Promoter DNA hypermethylation of TaGli-γ-2.1 positively regulates gluten strength in bread wheat

•TaGli-γ-2.1 belonged to a subgroup of γ-gliadin multigene family.•TaGli-γ-2.1 was a negative regulatory factor in gluten strength.•Methylation of pTaGli-γ-2.1 played a key role in regulating TaGli-γ-2.1 expression.•Lower γ-gliadin content followed with hypermethylation of pTaGli-γ-2.1.•Decreasing TaGli-γ-2.1 expression could be used to improve gluten strength in wheat breeding.