Mutations in Durum Wheat SBEII Genes affect Grain Yield Components, Quality, and Fermentation Responses in Rats

Abstract

Increased amylose in wheat (Triticum ssp.) starch is associated with increased resistant starch, a fermentable dietary fiber. Fermentation of resistant starch in the large intestine produces short‐chain fatty acids that are associated with human health benefits. Since wheat foods are an important component of the human diet, increases in amylose and resistant starch in wheat grains have the potential to deliver health benefits to a large number of people. In three replicated field trials we found that mutations in starch branching enzyme II genes (SBEIIa and SBEIIb) in both A and B genomes (SBEIIa/b‐AB) of durum wheat [T. turgidum L. subsp. durum (Desf.) Husn.] resulted in large increases of amylose and resistant starch content. The presence of these four mutations was also associated with an average 5% reduction in kernel weight (P = 0.0007) and 15% reduction in grain yield (P = 0.06) compared to the wild type. Complete milling and pasta quality analysis showed that the mutant lines have an acceptable quality with positive effects on pasta firmness and negative effects on semolina extraction and pasta color. Positive fermentation responses were detected in rats (Rattus spp.) fed with diets incorporating mutant wheat flour. This study quantifies benefits and limitations associated with the deployment of the SBEIIa/b‐AB mutations in durum wheat and provides the information required to develop realistic strategies to deploy durum wheat varieties with increased levels of amylose and resistant starch.

Milling and baking quality of hexaploid spring wheat starch synthase IIa (ssIIa) mutants with elevated amylose content

“…Due to the change in amylose content, significant increases in resistant starch (up to 14%) have been observed in SBEII nulls (Botticella et al, ; Regina et al, ; Schönhofen et al, ; Slade et al, ). Again, similar outcomes were observed in durum wheat (Hazard et al, , ; Sestili et al, , ; Slade et al, ) and barley (Carciofi et al, ; Regina et al, , ).…”

Uncovering hidden variation in polyploid wheat

“…Strategies to account for this high level of background mutation include the use of multiple independent mutants, backcrossing to reduce mutation load, and selecting for isogenic sibling lines that share background mutations. For mutations with subtle phenotypic effects or that require field phenotyping, it is advisable to backcross the mutant lines to the nonmutagenized parent for at least two generations before combining homeologous mutations (30,31). Sibling lines can then be selected for homozygous WT or null-mutant alleles.…”

Novel ssIIa Alleles Produce Specific Seed Amylose Levels in Hexaploid Wheat

“…Starch is an important component of human daily caloric intake, and increasing the proportion of resistant starch (RS) by increasing amylose content has health benefits similar to increasing dietary fiber. Some of these benefits are improved colon health through increased fermentation and production of short‐chain fatty acids by gut bacteria in the lower intestine and the slowed release of glucose into the body (reviewed in Nugent 2005; Sajilata et al 2006; Regina et al 2006; Anderson et al 2009; Hazard et al 2015). Starch from high‐amylose maize ( Zea mays L.) created by amylose‐extender mutations impacting starch branching enzyme IIb (SBEIIb) is considered type II RS owing to its high gelatinization temperature, which allows it to retain its crystalline structure after cooking.…”

“…Flours from high‐amylose ssIIa null lines also have altered starch pasting properties, seen as reduced RVA peak, trough, and final viscosity (Yamamori et al 2006; Konik‐Rose et al 2007; Rakszegi et al 2015). Unlike starch from high‐amylose maize or wheat owing to loss of SBEII function, which has a high gelatinization temperature compared with normal starch (Liu et al 2012; Hazard et al 2015), starch from ssIIa null lines has a lower gelatinization temperature (Yamamori et al 2000; Morita et al 2002; Konik‐Rose et al 2007; Shimbata et al 2012; Hogg et al 2013). When flour from ssIIa null lines was used to make bread, the loaves had inferior dough properties, decreased loaf volume, and increased firmness (Morita et al 2002; Van Hung et al 2005), all of which are generally viewed as negative bread traits.…”