28 results on '"Zeeman, Samuel C."'
Search Results
2. Starch-Excess4 is a laforin-like phosphoglucan phosphatase required for starch degradation in Arabidopsis thaliana
- Author
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Kotting, Oliver, Santelia, Diana, Edner, Christoph, Eicke, Simona, Marthaler, Tina, Gentry, Matthew S., Comparot-Moss, Sylviane, Chen, Jychian, Smith, Alison M., Steup, Martin, Ritte, Gerhard, and Zeeman, Samuel C.
- Subjects
Arabidopsis thaliana -- Physiological aspects ,Arabidopsis thaliana -- Research ,Carbohydrate metabolism -- Research ,Starch -- Physiological aspects ,Starch -- Research ,Biological sciences ,Science and technology - Published
- 2009
3. Starch granule biosynthesis in arabidopsis is abolished by removal of all debranching enzymes but restored by the subsequent removal of an endoamylase
- Author
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Streb, Sebastian, Delatte, Thierry, Umhang, Martin, Eicke, Simona, Schorderet, Martine, Reinhardt, Didier, and Zeeman, Samuel C.
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Amylases -- Physiological aspects ,Sugars -- Physiological aspects ,Arabidopsis thaliana -- Physiological aspects ,Biological sciences ,Science and technology - Published
- 2008
4. [beta]-amylase4, a noncatalytic protein required for starch breakdown, acts upstream of three active [beta]-amylases in Arabidopsis chloroplasts
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Fulton, Daniel C., Stettler, Michaela, Mettler, Tabea, Vaughan, Cara K., Li, Jing, Francisco, Perigio, Gil, (d) Manuel, Reinhold, Heike, Eicke, Simona, Messerli, Gaelle, Dorken, Gary, Halliday, Karen, Smith, Alison M., Smith, Steven M., and Zeeman, Samuel C.
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Amylases ,Arabidopsis thaliana ,Recombinant proteins ,Amino acids ,Biological sciences ,Science and technology - Published
- 2008
5. Rapid classification of phenotypic mutants of arabidopsis via metabolite fingerprinting (1)([W])([OA])
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Messerli, Gaelle, Nia, Vahid Partovi, Trevisan, Martine, Kolbe, Anna, Schauer, Nicolas, Geigenberger, Peter, Chen, Jychian, Davison, Anthony C., Fernie, Alisdair R., and Zeeman, Samuel C.
- Subjects
Gene mutations -- Research ,Arabidopsis -- Genetic aspects ,Arabidopsis -- Research ,Metabolites -- Research ,DNA testing -- Usage ,Biological sciences ,Science and technology - Published
- 2007
6. Diurnal changes in the transcriptome encoding enzymes of starch metabolism provide evidence for both transcriptional and posttranscriptional regulation of starch metabolism in Arabidopsis leaves (1)
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Smith, Steven M., Fulton, Daniel C., Chia,Tansy, Thorneycroft, David, Chapple, Andrew, Dunstan, Hannah, Hylton, Christopher, Zeeman, Samuel C., and Smith, Alison M.
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Starch -- Research ,Arabidopsis -- Genetic aspects ,Arabidopsis -- Physiological aspects ,Genetic regulation -- Research ,Biological sciences ,Science and technology - Published
- 2004
7. Plastidial [alpha]-glucan phosphorylase is not required for starch degradation in Arabidopsis leaves but has a role in the tolerance of abiotic stress (1)
- Author
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Zeeman, Samuel C., Thorneycroft, David, Schupp, Nicole, Chapple, Andrew, Weck, Melanie, Dunstan, Hannah, Haldimann, Pierre, Bechtold, Nicole, Smith, Alison M., and Smith, Steven M.
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Arabidopsis -- Physiological aspects ,Phosphorylase -- Chemical properties ,Biological sciences ,Science and technology - Published
- 2004
8. Starch synthesis in Arabidopsis. Granule synthesis, composition, and structure (1)
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Zeeman, Samuel C., Tiessen, Axel, Pilling, Emma, Kato, K. Lisa, Donald, Athene M., and Smith, Alison M.
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Starch -- Chemical properties ,Arabidopsis -- Physiological aspects ,Enzymes -- Chemical properties ,Biological sciences ,Science and technology - Published
- 2002
9. The priming of amylose synthesis in arabidopsis leaves (1)
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Zeeman, Samuel C., Smith, Steven M., and Smith, Alison M.
