The effects of SBEIIb gene mutation on physicochemical properties of starch in maize

Maize ( Zea mays L.) is one of the most important crops in the world. In the starch industry and nutraceutical fields, maize ( Zea mays L.) varieties containing a high percentage of amylose show considerable value because of the ability to form gels and films, and to be used as a source for production of resistant starch, which may prevent diseases such as diabetes and obesity. The SBEIIb gene encodes the starch-branching enzyme, SBEIIb, one of the starch-branching isozymes (SBEI, SBEIIa, and SBEIIb). The amylose-extender ( ae/sbe2b ) locus is the structural gene for SBEIIb. Its recessive mutant ae/sbe2b decreases the total activities of the SBEs and increases the amylose proportion from 20 to 30% up to 70%. To evaluate the effects of SBEIIb gene mutation on the starch concentration, physicochemical properties of endosperm starch and agronomic traits, we genotyped the high-amylose germplasm line GEMS-0067 for the ae/sbe2b mutation. We also measured starch concentration, amylose proportion and major agronomic traits, and observed the morphology of starch granules through scanning electron microscopy (SEM). We additionally determined the physicochemical properties of high-amylose endosperm starch, including gelatinization properties, thermal properties and the degree of starch chain polymerization by using rapid viscosity analysis (RVA), differential scanning calorimetry (DSC) and high-performance anion-exchange chromatography (HPAEC). The production of high-amylose starch, the typical irregular starch granules and the typical physicochemical properties of high amylose endosperm starch suggested the deletion of the ninth exon of SBEIIb increased the amylose concentration and further affected the physicochemical properties of maize starch. Its useful gelatinization and thermal properties, and the degree of polymerization of the starch chains demonstrated the advantages of using GEMS-0067 as a commercial variety with high-amylose starch for applications in the starch industry and nutraceutical fields, and as a parental strain for high-amylose maize breeding.