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Behjat Kosar-hashemi - One of the best experts on this subject based on the ideXlab platform.
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Multiple effects of the Starch Synthase II mutation in developing wheat endosperm.
Functional plant biology : FPB, 2007Co-Authors: Behjat Kosar-hashemi, Oscar Larroque, Matthew K. Morell, Ahmed Regina, Makoto Yamamori, Sadequr RahmanAbstract:A line of wheat (Triticum aestivum L.), sgp-1, that does not express Starch Synthase II (SSII, also known as SGP-1) has previously been reported. In this study, F1 derived doubled haploid lines with homozygous wild type or mutant alleles for SGP-1 genes were identified from a cross between the original mutant and a wild type Australian cultivar. Analysis of the Starch granules showed that in the mutant lines they are markedly distorted from 15 days postanthesis during grain development. Starch branching patterns showed an increase in the proportion of short chains (DP 6-10) at an earlier stage, but this increase became much more pronounced at 15 days postanthesis and persisted until maturity. There was also a consistent and drastic reduction throughout seed development in the relative amounts of Starch branching enzyme II (SBEII, comprising SBEIIa and SBEIIb) and Starch Synthase I (SSI) bound to the Starch granules. In the soluble phase, however, there was relatively little change in the amount of SBEIIb, SBEIIa or SSI protein. Therefore loss of SSII specifically leads to the loss of SBEIIb, SBEIIa and SSI protein in the granule-bound phase and the effect of this mutation is clearly manifest from the mid-stage of endosperm development in wheat.
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The structure and expression of the wheat Starch Synthase III gene. Motifs in the expressed gene define the lineage of the Starch Synthase III gene family
Plant Physiology, 2000Co-Authors: Greg Mouille, Behjat Kosar-hashemi, Rudi Appels, Sadequr Rahman, Bryan Clarke, Kevin R. Gale, Matthiew K. MorellAbstract:The endosperm of hexaploid wheat (Triticum aestivum [L.]) was shown to contain a high molecular weight Starch Synthase (SS) analogous to the product of the maize du1 gene, Starch Synthase III (SSIII; DU1). cDNA and genomic DNA sequences encoding wheat SSIII were isolated and characterized. The wheat SSIII cDNA is 5,346 bp long and contains an open reading frame that encodes a 1,628-amino acid polypeptide. A putative N-terminal transit peptide, a 436-amino acid C-terminal catalytic domain, and a central 470-amino acid SSIII-specific domain containing three regions of repeated amino acid similarity were identified in the wheat gene. A fourth region between the transit peptide and the SSIII-specific domain contains repeat motifs that are variable with respect to motif sequence and repeat number between wheat and maize. In dicots, this N-terminal region does not contain repeat motifs and is truncated. The gene encoding wheat SSIII, designated ss3, consists of 16 exons extending over 10 kb, and is located on wheat chromosome I. Expression of ss3 mRNA in wheat was detected in leaves, pre-anthesis florets, and from very early to middle stage of endosperm development. The entire N-terminal variable repeat region and the majority of the SSIII-specific domain are encoded on a single 2,703-bp exon. A gene encoding a class III SS from the Arabidopsis genome sequencing project shows a strongly conserved exon structure to the wheat ss3 gene, with the exception of the N-terminal region. The evolutionary relationships of the genes encoding monocot and dicot class III SSs are discussed.
