Highly phosphorylated functionalized rice starch produced by transgenic rice expressing the potato GWD1 gene

Abstract

Starch phosphorylation occurs naturally during starch metabolism in the plant and is catalysed by glucan water dikinases (GWD1) and phosphoglucan water dikinase/glucan water dikinase 3 (PWD/GWD3). We generated six stable individual transgenic lines by over-expressing the potato GWD1 in rice. Transgenic rice grain starch had 9-fold higher 6-phospho (6-P) monoesters and double amounts of 3-phospho (3-P) monoesters, respectively, compared to control grain. The shape and topography of the transgenic starch granules were moderately altered including surface pores and less well defined edges. The gelatinization temperatures of both rice flour and extracted starch were significantly lower than those of the control and hence negatively correlated with the starch phosphate content. The 6-P content was positively correlated with amylose content and relatively long amylopectin chains with DP25-36, and the 3-P content was positively correlated with short chains of DP6-12. The starch pasting temperature, peak viscosity and the breakdown were lower but the setback was higher for transgenic rice flour. The 6-P content was negatively correlated with texture adhesiveness but positively correlated with the cohesiveness of rice flour gels. Our data demonstrate a way forward to employ a starch bioengineering approach for clean modification of starch, opening up completely new applications for rice starch.

Starch Biosynthesis in the Developing Endosperms of Grasses and Cereals

“…For example, the down regulation of GWD in wheat endosperm resulted in a remarkable increase in plant biomass and a 29% increase in grain yield [383]. Over-expression of potato GWD in rice endosperm resulted in alterations in starch granule morphology and physicochemical characteristics [384].…”

Preparation of Starch Citrates Using Solvent Free Reaction and Comparison with Aqueous and Ethanol Mediated Reactions

“…PV is also influenced by shearing between swollen granules and shear resistance also depends on granule size. We did not observe any significant difference in granule size following modification, hence the reduced PV is related to other factors such as amylose content, [ 1 ] extent, and chain length of leached amylose as well as more extensive thermal granule fragmentation and interactions of swollen granules. [ 39 ] AQ sample showed higher M w and M n values than native starch which might have affected PV value for this modification besides interaction between starch chains.…”

“…However, starch can also be modified by substitution directly in the grain using a starch bioengineering strategy in planta to avoid downstream polluting waste, for example, phosphorylation rice starch. [ 1 ] In addition to such strategies, physical treatments like heat moisture treatment, ultrasonication, dry heating, high pressure processing as well as chemical treatments with organic acids are also be considered as clean.…”

Phosphorylated Starches: Preparation, Properties, Functionality, and Techno‐Applications

“…[ 51,52 ] Phosphorylation by GWD1 disrupts the starch crystalline structure and increases the hydrolytic effect of plastidial β‐amylase. [ 53–55 ] GWD1 level remains constant during the diurnal cycle, while the starch biosynthesis is influenced by phosphorylation as demonstrated by metabolic and structural impacts in barley and Arabidopsis. [ 55,56 ]…”

“…[ 53–55 ] GWD1 level remains constant during the diurnal cycle, while the starch biosynthesis is influenced by phosphorylation as demonstrated by metabolic and structural impacts in barley and Arabidopsis. [ 55,56 ]…”