[FISH analysis of a CRW-homology sequence from Pseudoroegneria spicata in Thinopyrum ponticum and Th. intermedium]

To verify the genome components of Thinopyrum ponticum Liu alt; Wang and Th. intermedium [Host] Barkworth alt; Dewey, six specific primer pairs were designed according to the sequence of an autonomous centromeric retrotransposon of wheat (CRW) from Triticum boeoticum. Several DNA fragments were amplified by PCR from the genomic DNA of the diploid species Pseudoroegneria spicata A Löve. After sequence alignment, a 1.755 kb fragment was obtained and named as pStC1 (St genome centromere associated sequence, GenBank accession No. FJ952565). This fragment contained an 800 bp fragment highly homologous to the LTR region of autonomous CRW, a short fragment partial homology to the gag region of CRW, and an AGCAAC-rich tandem repeat. Fluorescent in situ hybridization (FISH) using pStC1 as a probe was carried out on the chromosomes of Th. ponticum, Th. intermedium and Triticum aestivum cv. Chinese Spring. Th. ponticum was proved to have two St and three E genomes (St1St2EeEbEx). In Th. intermedium, strong FISH signals were observed on St genome chromosomes, while faint signals were also found on some E-genome chromosomes at their pericentromeric regions. These results indicated that during speciation of sub-genomes in the allopolyploids of Thinopyrum genus, concerted evolution might have occurred at centromeric and pericentromeric regions.