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Cloning and characterization of a gene encoding wheat Starch Synthase I
Theoretical and Applied Genetics, 1999Co-Authors: S. Rahman, Behjat Kosar-hashemi, Grégory Mouille, Rudi Appels, Matthew K. MorellAbstract:A cDNA clone, and a corresponding genomic DNA clone, containing full-length sequences encoding wheat Starch Synthase I, were isolated from a cDNA library of hexaploid wheat (Triticum aestivum) and a genomic DNA library of Triticum tauschii, respectively. The entire sequence of the Starch Synthase-I cDNA (wSSI-cDNA) is 2591 bp, and it encodes a polypeptide of 647 amino-acid residues that shows 81% and 61% identity to the amino-acid sequences of SSI-type Starch Synthases from rice and potato, respectively. In addition, the putative N-terminal amino-acid sequence of the encoded protein is identical to that determined for the N-terminal region of the 75-kDa Starch Synthase present in the Starch granule of hexaploid wheat. Two prominent Starch Synthase activities were demonstrated to be present in the soluble fraction of wheat endosperm by activity staining of the non-denaturing PAGE gels. The most anodal band (wheat SSI) shows the highest staining intensity and results from the activity of a 75-kDa protein. The wheat SSI mRNA is expressed in the endosperm during the early to mid stages of wheat grain development but was not detected by Northern blotting in other tissues from the wheat plant. The gene encoding the wheat SSI (SsI-D1) consists of 15 exons and 14 introns, similar to the structure of the rice Starch Synthase-I gene. While the exons of wheat and rice are virtually identical in length, the wheat SsI-D1 gene has longer sequences in introns 1, 2, 4 and 10, and shorter sequences in introns 6, 11 and 14, than the corresponding rice gene.
Matthew K. Morell - One of the best experts on this subject based on the ideXlab platform.
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Multiple effects of the Starch Synthase II mutation in developing wheat endosperm.
Functional plant biology : FPB, 2007Co-Authors: Behjat Kosar-hashemi, Oscar Larroque, Matthew K. Morell, Ahmed Regina, Makoto Yamamori, Sadequr RahmanAbstract:A line of wheat (Triticum aestivum L.), sgp-1, that does not express Starch Synthase II (SSII, also known as SGP-1) has previously been reported. In this study, F1 derived doubled haploid lines with homozygous wild type or mutant alleles for SGP-1 genes were identified from a cross between the original mutant and a wild type Australian cultivar. Analysis of the Starch granules showed that in the mutant lines they are markedly distorted from 15 days postanthesis during grain development. Starch branching patterns showed an increase in the proportion of short chains (DP 6-10) at an earlier stage, but this increase became much more pronounced at 15 days postanthesis and persisted until maturity. There was also a consistent and drastic reduction throughout seed development in the relative amounts of Starch branching enzyme II (SBEII, comprising SBEIIa and SBEIIb) and Starch Synthase I (SSI) bound to the Starch granules. In the soluble phase, however, there was relatively little change in the amount of SBEIIb, SBEIIa or SSI protein. Therefore loss of SSII specifically leads to the loss of SBEIIb, SBEIIa and SSI protein in the granule-bound phase and the effect of this mutation is clearly manifest from the mid-stage of endosperm development in wheat.
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barley sex6 mutants lack Starch Synthase iia activity and contain a Starch with novel properties
Plant Journal, 2003Co-Authors: Matthew K. Morell, Behjat Kosarhashemi, Sadequr Rahman, Alain Buleon, Mark Cmiel, Michael S Samuel, Peter M Chandler, I L BateyAbstract:Analysis of barley shrunken grain mutants has identified lines with a novel high amylose Starch phenotype. The causal mutation is located at the sex6 locus on chromosome 7H, suggesting the Starch Synthase IIa (ssIIa) gene as a candidate gene altered by the mutation. Consistent with this hypothesis, no evidence of SSIIa protein expression in either the Starch granule or soluble fractions of the endosperm was found. Sequences of the Starch Synthase IIa gene, ssIIa, from three independent sex6 lines showed the presence of a stop codon preventing translation of the ssIIa transcript in each line. Perfect segregation of the Starch phenotype with the presence of stop codons in the ssIIa gene was obtained, providing strong evidence for the lesion in the ssIIa gene being the causal mutation for the sex6 phenotype. The loss of SSIIa activity in barley leads to novel and informative phenotypes. First, a decrease in amylopectin synthesis to less than 20% of the wild-type levels indicates that SSIIa accounts for the majority of the amylopectin polymer elongation activity in barley. Secondly, in contrast to high amylose Starches resulting from branching enzyme downregulation, the sex6 Starches have a shortened amylopectin chain length distribution and a reduced gelatinisation temperature. Thirdly, the mutation leads to pleiotropic effects on other enzymes of the Starch biosynthesis pathway, abolishing the binding of SSI, branching enzyme IIa and branching enzyme IIb to the Starch granules of sex6 mutants, while not significantly altering their expression levels in the soluble fraction.
