Induced Mutations in the Starch Branching Enzyme II (SBEII) Genes Increase Amylose and Resistant Starch Content in Durum Wheat

Starch is the largest component of the wheat (Triticum aestivum L.) grain and consists of approximately 70 to 80% amylopectin and 20 to 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). Downregulation of the starch branching enzyme II (SBEII) gene by RNA interference (RNAi) was previously shown to increase amylose content in both hexaploid and tetraploid wheat. We generated ethyl methane sulfonate (EMS) mutants for the SBEIIa-A and SBEIIa-B homeologs in the tetraploid durum wheat variety Kronos [Triticum turgidum L. subsp. durum (Desf.) Husn.]. Single-gene mutants showed nonsignifi cant increases in amylose and resistant starch content, but a double mutant combining a SBEIIa-A knock-out mutation with a SBEIIa-B splice-site mutation showed a 22% increase in amylose content (P < 0.0001) and a 115% increase in resistant starch content (P < 0.0001). In addition, we obtained mutants for the A and B genome copies of the paralogous SBEIIb gene, mapped them 1 to 2 cM from SBEIIa, and generated double SBEIIa-SBEIIb mutants to study the effect of the SBEIIb gene in the absence of SBEIIa. These mutants are available to those interested in increasing amylose content and resistant starch in durum wheat.