Submitted to: Molecular and General Genetics
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/16/2004
Publication Date: 3/11/2004
Citation: Chantret, N., Cenci, A., Sabot, F., Anderson, O.D., Dubcovsky, J. 2004. Sequencing of triticum monococcum hardness locus reveals good microcolinearity with rice. Molecular and General Genetics. 271:377-386. Interpretive Summary: The classification of wheat varieties is an integral part of the farming, marketing, processing, and utilization of the U.S. wheat crop. One fundamental aspect of this classification is the determination of the "hardness" of the wheat kernel;i.e., the firmness of the kernel and its ability to be milled into defined flour particles. The hardness characteristic of wheat kernels is largely determined by puroindoline protein associated with starch granules. This paper reports the isolation and DNA sequencing of the main hardness locus that includes the genes encoding the puroindoline proteins. Results show the general organization of this region of the wheat genome, its similarity to the rice genome (the currrent model organization for the grass crops), and the fine detail structure of the puroindoline genes and regions of the genome surrounding those genes.
Technical Abstract: The Hardness (Ha) locus on chromosome 5D is the main determinant of grain texture in hexaploid wheat. The related Puroindoline (Pina-D1, Pinb-D1) and Grain Softness Protein (Gsp-D1) genes are tightly linked at this locus. Mutations at the Pina-D1 and Pinb-D1 genes are associated with increased hardness. We report here the complete sequence of a 101-kb BAC clone from Triticum monococcum (Am genome) including these three genes and its comparison with the orthologous region in rice. Genes Gsp-Am1, Pina-Am1 and Pinb-Am1 were separated by 37-kb and 32-kb respectively, and were in the same transcriptional orientation. Four additional genes, including a pair of duplicated genes, were identified upstream Gsp-Am1 within a high-density gene island. These additional genes were in the same order and orientation, and at the same relative distances than similar rice genes previously annotated on rice chromosome 12. An interesting discovery was an un-annotated rice gene that was similar to the GSP-Am1 gene (65% similarity at the protein level), and that was in the same orientation, and in the same position relative to the other orthologous genes. Most of the BAC sequence (40%) was represented by repetitive elements, mainly concentrated in regions adjacent to the two Pina-Am1 and Pinb-Am1 genes. Rearrangements among these repetitive elements might provide an explanation for the frequent deletions observed in the genomes of the polyploid wheat species.