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Cloning and characterization of a gene encoding wheat Starch Synthase I
Theoretical and Applied Genetics, 1999Co-Authors: S. Rahman, Behjat Kosar-hashemi, Grégory Mouille, Rudi Appels, Matthew K. MorellAbstract:A cDNA clone, and a corresponding genomic DNA clone, containing full-length sequences encoding wheat Starch Synthase I, were isolated from a cDNA library of hexaploid wheat (Triticum aestivum) and a genomic DNA library of Triticum tauschii, respectively. The entire sequence of the Starch Synthase-I cDNA (wSSI-cDNA) is 2591 bp, and it encodes a polypeptide of 647 amino-acid residues that shows 81% and 61% identity to the amino-acid sequences of SSI-type Starch Synthases from rice and potato, respectively. In addition, the putative N-terminal amino-acid sequence of the encoded protein is identical to that determined for the N-terminal region of the 75-kDa Starch Synthase present in the Starch granule of hexaploid wheat. Two prominent Starch Synthase activities were demonstrated to be present in the soluble fraction of wheat endosperm by activity staining of the non-denaturing PAGE gels. The most anodal band (wheat SSI) shows the highest staining intensity and results from the activity of a 75-kDa protein. The wheat SSI mRNA is expressed in the endosperm during the early to mid stages of wheat grain development but was not detected by Northern blotting in other tissues from the wheat plant. The gene encoding the wheat SSI (SsI-D1) consists of 15 exons and 14 introns, similar to the structure of the rice Starch Synthase-I gene. While the exons of wheat and rice are virtually identical in length, the wheat SsI-D1 gene has longer sequences in introns 1, 2, 4 and 10, and shorter sequences in introns 6, 11 and 14, than the corresponding rice gene.
Rudi Appels - One of the best experts on this subject based on the ideXlab platform.
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The structure and expression of the wheat Starch Synthase III gene. Motifs in the expressed gene define the lineage of the Starch Synthase III gene family
Plant Physiology, 2000Co-Authors: Greg Mouille, Behjat Kosar-hashemi, Rudi Appels, Sadequr Rahman, Bryan Clarke, Kevin R. Gale, Matthiew K. MorellAbstract:The endosperm of hexaploid wheat (Triticum aestivum [L.]) was shown to contain a high molecular weight Starch Synthase (SS) analogous to the product of the maize du1 gene, Starch Synthase III (SSIII; DU1). cDNA and genomic DNA sequences encoding wheat SSIII were isolated and characterized. The wheat SSIII cDNA is 5,346 bp long and contains an open reading frame that encodes a 1,628-amino acid polypeptide. A putative N-terminal transit peptide, a 436-amino acid C-terminal catalytic domain, and a central 470-amino acid SSIII-specific domain containing three regions of repeated amino acid similarity were identified in the wheat gene. A fourth region between the transit peptide and the SSIII-specific domain contains repeat motifs that are variable with respect to motif sequence and repeat number between wheat and maize. In dicots, this N-terminal region does not contain repeat motifs and is truncated. The gene encoding wheat SSIII, designated ss3, consists of 16 exons extending over 10 kb, and is located on wheat chromosome I. Expression of ss3 mRNA in wheat was detected in leaves, pre-anthesis florets, and from very early to middle stage of endosperm development. The entire N-terminal variable repeat region and the majority of the SSIII-specific domain are encoded on a single 2,703-bp exon. A gene encoding a class III SS from the Arabidopsis genome sequencing project shows a strongly conserved exon structure to the wheat ss3 gene, with the exception of the N-terminal region. The evolutionary relationships of the genes encoding monocot and dicot class III SSs are discussed.