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Arabidopsis -- Physiological aspects ,Arabidopsis -- Research ,Leaves -- Research ,Biological sciences ,Science and technology - Published
- 2002
10. The Arabidopsis sex1 mutant is defective in the R1 protein, a general regulator of starch degradation in plants, and not in the chloroplast hexose transporter
- Author
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Yu, Tien-Shin, Kofler, Heike, Hausler, Rainer E., Hille, Diana, Flugge, Ulf-Ingo, Zeeman, Samuel C., Smith, Alison M., Kossmann, Jens, Lloyd, James, Ritte, Gerhard, Steup, Martin, Lue, Wei-Ling, Chen, Jychian, and Weber, Andreas
- Subjects
Arabidopsis -- Genetic aspects ,Photosynthesis -- Research ,Chloroplasts -- Research ,Biological sciences ,Science and technology - Published
- 2001
11. Distinct Functions of STARCH SYNTHASE 4 Domains in Starch Granule Formation1[OPEN]
- Author
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Lu, Kuan-Jen, Pfister, Barbara, Jenny, Camilla, Eicke, Simona, and Zeeman, Samuel C.
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Chloroplasts ,Arabidopsis Proteins ,Arabidopsis ,food and beverages ,Plant Development ,Germination ,Starch ,Cytoplasmic Granules ,Plants, Genetically Modified ,Plant Leaves ,Glycogen Synthase ,Phenotype ,Starch Synthase ,Biochemistry and Metabolism ,Protein Domains ,Agrobacterium tumefaciens - Abstract
In Arabidopsis leaves, the catalytic C-terminal region of STARCH SYNTHASE 4 promotes starch granule initiation while its noncatalytic N-terminal region determines starch granules morphology.
- Published
- 2017
12. Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day1[OPEN]
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Fernandez, Olivier, Ishihara, Hirofumi, George, Gavin M., Mengin, Virginie, Flis, Anna, Sumner, Dean, Arrivault, Stéphanie, Feil, Regina, Lunn, John E., Zeeman, Samuel C., Smith, Alison M., and Stitt, Mark
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Sucrose ,Light ,Photoperiod ,fungi ,Arabidopsis ,Starch ,Articles ,Carbon Dioxide ,Plant Leaves ,Circadian Clocks ,parasitic diseases ,Mutation ,sense organs ,Photosynthesis ,Maltose - Abstract
Starch in Arabidopsis leaves is increasingly liable to degradation with time after dawn, so that accumulation slows and turnover in response to falling light accelerates as the day proceeds.
- Published
- 2017
13. Starch Metabolism in Arabidopsis
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Streb, Sebastian and Zeeman, Samuel C.
- Published
- 2012
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14. LIKE EARLY STARVATION 1 interacts with amylopectin during starch biosynthesis.
- Author
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Osman R, Bossu M, Dauvillée D, Spriet C, Liu C, Zeeman SC, D'Hulst C, and Bompard C
- Subjects
- Protein Binding, Amylose metabolism, Amylopectin metabolism, Arabidopsis metabolism, Arabidopsis genetics, Starch metabolism, Starch biosynthesis, Arabidopsis Proteins metabolism, Arabidopsis Proteins genetics
- Abstract
Starch is the major energy storage compound in plants. Both transient starch and long-lasting storage starch accumulate in the form of insoluble, partly crystalline granules. The structure of these granules is related to the structure of the branched polymer amylopectin: linear chains of glucose units organized in double helices that align to form semicrystalline lamellae, with branching points located in amorphous regions between them. EARLY STARVATION 1 (ESV1) and LIKE EARLY STARVATION 1 (LESV) proteins are involved in the maintenance of starch granule structure and in the phase transition of amylopectin, respectively, in Arabidopsis (Arabidopsis thaliana). These proteins contain a conserved tryptophan-rich C-terminal domain folded into an antiparallel β-sheet, likely responsible for binding of the proteins to starch, and different N-terminal domains whose structure and function are unknown. In this work, we combined biochemical and biophysical approaches to analyze the structures of LESV and ESV1 and their interactions with the different starch polyglucans. We determined that both proteins interact with amylopectin but not with amylose and that only LESV is capable of interacting with amylopectin during starch biosynthesis. While the C-terminal domain interacts with amylopectin in its semicrystalline form, the N-terminal domain of LESV undergoes induced conformational changes that are probably involved in its specific function of mediating glucan phase transition. These results clarify the specific mechanism of action of these 2 proteins in the biosynthesis of starch granules., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of American Society of Plant Biologists. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)
- Published
- 2024
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15. Soluble and insoluble α-glucan synthesis in yeast by enzyme suites derived exclusively from maize endosperm.
