Radiation of the Nod-independent Aeschynomene relies on multiple allopolyploid speciation events

Authors

  • Jean-François Arrighi,

    Corresponding author
    1. IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, Montpellier Cedex 5, France
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  • Clémence Chaintreuil,

    1. IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, Montpellier Cedex 5, France
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  • Fabienne Cartieaux,

    1. IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, Montpellier Cedex 5, France
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  • C. Cardi,

    1. CIRAD, UMR AGAP, Plateau de Cytogénétique Moléculaire, Montpellier Cedex 5, France
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  • M. Rodier-Goud,

    1. CIRAD, UMR AGAP, Plateau de Cytogénétique Moléculaire, Montpellier Cedex 5, France
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  • Spencer C. Brown,

    1. CNRS, IBiSA Imagerie Gif et Imagif BioCell, Institut des Sciences du Végétal, UPR 2355, Gif-sur-Yvette, France
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  • Marc Boursot,

    1. IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, Montpellier Cedex 5, France
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  • Angélique D'Hont,

    1. CIRAD, UMR AGAP, Plateau de Cytogénétique Moléculaire, Montpellier Cedex 5, France
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  • Bernard Dreyfus,

    1. IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, Montpellier Cedex 5, France
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  • Eric Giraud

    1. IRD, Laboratoire des Symbioses Tropicales et Méditerranéennes, UMR IRD/SupAgro/INRA/UM2/CIRAD, Campus International de Baillarguet, Montpellier Cedex 5, France
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Summary

  • The semi-aquatic legumes belonging to the genus Aeschynomene constitute a premium system for investigating the origin and evolution of unusual symbiotic features such as stem nodulation and the presence of a Nod-independent infection process. This latter apparently arose in a single Aeschynomene lineage. But how this unique Nod-independent group then radiated is not yet known.
  • We have investigated the role of polyploidy in Aeschynomene speciation via a case study of the pantropical A. indica and then extended the analysis to the other Nod-independent species. For this, we combined SSR genotyping, genome characterization through flow cytometry, chromosome counting, FISH and GISH experiments, molecular phylogenies using ITS and single nuclear gene sequences, and artificial hybridizations.
  • These analyses demonstrate the existence of an A. indica polyploid species complex comprising A. evenia (C. Wright) (2= 2x = 20), A. indica L. s.s. (2n = 4x = 40) and a new hexaploid form (2= 6x = 60). This latter contains the two genomes present in the tetraploid (A. evenia and A. scabra) and another unidentified genome. Two other species, A. pratensis and A. virginica, are also shown to be of allopolyploid origin.
  • This work reveals multiple hybridization/polyploidization events, thus highlighting a prominent role of allopolyploidy in the radiation of the Nod-independent Aeschynomene.

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