Iminosugar inhibitors of carbohydrate-active enzymes that underpin cereal grain germination and endosperm metabolism.

Vasilios M E Andriotis,Birte Svensson,Martin Rejzek,Michael D Rugen,Robert A Field,Alison M Smith

doi:10.1042/bst20150222

Abstract

Starch is a major energy store in plants. It provides most of the calories in the human diet and, as a bulk commodity, it is used across broad industry sectors. Starch synthesis and degradation are not fully understood, owing to challenging biochemistry at the liquid/solid interface and relatively limited knowledge about the nature and control of starch degradation in plants. Increased societal and commercial demand for enhanced yield and quality in starch crops requires a better understanding of starch metabolism as a whole. Here we review recent advances in understanding the roles of carbohydrate-active enzymes in starch degradation in cereal grains through complementary chemical and molecular genetics. These approaches have allowed us to start dissecting aspects of starch degradation and the interplay with cell-wall polysaccharide hydrolysis during germination. With a view to improving and diversifying the properties and uses of cereal grains, it is possible that starch degradation may be amenable to manipulation through genetic or chemical intervention at the level of cell wall metabolism, rather than simply in the starch degradation pathway per se.

Highlights

Starch, a glucose polymer, is of enormous biological and commercial importance
We discuss recent advances in understanding starch degradation during cereal grain germination. These have been facilitated through chemical genetics approaches, exploring the function of carbohydrate active enzymes in endosperm metabolism and in early seedling growth
When applied to germinating barley grains, they retard a wave-like spread of AX degradation through the endosperm and retard starch loss over the same period. These findings strongly suggest that diffusion of macromolecules is restricted by endosperm cell walls; cell wall degradation is required for normal rates of starch mobilization to occur

Summary

Introduction

A glucose polymer, is of enormous biological and commercial importance. Starch, in roots, tubers and seeds, provides a carbon store for use by the plant during times when photosynthesis is not possible, such as regrowth following winter dormancy and during seed germination [1,2,3,4,5]. These have been facilitated through chemical genetics approaches, exploring the function of carbohydrate active enzymes in endosperm metabolism and in early seedling growth. In addition to the limited availability of genomic resources and the greater difficulty of cereal transformation, the application of molecular genetics is problematic because several enzyme activities for endosperm starch degradation are represented by multigene families and/or undergo extensive post-translational processing.

Results

Conclusion