Comparative RFLP mapping of Hordeum vulgare and Triticum tauschii

Abstract

Hordeum vulgare (barley) and Triticum tauschii are related, but sexually incompatible, species. This study was conducted to determine the extent of homology between the genomes of barley and T. tauschii using a common set of restriction fragment length polymorphism (RFLP) markers. Results showed that >95% of low-copy sequences are shared, but 42% of the conserved sequences showed copy-number differences. Sixty-three loci were mapped in T. tauschii using RFLP markers previously mapped in barley. A comparison of RFLP marker order showed that, in general, barley and T. tauschii have conserved linkage groups, with markers in the same linear orders. However, six of the seven linkage groups of T. tauschii contained markers which mapped to unrelated (i.e., non-homoeologous) barley chromosomes. Additionally, four of the T. tauschii linkage groups contained markers that were switched in order with respect to barley. All the chromosome segments differing between T. tauschii and barley contained markers that were detected by multi-copy probes. The results suggest that the observed differences between the T. tauschii and barley genomes were brought about by duplications or deletions of segments in one or both species. The implications of these findings for genetic mapping, breeding, and plant genome evolution are discussed.

Compensating ability in pollen fertilization between group-6 and -7 homoeologous chromosomes of barley and wheat.

“…squarrosa was the last to be incorporated into wheat and is the least-modified genome. Namuth et al (1994) confirmed the homoeologous relationships between barley and Ae. squarrosa based on the molecular maps of the complete barley genome and the D genome.…”

“…Shepherd and Islam (1992) reported that telocentric barley chromosomes would pair and recombine with wheat chromosomes in the absence of the effect of the Ph1 gene in wheat. The most comprehensive data on the genetic relationship between barley and wheat chromosomes came from the comparative mapping studies where the map locations of molecular markers were compared among the barley and the three wheat genomes , Namuth et al 1994, Hohmann et al 1995. The results of these studies indicated a very close collinearity of molecular markers between barley chromosomes and related wheat chromosomes, except that evolutionary translocations present in the A and B genomes of wheat are not present in either the barley or the D genome of wheat (Linde-Laursen et al 1997).…”

Genome Relationships: The Grass Model in Current Research

“…When different members of a single family are mapped in different species, the impression is created that colinearity is disrupted. For example, all probes that detected noncolinear loci in a comparative study between the barley and A. tauschii genomes were multicopy in one or both of the species (Namuth et al, 1994). Similarly, in a comparison between foxtail millet and rice, of the probes that mapped to noncolinear positions, all but one detected at least two copies in the foxtail millet genome (Devos et al, 1998).…”

Comparative Genomics of Plant Chromosomes

“…Pioneering efforts in the comparative mapping of maize and sorghum (Hulbert et al, 1990) have been supported by more detailed studies (Whitkus et al, 1992;Berhan et al, 1993;Binelli et al, 1993;Chittenden et al, 1994;Pereira et al, 1994) and supplemented by the comparative organization of maize and rice , wheat and rice (Kurata et al, 1994), and maize, wheat, and rice . A host of investigations additionally encompasses many other cultivated Poaceae, with particular emphasis on the interrelationships among the homeologous chromosome sets of the Triticeae and their relatives (see Naranjo et al, 1987;Chao et al, 1989;Liu and Tsunewaki, 1991;Devos et al, 1992aDevos et al, , 1992bDevos et al, , 1993Devos et al, , 1995Liu et al, 1992;Xie et al, 1993;Namuth et al, 1994;Hohmann et al, 1995;Marino et al, 1996;Mickelson-Young et al, 1995;Nelson et al, 1995aNelson et al, , 1995bNelson et al, , 1995cVan Deynze et al, 1995). Curiously, even in the relatively "conservative" Poaceae, certain lineages appear to be rapidly evolving.…”