September 22, 2019  |  

Dynamic evolution of a-gliadin prolamin gene family in homeologous genomes of hexaploid wheat.

Authors: Huo, Naxin and Zhu, Tingting and Altenbach, Susan and Dong, Lingli and Wang, Yi and Mohr, Toni and Liu, Zhiyong and Dvorak, Jan and Luo, Ming-Cheng and Gu, Yong Q

Wheat Gli-2 loci encode complex groups of a-gliadin prolamins that are important for breadmaking, but also major triggers of celiac disease (CD). Elucidation of a-gliadin evolution provides knowledge to produce wheat with better end-use properties and reduced immunogenic potential. The Gli-2 loci contain a large number of tandemly duplicated genes and highly repetitive DNA, making sequence assembly of their genomic regions challenging. Here, we constructed high-quality sequences spanning the three wheat homeologous a-gliadin loci by aligning PacBio-based sequence contigs with BioNano genome maps. A total of 47 a-gliadin genes were identified with only 26 encoding intact full-length protein products. Analyses of a-gliadin loci and phylogenetic tree reconstruction indicate significant duplications of a-gliadin genes in the last ~2.5 million years after the divergence of the A, B and D genomes, supporting its rapid lineage-independent expansion in different Triticeae genomes. We showed that dramatic divergence in expression of a-gliadin genes could not be attributed to sequence variations in the promoter regions. The study also provided insights into the evolution of CD epitopes and identified a single indel event in the hexaploid wheat D genome that likely resulted in the generation of the highly toxic 33-mer CD epitope.

Journal: Scientific reports
DOI: 10.1038/s41598-018-23570-5
Year: 2018

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