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Title: Rice functionality, starch structure and the genes

item Chen, Ming Hsuan
item Fjellstrom, Robert
item Pinson, Shannon
item McClung, Anna

Submitted to: Experiment Station Bulletins
Publication Type: Experiment Station
Publication Acceptance Date: 6/15/2006
Publication Date: 7/13/2006
Citation: Chen, M.H., Fjellstrom, R.G., Pinson, S.R., McClung, A.M., Bergman, C.J. 2006. Rice functionality, starch structure and the genes. Rice, Highlighting Research in 2006. p. XII.

Interpretive Summary:

Technical Abstract: Through collaborative efforts among USDA scientists at Beaumont, Texas, we have gained in-depth knowledge of how rice functionality, i.e. the texture of the cooked rice, rice processing properties, and starch gelatinization temperature, are associated with starch-synthesis genes and starch structure. Ninety percent of milled rice is starch, which is made up of two kinds of large molecules, amylose and amylopectin. Amylose content is a key determinant of cooked rice texture and processing properties. The Waxy gene is primarily responsible for amylose synthesis. The synthesis of amylopectin is a concerted effort of multiple forms of starch-synthase enzymes, branching- and debranching-enzymes. We have identified four DNA sequence changes in the rice Waxy gene that are strongly associated with grain amylose content. These DNA sequence differences discriminate low-, intermediate-, and high-amylose classes of rice apart from each other and also identify pasting properties separating Dixiebelle-type from Jodon-type rice. Detailed study of starch structures indicated that not only the quantity of amylose, but also its molecular structure might contribute to the functional attributes of rice. The Alk gene, which is associated with rice gelatinization temperature (GT), encodes the starch synthase IIa enzyme, which is one of the enzymes responsible for amylopectin synthesis. Several DNA sequence changes in the Alk gene were identified that strongly associated with the GT of rice. Analysis of amylopectin fine structure demonstrated that high- and intermediate-GT rice (Dellmont) has higher percentage of longer exterior-chains of amylopectin than does the low-GT rice (Bengal). DNA sequence specific markers of the Waxy and Alk genes were developed, and have been incorporated into the marker assisted breeding program. Currently, we are investigating other functional attributes of rice that have not yet been explained through functional and starch-structural studies.