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© 2007 Dunbar et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited: Dunbar HE, Wilson ACC, Ferguson NR, Moran NA (2007) Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts. PLoS Biol 5(5): e96. doi:10.1371/journal.pbio.0050096

Abstract

Symbiosis is a ubiquitous phenomenon generating biological complexity, affecting adaptation, and expanding ecological capabilities. However, symbionts, which can be subject to genetic limitations such as clonality and genomic degradation, also impose constraints on hosts. A model of obligate symbiosis is that between aphids and the bacterium Buchnera aphidicola, which supplies essential nutrients. We report a mutation in Buchnera of the aphid Acyrthosiphon pisum that recurs in laboratory lines and occurs in field populations. This single nucleotide deletion affects a homopolymeric run within the heat-shock transcriptional promoter for ibpA, encoding a small heat-shock protein. This Buchnera mutation virtually eliminates the transcriptional response of ibpA to heat stress and lowers its expression even at cool or moderate temperatures. Furthermore, this symbiont mutation dramatically affects host fitness in a manner dependent on thermal environment. Following a short heat exposure as juveniles, aphids bearing short-allele symbionts produced few or no progeny and contained almost no Buchnera, in contrast to aphids bearing symbionts without the deletion. Conversely, under constant cool conditions, aphids containing symbionts with the short allele reproduced earlier and maintained higher reproductive rates. The short allele has appreciable frequencies in field populations (up to 20%), further supporting the view that lowering of ibpA expression improves host fitness under some conditions. This recurring Buchnera mutation governs thermal tolerance of aphid hosts. Other cases in which symbiont microevolution has a major effect on host ecological tolerance are likely to be widespread because of the high mutation rates of symbiotic bacteria and their crucial roles in host metabolism and development.

Details

Title
Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts
Author
Dunbar, Helen E; Wilson, Alex CC; Ferguson, Nicole R; Moran, Nancy A
Pages
e96
Section
Research Article
Publication year
2007
Publication date
May 2007
Publisher
Public Library of Science
ISSN
15449173
e-ISSN
15457885
Source type
Scholarly Journal
Language of publication
English
ProQuest document ID
1292065012
Copyright
© 2007 Dunbar et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited: Dunbar HE, Wilson ACC, Ferguson NR, Moran NA (2007) Aphid Thermal Tolerance Is Governed by a Point Mutation in Bacterial Symbionts. PLoS Biol 5(5): e96. doi:10.1371/journal.pbio.0050096