Multiple evolutionary origins of legume traits leading to extreme rhizobial differentiation

When rhizobia differentiate inside legume host nodules to become nitrogen-fixing bacteroids, they undergo a physiological as well as a morphological transformation. These transformations are more extreme in some legume species than others, leading to fundamental differences in rhizobial life history...

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Bibliographic Details
Published in:The New phytologist 2010-07, Vol.187 (2), p.508-520
Main Authors: Oono, Ryoko, Schmitt, Imke, Sprent, Janet I., Denison, R. Ford
Format: Article
Language:English
Subjects:
ancestral character state reconstruction
Bacteria
bacteroid
Bacteroids
Bayesian analysis
Biological taxonomies
Differentiation
Electron micrographs
Evolution
Evolution, Molecular
Fabaceae - genetics
Fabaceae - microbiology
Flow Cytometry
Legumes
Life history
Morphology
nodule type
Nodules
Origins
papilionoid legumes
Papilionoideae
Phylogeny
Plants
Probability theory
Quantitative Trait, Heritable
rhizobia
Rhizobium - cytology
Rhizobium - physiology
Root Nodules, Plant - genetics
Root Nodules, Plant - microbiology
Species Specificity
Swelling
Symbiosis
Viability
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Summary:When rhizobia differentiate inside legume host nodules to become nitrogen-fixing bacteroids, they undergo a physiological as well as a morphological transformation. These transformations are more extreme in some legume species than others, leading to fundamental differences in rhizobial life history and evolution. Here, we analysed the distribution of different bacteroid morphologies over a legume phylogeny to understand the evolutionary history of this host-influenced differentiation. Using existing electron micrographs and new flow cytometric analyses, bacteroid morphologies were categorized as swollen or nonswollen for 40 legume species in the subfamily Papilionoideae. Maximum likelihood and Bayesian frameworks were used to reconstruct ancestral states at the bases of all major subclades within the papilionoids. Extreme bacteroid differentiation leading to swelling was found in five out of the six major papilionoid subclades. The inferred ancestral state for the Papilionoideae was hosting nonswollen bacteroids, indicating at least five independent origins of host traits leading to swollen bacteroids. Repeated evolution of host traits causing bacteroid swelling indicates a possible fitness benefit to the plant. Furthermore, as bacteroid swelling is often correlated with loss of reproductive viability, the evolution of bacteroid cooperation or cheating strategies could be fundamentally different between the two bacteroid morphologies.
ISSN:0028-646X
1469-8137
DOI:10.1111/j.1469-8137.2010.03261.x