ORCID Profile
0000-0001-6649-7329
Current Organisations
CSIRO
,
CSIRO Black Mountain Laboratories
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Publisher: Elsevier BV
Date: 2015
DOI: 10.1016/J.CARBPOL.2014.08.091
Abstract: The underlying mechanism of amylolysis of rice starch granules was investigated using isolated starch granules from wild-type, as well as SBEIIb mutant and down-regulated lines. Fused granule agglomerates isolated from mutant and transgenic lines were hydrolysed at similar rates by amylases, and had similar crystalline patterns and thermal properties as in idual granules. Surface pores, a feature previously only reported for A-polymorphic starch granules, were also observed in B- and C-polymorphic rice starch granules. Although the microscopic patterns of hydrolysis among granules with different crystalline polymorphs were qualitatively similar, the extent and the rate of amylolysis were different, suggesting that B-type crystalline polymorphs are intrinsically more resistant to enzymatic hydrolysis than A-type in rice starch granules. It is proposed that the slightly longer branch lengths of amylopectin which leads to the formation of more stable B-type double helical structures compared to their A-type counterparts is the major parameter, with other factors such as granule size, surface pores and interior channels having secondary roles, in determining the rate of enzymatic hydrolysis of rice starch granules.
Publisher: Springer Science and Business Media LLC
Date: 19-04-2015
DOI: 10.1007/S00122-015-2515-Z
Abstract: The distribution of starch synthase I and starch branching enzyme IIb between the starch granule and amyloplast stroma plays an important role in determining endosperm amylose content of cereal grains. Starch synthase IIa (SSIIa) catalyses the polymerisation of intermediate length glucan chains of amylopectin in the endosperm of cereals. Mutations of SSIIa genes in barley and wheat and inactive SSIIa variant in rice induce similar effects on the starch structure and the amylose content, but the severity of the phenotypes is different. This study compared the levels of transcripts and partitioning of proteins of starch synthase I (SSI) and starch branching enzyme IIb (SBEIIb) inside and outside the starch granules in the developing endosperms of these ssIIa mutants and inactive SSIIa variant. Pleiotropic effects on starch granule-bound proteins suggested that the different effects of SSIIa mutations on endosperm amylose content of barley, wheat and rice are determined by the distribution of SSI and SBEIIb between the starch granule and amyloplast stroma in cereals. Regulation of starch synthesis in ssIIa mutants and inactive SSIIa variant may be at post-translational level or the altered amylopectin structure deprives the affinity of SSI and SBEIIb to amylopectin.
Publisher: Elsevier BV
Date: 02-2015
DOI: 10.1016/J.NUTRES.2014.12.006
Abstract: Fermentation of oat and barley β-glucans is believed to mediate in part their metabolic health benefits, but the exact mechanisms remain unclear. In this study, we sought to test the hypothesis that barley β-glucan fermentation raises circulating incretin hormone levels and improves glucose control, independent of other grain components. Male Sprague-Dawley rats (n = 30) were fed a high-fat diet for 6 weeks and then randomly allocated to 1 of 3 dietary treatments for 2 weeks. The low- (LBG, 0% β-glucan) and high- (HBG, 3% β-glucan) β-glucan diets contained 25% wholegrain barley and similar levels of insoluble dietary fiber, available carbohydrate, and energy. A low-fiber diet (basal) was included for comparison. Immediately prior to the dietary intervention, gastric emptying rate (using the (13)C-octanoic breath test) and postprandial glycemic response of each diet were determined. At the end of the study, circulating gut hormone levels were determined and a glucose tolerance test was performed. The rats were then killed, and indices of cecal fermentation were assessed. Diet did not affect live weight however, the HBG diet, compared to basal and LBG, reduced food intake, tended to slow gastric emptying, increased cecal digesta mass and in idual and total short-chain fatty acid pools, and lowered digesta pH. In contrast, circulating levels of glucose, insulin, gastric-inhibitory peptide, and glucagon-like peptide-1, and glucose tolerance were unaffected by diet. In conclusion, wholegrain barley β-glucan suppressed feed intake and increased cecal fermentation but did not improve postprandial glucose control or insulin sensitivity.
