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Title: Conserved globulin gene across eight grass genomes identify fundamental units of the loci encoding seed storage proteins

item Gu, Yong
item WANJUGI, HUMPHREY - University Of California
item COLEMAN-DERR, DEVIN - University Of California
item KONG, XIUYING - Chinese Academy Of Agricultural Sciences
item Anderson, Olin

Submitted to: Functional and Integrative Genomics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/8/2009
Publication Date: 8/26/2009
Citation: Gu, Y.Q., Wanjugi, H., Coleman-Derr, D., Kong, X., Anderson, O.D. 2009. Conserved globulin gene across eight grass genomes identify fundamental units of the loci encoding seed storage proteins. Functional and Integrative Genomics. 10:111-122.

Interpretive Summary: In wheat, the Glu-1 locus is one of the most important single genetic loci because it encodes the HMW-glutenin protein subunits, which are the major determinants of bread-making quality for wheat flour. Therefore, the HMW-glutenin gene is also an important domestication gene in wheat. Previous studies indicated that the HMW-glutenin is unique to wheat. However, origin and evolution of this important wheat gene remains unclear. In this study, we sequenced and analyzed corresponding HMW-glutenin regions from eight grass genomes for comparative genomics analysis. Our results reveal the wheat HMW-glutenin gene is derived a duplication of an ancient globulin gene present in all the grass genomes examined. The knowledge gained from this study can help us not only understand the genome evolution and wheat domestication, but also provide potential strategies to genetic improvement of wheat quality.

Technical Abstract: The wheat high molecular weight (HMW)-glutenins are important seed storage proteins that determine bread-making quality in hexaploid wheat (Triticum aestivum). In this study, detailed comparative sequence analyses of large orthologous HMW-glutenin genomic regions from eight grass species, representing a wide evolutionary history of grass genomes, reveal a number of lineage-specific sequence changes. These lineage-specific changes, which resulted in duplications, insertions, and deletions of genes, are the major forces disrupting gene colinearity among grass genomes. Our results indicate that the presence of the HMW-glutenin gene in Triticeae genomes was caused by lineage-specific duplication of a globulin gene. This tandem duplication event is shared by Brachypodium and Triticeae genomes, but is absent in rice, maize, and sorghum, suggesting the duplication occurred after Brachypodium and Triticeae genomes diverged from the other grasses ~35 million years ago (mya). Aside from their physical location in tandem, the sequence similarity, expression pattern, and conserved cis-acting elements responsible for endosperm specific expression further support the paralogous relationship between the HMW-glutenin and globulin genes. While the duplicated copy in Brachypodium has apparently become non-functional, the duplicated copy in wheat has evolved to become the HMW-glutenin gene by gaining a central prolamin repetitive domain.