title: Allotetraploid origin and divergence in Eleusine (Chloridoideae, Poaceae): evidence from low-copy nuclear gene phylogenies and a plastid gene chronogram.
abstract: OBJECTIVE
  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.
  
  
  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.
authors: Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China. liuqing@scib.ac.cn
authors: Qing
authors: Q
authors: Liu
authors: Jimmy K
authors: JK
authors: Triplett
authors: Jun
authors: J
authors: Wen
authors: Paul M
authors: PM
authors: Peterson
mesh_terms: D000351:Africa, Eastern; D000569:Americas; D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics*; D018744:DNA, Plant / Q000235:genetics; D031748:Eleusine / Q000145:classification* / Q000235:genetics*; D019143:Evolution, Molecular; D005819:Genetic Markers; D008969:Molecular Sequence Data; D010163:Paleontology; D010802:Phylogeny; D018087:Plastids / Q000235:genetics*; D017422:Sequence Analysis, DNA; D057891:Tetraploidy
chemical_list: D018744:DNA, Plant; D005819:Genetic Markers