Triple null mutations in starch synthase SSIIa gene homoeologs lead to high amylose and resistant starch in hexaploid wheat
Abstract Background Lack of nutritionally appropriate foods is one of the leading causes of obesity in the US and worldwide. Wheat (Triticum aestivum) provides 20% of the calories consumed daily across the globe. The nutrients in the wheat kernel come primarily from the starch composed of amylose and amylopectin. Resistant starch content, which is known to have significant human health benefits, can be increased by modifying starch synthesis pathways. Starch synthase enzyme SSIIa, also known as starch granule proteins isoform-1 (SGP-1), is integral to the biosynthesis of the branched and readily digestible glucose polymer amylopectin. In this study, a triple knockout mutant genotype (ssiia ∆ ABD) at the SSIIa locus was developed in elite hard red winter wheat variety ‘Jagger’. Results Knock-out mutations in SSIIa in the three genomes of wheat variety ‘Jagger’ were identified using TILLING. Subsequently, these loss-of function mutations on A, B, and D genomes were genetically combined to generate a triple knockout mutant genotype ssiia ∆ ABD. The ssiia ∆ ABD had an amylose content of 35.70% compared to 31.15% in Jagger, leading to ~ 118% increase in resistant starch in the ssiia ∆ ABD genotype of Jagger wheat. The single individual genome mutations also had various effects on starch composition. Conclusions This marks the first time a full null ssiia knockout has been achieved in a single elite cultivar background and shows the potential for developing nutritionally superior foods in a non-GM approach. Since all the mutants have been developed in an elite wheat cultivar, their adoption in production and supply will be easy.