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Title: Structure organization of barley D-hordein locus in comparison with its orthologous regions of wheat genomes

item Gu, Yong
item Anderson, Olin
item Lazo, Gerard

Submitted to: Genome
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/10/2003
Publication Date: 10/30/2003
Citation: Gu, Y.Q., Anderson, O.D., Kong, X., Lazo, G.R., Wilson, C. 2003. Structure organization of barley D-hordein locus in comparison with its orthologous regions of wheat genomes. Genome. 46:1084-1097.

Interpretive Summary: Barley is an economically important cereal crop mainly used as raw material for brewing and the food for livestock. However, the malting quality of barley is a prime consideration for plant breeders because of its major industry usage in brewing and distilling. The malting quality is determined by many factors including the amount and composition of the storage proteins in barley grains. One of such storage proteins is the D-Hordein. Interestingly, the D-Hordein protein is highly related to the wheat high molecular weight glutenin protein that is the major determinants of the breadmaking quality of wheat flour. To understand the evolutionary relationship between wheat and barley for the improvement of grain quality of both barley and wheat by using comparative genomics approach, we reported isolation and sequencing of a large chromosome region that containing the barley D-hordein gene. The large chromosome region was isolated by screening a bacterial artificial library consisting of thousands of bacteria clones carrying large fragment of barley genome. The targeted region was fully sequenced, with a total of 120,652 base pairs. Sequence analysis revealed that there are four genes residing in this region. The genes included are arranged in the following order: protein receptor kinase, globulin, D-hordein, and protein kinase. The spaces between these genes are mainly composed of repetitive DNAs. The study will greatly enhance our understanding of structure and organization of important cereal genomes.

Technical Abstract: D-hordein, a storage protein in barley endosperms is highly homologous to the high molecular weight (HWM) glutenin subunits, which are the major determinants of breadmaking quality of wheat flour. However, in hexaploid wheat (AABBDD), each genome contains two paralogous copies of HMW-glutenin genes that encode the x- and y-type HMW-glutenin subunits. Previously, we reported the sequence analysis of a 102-kb genomic region containing the HMW-glutenin locus of the D genome from Aegilops taushii. Here, we present the sequence analysis of 120-kb D-hordein region of the barley genome. Comparative sequence analysis reveals that gene content and order are generally conserved. Genes included in these orthologous regions are arranged in the following order: Xa21-like receptor kinase, globulin, HMW-glutenin, and serine/threonine protein kinase. However, in the wheat D genome, a region containing both the globulin and HMW-glutenin genes were duplicated, indicating that this duplication event occurred after the separation of wheat and barley genomes. The intergenic regions are largely divergent with regard to the sequence and structure organization. It was found that different types of retroelements are responsible for the intergenic structure divergence in the wheat and barley genomes.