Improved understanding of rice amylose biosynthesis from advanced starch structural characterization.

Enpeng Li,Qiaoquan Liu,Robert G Gilbert,Juan Li,Alex Chi Wu

doi:10.1186/s12284-015-0055-4

Abstract

BackgroundIt has been shown from the chain length distributions (CLDs) that amylose chains can be divided into at least two groups: long and short amylose chains. These molecular structures influence some functional properties of starch, such as digestibility and mouth-feel. GBSSI is the key enzyme for the elongation of amylose chains; however, the effect of other starch biosynthesis enzymes in amylose synthesis is still not fully understood. Two advanced starch characterization techniques, size exclusion chromatography (SEC) and fluorophore-assissted carbohydrate electrophoresis (FACE), together with a newly developed starch biosynthesis model, are used to improve understanding of amylose biosynthesis.ResultsSEC and FACE were used to determine the CLD of amylose and amylopectin in various native and mutant rice starches. The types of starch branching enzymes (SBEs) involved in the synthesis of the distinct features seen for shorter degrees of polymerization, DP, < 2000, and longer (DP > 2000) amylose chains are identified by combining these data with a mathematical model of amylopectin biosynthesis. The model enables each feature in the amylopectin CLD to be parameterized in terms of relative SBE activities, which are used to explain differences in the genotypes.ConclusionsThe results suggest that while GBSSI is the predominant enzyme controlling the synthesis of longer amylose chains, some branching enzymes (such as BEI and BEIIb) also play important roles in the synthesis of shorter amylose chains.

Highlights

It has been shown from the chain length distributions (CLDs) that amylose chains can be divided into at least two groups: long and short amylose chains
The Wu-Gilbert model fitting result (Table 1) shows that the values of the most important parameters governing the shape of the amylopectin CLD, β(ii), β(iv) and β(vi) are not very different between both rice starches, while those of β(i), β(iii) and β(v) (and γ(i,ii), γ(iii,iv), γ(v, vi)) for wild-type Wuxiangjing 14 (WXJ) rice starch are significantly larger than those of BEI- and BEIIb-knockout WXJ rice starch
Our results shows that BEI and BEIIb knockout significantly reduces branching ability in rice endosperm: BEI and BEIIb knockout WXJ rice have significantly lower amylopectin content than wild type WXJ rice (Fig. 2a) (Zhu et al 2012)

Summary

Introduction

It has been shown from the chain length distributions (CLDs) that amylose chains can be divided into at least two groups: long and short amylose chains. These molecular structures influence some functional properties of starch, such as digestibility and mouth-feel. GBSSI is the key enzyme for the elongation of amylose chains; the effect of other starch biosynthesis enzymes in amylose synthesis is still not fully understood. Starch is a homopolymer of glucosyl units, with two main components: amylose and amylopectin. Amylose is a slightly branched molecule, and amylopectin is highly branched (Buleon et al 1998; Tester et al 2004). Granule-bound starch synthase I (GBSSI) is the key enzyme for amylose biosynthesis. Two amylose synthesis models have been proposed based on in vitro experiments.

Methods

Results

Conclusion