Comparative nucleotide sequence analysis of the D genome-specific sequence-tagged-site locus A1 in Triticum aestivum and its implication for the origin of subspecies sphaerococcum

Abstract

Common wheat (Triticum aestivum) evolved through hybridization between cultivated tetraploid emmer wheat (T. turgidum), which has A and B genomes, and the wild diploid species, Aegilops tauschii, which has the D genome. Although the evolution of common wheat is generally understood, specific details remain unclear. For example, the phylogenetic relationships and origins of the six wheat subspecies (ssp. spelta, macha, vavilovi, aestivum, compactum, and sphaerococcum) have not yet been thoroughly resolved. To clarify the origin of ssp. sphaerococcum, we employed comparative sequence analysis of the D genome-specific sequence-tagged-site (STS) locus A1 in common wheat accessions, including sphaerococcum. Only the two known alleles, type A and type B were found among the accessions. Of the two sphaerococcum accessions, both possessed the type A allele. Four aestivum accessions also possessed the type A allele, while the remaining three accessions possessed the type B allele. Conversely, the accessions of the four remaining subspecies possessed the type B allele. Since sphaerococcum has morphological traits that differ from aestivum and which are pleiotropically regulated by a single recessive gene designated s, sphaerococcum most likely originated from aestivum, with the type A allele at the A1 locus arising through a spontaneous mutation at the s locus.