Single-copy nuclear PolA1 gene sheds light on the origin of S genome with relationships to B and G genomes of polyploid wheat species

Bhuwan Rai, Hiroko Takahashi, Kenji Kato, Yo ichiro Sato, Ikuo Nakamura

Research output: Contribution to journalArticlepeer-review

7 Citations (Scopus)


PolA1, a single-copy nuclear gene encoding the largest subunit of RNA polymerase I, comprises highly polymorphic intron 19 and nucleotide tag (Ntag) sequences. We analyzed these sequences in 42 accessions, which differed in ploidy, of Triticum-Aegilops and Hordeum species. The lengths of the intron 19 sequences were ca. 110 bp long in Triticum-Aegilops species, except in four Sitopsis species, Ae. longissima, Ae. searsii, Ae. sharonensis, Ae. speltoides, which had introns similar in length to those of Hordeum species, i. e., ca. 240 bp long. Phylogenetic analyses of the Ntag sequences showed that the four Sitopsis and remaining Triticum-Aegilops species were classified into two discrete Hordeum and Triticum clades, respectively. The A and D genome-specific Ntag sequences of polyploid wheats were highly homologous with those of T. urartu and Ae. tauschii, respectively. In Ae. bicornis, another Sitopsis species, two accessions had the short intron 19 and Triticum-type Ntag sequence, which were highly homologous with those of the B genome in polyploid wheats, whereas one accession contained the long intron 19 and Hordeum-type Ntag sequences. In contrast, partial sequence analyses revealed that the three accessions of Ae. bicornis shared highly homology to single-copy DMC1 and EF-G genes. The discrepancy between these results indicates that the Sitopsis species were probably established by hybrid speciation including ancient introgressive hybridization between progenitors of Triticum-Aegilops and Hordeum. Although many researchers have proposed Ae. speltoides as a candidate for the B genome donor, our data suggest the existence of diploid B genome species in the past that were responsible for the origin of both polyploid wheats and Sitopsis species, including Ae. speltoides.

Original languageEnglish
Pages (from-to)1713-1726
Number of pages14
JournalGenetic Resources and Crop Evolution
Issue number8
Publication statusPublished - Dec 2012


  • Homoploid hybrid speciation
  • Introgression
  • Sequence homogenization
  • Single-copy gene
  • Sitopsis
  • Triticum-Aegilops

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Agronomy and Crop Science
  • Genetics
  • Plant Science


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