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Cloning and characterization of a gene encoding wheat Starch Synthase I
Theoretical and Applied Genetics, 1999Co-Authors: S. Rahman, Behjat Kosar-hashemi, Grégory Mouille, Rudi Appels, Matthew K. MorellAbstract:A cDNA clone, and a corresponding genomic DNA clone, containing full-length sequences encoding wheat Starch Synthase I, were isolated from a cDNA library of hexaploid wheat (Triticum aestivum) and a genomic DNA library of Triticum tauschii, respectively. The entire sequence of the Starch Synthase-I cDNA (wSSI-cDNA) is 2591 bp, and it encodes a polypeptide of 647 amino-acid residues that shows 81% and 61% identity to the amino-acid sequences of SSI-type Starch Synthases from rice and potato, respectively. In addition, the putative N-terminal amino-acid sequence of the encoded protein is identical to that determined for the N-terminal region of the 75-kDa Starch Synthase present in the Starch granule of hexaploid wheat. Two prominent Starch Synthase activities were demonstrated to be present in the soluble fraction of wheat endosperm by activity staining of the non-denaturing PAGE gels. The most anodal band (wheat SSI) shows the highest staining intensity and results from the activity of a 75-kDa protein. The wheat SSI mRNA is expressed in the endosperm during the early to mid stages of wheat grain development but was not detected by Northern blotting in other tissues from the wheat plant. The gene encoding the wheat SSI (SsI-D1) consists of 15 exons and 14 introns, similar to the structure of the rice Starch Synthase-I gene. While the exons of wheat and rice are virtually identical in length, the wheat SsI-D1 gene has longer sequences in introns 1, 2, 4 and 10, and shorter sequences in introns 6, 11 and 14, than the corresponding rice gene.
Sadequr Rahman - One of the best experts on this subject based on the ideXlab platform.
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Multiple effects of the Starch Synthase II mutation in developing wheat endosperm.
Functional plant biology : FPB, 2007Co-Authors: Behjat Kosar-hashemi, Oscar Larroque, Matthew K. Morell, Ahmed Regina, Makoto Yamamori, Sadequr RahmanAbstract:A line of wheat (Triticum aestivum L.), sgp-1, that does not express Starch Synthase II (SSII, also known as SGP-1) has previously been reported. In this study, F1 derived doubled haploid lines with homozygous wild type or mutant alleles for SGP-1 genes were identified from a cross between the original mutant and a wild type Australian cultivar. Analysis of the Starch granules showed that in the mutant lines they are markedly distorted from 15 days postanthesis during grain development. Starch branching patterns showed an increase in the proportion of short chains (DP 6-10) at an earlier stage, but this increase became much more pronounced at 15 days postanthesis and persisted until maturity. There was also a consistent and drastic reduction throughout seed development in the relative amounts of Starch branching enzyme II (SBEII, comprising SBEIIa and SBEIIb) and Starch Synthase I (SSI) bound to the Starch granules. In the soluble phase, however, there was relatively little change in the amount of SBEIIb, SBEIIa or SSI protein. Therefore loss of SSII specifically leads to the loss of SBEIIb, SBEIIa and SSI protein in the granule-bound phase and the effect of this mutation is clearly manifest from the mid-stage of endosperm development in wheat.
