Endosperm Carbohydrates and Debranching Enzyme Activity in Five Native sugary1 Alleles in Maize

Abstract

The su1‐ref allele, the only mutant used in sweet maize (Zea mays L.) until the 1960s, continues to be used in sweet maize improvement programs. Wild‐type Su1 encodes the starch debranching enzyme (DBE) isoamylase1 (ISA1) that is required for amylopectin production. Loss of Su1 function also leads to a reduction in activity of another DBE enzyme, pullulanase. Five naturally occurring su1 mutations have been identified and characterized as having different carbohydrate compositions. The alleles have not been evaluated for isoamylase and pullulanase DBE activity or for mature kernel composition of hybrid allele combinations. The five su1 alleles were backcrossed into two field corn lines, A619 and A632. The resulting inbreds were crossed in a factorial design. The hybrids were grown in 2015 and 2016 in Madison, WI, for an evaluation of mature kernel composition. In 2016, the su1 inbreds were grown and immature tissue was harvested 21 d after pollination for enzymatic analysis. Significant differences were identified among the su1 hybrids for starch and water‐soluble polysaccharides (WSP). Hybrids containing the su1‐p allele consistently accumulated the greatest amount of starch and the lowest amount of WSP, and those with the su1‐ne allele had the lowest amount of starch and greatest WSP content. No significant differences were observed among the su1 inbreds for isoamylase or pullulanase activity. Little to no isoamylase activity was observed, whereas pullulanase activity was reduced among the su1 mutants compared with the wild type, Ia453‐Su1. Our data indicated that differences in starch and WSP observed among the su1 alleles was not due to isoamylase or pullulanase DBE activity.

Morphological, Structural, and Physicochemical Properties of Starch in Hybrids and Inbred Lines from Sweet–Waxy Maize

“…The low branching degree of inbred lines may be because the su1 mutation reduces the activities of starch branching enzymes (isoamylase1 and pullulanase). [30] This observation is similar to the results on high-amylose starch, demonstrating that hybrid has higher branching degree than the inbred lines. [11]…”

“…[27] The small granules of inbred lines might be because the mutation of shrunken1 (sh1), sh2, su2, and se1 affects the conversion of sugar to starch and restrict the starch deposition and development. [17,24,[28][29][30]…”

Genetic Perturbation of the Starch Biosynthesis in Maize Endosperm Reveals Sugar-Responsive Gene Networks

“…Mutations in the starch biosynthetic pathway have variable effects depending on the genetic background ( Shuler et al, 2017 ). To assess the degree of difference between our isogenic lines, sugar levels were quantified in kernels at three key stages of development.…”

Sweet Corn Research around the World 2015–2020

“…Wild-type Su1 encodes the starch debranching enzyme isoamylase1 required for amylopectin production. Shuler et al [27] characterized five naturally occurring su1 mutations with different carbohydrate compositions. Significant differences in carbohydrate composition were identified among the su1 alleles for starch and water-soluble polysaccharides.…”