Cloning and Localization of α-Gliadin Genes from Common Wheat and Aegilops tauschii and Their Molecular Evolution

Gliadins are in high polymorphism and stable inheritance in common wheat (Triticum aestivum L.). It not only has a close relationship with wheat quality but also acts as an index in researches on genetic diversity and evolution of wheat. In this study, 7 novel α-gliadin genes were cloned from common wheat (cv. Yumai 34 and Yannong 19) and Aegilops tauschii (T9, T197, T48, T176, and T17) using a PCR-based strategy, which were designated Gli-YM34, Gli-YN19, Gli-T9, Gli-T197, Gli-T48, Gli-T176, and Gli-T17. The open reading frames of these genes ranged from 846 to 891 bp in length, which encoded 282–297 amino acid residues. Comparative analysis showed that all the genes isolated had typical structural characters of α-gliadin genes reported previously. Particularly, Gli-YM34 and Gli-YN19 from common wheat might have a positive effect on dough quality for the presence of an additional cysteine residue. Both of them were located on the Gli-D2 locus on the chromosome 6D based on analyses of the 4 T-cell epitopes, average length of polyglutamine domain, and the nullisomic–tetrasomic lines of Chinese Spring, and they were highly homologous to the α-gliadin genes from Ae. tauschii. The sequences of 4 typical α-gliadin genes were compared with those of 10 published α-gliadin genes, and 21 single nucleotide polymorphisms (SNPs) and a 9 bp deletion were detected. Based on the neighbor-jointing unrooted phylogene tree of 39 storage protein genes from different Triticum species, the α-gliadin genes showed a close relationship with LMW-GS genes, and their divergence occurred 43.69 million years ago. There was little homology between α-gliadin genes and HMW-GS genes/ω-gliadin genes, and their divergence occurred 73.72 million years ago.

摘要通过特异PCR引物设计, 从普通小麦品种(豫麦34和烟农19)和粗山羊草(T9、T197、T48、T176和T17)中扩增、克隆了7个新的α-醇溶蛋白基因, 分别命名为Gli-YM34、Gli-YN19、Gli-T9、Gli-T197、Gli-T48、Gli-T176和Gli-T17, 基因序列长度为846∼891 bp, 编码282∼297个氨基酸残基, 都具有α-醇溶蛋白的典型结构特点。其中Gli-YM34和Gli-YN19基因推导的醇溶蛋白都含有一个额外的半胱氨酸残基, 可能对面筋品质有正向作用。根据α-醇溶蛋白氨基酸序列所具有的4种T细胞抗原表位和多聚谷氨酰胺重复区的平均长度以及中国春缺体―四体分析, 将来自普通小麦品种的Gli-YM34和Gli-YN19基因定位在6D染色体上的Gli-D2位点, 而且Gli-YM34和Gli-YN19与来自粗山羊草的α-醇溶蛋白基因具有很高的序列相似性, 进一步证明粗山羊草是普通小麦D基因组的供体。在克隆的4个典型α-醇溶蛋白基因中检测到21个SNP和1个9 bp的缺失。系统进化分析表明, α-醇溶蛋白基因与低分子量谷蛋白亚基基因关系较近, 在大约43.69百万年时分化, 与ω-醇溶蛋白和HMW-GS基因亲缘关系较远, 它们的分化时间大约为79.39百万年。