Inhibition of the expression of the starch synthase II gene leads to lower pasting temperature in sweetpotato starch

Abstract

The sweetpotato cultivar Quick Sweet (QS) with a lower pasting temperature of starch is a unique breeding material, but the biochemical background of this property has been unknown. To assess the physiological impact of the reduced isoform II activity of starch synthase (SSII) on the starch properties in sweetpotato storage root, transgenic sweetpotato plants with reduced expressions of the SSII gene were generated and evaluated. All of the starches from transgenic plants showed lower pasting temperatures and breakdown measured by a Rapid Visco Analyzer. The pasting temperatures in transgenic plants were approximately 10-15 degrees C lower than in wild-type plants. Distribution of the amylopectin chain length of the transgenic lines showed marked differences compared to that in wild-type plants: more chains with degree of polymerization (DP) 6-11 and fewer chains with DP 13-25. The starch granules from the storage root of transgenic plants showed cracking on the hilum, while those from wild-type plants appeared to be typical sweetpotato starch. In accordance with these observations, the expression of SSII in the storage roots of the sweetpotato cultivar with low pasting temperature starch (QS) was notably lower than in cultivars with normal starch. Moreover, nucleotide sequence analysis suggested that most of the SSII transcripts in the cultivar with low pasting temperature starch were inactive alleles. These results clearly indicate that the activity of SSII in sweetpotato storage roots, like those in other plants, affects the pasting properties of starch through alteration of the amylopectin structure.

On the molecular structure of the amylopectin fraction isolated from “high-amylose” ae maize starches

“…Most of the investigations made so far have concentrated the analyses on the composition of amylose in the starch granules [19][20][21][22][23][24] and the composition of unit chains in the amylopectin component [19][20][21][22][23][24][25][26][27][28]. A few studies have also focussed on the internal unit chain composition, i.e.…”

A soluble starch synthase I gene, IbSSI, alters the content, composition, granule size and structure of starch in transgenic sweet potato

“…In sweet potato, several genes that encode the starch biosynthetic enzymes have been cloned and characterized 13, 14, 23–27 . These genes have been reported to impact the starch composition, structure and physicochemical properties and minimally influence the starch content.…”

Carotenoid analysis of sweetpotatoIpomoea batatasand functional identification of its lycopene β- and ε-cyclase genes

“…We selected two sweetpotato (I. batatas) cultivars, WS and W71, as representative genotypes, exhibiting white and orange tuberous roots (tubers), respectively, since they have also been used in Agrobacterium tumefaciensmediated transformation ( [13,14], and our unpublished results). Carotenoid pigments were extracted from the two cultivars and subjected to HPLC-PDA-HRMS analysis.…”

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