Barley <i>sex6</i> mutants lack starch synthase IIa activity and contain a starch with novel properties

Morell, Matthew K.; Kosar-Hashemi, Behjat; Cmiel, Mark; Samuel, Michael S.; Chandler, Peter M.; Rahman, Sadequr; Buléon, Alain; Batey, I. L.; Li, Zhongyi

doi:10.1046/j.1365-313x.2003.01712.x

Cited by 302 publications

(250 citation statements)

References 49 publications

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“…This study also showed unambiguously that the large increase in apparent amylose content in the mutant starch was partly due to an increased amount of long chains of amylopectin. Similar effects on amylopectin structure by loss of starch synthase II activity were reported for mutants of pea (rug5) 18) and barley (sex6), 19) and Umemoto et al . 20) suggested reduced starch synthase II activity in japonica rice results in structural differences between japonica and indica rice amylopectins, which is similar to those of the wheat starches examined in this study.…”

Section: Molar Composition Of Amylose and Amylopectinsupporting

confidence: 80%

Increased Amylose Content and Altered Molecular Structures of Wheat Starch by SGP-1 Null Mutation

勲¹,

育雄²,

誠³

et al. 2004

J. Appl. Glycosci.

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Starch biosynthesis is a complex, concerted process by various enzymes, involving elongation of an existing 1,4 glucoside chain, branching of glucoside chains by forming 1,6 linkages and debranching by hydrolysis of 1,6 linkages. Some of these enzymes are found to be bound to or trapped in starch granules. In wheat (Triticum aestivum L.), at least three proteins, other than waxy protein, have been identified as starch granule bound proteins (starch granule protein, SGP) 1,2) and are designated as SGP 1, 2 and 3. 1) The SGPs are thought to be isoforms of starch synthase II, starch branching enzyme II and starch synthase I, respectively, based on their biochemical properties and nucleotide sequence. 2 5) Three isoforms with different molecular weight (100 115 kDa 2 5) ) of SGP 1 are present in wheat starch granules and they are designated SGP A1, B1, D1, 1) each encoded at loci on the short arms o f chromosome 7A, 7 B and 7 D , respectively . 1,2) SGP B1, and very likely the other two isofomrs also, exist in both starch granule and soluble fractions at early stages of endosperm development but at late stages they are exclusively granule bound. 3,5) Yamamori et al . 6) generated a mutant line that lacked all three isoforms of SGP 1 and reported that starch granules from the SGP 1 null mutant have altered properties, such as absence of birefringence under polarized light, absence of diffraction of X ray (crystallinity of starch granules), and an increased amylose content. Effects on molecular structures were also examined, and high performance size exclusion chromatography (HPSEC) and high performance anion exchange chromatography with pulsed amperometric detection (HPAEC PAD) revealed that chain length distribution of amylopectin was significantly altered by the mutation. 6) However, the elucidation of structural changes was limited to a certain extent because the structural characterization was carried out without fractionation of starch into amylose and amylopectin, and consequently changes occurring in amylose were not examined at all. In this study, amylose and amylopectin were fractionated from SGP 1 null starch and their molecular structures were examined in more detail and compared with those of a wheat starch with normal amylose content (cv. Chinese Spring). MATERIALS AND METHODS Materials.Starches were the same specimens used in a previous study. 6) Amylose and amylopectin were fractionated from defatted starch by the method of Takeda et al . 7) Pseudomonas isoamylase was a product of Hayashi- Abstract: Amylose content and molecular structures of starch from a mutant of wheat (Triticum aestivum L.) that lacks a starch granule bound protein, SGP-1, have been compared with those from normal wheat (cv. Chinese Spring). Actual amylose contents, calculated by taking iodine affinity of amylopectin into consideration, for the mutant (SGP-1 null) and normal wheat starches were 34 and 26%, respectively. The amylopectins from SGP-1 null and normal starches had number-average degree of polymerization (DPn) of 4200 ...

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Section: Molar Composition Of Amylose and Amylopectinsupporting

confidence: 80%

Increased Amylose Content and Altered Molecular Structures of Wheat Starch by SGP-1 Null Mutation

勲¹,

育雄²,

誠³

et al. 2004

J. Appl. Glycosci.

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“…2). Other starch mutants, such as the shrunken mutants of maize (Tracy, 2000), the wrinkled mutant of pea (Bhattacharyya et al, 1990) and the barley sex6 mutant (Morell et al, 2003) also exhibit a shrunken seed shape. As expected, the SW double mutant was amylose-free and cut kernels stained redbrown with iodine (data not shown).…”

Section: Textmentioning

confidence: 99%

Sweet Wheat

et al. 2006

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The major components of storage starch are amylose and amylopectin, and in wheat, both an amylose-free mutant lacking granule-bound starch synthase I and a high-amylose mutant lacking starch synthase IIa have been produced recently. Here, we report the production of an amylose-free/ high-amylose double mutant. This double mutant has kernel and carbohydrate characteristics that are remarkably different than those of either single mutant, including a dramatically shrunken seed shape. Surprisingly, the double mutant has maltose and sucrose levels that are high enough to make it worthy of being called "sweet wheat".

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“…The synthesis pathway of the rather complex amylopectin molecule includes soluble starch synthase (SS), starchbranching enzyme (SBE), and starch-debranching enzyme (DBE). Each individual SS isoform is believed to have a unique function in amylopectin synthesis Li et al, 2003;Morell et al, 2003;Morell and Myers, 2005). Distinct SBE isoforms are recruited for starch synthesis during particular stages of seed filling in barley (Mutisya et al, 2003).…”

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confidence: 99%

Spatiotemporal Profiling of Starch Biosynthesis and Degradation in the Developing Barley Grain

Borisjuk²,

et al. 2009

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Barley (Hordeum vulgare) grains synthesize starch as the main storage compound. However, some starch is degraded already during caryopsis development. We studied temporal and spatial expression patterns of genes coding for enzymes of starch synthesis and degradation. These profiles coupled with measurements of selected enzyme activities and metabolites have allowed us to propose a role for starch degradation in maternal and filial tissues of developing grains. Early maternal pericarp functions as a major short-term starch storage tissue, possibly ensuring sink strength of the young caryopsis. Gene expression patterns and enzyme activities suggest two different pathways for starch degradation in maternal tissues. One pathway possibly occurs via a-amylases 1 and 4 and b-amylase 1 in pericarp, nucellus, and nucellar projection, tissues that undergo programmed cell death. Another pathway is deducted for living pericarp and chlorenchyma cells, where transient starch breakdown correlates with expression of chloroplast-localized b-amylases 5, 6, and 7, glucan, water dikinase 1, phosphoglucan, water dikinase, isoamylase 3, and disproportionating enzyme. The suite of genes involved in starch synthesis in filial starchy endosperm is much more complex than in pericarp and involves several endosperm-specific genes. Transient starch turnover occurs in transfer cells, ensuring the maintenance of sink strength in filial tissues and the reallocation of sugars into more proximal regions of the starchy endosperm. Starch is temporally accumulated also in aleurone cells, where it is degraded during the seed filling period, to be replaced by storage proteins and lipids.

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Barley sex6 mutants lack starch synthase IIa activity and contain a starch with novel properties

Cited by 302 publications

References 49 publications

Increased Amylose Content and Altered Molecular Structures of Wheat Starch by SGP-1 Null Mutation

Increased Amylose Content and Altered Molecular Structures of Wheat Starch by SGP-1 Null Mutation

Sweet Wheat

Spatiotemporal Profiling of Starch Biosynthesis and Degradation in the Developing Barley Grain

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