Genetic polymorphism in low-molecular-weight glutenin genes from Triticum aestivum, variety Chinese Spring

Low-molecular-weight (LMW) glutenin subunits consist mainly of two domains, one at the N-terminus which contains repeats of short amino-acid motifs, a nd a non-repetitive one rich in cysteine, at the C-terminal region. In prev ious reports, polyacrylamide-gel electrophoresis has been used to show that large size variation exists among LMW and HMW glutenin subunits, and it ha s been suggested that deletions and insertions within the repetitive region are responsible for these variations in length. In this study, PCR-amplifi cation of genomic DNA (Triticum aestivum variety Chinese Spring) was used t o isolate three full-length LMW glutenin genes: LMWG-MB1, LMWG-MB2 and LMWG -MB3. The deduced amino-acid Sequences show a high similarity between these ORFs, and with those of other LMW glutenin genes. Comparisons indicate tha t LMWG-MB1 has probably lost a 12-bp fragment through deletion and that LMW G-MB1 and LMWG-MB2 have an insertion of 81 bp within the repetitive domain. The current study has shown direct evidence that insertions and/or deletio ns provide a mechanistic explanation for the allelic variation, and the res ultant evolution, of prolamin genes. Single-base substitutions at identical sites generate stop codons in both LMWG-MB2, and LMWG-MB3 indicating that these clones are pseudogenes.