The evolution and organization of multigene families exemplified by the hordein genes in barley

Författare

Susanne Pelger

Summary, in English

Hordein, the seed storage protein in barley, is encoded by a multigene family. All wild and cultivated species of the Hordeum genus were investigated electrophoretically and imunologically for their hordein composition. The reactions of specific monoclonal antibodies showed that particular polypeptide regions have been conserved throughout the genus. Some of the regions could also be recognize in many other species belonging to the Triticeae tribe. The results indicate that functional constraints prevent extensive structural changes of hordein coding genes.

The chromosomal location of the hordein genes was determined in two wild Hordeum species, murinum and pusillum, and compared with that of cultivated barley, H. vulgare. All the species are self-fertilizing diploids. The number of hordein loci, and the recombination frequencies between them, differed among the species. Most of the loci were closely or moderately linked, although independent segregation was observed in one case. The differing distribution patterns imply that reorganizations of the hordein gene family have taken place since the divergence of these species. Thus, gene function seems to depend less on organization than on structure.

There are indications that the hordein genes may have changed positions in a transposon-like fashion, rather than by inversion and translocation events. Transposition of genes is facilitated by tandem repetition, and has been observed in other multigene families. Although transposable elements have so far not been identified in barley, gene transposition is a likely mechanism to explain the reorganizations in the hordein gene family.

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