Abstract:The high-molecular-weight glutenin subunits (HMW-GSs) are a major class of common wheat storage proteins. The bread-making quality of common wheat flour is influenced by the composition of HMW-GSs. In the present study, two unexpressed 1By genes from Triticum aesitvum ssp.yunnanese AS332 and T. aesitvum ssp.tibetanum AS908 were respectively cloned and characterized. The results indicated that both of the silenced 1By genes in AS332 and AS908 were 1By9. Different from previously reported mechanisms for silenced genes 1Ax and 1Ay, which was due to the insertion of transposon elements or presence of premature stop codon via base substitution of C→T transition in trinucleotides CAA or CAG, the silence of 1By9 genes were caused by premature stop codons via the deletion of base A in trinucleotide CAA, which leaded to frameshift mutation and indirectly produced several premature stop codons (TAG) at the downstream of the coding sequence.