- Author
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Boehlein SK, Pfister B, Hennen-Bierwagen TA, Liu C, Ritter M, Hannah LC, Zeeman SC, Resende MFR, and Myers AM
- Subjects
- Saccharomyces cerevisiae, Zea mays genetics, Plant Proteins chemistry, Starch, Glucans, Endosperm, Starch Synthase chemistry
- Abstract
Molecular mechanisms that distinguish the synthesis of semi-crystalline α-glucan polymers found in plant starch granules from the synthesis of water-soluble polymers by nonplant species are not well understood. To address this, starch biosynthetic enzymes from maize (Zea mays L.) endosperm were isolated in a reconstituted environment using yeast (Saccharomyces cerevisiae) as a test bed. Ninety strains were constructed containing unique combinations of 11 synthetic transcription units specifying maize starch synthase (SS), starch phosphorylase (PHO), starch branching enzyme (SBE), or isoamylase-type starch debranching enzyme (ISA). Soluble and insoluble branched α-glucans accumulated in varying proportions depending on the enzyme suite, with ISA function stimulating distribution into the insoluble form. Among the SS isoforms, SSIIa, SSIII, and SSIV individually supported the accumulation of glucan polymer. Neither SSI nor SSV alone produced polymers; however, synergistic effects demonstrated that both isoforms can stimulate α-glucan accumulation. PHO did not support α-glucan production by itself, but it had either positive or negative effects on polymer content depending on which SS or a combination thereof was present. The complete suite of maize enzymes generated insoluble particles resembling native starch granules in size, shape, and crystallinity. Ultrastructural analysis revealed a hierarchical assembly starting with subparticles of approximately 50 nm diameter that coalesce into discrete structures of approximately 200 nm diameter. These are assembled into semi-crystalline α-glucan superstructures up to 4 μm in length filling most of the yeast cytosol. ISA was not essential for the formation of such particles, but their abundance was increased dramatically by ISA presence., Competing Interests: Conflict of interest statement. None declared., (© The Author(s) 2023. Published by Oxford University Press on behalf of American Society of Plant Biologists.)
- Published
- 2023
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16. Abscisic acid modulates neighbor proximity-induced leaf hyponasty in Arabidopsis.
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Michaud O, Krahmer J, Galbier F, Lagier M, Galvão VC, Ince YÇ, Trevisan M, Knerova J, Dickinson P, Hibberd JM, Zeeman SC, and Fankhauser C
- Subjects
- Abscisic Acid pharmacology, Abscisic Acid metabolism, Transcription Factors genetics, Transcription Factors metabolism, Plant Leaves genetics, Plant Leaves metabolism, Gene Expression Regulation, Plant, Arabidopsis metabolism, Arabidopsis Proteins genetics, Arabidopsis Proteins metabolism, Phytochrome metabolism
- Abstract
Leaves of shade-avoiding plants such as Arabidopsis (Arabidopsis thaliana) change their growth pattern and position in response to low red to far-red ratios (LRFRs) encountered in dense plant communities. Under LRFR, transcription factors of the phytochrome-interacting factor (PIF) family are derepressed. PIFs induce auxin production, which is required for promoting leaf hyponasty, thereby favoring access to unfiltered sunlight. Abscisic acid (ABA) has also been implicated in the control of leaf hyponasty, with gene expression patterns suggesting that LRFR regulates the ABA response. Here, we show that LRFR leads to a rapid increase in ABA levels in leaves. Changes in ABA levels depend on PIFs, which regulate the expression of genes encoding isoforms of the enzyme catalyzing a rate-limiting step in ABA biosynthesis. Interestingly, ABA biosynthesis and signaling mutants have more erect leaves than wild-type Arabidopsis under white light but respond less to LRFR. Consistent with this, ABA application decreases leaf angle under white light; however, this response is inhibited under LRFR. Tissue-specific interference with ABA signaling indicates that an ABA response is required in different cell types for LRFR-induced hyponasty. Collectively, our data indicate that LRFR triggers rapid PIF-mediated ABA production. ABA plays a different role in controlling hyponasty under white light than under LRFR. Moreover, ABA exerts its activity in multiple cell types to control leaf position., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society of Plant Biologists.)
