Jiang Qian-Tao, Wei Yu-Ming, Wang Feng, Wang Ji-Rui, Yan Ze-Hong, Zheng You-Liang
Triticeae Research Institute, Sichuan Agricultural University, Ya'an, Sichuan, 625014, PR China.
BMC Plant Biol. 2009 Feb 6;9:16. doi: 10.1186/1471-2229-9-16.
High-molecular-weight glutenin subunits (HMW-GSs) have been considered as most important seed storage proteins for wheat flour quality. 1Ay subunits are of great interest because they are always silent in common wheat. The presence of expressed 1Ay subunits in diploid and tetraploid wheat genotypes makes it possible to investigate molecular information of active 1Ay genes.
We identified 1Ay subunits with different electrophoretic mobility from 141 accessions of diploid and tetraploid wheats, and obtained the complete ORFs and 5' flanking sequences of 1Ay genes including 6 active and 3 inactive ones. Furthermore, the 5' flanking sequences were characterized from 23 wild diploid species of Triticeae. All 6 active 1Ay possess a typical HMW-GS primary structure and some novel characteristics. The conserved cysteine residue within the repetitive domain of y-type subunits was replaced by phenylalanine residue in subunits of 1Ay (Tu-e1), 1Ay (Tu-e2), 1Ay (Ta-e2) and 1Ay (Td-e). Particularly, 1Ay (Ta-e3) has an unusual large molecular weight of 2202 bp and was one of the known largest y-type HMW-GSs. The translations of 1Ay (Tu-s), 1Ay (Ta-s) and 1Ay (Td-s) were disrupted by premature stop codons in their coding regions. The 5' flanking sequences of active and inactive 1Ay genes differ in a few base substitutions and insertions or deletions. The 85 bp deletions have been found in promoter regions of all 1Ay genes and the corresponding positions of 6 species from Aegilops and Hordeum.
The possession of larger molecular weight and fewer conserved cysteine residues are unique structural features of 1Ay genes; it would be interested to express them in bread wheat and further to examine their impact to processing quality of wheat. The 1Ay genes from T. urartu are closer to the genes from T. turgidum dicoccon and T. aestivum, than those from T. monococcum aegilopoides. The 85 bp deletion and some variations in the 5'flanking region, have not interrupted expression of 1Ay genes, whereas the defects in the coding regions could be responsible to the silence of the 1Ay genes. Some mutational events in more distant distal promoter regions are also possible causes for the inactivation of 1Ay genes.
高分子量谷蛋白亚基（HMW - GSs）被认为是影响小麦面粉品质的最重要的种子贮藏蛋白。1Ay亚基备受关注，因为它们在普通小麦中通常不表达。二倍体和四倍体小麦基因型中存在表达的1Ay亚基，这使得研究活性1Ay基因的分子信息成为可能。
我们从141份二倍体和四倍体小麦材料中鉴定出具有不同电泳迁移率的1Ay亚基，并获得了1Ay基因的完整开放阅读框（ORF）和5'侧翼序列，其中包括6个活性基因和3个非活性基因。此外，还对23种小麦族野生二倍体物种的5'侧翼序列进行了特征分析。所有6个活性1Ay亚基都具有典型的HMW - GS一级结构和一些新特征。y型亚基重复结构域内保守的半胱氨酸残基在1Ay（Tu - e1）、1Ay（Tu - e2）、1Ay（Ta - e2）和1Ay（Td - e）亚基中被苯丙氨酸残基取代。特别地，1Ay（Ta - e3）具有异常大的分子量，为2202 bp，是已知最大的y型HMW - GS之一。1Ay（Tu - s）、1Ay（Ta - s）和1Ay（Td - s）的编码区翻译因提前出现的终止密码子而中断。活性和非活性1Ay基因的5'侧翼序列在一些碱基替换、插入或缺失方面存在差异。在所有1Ay基因以及来自山羊草属和大麦属的6个物种的相应位置的启动子区域中都发现了85 bp的缺失。
分子量较大且保守半胱氨酸残基较少是1Ay基因独特的结构特征；将它们在面包小麦中表达并进一步研究其对小麦加工品质的影响将很有意义。乌拉尔图小麦的1Ay基因与硬粒小麦二粒系和普通小麦的基因相比，比一粒小麦拟斯卑尔脱山羊草的基因更接近。5'侧翼区域的85 bp缺失和一些变异并未中断1Ay基因的表达，而编码区的缺陷可能是1Ay基因沉默的原因。更远端启动子区域的一些突变事件也可能是1Ay基因失活的原因。
