Parallel acceleration of evolutionary rates in symbiont genes underlying host nutrition.
Journal Article (Journal Article)
The overproduction of essential amino acids by Buchnera aphidicola, the primary bacterial mutualist of aphids, is considered an adaptation for increased production of nutrients that are lacking in aphids' diet of plant sap. Given their shared role in host nutrition, amino acid biosynthetic genes of Buchnera are expected to experience parallel changes in selection that depend on host diet quality, growth rate, and population structure. This study evaluates the hypothesis of parallel selection across biosynthetic pathways by testing for correlated changes in evolutionary rates at biosynthetic genes of Buchnera. Previous studies show fast evolutionary rates at tryptophan biosynthetic genes among Buchnera associated with the aphid genus Uroleucon and suggest reduced purifying selection on symbiont nutritional functions in this aphid group. Here, we test for parallel rate acceleration at other amino acid biosynthetic genes of Buchnera-Uroleucon, including those for leucine (leuABC) and isoleucine/valine biosynthesis (ilvC). Ratios of nonsynonymous to synonymous substitutions (d(N)/d(S)) were estimated using codon-based maximum-likelihood methods that account for the extreme AT compositional bias of Buchnera sequences. A significant elevation in d(N)/d(S) at biosynthetic loci but not at two housekeeping genes sampled (dnaN and tuf) suggests reduced host-level selection on biosynthetic capabilities of Buchnera-Uroleucon. In addition, the discovery of trpEG pseudogenes in Buchnera-U. obscurum further supports reduced selection on amino acid biosynthesis.
Full Text
Duke Authors
Cited Authors
- Wernegreen, JJ; Richardson, AO; Moran, NA
Published Date
- June 2001
Published In
Volume / Issue
- 19 / 3
Start / End Page
- 479 - 485
PubMed ID
- 11399154
Electronic International Standard Serial Number (EISSN)
- 1095-9513
International Standard Serial Number (ISSN)
- 1055-7903
Digital Object Identifier (DOI)
- 10.1006/mpev.2001.0929
Language
- eng