|HUO, NAXIN - University Of California|
|DONG, LINGLI - Chinese Academy Of Sciences|
|ZHANG, SHENGLI - Henan Institute Of Science And Technology|
|WANG, YI - University Of California|
|ZHU, TINGTING - University Of California|
|LIU, ZHIYONG - Chinese Academy Of Sciences|
|DVORAK, JAN - University Of California|
|ANDERSON, OLIN - Retired ARS Employee|
|LUO, MING-CHENG - University Of California|
|WANG, DAOWEN - Chinese Academy Of Sciences|
Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/22/2017
Publication Date: 8/30/2017
Citation: Huo, N., Dong, L., Zhang, S., Wang, Y., Zhu, T., Mohr, T.J., Altenbach, S.B., Liu, Z., Dvorak, J., Anderson, O.D., Luo, M., Wang, D., Gu, Y.Q. 2017. New insights into structural organization and gene duplication in a 1.75-Mb chromosomal region harboring the alpha-gliadin gene family in Aegilops tauschii. Plant Journal. 92(4):571–583. https://doi.org/10.1111/tpj.13675.
Interpretive Summary: Wheat (Triticum aestivum) accounts for approximately 30% of the global cereal consumption. Wheat prolamins are the main repository for nitrogen in the endosperm of the seeds, important protein sources in human diets, and are essential in determining the processing quality in the production of a range of end products. However, wheat prolamins also cause food-related allergies and intolerances such as celiac disease. To better understand the evolution, structure and functions of these proteins, we employed the available genomics resources from Aegilops tauschii (Tausch’s goatgrass), one of the three ancestors of modern bread wheat. In this study, we identified, sequenced, and analyzed a 1.75 million base pair segment of Aegilops tauschii genomic DNA. We compared that sequence to the comparable regions of rice, sorghum and the wild grass Brachypodium. We found that Aegilops tauschii contains many more members of both the prolamin (alpha gliadin type) and non-prolamin genes than the other grasses. The new genes were added to this region by rapid and dynamic evolution after the separation of the Brachypodia and Triticeae lineages and before wheat domestication. These results show that alpha gliadins are the youngest prolamins and that their numbers expanded recently in wheat evolution. The insights and resources generated by this research will facilitate further studies of alpha-gliadin gene regions, which may lead to novel strategies for enhancing the end-use and nutritional quality traits and reducing the allergenicity of bread wheat and related crops.
Technical Abstract: Among the wheat prolamins important for its end-use traits, alpha-gliadins are abundant and also a major cause of food-related allergies and intolerances. Previous studies of various wheat species estimated between 25 to 150 alpha-gliadin genes reside in the Gli-2 locus regions. To better understand the evolution of this complex gene family, the DNA sequence of a 1.75-Mb genomic region spanning the Gli-2 locus was analyzed in the diploid grass, Aegilops tauschii, the ancestral source of the D genome in hexaploid bread wheat. Comparison with orthologous regions from rice, sorghum, and Brachypodium revealed rapid and dynamic changes only occurring in the Ae. tauschii Gli-2 region, including insertions of high numbers of non-syntenic genes and a high rate of tandem gene duplications, the latter of which have given rise to 12 copies of alpha-gliadin genes clustered within a 550-kb region. Among them, five copies have undergone pseudogenization by various mutation events. Insights into the evolutionary relationship of the duplicated alpha-gliadin genes were obtained from their genomic organization, transcription patterns, transposable element insertions, and phylogenetic analyses. An ancestral GLR gene encoding a putative amino acid sensor in all four grass species has duplicated only in Ae. tauschii and generated three more copies that are interleaved with the alpha-gliadin genes. Phylogenetic inference and different gene expression patterns support functional divergence of the Ae. tauschii GLR copies after duplication. Our results suggest that the duplicates of alpha-gliadin and GLR genes have likely taken different evolutionary paths, conservation for the former and neofunctionalization for the latter.