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barley sex6 mutants lack Starch Synthase iia activity and contain a Starch with novel properties
Plant Journal, 2003Co-Authors: Matthew K. Morell, Behjat Kosarhashemi, Sadequr Rahman, Alain Buleon, Mark Cmiel, Michael S Samuel, Peter M Chandler, I L BateyAbstract:Analysis of barley shrunken grain mutants has identified lines with a novel high amylose Starch phenotype. The causal mutation is located at the sex6 locus on chromosome 7H, suggesting the Starch Synthase IIa (ssIIa) gene as a candidate gene altered by the mutation. Consistent with this hypothesis, no evidence of SSIIa protein expression in either the Starch granule or soluble fractions of the endosperm was found. Sequences of the Starch Synthase IIa gene, ssIIa, from three independent sex6 lines showed the presence of a stop codon preventing translation of the ssIIa transcript in each line. Perfect segregation of the Starch phenotype with the presence of stop codons in the ssIIa gene was obtained, providing strong evidence for the lesion in the ssIIa gene being the causal mutation for the sex6 phenotype. The loss of SSIIa activity in barley leads to novel and informative phenotypes. First, a decrease in amylopectin synthesis to less than 20% of the wild-type levels indicates that SSIIa accounts for the majority of the amylopectin polymer elongation activity in barley. Secondly, in contrast to high amylose Starches resulting from branching enzyme downregulation, the sex6 Starches have a shortened amylopectin chain length distribution and a reduced gelatinisation temperature. Thirdly, the mutation leads to pleiotropic effects on other enzymes of the Starch biosynthesis pathway, abolishing the binding of SSI, branching enzyme IIa and branching enzyme IIb to the Starch granules of sex6 mutants, while not significantly altering their expression levels in the soluble fraction.
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The structure and expression of the wheat Starch Synthase III gene. Motifs in the expressed gene define the lineage of the Starch Synthase III gene family
Plant Physiology, 2000Co-Authors: Greg Mouille, Behjat Kosar-hashemi, Rudi Appels, Sadequr Rahman, Bryan Clarke, Kevin R. Gale, Matthiew K. MorellAbstract:The endosperm of hexaploid wheat (Triticum aestivum [L.]) was shown to contain a high molecular weight Starch Synthase (SS) analogous to the product of the maize du1 gene, Starch Synthase III (SSIII; DU1). cDNA and genomic DNA sequences encoding wheat SSIII were isolated and characterized. The wheat SSIII cDNA is 5,346 bp long and contains an open reading frame that encodes a 1,628-amino acid polypeptide. A putative N-terminal transit peptide, a 436-amino acid C-terminal catalytic domain, and a central 470-amino acid SSIII-specific domain containing three regions of repeated amino acid similarity were identified in the wheat gene. A fourth region between the transit peptide and the SSIII-specific domain contains repeat motifs that are variable with respect to motif sequence and repeat number between wheat and maize. In dicots, this N-terminal region does not contain repeat motifs and is truncated. The gene encoding wheat SSIII, designated ss3, consists of 16 exons extending over 10 kb, and is located on wheat chromosome I. Expression of ss3 mRNA in wheat was detected in leaves, pre-anthesis florets, and from very early to middle stage of endosperm development. The entire N-terminal variable repeat region and the majority of the SSIII-specific domain are encoded on a single 2,703-bp exon. A gene encoding a class III SS from the Arabidopsis genome sequencing project shows a strongly conserved exon structure to the wheat ss3 gene, with the exception of the N-terminal region. The evolutionary relationships of the genes encoding monocot and dicot class III SSs are discussed.
Alison M. Smith - One of the best experts on this subject based on the ideXlab platform.
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Starch Synthase 4 is essential for coordination of Starch granule formation with chloroplast division during arabidopsis leaf expansion
New Phytologist, 2013Co-Authors: Matilda Crumptontaylor, Christopher M Hylton, Regina Feil, John E Lunn, Simona Eicke, Samuel C Zeeman, Marilyn J Pike, Alison M. SmithAbstract:Arabidopsis thaliana mutants lacking the SS4 isoform of Starch Synthase have strongly reduced numbers of Starch granules per chloroplast, suggesting that SS4 is necessary for the normal generation of Starch granules. To establish whether it plays a direct role in this process, we investigated the circumstances in which granules are formed in ss4 mutants. Starch granule numbers and distribution and the accumulation of Starch Synthase substrates and products were investigated during ss4 leaf development, and in ss4 mutants carrying mutations or transgenes that affect Starch turnover or chloroplast volume. We found that immature ss4 leaves have no Starch granules, but accumulate high concentrations of the Starch Synthase substrate ADPglucose. Granule numbers are partially restored by elevating the capacity for glucan synthesis (via expression of bacterial glycogen Synthase) or by increasing the volumes of individual chloroplasts (via introduction of arc mutations). However, these granules are abnormal in distribution, size and shape. SS4 is an essential component of a mechanism that coordinates granule formation with chloroplast division during leaf expansion and determines the abundance and the flattened, discoid shape of leaf Starch granules. Keywords: ADPglucose, Arabidopsis thaliana, chloroplast, leaf expansion, Starch granule, Starch Synthase, Starch synthesis Introduction The process by which Starch granules arise is not known. Suggestions range from largely physico-chemical mechanisms (Doi, 1965; Geddes & Greenwood, 1969; Ziegler et al., 2005) to the existence of specific protein primers analogous to the glycogenins of fungi and animals (e.g. Rothschild & Tandecarz, 1994; Singh et al., 1995; Langeveld et al., 2002; Chatterjee et al., 2005). Recent attention has focussed on the role of one isoform of soluble Starch Synthase, Starch Synthase 4 (SS4, At4 g18240). Although SS4 contributes little to total Starch Synthase activity, ss4 mutants of Arabidopsis have at most one or two Starch granules per chloroplast (Roldan et al., 2007) rather than the normal five or six (Crumpton-Taylor et al., 2012). No other Starch Synthase is individually necessary for normal granule numbers (Roldan et al., 2007), thus SS4 may have a specific function in granule formation. However, other isoforms of Starch Synthase may partially substitute for this function. The additional loss of SS3 further reduces Starch granule numbers in the ss4 mutant background (Szydlowski et al., 2009; Merida & D′Hulst, 2012). The importance of SS4 for Starch granule formation remains to be established. First, it is not known whether SS4 is required primarily for maintenance of Starch granule numbers in mature leaves, or whether it also has a role in immature leaves where new granules arise in concert with chloroplast division (Crumpton-Taylor et al., 2012). Second, it is not clear whether the reduction in Starch granule numbers in ss4 mutants is a direct or an indirect consequence of the loss of SS4. Mutants have several additional phenotypes including reduced growth rates, altered Starch granule anatomy and morphology and a reduction in the extent of diel Starch turnover (Roldan et al., 2007). It remains possible that the reduction in granule numbers in ss4 mutants is an indirect consequence of one of these alterations. Third, a recent study suggests that SS4 may be limiting for Starch synthesis in wild-type plants. Its overexpression reportedly results in higher concentrations of Starch at the end of the day and accelerated plant growth (Gamez-Arjona et al., 2011). These results have important implications for the control of Starch turnover and are of biotechnological interest, but the relationship between Starch concentrations and Starch granule numbers and sizes in plants with elevated SS4 was not reported. The aim of our work was to establish whether SS4 has a direct or an indirect role in Starch granule formation, and to shed further light on where and when its actions are required for the establishment of normal granule numbers. To this end we examined the phenotype of the ss4 mutant through leaf development, and investigated the impact of loss of SS4 in mutant and transgenic backgrounds in which Starch metabolism is altered or chloroplast volumes are abnormally large. Our results indicate that SS4 is directly and specifically required for the establishment of normal numbers and distributions of Starch granules during leaf expansion, and that it is also necessary for the normal flattened, discoid shape of leaf Starch granules.
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Specificity of Starch Synthase isoforms from potato.
European journal of biochemistry, 1999Co-Authors: Anne Edwards, Alison M. Smith, Alip Borthakur, Stephen Bornemann, Julien Venail, Kay Denyer, Darren Waite, Dan Fulton, Cathie MartinAbstract:In higher plants several isoforms of Starch Synthase contribute to the extension of glucan chains in the synthesis of Starch. Different isoforms are responsible for the synthesis of essentially linear amylose chains and branched, amylopectin chains. The activity of granule-bound Starch Synthase I from potato has been compared with that of Starch Synthase II from potato following expression of both isoforms in Escherichia coli. Significant differences in their activities are apparent which may be important in determining their specificities in vivo. These differences include affinities for ADPglucose and glucan substrates, activation by amylopectin, response to citrate, thermosensitivity and the processivity of glucan chain extension. To define regions of the isoforms determining these characteristic traits, chimeric proteins have been produced by expression in E. coli. These experiments reveal that the C-terminal region of granule-bound Starch Synthase I confers most of the specific properties of this isoform, except its processive elongation of glucan chains. This region of granule-bound Starch Synthase I is distinct from the C-terminal region of other Starch Synthases. The specific properties it confers may be important in defining the specificity of granule-bound Starch Synthase I in producing amylose in vivo.
