Abstract
Key messageSeven novel alleles of SBEIIb and one allele of SSIIa co-segregated with the ASV phenotype and contributed to distinct starch quality traits important for food-processing applications.Sorghum is an important food crop for millions of people in Africa and Asia. Whole-genome re-sequencing of sorghum EMS mutants exhibiting an alkali spreading value (ASV) phenotype revealed candidate SNPs in Sobic.004G163700 and Sobic.010G093400. Comparative genomics identified Sobic.010G093400 as a starch synthase IIa and Sobic.004G163700 as a starch branching enzyme IIb. Segregation analyses showed that mutations in Sobic.010G093400 or Sobic.004G163700 co-segregated with the ASV phenotype. Mutants in SSIIa exhibited no change in amylose content but expressed lower final viscosity and lower starch gelatinization temperature (GT) than starches from non-mutant plants. The sbeIIb mutants exhibited significantly higher amylose levels and starch GT and lower viscosity compared to non-mutant starches and ssIIa mutants. Mutations in SBEIIb had a dosage-dependent effect on amylose content. Double mutants of sbeIIb and ssIIa resembled their sbeIIb parent in amylose content, starch thermal properties and viscosity profiles. These variants will provide opportunities to produce sorghum varieties with modified starch end-use qualities important for the beer brewing and baking industries and specialty foods for humans with diabetes.
Highlights
Sorghum [Sorghum bicolor (L.) Moench] is important in drought-prone environments (Food and Agriculture Organization of the United Nations 2019a, b; Kimber 2000)
Sequence comparisons suggest that Sobic.004G163700 codes for a SBEIIb with high sequence similarity to the one reported previously by Mutisya et al (2003) and is closely related to amylose extender (SBEIIb) in maize (Fig. 2)
The SBEIIb of sorghum reported by Mutisya et al (2003) showed high sequence similarity with other cereals too
Summary
Sorghum [Sorghum bicolor (L.) Moench] is important in drought-prone environments (Food and Agriculture Organization of the United Nations 2019a, b; Kimber 2000). It is a staple crop in Africa and Asia and is utilized to produce traditional foods such as stiff porridges and beverages (House et al 2000). The two major starch fractions, amylose and amylopectin and their ratio, influence starch functionality (BeMiller and Huber 2008; Jane 2009; Tetlow et al 2004), where amorphous (α-1,6 branch points) and crystalline (linear α-1,4 glucan chains) regions play important roles (Tetlow and Emes 2014). Starch compositions of 70–80% amylopectin and 15–30% amylose are reported in normal starches of maize, rice wheat and sorghum
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