Publisher: Wiley
Date: 03-02-2015
DOI: 10.1111/PBI.12345
Abstract: Resistant starch (RS), a type of dietary fibre, plays an important role in human health however, the content of RS in most modern processed starchy foods is low. Cereal starch, when structurally manipulated through a modified starch biosynthetic pathway to greatly increase the amylose content, could be an important food source of RS. Transgenic studies have previously revealed the requirement of simultaneous down-regulation of two starch branching enzyme (SBE) II isoforms both located on the long arm of chromosome 2, namely SBEIIa and SBEIIb, to elevate the amylose content in wheat from ~25% to ~75%. The current study revealed close proximity of genes encoding SBEIIa and SBEIIb isoforms in wheat with a genetic distance of 0.5 cM on chromosome 2B. A series of deletion and single nucleotide polymorphism (SNP) loss of function alleles in SBEIIa, SBEIIb or both was isolated from two different wheat populations. A breeding strategy to combine deletions and SNPs generated wheat genotypes with altered expression levels of SBEIIa and SBEIIb, elevating the amylose content to an unprecedented ~85%, with a marked concomitant increase in RS content. Biochemical assays were used to confirm the complete absence in the grain of expression of SBEIIa from all three genomes in combination with the absence of SBEIIb from one of the genomes.
Publisher: Springer Science and Business Media LLC
Date: 16-12-2002
DOI: 10.1038/NBT772
Publisher: Oxford University Press (OUP)
Date: 02-03-2012
Abstract: Mixed-linkage glucan (MLG) is a cell wall polysaccharide containing a backbone of unbranched (1,3)- and (1,4)-linked β-glucosyl residues. Based on its occurrence in plants and chemical characteristics, MLG has primarily been associated with the regulation of cell wall expansion due to its high and transient accumulation in young, expanding tissues. The Cellulose synthase-like F (CslF) subfamily of glycosyltransferases has previously been implicated in mediating the biosynthesis of this polymer. We confirmed that the rice (Oryza sativa) CslF6 gene mediates the biosynthesis of MLG by overexpressing it in Nicotiana benthamiana. Rice cslf6 knockout mutants show a slight decrease in height and stem diameter but otherwise grew normally during vegetative development. However, cslf6 mutants display a drastic decrease in MLG content (97% reduction in coleoptiles and virtually undetectable in other tissues). Immunodetection with an anti-MLG monoclonal antibody revealed that the coleoptiles and leaves retain trace amounts of MLG only in specific cell types such as sclerenchyma fibers. These results correlate with the absence of endogenous MLG synthase activity in mutant seedlings and 4-week-old sheaths. Mutant cell walls are weaker in mature stems but not seedlings, and more brittle in both stems and seedlings, compared to wild type. Mutants also display lesion mimic phenotypes in leaves, which correlates with enhanced defense-related gene expression and enhanced disease resistance. Taken together, our results underline a weaker role of MLG in cell expansion than previously thought, and highlight a structural role for MLG in nonexpanding, mature stem tissues in rice.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 05-06-2015
Abstract: The architecture of the pore membrane can control translocation of a growing polysaccharide across the membrane and alter the final polymer structure.
Publisher: Elsevier BV
Date: 2022
Publisher: Oxford University Press (OUP)
Date: 03-08-2011
DOI: 10.1093/JXB/ERR239
Publisher: Elsevier BV
Date: 04-2004
Publisher: Oxford University Press (OUP)
Date: 29-02-2012
DOI: 10.1093/JXB/ERS019
Publisher: Frontiers Media SA
Date: 02-04-2020
Publisher: Springer Science and Business Media LLC
Date: 10-07-2020
DOI: 10.1007/S00122-020-03649-2
Abstract: Catalytically active indica SSIIa allele in high amylose rice with down-regulated japonica SBEIIb can increase starch content and modify the starch structure and properties without changing its amylose content. Rice (Oryza sativa) genotypes with inactive starch synthase IIa (SSIIa) with recessive variants of starch branching enzyme IIb (SBEIIb) exhibit a range of alterations in grain phenotype, starch granule morphology, starch granule bound proteins, starch structure, and functional properties. However, the interactions between the two enzymes have not been thoroughly investigated yet. We analysed recombinant rice lines having down-regulated SBEIIb expression (SBEIIb
Publisher: Elsevier BV
Date: 2017
Publisher: Wiley
Date: 09-10-2015
DOI: 10.1002/HEC.3272
Abstract: This study uses data from the 2004-2006 Australian National Survey of Adult Oral Health and a simultaneous equation framework to investigate the interrelationships between dental health, private dental insurance and the use of dental services. The results show that insurance participation is influenced by social and demographic factors, health and health behaviours. In turn, these factors affect the use of dental services, both directly and through insurance participation. Our findings confirm that affordability is a major barrier to visiting the dentist for oral health maintenance and treatment. Our results suggest that having supplementary insurance is associated with some 56 percentage points higher probability of seeing the dentist in the general population. For those who did not have private insurance cover, we predict that conditional on them facing the same insurance conditions, on average, having insurance would increase their visits to the dentist by 43 percentage points. The uninsured in the survey have lower income, worse oral health and lower rates of preventive and treatment visits. Copyright © 2015 John Wiley & Sons, Ltd.