- Published
- 2023
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17. Rising rates of starch degradation during daytime and trehalose 6-phosphate optimize carbon availability.
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Ishihara H, Alseekh S, Feil R, Perera P, George GM, Niedźwiecki P, Arrivault S, Zeeman SC, Fernie AR, Lunn JE, Smith AM, and Stitt M
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- Carbon metabolism, Phosphates metabolism, Photosynthesis physiology, Starch metabolism, Trehalose metabolism, Arabidopsis metabolism, Arabidopsis Proteins genetics, Arabidopsis Proteins metabolism
- Abstract
Many plants, including Arabidopsis (Arabidopsis thaliana), accumulate starch in the light and remobilize it to support maintenance and growth at night. Starch synthesis and degradation are usually viewed as temporally separate processes. Recently, we reported that starch is also degraded in the light. Degradation rates are generally low early in the day but rise with time. Here, we show that the rate of degradation in the light depends on time relative to dawn rather than dusk. We also show that degradation in the light is inhibited by trehalose 6-phosphate, a signal for sucrose availability. The observed responses of degradation in the light can be simulated by a skeletal model in which the rate of degradation is a function of starch content divided by time remaining until dawn. The fit is improved by extension to include feedback inhibition of starch degradation by trehalose 6-phosphate. We also investigate possible functions of simultaneous starch synthesis and degradation in the light, using empirically parameterized models and experimental approaches. The idea that this cycle buffers growth against falling rates of photosynthesis at twilight is supported by data showing that rates of protein and cell wall synthesis remain high during a simulated dusk twilight. Degradation of starch in the light may also counter over-accumulation of starch in long photoperiods and stabilize signaling around dusk. We conclude that starch degradation in the light is regulated by mechanisms similar to those that operate at night and is important for stabilizing carbon availability and signaling, thus optimizing growth in natural light conditions., (© The Author(s) 2022. Published by Oxford University Press on behalf of American Society of Plant Biologists.)
- Published
- 2022
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18. BETA-AMYLASE9 is a plastidial nonenzymatic regulator of leaf starch degradation.
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David LC, Lee SK, Bruderer E, Abt MR, Fischer-Stettler M, Tschopp MA, Solhaug EM, Sanchez K, and Zeeman SC
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- Gene Expression Regulation, Plant, Genes, Plant, Plant Growth Regulators genetics, Plant Leaves genetics, Plastids genetics, Starch genetics, beta-Amylase genetics, Arabidopsis genetics, Arabidopsis metabolism, Plant Growth Regulators metabolism, Plant Leaves metabolism, Plastids metabolism, Starch metabolism, beta-Amylase metabolism
- Abstract
β-Amylases (BAMs) are key enzymes of transitory starch degradation in chloroplasts, a process that buffers the availability of photosynthetically fixed carbon over the diel cycle to maintain energy levels and plant growth at night. However, during vascular plant evolution, the BAM gene family diversified, giving rise to isoforms with different compartmentation and biological activities. Here, we characterized BETA-AMYLASE 9 (BAM9) of Arabidopsis (Arabidopsis thaliana). Among the BAMs, BAM9 is most closely related to BAM4 but is more widely conserved in plants. BAM9 and BAM4 share features including their plastidial localization and lack of measurable α-1,4-glucan hydrolyzing capacity. BAM4 is a regulator of starch degradation, and bam4 mutants display a starch-excess phenotype. Although bam9 single mutants resemble the wild-type (WT), genetic experiments reveal that the loss of BAM9 markedly enhances the starch-excess phenotypes of mutants already impaired in starch degradation. Thus, BAM9 also regulates starch breakdown, but in a different way. Interestingly, BAM9 gene expression is responsive to several environmental changes, while that of BAM4 is not. Furthermore, overexpression of BAM9 in the WT reduced leaf starch content, but overexpression in bam4 failed to complement fully that mutant's starch-excess phenotype, suggesting that BAM9 and BAM4 are not redundant. We propose that BAM9 activates starch degradation, helping to manage carbohydrate availability in response to fluctuations in environmental conditions. As such, BAM9 represents an interesting gene target to explore in crop species., (© The Author(s) 2021. Published by Oxford University Press on behalf of American Society of Plant Biologists.)
