Carciofi, Massimiliano3; Blennow, Per Gunnar Andreas10; Jensen, Susanne Langgård11; Shaik, Shahnoor Sultana12; Henriksen, Anette6; Buléon, Alain7; Holm, Preben Bach8; Hebelstrup, Kim Henrik9
1 Plant Glycobiology, Department of Plant Biology, Faculty of Life Sciences, Københavns Universitet2 Molecular Plant Fysiology, Department of Plant Biology, Faculty of Life Sciences, Københavns Universitet3 Molekylær Genetik og Bioteknologi4 Section for Plant Glycobiology, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet5 Department of Plant Biology, Faculty of Life Sciences, Københavns Universitet6 Carlsberg Laboratory (Biz)7 Institut National de la Recherche Agronomique8 Institut for Molekylærbiologi og Genetik - Afgrødegenetik og Bioteknologi9 Molekylærbiologisk Institut10 Section for Plant Glycobiology, Department of Plant and Environmental Sciences, Faculty of Science, Københavns Universitet11 Department of Plant Biology, Faculty of Life Sciences, Københavns Universitet12 Plant Glycobiology, Department of Plant Biology, Faculty of Life Sciences, Københavns Universitet
Background Starch is stored in higher plants as granules composed of semi-crystalline amylopectin and amorphous amylose. Starch granules provide energy for the plant during dark periods and for germination of seeds and tubers. Dietary starch is also a highly glycemic carbohydrate being degraded to glucose and rapidly absorbed in the small intestine. But a portion of dietary starch, termed "resistant starch" (RS) escapes digestion and reaches the large intestine, where it is fermented by colonic bacteria producing short chain fatty acids (SCFA) which are linked to several health benefits. The RS is preferentially derived from amylose, which can be increased by suppressing amylopectin synthesis by silencing of starch branching enzymes (SBEs). However all the previous works attempting the production of high RS crops resulted in only partly increased amylose-content and/or significant yield loss. Results 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. Conclusions 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.
B M C Plant Biology, 2012, Vol 12, Issue 223, p. 1-16