Heterogeneity of genes encoding the low molecular weight glutenin subunits of bread wheat

Among the wheat storage proteins, the low molecular weight glutenin subunit (LMW-GS) group is probably the more complex. It encompasses several subgroups which differ by their N-terminal amino acid sequences. To get more information on the diversity of the genes encoding the LMW-GS, we attempted to clone some of them. Two different strategies were used to amplify their coding sequences from genomic DNA using PCR techniques. The first strategy used primers corresponding to the N- and C-terminal sequences of already published mature peptides. Several DNA fragments with various sizes were amplified and more than 2500 clones were obtained. Among them 95 clones were further analyzed. The size of their insert ranged from 1200 to 800 and less bp. Restriction analysis of these inserts showed that they can be gathered in ten families. 13 Clones have been sequenced and all exhibited the features of LMW-GS coding sequences. For eight of the sequences, the coding frame was interrupted by I to 10 stops codons, for three sequences only parts of a LMW-GS coding frame could be recognized. The two last sequences were encoding for LMW-GS which were 270 and 327 residues long. The second strategy used primers anchored in the promoters and in the C-terminal part. We obtained four different clones with complete coding sequence and part of the promoting sequence. They were LMW-GS coding sequences (852 bp, 284 amino acid residues) and did not contain any interruption of the coding frame. The use of PCR techniques is a convenient way for investigating the complexity of the wheat LMW-GS multigenic family. The existence of numerous pseudo 24 genes gives interesting insights into the evolution of this multigenic family. Extinguished LMW-GS may be a reservoir for the future?