Multiple origins of U genome in two UM genome tetraploid Aegilops species, Ae. biuncialis and Ae. ovata

Tsuneo Sasanuma¹, Sayo Kadosumi¹ and Taihachi Kawahara²

¹ Division of Evolutionary Genetics, Kihara Institute for Biological Research, Yokohama City University, Maioka-cho 641-12, Totsuka-ku, Yokohama 244-0813, Japan

² Laboratory of Crop Evolution, Plant Germ-plasm Institute, Graduate School of Agriculture, Kyoto University, Mozume, Muko, Kyoto 617-0001, Japan

Corresponding author: Tsuneo Sasanuma

    e-mail: sasanuma@yokohama-cu.ac.jp

    tel: +81-45-820-1902

    fax: +81-45-820-1901

The genera Aegilops and Triticum include a lot of polyploid species that contain various combinations of genomes. Recent molecular analyses have gradually revealed that some of the polyploid species was not formed by a single polyploidization event, but by several times events. In other words, some polyploids have polyphyletic multiple origins within a species. Table 1 summarizes the molecular evidence for multiple origins of polyploid species in the genera Aegilops and Triticum reported to date. As you see in Table 1, multiple origins are likely to be the general rule for polyploid species in these genera. 

Here, we report a new evidence for the multiple origins of the U genome in two UM genome tetraploid species, Ae. biuncialis and Ae. ovata, based on the PCR-RFLP of the U genome-specific U31 fragment that we developed previously (Kadosumi et al. 2005). We investigated the PCR-RFLP of the U31 fragment of 48 accessions each of Ae. biuncialis and Ae. ovata. All the accessions used were the collection of the Plant Germ-plasm Institute, Graduate School of Agriculture, Kyoto University. The allelic variation of U31 fragment observed in the two species was shown in Table 2. We found common alleles between the U genome diploid Ae. umbellulata and Ae. biuncialis, and between Ae. umbellulata and Ae. ovata. These results suggested the multiple origins of the U genome in the two tetraploid species.

Sequencing analysis revealed that the allele II detected in Ae. biuncialis has the CCAG at the MspI site, which was also found in 21 accessions of Ae. umbellulata. This result strongly supports the hypothesis that the allele II of Ae. biuncialis has been derived from Ae. umbellulata by secondary polyploidization, although the order of the polyploidization is indeterminable. The multiple origins of the M genome in Ae. biuncialis has been reported by Chee et al. (1995), but our present study is the first report of multiple origins of the U genome in this species. As for Ae. ovata, the alleles shared with Ae. umbellulata were alleles I and IV. Since the allele IV is null allele, we could not determine the sequence of this allele. Therefore, strictly speaking, it is not conclusive that the allele IV in Ae. ovata has been derived from Ae. umbellulata. To ascertain the multiple origins of Ae. ovata, more information on other loci are necessary. 

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