Comparative genomics reveals high rates of horizontal transfer and strong purifying selection on rhizobial symbiosis genes

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Abstract

Horizontal transfer (HT) alters the repertoire of symbiosis genes in rhizobial genomes and may play an important role in the on-going evolution of the rhizobia-legume symbiosis. To gain insight into the extent of HT of symbiosis genes with different functional roles (nodulation, N-fixation, host benefit and rhizobial fitness), we conducted comparative genomic and selection analyses of the full-genome sequences from 27 rhizobial genomes. We find that symbiosis genes experience high rates of HT among rhizobial lineages but also bear signatures of purifying selection (low Ka: Ks). HT and purifying selection appear to be particularly strong in genes involved in initiating the symbiosis (e.g. nodulation) and in genome-wide association candidates for mediating benefits provided to the host. These patterns are consistent with rhizobia adapting to the host environment through the loss and gain of symbiosis genes, but not with host-imposed positive selection driving divergence of symbiosis genes through recurring bouts of positive selection.

Original languageEnglish (US)
Article number20201804
JournalProceedings of the Royal Society B: Biological Sciences
Volume288
Issue number1942
DOIs
StatePublished - Jan 13 2021

Bibliographical note

Publisher Copyright:
© 2021 The Author(s).

Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.

Keywords

  • coevolution
  • generax
  • lateral gene transfer
  • microbial evolution
  • mutualism
  • plant-microbe

PubMed: MeSH publication types

  • Journal Article
  • Research Support, U.S. Gov't, Non-P.H.S.

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