Journal Article

Allotetraploid origin and divergence in <i>Eleusine</i> (Chloridoideae, Poaceae): evidence from low-copy nuclear gene phylogenies and a plastid gene chronogram

Qing Liu, Jimmy K. Triplett, Jun Wen and Paul M. Peterson

in Annals of Botany

Published on behalf of The Annals of Botany Company

Volume 108, issue 7, pages 1287-1298
Published in print November 2011 | ISSN: 0305-7364
Published online August 2011 | e-ISSN: 1095-8290 | DOI: http://dx.doi.org/10.1093/aob/mcr231
Allotetraploid origin and divergence in Eleusine (Chloridoideae, Poaceae): evidence from low-copy nuclear gene phylogenies and a plastid gene chronogram

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  • Ecology and Conservation
  • Evolutionary Biology
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Background and Aims Eleusine

(Poaceae) is a small genus of the subfamily Chloridoideae exhibiting considerable morphological and ecological diversity in East Africa and the Americas. The interspecific phylogenetic relationships of Eleusine are investigated in order to identify its allotetraploid origin, and a chronogram is estimated to infer temporal relationships between palaeoenvironment changes and divergence of Eleusine in East Africa.

Methods

Two low-copy nuclear (LCN) markers, Pepc4 and EF-1α, were analysed using parsimony, likelihood and Bayesian approaches. A chronogram of Eleusine was inferred from a combined data set of six plastid DNA markers (ndhA intron, ndhF, rps16-trnK, rps16 intron, rps3, and rpl32-trnL) using the Bayesian dating method.

Key Results

The monophyly of Eleusine is strongly supported by sequence data from two LCN markers. In the cpDNA phylogeny, three tetraploid species (E. africana, E. coracana and E. kigeziensis) share a common ancestor with the E. indica–E. tristachya clade, which is considered a source of maternal parents for allotetraploids. Two homoeologous loci are isolated from three tetraploid species in the Pepc4 phylogeny, and the maternal parents receive further support. The A-type EF-1α sequences possess three characters, i.e. a large number of variations of intron 2; clade E-A distantly diverged from clade E-B and other diploid species; and seven deletions in intron 2, implying a possible derivation through a gene duplication event. The crown age of Eleusine and the allotetraploid lineage are 3·89 million years ago (mya) and 1·40 mya, respectively.

Conclusions

The molecular data support independent allotetraploid origins for E. kigeziensis and the E. africana–E. coracana clade. Both events may have involved diploids E. indica and E. tristachya as the maternal parents, but the paternal parents remain unidentified. The habitat-specific hypothesis is proposed to explain the divergence of Eleusine and its allotetraploid lineage.

Keywords: Allotetraploid origin; chloroplast markers; East Africa; Eleusine; low-copy nuclear markers; phylogeny; Poaceae

Journal Article.  6873 words.  Illustrated.

Subjects: Ecology and Conservation ; Evolutionary Biology ; Plant Sciences and Forestry

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