Abstract

BackgroundThe insect midgut and fat body represent major tissue interfaces that deal with several important physiological functions including digestion, detoxification and immune response. The emerald ash borer (Agrilus planipennis), is an exotic invasive insect pest that has killed millions of ash trees (Fraxinus spp.) primarily in the Midwestern United States and Ontario, Canada. However, despite its high impact status little knowledge exists for A. planipennis at the molecular level.Methodology and Principal FindingsNewer-generation Roche-454 pyrosequencing was used to obtain 126,185 reads for the midgut and 240,848 reads for the fat body, which were assembled into 25,173 and 37,661 high quality expressed sequence tags (ESTs) for the midgut and the fat body of A. planipennis larvae, respectively. Among these ESTs, 36% of the midgut and 38% of the fat body sequences showed similarity to proteins in the GenBank nr database. A high number of the midgut sequences contained chitin-binding peritrophin (248)and trypsin (98) domains; while the fat body sequences showed high occurrence of cytochrome P450s (85) and protein kinase (123) domains. Further, the midgut transcriptome of A. planipennis revealed putative microbial transcripts encoding for cell-wall degrading enzymes such as polygalacturonases and endoglucanases. A significant number of SNPs (137 in midgut and 347 in fat body) and microsatellite loci (317 in midgut and 571 in fat body) were predicted in the A. planipennis transcripts. An initial assessment of cytochrome P450s belonging to various CYP clades revealed distinct expression patterns at the tissue level.Conclusions and SignificanceTo our knowledge this study is one of the first to illuminate tissue-specific gene expression in an invasive insect of high ecological and economic consequence. These findings will lay the foundation for future gene expression and functional studies in A. planipennis.

Highlights

  • The insect midgut and fat body are important metabolic tissues and represent key physiological interfaces during interactions with hosts

  • To our knowledge this study is one of the first to illuminate tissue-specific gene expression in an invasive insect of high ecological and economic consequence. These findings will lay the foundation for future gene expression and functional studies in A. planipennis

  • Similar nomenclature was adopted to describe the fat body transcriptomic sequences with MG replaced by FB for fat body

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Summary

Introduction

The insect midgut and fat body are important metabolic tissues and represent key physiological interfaces during interactions with hosts. While both tissues are highly specialized and play major roles in the life of insects, they possess discrete physiological functions essential for growth and development. The insect fat body is a dynamic tissue, which plays vital roles in intermediary metabolism, energy storage/utilization, detoxification and immune response [7,8]. Functions performed by the insect fat body are correlated to those of adipose tissue and liver of vertebrates. The insect midgut and fat body represent major tissue interfaces that deal with several important physiological functions including digestion, detoxification and immune response. Despite its high impact status little knowledge exists for A. planipennis at the molecular level

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