an undergraduate research project and we are analyzing SPME-collected volatiles on a GC-MS. Neonate attraction to odors from mature leaves, mature leaves with feeding damage and new leaves will be tested using a custom-built olfactometer. Candidate odors will be screened against the larval specific receptors expressed in vitro.

We have demonstrated significant orthology of Ors from different lepidopteran families (Wanner et al., 2007) and we are using this to extend our research to significant pest species (USDA NRI Funded Project Proposal).

Calling female Bombyx moriMating Bombyx moriMale silkmoth

The olfactory system of male moths is highly sensitive to the female-produced sex pheromones. The chemistry of lepidopteran sex pheromones has been extensively studied and has yielded many significant tools for the management of insect pests. We now know that the lepidopteran pheromone receptors form a conserved subfamily. We are using degenerate PCR, high-throughput sequencing (454 Life Sciences platform), and in vitro functional assays to identify and characterize the pheromone receptors of several economically important pest species (collaborators include Stephen Garczynski and Thomas Unruh, USDA-ARS, Wapato WA).

There are many future applications of this research. Receptors that mediate critical pest behaviors can be screened in vitro in a pharmacological approach to identify better attractants or deterrents that can be used in traps or baits. High-throughput in vitro assays will provide a “receptor to behavior” approach to identifying important semiochemicals.   Furthermore this research will provide the basis to address many fascinating questions relating to the ecology of plant-insect interactions and the evolution of their chemosensory systems, such as plasticity of the gustatory system in response to feeding experience (NIH R03 Proposal).

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