Abstract
Bacteria to eukaryote lateral gene transfers (LGT) are an important potential source of material for the evolution of novel genetic traits. The explosion in the number of newly sequenced genomes provides opportunities to identify and characterize examples of these lateral gene transfer events, and to assess their role in the evolution of new genes. In this paper, we describe an ancient lepidopteran LGT of a glycosyl hydrolase family 31 gene (GH31) from an Enterococcus bacteria. PCR amplification between the LGT and a flanking insect gene confirmed that the GH31 was integrated into the Bombyx mori genome and was not a result of an assembly error. Database searches in combination with degenerate PCR on a panel of 7 lepidopteran families confirmed that the GH31 LGT event occurred deep within the Order approximately 65–145 million years ago. The most basal species in which the LGT was found is Plutella xylostella (superfamily: Yponomeutoidea). Array data from Bombyx mori shows that GH31 is expressed, and low dN/dS ratios indicates the LGT coding sequence is under strong stabilizing selection. These findings provide further support for the proposition that bacterial LGTs are relatively common in insects and likely to be an underappreciated source of adaptive genetic material.
Highlights
New coding genes can arise in genomes through several processes, including gene duplication, gene fusion, de novo formation from non-coding DNA, or lateral gene transfer (LGT) from another species
The single best candidate LGT in the D. plexippus genome based on the BLASTN searches, with a strong BLAST match to the glycosyl hydrolase family 31 (GH31) from Enterococcus faecalis, was on scaffold 15050 located within a predicted gene called DPGLEAN20412
Reciprocal BLASTP comparisons of all D. plexippus and B. mori proteins revealed that DpGH31 and BGIBMGA013995 are 1:1 BLAST orthologs
Summary
New coding genes can arise in genomes through several processes, including gene duplication, gene fusion, de novo formation from non-coding DNA, or lateral gene transfer (LGT) from another species. Once an LGT has occurred, it will either degrade through mutational processes (deletions and mutations) or, in some cases, evolve into a functional gene The latter process is poorly understood, but several examples have been found, including actively transcribed Wolbachia LGTs in the parasitoid Nasonia vitripennis [4], fungal-origin genes for carotenoids in aphids and spider mites [5,6], and bacterially derived plant cellulases in plant parasitic nematodes [7]. These and many other examples of LGTs can contribute to the adaptive potential of the recipient. Acuna et al (2012) [8] posit that the H. hampei LGT may be responsible for processing galactomannan, which is the most common polysaccharide in coffee beans, facilitating specialization of this pest species on coffee plants
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