High frequency of HMW-GS sequence variation through somatic hybridization between Agropyron elongatum and common wheat.

A symmetric somatic hybridization was performed to combine the protoplasts of tall wheatgrass (Agropyron elongatum) and bread wheat (Triticum aestivum). Fertile regenerants were obtained which were morphologically similar to tall wheatgrass, but which contained some introgression segments from wheat. An SDS-PAGE analysis showed that a number of non-parental high-molecular weight glutenin subunits (HMW-GS) were present in the symmetric somatic hybridization derivatives. These sequences were amplified, cloned and sequenced, to deliver 14 distinct HMW-GS coding sequences, eight of which were of the y-type (Hy1-Hy8) and six x-type (Hx1-Hx6). Five of the cloned HMW-GS sequences were successfully expressed in E. coli. The analysis of their deduced peptide sequences showed that they all possessed the typical HMW-GS primary structure. Sequence alignments indicated that Hx5 and Hy1 were probably derived from the tall wheatgrass genes Aex5 and Aey6, while Hy2, Hy3, Hx1 and Hy6 may have resulted from slippage in the replication of a related biparental gene. We found that both symmetric and asymmetric somatic hybridization could promote the emergence of novel alleles. We discussed the origination of allelic variation of HMW-GS genes in somatic hybridization, which might be the result from the response to genomic shock triggered by the merger and interaction of biparent genomes.