Publisher: Oxford University Press (OUP)
Date: 21-09-2011
DOI: 10.1093/JXB/ERR285
Publisher: Wiley
Date: 2015
Publisher: Oxford University Press (OUP)
Date: 25-07-2011
DOI: 10.1093/JXB/ERR188
Publisher: American Chemical Society (ACS)
Date: 08-11-2012
DOI: 10.1021/JF303205P
Abstract: Elevated proportions of amylose in cereals are commonly associated with either the loss of starch branching or starch synthase activity. Goami 2 is a high-amylose mutant of the temperate japonica rice variety Ilpumbyeo. Genotyping revealed that Goami 2 and Ilpumbyeo carry the same alleles for starch synthase IIa and granule-bound starch synthase I genes. Analyses of granule-bound proteins revealed that SSI and SSIIa accumulate inside the mature starch granules of Goami 2, which is similar to the amylose extender mutant IR36ae. However, unlike the amylose extender mutants, SBEIIb was still detectable inside the starch granules of Goami 2. Detection of SBEIIb after protein fractionation revealed that most of the SBEIIb in Goami 2 accumulates inside the starch granules, whereas most of it accumulates at the granule surface in Ilpumbyeo. Exhaustive mass spectrometric characterisations of granule-bound proteins failed to detect any peptide sequence mutation or major post-translational modifications in Goami 2. Moreover, the signal peptide was found to be cleaved normally from the precursor protein, and there is no apparent N-linked glycosylation. Finally, no difference was found in the SBEIIb structural gene sequence of Goami 2 compared with Ilpumbyeo. In contrast, a G-to-A mutation was detected in the SBEIIb gene of IR36ae located at the splice site between exon and intron 11, which could potentially introduce a premature stop codon and produce a truncated form of SBEIIb. It is suggested that the mutation responsible for producing high amylose in Goami 2 is not due to a defect in SBEIIb gene as was observed in IR36ae, even though it produces a phenotype analogous to the amylose extender mutation. Understanding the molecular genetic basis of this mutation will be important in identifying novel targets for increasing amylose and resistant starch contents in rice and other cereals.
Publisher: Oxford University Press (OUP)
Date: 14-03-2014
DOI: 10.1093/JXB/ERU095
Publisher: Oxford University Press (OUP)
Date: 12-07-2012
DOI: 10.1093/JXB/ERS182
Publisher: Springer Science and Business Media LLC
Date: 04-03-2015
DOI: 10.1186/S12284-015-0046-5
Abstract: The genetic ersity of six starch biosynthetic genes ( Wx , SSI , SSIIa , SBEI , SBEIIa and SBEIIb ) in indica and japonica rices opens an opportunity to produce a new variety with more favourable grain starch quality. However, there is limited information about the effects of these six gene allele combinations on starch structure and properties. A recombinant inbred line population from a cross between indica and japonica varieties offers opportunities to combine specific alleles of the six genes. The allelic ( indica vs japonica ) effects of six starch biosynthetic genes on starch structure, functional properties, and abundance of granule bound proteins in rice grains were investigated in a common genetic background using a recombinant inbred line population. The indica Wx ( Wxi ) allele played a major role while indica SSI ( SSIi ), japonica SSIIa ( SSIIaj ) and indica SBEI ( SBEIi ) alleles had minor roles on the increase of amylose content. SSIIaj and japonica SBEIIb ( SBEIIbj ) alleles had a major and a minor role on high ratio of ∑DP ≤ 10 to ∑DP ≤ 24 fractions (R CL10/24 ), respectively. Both major alleles ( Wxi and SSIIaj ) reduced peak viscosity (PV), onset, peak and end gelatinization temperatures (GTs) of amylopectin, and increased amylose-lipid complex dissociation enthalpy compared with their counterpart-alleles, respectively. SBEIIai and SBEIIbj decreased PV, whereas SSIi and SBEIIbj decreased FV. SBEIi reduced setback viscosity and gelatinization enthalpy. R CL10/24 of chain length distribution in amylopectin is negatively correlated with PV and BD of paste property and GTs of thermal properties. We also report RILs with superior starch properties combining Wxi , SSIj , SSIIaj , SBEIi and SBEIIbj alleles. Additionally, a clear relation is drawn to starch biosynthetic gene alleles, starch structure, properties, and abundance of granule bound starch biosynthetic enzymes inside starch granules. Rice Wxi and SSIIaj alleles play major roles, while SSIi , SBEIi , SBEIIai and SBEIIbj alleles have minor roles in the determination of starch properties between indica and japonica rice through starch structural modification. The combination of these alleles is a key factor for starch quality improvement in rice breeding programs. R CL10/24 value is critical for starch structure and property determination.
Location: Australia
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Steve Jobling.