Genomic relationships between Dasypyrum villosum (L.) Candargy and D. hordeaceum (Cosson et Durieu) Candargy

Abstract

The origin and genomic constitution of the tetraploid perennial species Dasypyrum hordeaceum (2n = 4x = 28) and its phylogenetic relationships with the annual diploid Dasypyrum villosum (2n = 2x = 14) have been investigated by comparing the two genomes using different methods. There is no apparent homology between the conventional or Giemsa C-banded karyotypes of the two Dasypyrum species, nor can the karyotype of D. hordeaceum be split up into two similar sets. Polymorphism within several chromosome pairs was observed in both karyotypes. Cytophotometric determinations of the Feulgen-DNA absorptions showed that the genome size of D. hordeaceum was twice as large as that of D. villosum. Both the cross D. villosum x D. hordeaceum (crossability rate 12.1%) and the reciprocal cross (crossability rate 50.7%) produced plump seeds. Only those from the former cross germinated, producing sterile plants with a phenotype that was intermediate between those of the parents. In these hybrids (2n = 21), an average of 13.77 chromosomes per cell paired at meiotic metaphase I. Trivalents were only rarely observed. Through dot-blot hybridizations, a highly repeated DNA sequence of D. villosum was found not to be represented in the genome of D. hordeaceum. By contrast, very similar restriction patterns were observed when a low-repeated DNA sequence or different single-copy sequences of D. villosum or two sequences in the plastidial DNA of rice were hybridized to Southern blots of the genomic DNAs of the two Dasypyrum species digested with different restriction endonucleases. By analyzing glutamic-oxaloacetic-transaminase, superoxide dismutase, alcohol dehydrogenase, and esterase isozyme systems, it was shown that both Dasypyrum species shared the same phenotypes, which differed from those found in hexaploid wheat. In situ hybridizations using DNA sequences encoding gliadins showed that these genes were located close to the centromere of three pairs of D. villosum chromosomes and that they had the same locations in six pairs of D. hordeaceum chromosomes. We conclude that the autoploid origin of D. hordeaceum from D. villosum, which cannot be defended on the basis of chromosomal traits, is suggested by the other findings obtained by comparing the two genomes. Key words : Dasypyrum hordeaceum, Dasypyrum villosum, phylogenetic relationships.

Genomic organization and phylogenetic relationships in the genus Dasypyrum analysed by Southern and in situ hybridization of total genomic and cloned DNA probes

“…The data indicate that the pericentromeric regions of chromosome arms in both the D. breviaristatum and D. villosum genomes are similar, while distal regions show reduced homologies and contain D. breviaristatum-and D. villosum-specific DNA sequences. Our observations are consistent with the findings of De Pace et al (1992), who isolated a highly repeated DNA sequence (p380) specific to D. villosum that is located near the telomeres and is not present in the tetraploid species (Blanco et al 1996). Conversely, in the closely related I-genome Hordeum species H. vulgare and H. bulbosum (with similar DNA content to D. villosum) major differences in DNA occur in the pericentromeric regions, which remain unlabelled on H. vulgare chromosomes when H. bulbosum DNA is used as a probe (Anamthawat-Jónsson et al 1993).…”

“…Linde-Laursen and , by comparison of C-banded characters, did not support an autoploid origin of the tetraploid based on D. villosum. Blanco et al (1996) also could not support an autoploid origin on the basis of chromosomal traits, although similar restriction patterns were present when genomic DNA from the two species was probed with lowcopy or plastid DNA sequences. It is clear that species within, and beyond, the Triticeae show high levels of synteny at the levels of gene or single-copy markers (Moore et al 1995), although the differences in their repetitive DNA may be substantial and of greater significance for evolution and speciation.…”

“…In the latter, two chromosome pairs usually showed 18S-25S rDNA sites on opposite arms, also found in the Triticeae species, Psathyrostachys stoloniformis and Leymus angustus (Ørgaard and Heslop-Harrison 1994a). C-banding of D. breviaristatum did not allow chromosome identification and matching of chromosome pairs (Linde-Laursen and Frederiksen 1991;Blanco et al 1996).…”

Identification of α-gliadin genes in Dasypyrum in relation to evolution and breeding

“…Earlier studies on the morphological characters (Frederiksen 1991), chromosomal pairing (Bothmer and Claesson 1990) and chromosomal banding (Blanco et al 1996;Linde-Laursen and Frederiksen 1991;Pignone et al 2000) demonstrated that the D. breviaristatum was not an autoploid of D. villosum. This also conWrmed by genomic in situ hybridization (GISH) studies (Blanco et al 1996;Galasso et al 1997;Yang et al 2005).…”

Isolation and phylogenetic analysis of novel γ-gliadin genes in genus Dasypyrum

“…According to Love (1984), the genomic formula of tetraploid D. breviarisatatum would be VVVV, which is the same as that of D. villosum. Similarly, this view was supported by biochemical evidence, such as the phenotypes of glutamic-oxaloacetic-transaminase, superoxide dismutase, alcohol dehydrogenase and esterase isozyme systems (Blanco et al, 1996). However, cytogenetic evidence such as fluorescence in situ hybridization patterns (Galasso et al, 1997;Uslu et al, 1999) and Giemsa C-banded karyotype (Frederiksen, 1991) seemed to be opposed to this view.…”