Wageningen UR Plant Breeding, Wageningen UR, P,O, Box 16, Wageningen, NL-6700 AA, The Netherlands.
BMC Evol Biol. 2012 Nov 8;12:215. doi: 10.1186/1471-2148-12-215.
The gamma-gliadins are considered to be the oldest of the gliadin family of storage proteins in Aegilops/Triticum. However, the expansion of this multigene family has not been studied in an evolutionary perspective.
We have cloned 59 gamma-gliadin genes from Aegilops and Triticum species (Aegilops caudata L., Aegilops comosa Sm. in Sibth. & Sm., Aegilops mutica Boiss., Aegilops speltoides Tausch, Aegilops tauschii Coss., Aegilops umbellulata Zhuk., Aegilops uniaristata Vis., and Triticum monococcum L.) representing eight different genomes: Am, B/S, C, D, M, N, T and U. Overall, 15% of the sequences contained internal stop codons resulting in pseudogenes, but this percentage was variable among genomes, up to over 50% in Ae. umbellulata. The most common length of the deduced protein, including the signal peptide, was 302 amino acids, but the length varied from 215 to 362 amino acids, both obtained from Ae. speltoides. Most genes encoded proteins with eight cysteines. However, all Aegilops species had genes that encoded a gamma-gliadin protein of 302 amino acids with an additional cysteine. These conserved nine-cysteine gamma-gliadins may perform a specific function, possibly as chain terminators in gluten network formation in protein bodies during endosperm development. A phylogenetic analysis of gamma-gliadins derived from Aegilops and Triticum species and the related genera Lophopyrum, Crithopsis, and Dasypyrum showed six groups of genes. Most Aegilops species contained gamma-gliadin genes from several of these groups, which also included sequences from the genera Lophopyrum, Crithopsis, and Dasypyrum. Hordein and secalin sequences formed separate groups.
We present a model for the evolution of the gamma-gliadins from which we deduce that the most recent common ancestor (MRCA) of Aegilops/Triticum-Dasypyrum-Lophopyrum-Crithopsis already had four groups of gamma-gliadin sequences, presumably the result of two rounds of duplication of the locus.
γ-醇溶蛋白被认为是麦类作物醇溶蛋白家族中最古老的家族。然而，这个多基因家族的扩张尚未从进化角度进行研究。
我们从 Aegilops 和小麦属物种（Aegilops caudata L.、Aegilops comosa Sm. in Sibth. & Sm.、Aegilops mutica Boiss.、Aegilops speltoides Tausch、Aegilops tauschii Coss.、Aegilops umbellulata Zhuk.、Aegilops uniaristata Vis. 和 Triticum monococcum L.）中克隆了 59 个 γ-醇溶蛋白基因，代表了八个不同的基因组：Am、B/S、C、D、M、N、T 和 U。总的来说，15%的序列包含内部终止密码子，导致假基因，但这个百分比在基因组之间是可变的，在 Ae. umbellulata 中高达 50%以上。推导蛋白的最常见长度（包括信号肽）为 302 个氨基酸，但长度从 215 到 362 个氨基酸不等，均来自 Ae. speltoides。大多数基因编码含有 8 个半胱氨酸的蛋白。然而，所有 Aegilops 物种都有基因编码 302 个氨基酸的 γ-醇溶蛋白，并有一个额外的半胱氨酸。这些保守的九个半胱氨酸 γ-醇溶蛋白可能具有特定的功能，可能在胚乳发育过程中作为蛋白质体中谷蛋白网络形成的链终止子。对来自 Aegilops 和小麦属物种以及相关属 Lophopyrum、Crithopsis 和 Dasypyrum 的 γ-醇溶蛋白的系统发育分析显示，有六个基因群。大多数 Aegilops 物种包含来自这些基因群的 γ-醇溶蛋白基因，这些基因群也包括来自 Lophopyrum、Crithopsis 和 Dasypyrum 的序列。麦醇溶蛋白和 secalin 序列形成单独的组。
我们提出了一个γ-醇溶蛋白进化的模型，从中我们推断出 Aegilops/Triticum-Dasypyrum-Lophopyrum-Crithopsis 的最近共同祖先（MRCA）已经有四个γ-醇溶蛋白序列群，大概是该基因座两轮复制的结果。
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