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Genetics, Vol. 178, 23-33, January 2008, Copyright © 2008
doi:10.1534/genetics.107.077412

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Novel x-Type High-Molecular-Weight Glutenin Genes From Aegilops tauschii and Their Implications on the Wheat Origin and Evolution Mechanism of Glu-D1-1 Proteins

Yanzhen Zhang*,1, Xiaohui Li*,1, Aili Wang*,{dagger}, Xueli An*, Qian Zhang*,{dagger}, Yuhe Pei*, Liyan Gao*, Wujun Ma{dagger},1, Rudi Appels{dagger} and Yueming Yan*,2

* Key Laboratory of Genetics and Biotechnology, College of Life Science, Capital Normal University, Beijing 100037, China and {dagger} State Agriculture Biotechnology Centre, Western Australian Department of Agriculture and Food, Murdoch University, Perth, Western Australia 6150, Australia

2 Corresponding author: Key Laboratory of Genetics and Biotechnology, College of Life Science, Capital Normal University, Beijing 100037, China.
E-mail: yanym{at}hotmail.com

Two new x-type high-molecular-weight glutenin subunits with similar size to 1Dx5, designated 1Dx5*t and 1Dx5.1*t in Aegilops tauschii, were identified by SDS–PAGE, RP-HPLC, and MALDI-TOF-MS. The coding sequences were isolated by AS-PCR and the complete ORFs were obtained. Allele 1Dx5*t consists of 2481 bp encoding a mature protein of 827 residues with deduced Mr of 85,782 Da whereas 1Dx5.1*t comprises 2526 bp encoding 842 residues with Mr of 87,663 Da. The deduced Mr's of both genes were consistent with those determined by MALDI-TOF-MS. Molecular structure analysis showed that the repeat motifs of 1Dx5*t were correspondingly closer to the consensus compared to 1Dx5.1*t and 1Dx5 subunits. A total of 11 SNPs (3 in 1Dx5*t and 8 in 1Dx5.1*t) and two indels in 1Dx5*t were identified, among which 8 SNPs were due to C-T or A-G transitions (an average of 73%). Expression of the cloned ORFs and N-terminal sequencing confirmed the authenticities of the two genes. Interestingly, several hybrid clones of 1Dx5*t expressed a slightly smaller protein relative to the authentic subunit present in seed proteins; this was confirmed to result from a deletion of 180 bp through illegitimate recombination as well as an in-frame stop codon. Network analysis demonstrated that 1Dx5*t, 1Dx2t, 1Dx1.6t, and 1Dx2.2* represent a root within a network and correspond to the common ancestors of the other Glu-D-1-1 alleles in an associated star-like phylogeny, suggesting that there were at least four independent origins of hexaploid wheat. In addition to unequal homologous recombination, duplication and deletion of large fragments occurring in Glu-D-1-1 alleles were attributed to illegitimate recombination.






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Copyright © 2008 by the Genetics Society of America.