Control of Starch Biosynthesis in Vascular Plants and Algae

Suppression of starch synthase I expression affects the granule morphology and granule size and fine structure of starch in wheat endosperm

“…The RNAi technology has been widely used for the suppression of endogenous genes in cereal and oil grains (Liu et al , 2002; Regina et al , 2006) since it was first discovered (Smith et al , 2000). Changes in the endosperm starch of the SSI-RNAi transgenic lines in this work included an increase in the abundance of very short chains (dp 6 and 7) and intermediate chains (dp 13–22), and a reduction in the abundance of short chains (dp 8–12) of amylopectin.…”

“…Changes in starch granule morphology and crystallinity were not detected in SSI mutants of rice endosperm starch and Arabidopsis leaf starch, although in the latter, starch granules were slightly elongated (Delvalle et al , 2005; Fujita et al ., 2006). In comparison with the suppression of SSI, the suppression of SSIIa or SBEIIa expression in mutants of pea, maize, wheat, and barley cause more severe changes in starch granule structure with many deformed granules, and nearly complete loss of birefringence for all starch granules (Wang et al , 1993; Craig et al , 1998; Yamamori et al , 2000; Morell et al , 2003; Regina et al , 2006; Konik-Rose et al , 2007). …”

“…The amylose fraction of wheat starch is a linear or infrequently branched (containing <1% α-1,6 linkages) molecule with a degree of polymerization (dp) of 500–3000. Amylopectin is a large and highly branched polymer (containing 5–6% α-1,6 linkages) reaching a dp of about 5000–50 000 (see reviews from Kossmann and Lloyd, 2000; Rahman et al , 2000; Ball and Morell, 2003; James et al , 2003; Tetlow et al , 2004; Morell et al , 2006). The ratio of these two polymers and the fine structure of amylopectin influence the processing, cooking, organoleptic qualities, and digestibility of starch-based foods.…”

“…Starch polymers are produced by a suite of enzymes including ADP-glucose pyrophosphorylases (EC 2.7.7.27), starch synthases (EC 2.4.1.21), starch-branching enzymes (EC 2.4.1.18), disproportionating enzymes (EC 2.4.1.25), and starch-debranching enzymes (EC 3.2.1.41 and 3.2.1.68) (see reviews from Kossmann and Lloyd, 2000; Rahman et al , 2000; Ball and Morell, 2003; James et al , 2003; Tetlow et al , 2004; Morell et al , 2006). ADP-glucose pyrophosphorylases catalyse the first committed step of starch synthesis in plant tissues by synthesizing ADP-glucose, the activated glucosyl precursor, as the source of glucose for starch elongation and subsequently branching.…”

The barley amo1 locus is tightly linked to the starch synthase IIIa gene and negatively regulates expression of granule-bound starch synthetic genes

“…wt of 10 5 –10 6  Da. A suite of enzymes are involved in cereal starch biosynthesis, including ADP-glucose pyrophosphorylases (EC 2.7.7.27), starch synthases (EC 2.4.1.21), starch branching enzymes (SBEs; EC 2.4.1.18), and starch debranching enzymes (EC 3.2.1.41 and 3.2.1.68) (see reviews by Kossmann and Lloyd, 2000; Rahman et al ., 2000; Ball and Morell, 2003; James et al ., 2003; Tetlow et al ., 2004; Morell et al ., 2006). …”