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Increasing resistant starch in wheat using TILLING
B. HAZARD (1), X. Zhang (1), P. Colasuonno (2), C. Uauy (3), D. Beckles (1), J. Dubcovsky (1). (1) University of California Davis - Department of Plant Sciences, Davis, CA, U.S.A.; (2) Dep. of Genetics and Plant Breeding, University of Bari, Bari, Italy; (3) Dep. of Crop Genetics, John Innes Centre, Norwich, United Kingdom

Wheat (<i>Triticum aestivum </i>L.) provides approximately one fifth of the calories consumed by the human population and is an important source of the carbohydrates, proteins, fats, vitamins and minerals that contribute to a healthy human diet. Since starch is the major component of the wheat kernel (~50-70% of its dry weight), any improvements in its nutritional composition have the potential to deliver benefits to many people. Starch in the wheat grain consists of approximately 70-80% amylopectin and 20-30% amylose. Amylopectin is a highly-branched, readily digested polysaccharide, whereas amylose has few branches and forms complexes that resist digestion and mimic dietary fiber (resistant starch). As with fiber, increased consumption of resistant starch has been associated with reduced risk of diseases such as diabetes, obesity, heart disease, and cancers of the colon and rectum. Down-regulation of the <i>starch branching enzyme II</i> (<i>SBEII</i>) gene by RNA interference (RNAi) was previously shown to increase amylose content in both hexaploid and tetraploid wheat. We generated ethyl methane sulphonate (EMS) mutants for the <i>SBEIIa-</i>A and <i>SBEIIa-</i>B homoeologs in the tetraploid durum wheat variety Kronos (<i>T. turgidum </i>ssp. <i>durum </i>L.). Single-gene mutants showed non-significant increases in amylose and resistant starch content, but a double mutant combining a <i>SBEIIa-</i>A knock-out mutation with a <i>SBEIIa-</i>B splice-site mutation showed a 22% increase in amylose content (<i>P</i><0.0001) and a 115% increase in resistant starch content (<i>P</i><0.0001). In addition, we obtained mutants for the A and B genome copies of the paralogous <i>SBEIIb </i>gene, mapped them 1-2 cM from <i>SBEIIa</i>, and generated double <i>SBEIIa-SBEIIb </i>mutants to study the effect of the <i>SBEIIb</i> gene in the absence of <i>SBEIIa</i>. These mutants are available to those interested in increasing amylose content and resistant starch content in durum wheat.

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