Modification of Cassava Root Starch Phosphorylation Enhances Starch Functional Properties

Abstract

Cassava (Manihot esculenta Crantz) is a root crop used as a foodstuff and as a starch source in industry. Starch functional properties are influenced by many structural features including the relative amounts of the two glucan polymers amylopectin and amylose, the branched structure of amylopectin, starch granule size and the presence of covalent modifications. Starch phosphorylation, where phosphates are linked either to the C3 or C6 carbon atoms of amylopectin glucosyl residues, is a naturally occurring modification known to be important for starch remobilization. The degree of phosphorylation has been altered in several crops using biotechnological approaches to change expression of the starch-phosphorylating enzyme GLUCAN WATER DIKINASE (GWD). Interestingly, this frequently alters other structural features of starch beside its phosphate content. Here, we aimed to alter starch phosphorylation in cassava storage roots either by manipulating the expression of the starch phosphorylating or dephosphorylating enzymes. Therefore, we generated transgenic plants in which either the wild-type potato GWD (StGWD) or a redox-insensitive version of it were overexpressed. Further plants were created in which we used RNAi to silence each of the endogenous phosphoglucan phosphatase genes STARCH EXCESS 4 (MeSEX4) and LIKE SEX4 2 (MeLSF), previously discovered by analyzing leaf starch metabolism in the model species Arabidopsis thaliana. Overexpressing the potato GWD gene (StGWD), which specifically phosphorylates the C6 position, increased the total starch-bound phosphate content at both the C6 and the C3 positions. Silencing endogenous LSF2 gene (MeLSF2), which specifically dephosphorylates the C3 position, increased the ratio of C3:C6 phosphorylation, showing that its function is conserved in storage tissues. In both cases, other structural features of starch (amylopectin structure, amylose content and starch granule size) were unaltered. This allowed us to directly relate the physicochemical properties of the starch to its phosphate content or phosphorylation pattern. Starch swelling power and paste clarity were specifically influenced by total phosphate content. However, phosphate position did not significantly influence starch functional properties. In conclusion, biotechnological manipulation of starch phosphorylation can specifically alter certain cassava storage root starch properties, potentially increasing its value in food and non-food industries.

Rheological characteristics and genotype correlation of cassava root for very high gravity ethanol production: The influence of cassava varieties and harvest times

“…Interestingly, this frequently alters other structural features of starch besides its phosphate content. It has been reported that starch functional properties are influenced by many structural features, including relative amounts of two glucan polymers, amylopectin and amylose; the branched structure of amylopectin; the starch granule size; and the presence of covalent modifications . de Graaf et al.…”

“…The genetic background was not a limiting factor to ethanol yield, but specific genes involved in important phonotype should have more effect to the traits related to phosphorylation in which the semi‐crystalline packing of amylopectin is disrupted, making the glucan chains at the granule surface more accessible to glucan‐degrading enzymes such as amylases, and enhancing the ethanol yield based on starch dry matter. Starch phosphorylation in the storage root of cassava is reported to be related to endogenous phosphoglucan phosphatase genes such as MeSEX4 and MeLSF2 . Another possible alteration of different genotypes among cultivars that influence starch degradation using alpha‐amylase and glucoamylase is the gene related to the lack of amylose in waxy genotypes.…”

Production of very‐high‐amylose cassava by post‐transcriptional silencing of branching enzyme genes

“…Cassava ( Manihot esculenta Crantz) is one of the most important starchy crops worldwide, providing staple food for more than 700 million people in the tropics and subtropics (Hershey 2017). Compared with other starches (e.g., from maize and potato), pure‐white cassava starch contains low levels of fat (0.08%–1.54%) and proteins (0.03%–0.6%); less phosphorylation of the glucose moieties has also been reported in cassava starches (Blennow et al 2001; Wang et al 2018). These features make cassava an excellent starch resource for various industrial applications (Richard et al 1991; Balagopalan 2002; Moorthy 2002; Sharma et al 2016).…”

Engineering Properties of Sweet Potato Starch for Industrial Applications by Biotechnological Techniques including Genome Editing

“…Sweet potato starch is particularly valued as an important ingredient in the manufacturing of starchbased food products, such as noodles, vermicelli, jellies, steamed bread, cakes, alcoholic beverages, soup, flavoring agents, sweeteners, and other consumables [61]. Sweet potato starch is suitable for producing resistant starch, which helps to reduce the postprandial blood glucose level and reduces the risk of obesity and diabetes [101]. Resistant starch is considered to be an important value-added starch product with increasing market demand.…”