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Interaction with amylopectin influences the ability of granule-bound Starch Synthase I to elongate malto-oligosaccharides
Biochemical Journal, 1999Co-Authors: Kay Denyer, Anne Edwards, Cathie Martin, Darren Waite, Alison M. SmithAbstract:This paper examines the properties in soluble form of two isoforms of Starch Synthase. One of these, granule-bound Starch Synthase I (GBSSI), is responsible for the synthesis of amylose inside the amylopectin matrix of the Starch granule in vivo. The other, Starch Synthase II (SSII), is involved in amylopectin synthesis. Both isoforms can use amylopectin and malto-oligosaccharide as substrates in vitro. As well as acting as a substrate for GBSSI, amylopectin acts as an effector of this isoform, increasing the rate at which it elongates malto-oligosaccharides and promoting a processive rather than distributive mode of elongation of these compounds. The affinity of GBSSI for amylopectin as an effector is greater than its affinity for amylopectin as a substrate. The rate and mode of elongation of malto-oligosaccharides by SSII are not influenced by amylopectin. These results suggest that specific interaction with amylopectin in the matrix of the Starch granule is a unique property of GBSSI and is critical in determining the nature of its products.
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Granule-bound Starch Synthase I in isolated Starch granules elongates malto-oligosaccharides processively.
Biochemical Journal, 1999Co-Authors: Kay Denyer, Darren Waite, Saddik Motawia, Birger Lindberg Møller, Alison M. SmithAbstract:Isoforms of Starch Synthase belonging to the granule-bound Starch Synthase I (GBSSI) class synthesize the amylose component of Starch in plants. Other granule-bound isoforms of Starch Synthase, such as Starch Synthase II (SSII), are unable to synthesize amylose. The kinetic properties of GBSSI and SSII that are responsible for these functional differences have been investigated using Starch granules from embryos of wild-type peas and rug5 and lam mutant peas, which contain, respectively, both GBSSI and SSII, GBSSI but not SSII and SSII but not GBSSI. We show that GBSSI in isolated granules elongates malto-oligosaccharides processively, adding more than one glucose molecule for each enzyme-glucan encounter. Granule-bound SSII can elongate malto-oligosaccharides, but has a lower affinity for these than GBSSI and does not elongate processively. As a result of these properties GBSSI synthesizes longer malto-oligosaccharides than SSII. The significance of these results with respect to the roles of GBSSI and SSII in vivo is discussed.
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mutations in the gene encoding Starch Synthase ii profoundly alter amylopectin structure in pea embryos
The Plant Cell, 1998Co-Authors: Josephine Craig, Anne Edwards, Cathie Martin, Kim Tomlinson, James R Lloyd, Lorraine Barber, T L Wang, C L Hedley, Alison M. SmithAbstract:Mutations at the rug5 (rugosus5) locus have been used to elucidate the role of the major soluble isoform of Starch Synthase II (SSII) in amylopectin synthesis in the developing pea embryo. The SSII gene maps to the rug5 locus, and the gene in one of three rug5 mutant lines has been shown to carry a base pair substitution that introduces a stop codon into the open reading frame. All three mutant alleles cause a dramatic reduction or loss of the SSII protein. The mutations have pleiotropic effects on the activities of other isoforms of Starch Synthase but apparently not on those of other enzymes of Starch synthesis. These mutations result in abnormal Starch granule morphology and amylopectin structure. Amylopectin contains fewer chains of intermediate length (B2 and B3 chains) and more very short and very long chains than does amylopectin from wild-type embryos. The results suggest that SSII may play a specific role in the synthesis of B2 and B3 chains of amylopectin. The extent to which these findings can be extrapolated to other species is discussed.