454 pyrosequencing based transcriptome analysis of Zygaena filipendulae with focus on genes involved in biosynthesis of cyanogenic glucosides

Abstract

<p>Abstract</p> <p>Background</p> <p>An essential driving component in the co-evolution of plants and insects is the ability to produce and handle bioactive compounds. Plants produce bioactive natural products for defense, but some insects detoxify and/or sequester the compounds, opening up for new niches with fewer competitors. To study the molecular mechanism behind the co-adaption in plant-insect interactions, we have investigated the interactions between <it>Lotus corniculatus </it>and <it>Zygaena filipendulae</it>. They both contain cyanogenic glucosides which liberate toxic hydrogen cyanide upon breakdown. Moths belonging to the <it>Zygaena </it>family are the only insects known, able to carry out both <it>de novo </it>biosynthesis and sequestration of the same cyanogenic glucosides as those from their feed plants. The biosynthetic pathway for cyanogenic glucoside biosynthesis in <it>Z. filipendulae </it>proceeds using the same intermediates as in the well known pathway from plants, but none of the enzymes responsible have been identified. A genomics strategy founded on 454 pyrosequencing of the <it>Z. filipendulae </it>transcriptome was undertaken to identify some of these enzymes in <it>Z. filipendulae</it>.</p> <p>Results</p> <p>Comparisons of the <it>Z. filipendulae </it>transcriptome with the sequenced genomes of <it>Bombyx mori</it>, <it>Drosophila melanogaster</it>, <it>Tribolium castaneum</it>, <it>Apis mellifera </it>and <it>Anopheles gambiae </it>indicate a high coverage of the <it>Z. filipendulae </it>transcriptome. 11% of the <it>Z. filipendulae </it>transcriptome sequences were assigned to Gene Ontology categories. Candidate genes for enzymes functioning in the biosynthesis of cyanogenic glucosides (cytochrome P450 and family 1 glycosyltransferases) were identified based on sequence length, number of copies and presence/absence of close homologs in <it>D. melanogaster</it>, <it>B. mori </it>and the cyanogenic butterfly <it>Heliconius</it>. Examination of biased codon usage, GC content and selection on gene candidates support the notion of cyanogenesis as an "old" trait within Ditrysia, as well as its origins being convergent between plants and insects.</p> <p>Conclusion</p> <p>Pyrosequencing is an attractive approach to gain access to genes in the biosynthesis of bio-active natural products from insects and other organisms, for which the genome sequence is not known. Based on analysis of the <it>Z. filipendulae </it>transcriptome, promising gene candidates for biosynthesis of cyanogenic glucosides was identified, and the suitability of <it>Z. filipendulae </it>as a model system for cyanogenesis in insects is evident.</p