Concerted suppression of all starch branching enzyme genes in barley produces amylose-only starch granules

In this study we invented a new method for silencing of multiple genes. Using a chimeric RNAi hairpin we simultaneously suppressed all genes coding for starch branching enzymes (SBE I, SBE IIa, SBE IIb) in barley (Hordeum vulgare L.), resulting in production of amylose-only starch granules in the endosperm. This trait was segregating 3:1. Amylose-only starch granules were irregularly shaped and showed peculiar thermal properties and crystallinity. Transgenic lines retained high-yield possibly due to a pleiotropic upregualtion of other starch biosynthetic genes compensating the SBEs loss. For gelatinized starch, a very high content of RS (65 %) was observed, which is 2.2-fold higher than control (29%). The amylose-only grains germinated with same frequency as control grains. However, initial growth was delayed in young plants.This is the first time that pure amylose has been generated with high yield in a living organism. This was achieved by a new method of simultaneous suppression of the entire complement of genes encoding starch branching enzymes. We demonstrate that amylopectin is not essential for starch granule crystallinity and integrity. However the slower initial growth of shoots from amylose-only grains may be due to an important physiological role played by amylopectin ordered crystallinity for rapid starch remobilization explaining the broad conservation in the plant kingdom of the amylopectin structure.Starch, a polysaccharide composed of glucose molecules, is a common constituent of higher plants and can be found in all the organs being the major forms in which carbohydrates are stored [1,2]. Biosynthesis and accumulation of starch takes place into two different forms of plastids, chloroplasts and amyloplasts, depending on the anatomical site. Starch produced in chloroplasts is called transient starch and is a primary product of photosynthesis, along with sucrose. Transient starch synthesised during daytime is degraded during the following night, provid