- Published
- 2022
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19. Ectopic maltase alleviates dwarf phenotype and improves plant frost tolerance of maltose transporter mutants.
- Author
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Cvetkovic J, Haferkamp I, Rode R, Keller I, Pommerrenig B, Trentmann O, Altensell J, Fischer-Stettler M, Eicke S, Zeeman SC, and Neuhaus HE
- Subjects
- Arabidopsis genetics, Arabidopsis Proteins metabolism, Membrane Transport Proteins metabolism, Arabidopsis physiology, Arabidopsis Proteins genetics, Cold Temperature, Membrane Transport Proteins genetics, Phenotype
- Abstract
Maltose, the major product of starch breakdown in Arabidopsis (Arabidopsis thaliana) leaves, exits the chloroplast via the maltose exporter1 MEX1. Consequently, mex1 loss-of-function plants exhibit substantial maltose accumulation, a starch-excess phenotype and a specific chlorotic phenotype during leaf development. Here, we investigated whether the introduction of an alternative metabolic route could suppress the marked developmental defects typical for mex1 loss-of-function mutants. To this end, we ectopically expressed in mex1 chloroplasts a functional maltase (MAL) from baker's yeast (Saccharomyces cerevisiae, chloroplastidial MAL [cpMAL] mutants). Remarkably, the stromal MAL activity substantially alleviates most phenotypic peculiarities typical for mex1 plants. However, the cpMAL lines contained only slightly less maltose than parental mex1 plants and their starch levels were, surprisingly, even higher. These findings point to a threshold level of maltose responsible for the marked developmental defects in mex1. While growth and flowering time were only slightly retarded, cpMAL lines exhibited a substantially improved frost tolerance, when compared to wild-types. In summary, these results demonstrate the possibility to bypass the MEX1 transporter, allow us to differentiate between possible starch-excess and maltose-excess responses, and demonstrate that stromal maltose accumulation prevents frost defects. The latter insight may be instrumental for the development of crop plants with improved frost tolerance., (© American Society of Plant Biologists 2021. All rights reserved. For permissions, please email: journals.permissions@oup.com.)
- Published
- 2021
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20. Distinct Functions of STARCH SYNTHASE 4 Domains in Starch Granule Formation.
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Lu KJ, Pfister B, Jenny C, Eicke S, and Zeeman SC
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- Agrobacterium tumefaciens metabolism, Arabidopsis genetics, Arabidopsis ultrastructure, Arabidopsis Proteins chemistry, Chloroplasts metabolism, Chloroplasts ultrastructure, Cytoplasmic Granules ultrastructure, Germination, Glycogen Synthase metabolism, Phenotype, Plant Development, Plant Leaves metabolism, Plant Leaves ultrastructure, Plants, Genetically Modified, Protein Domains, Starch Synthase chemistry, Arabidopsis enzymology, Arabidopsis Proteins metabolism, Cytoplasmic Granules metabolism, Starch metabolism, Starch Synthase metabolism
- Abstract
The formation of normal starch granules in Arabidopsis ( Arabidopsis thaliana ) leaf chloroplasts requires STARCH SYNTHASE 4 (SS4). In plants lacking SS4, chloroplasts typically produce only one round granule rather than multiple lenticular granules. The mechanisms by which SS4 determines granule number and morphology are not understood. The N-terminal region of SS4 is unique among SS isoforms and contains several long coiled-coil motifs, typically implicated in protein-protein interactions. The C-terminal region contains the catalytic glucosyltransferase domains, which are widely conserved in plant SS and bacterial glycogen synthase (GS) isoforms. We investigated the specific roles of the N- and C-terminal regions of SS4 by expressing truncated versions of SS4 and a fusion between the N-terminal region of SS4 and GS in the Arabidopsis ss4 mutant. Expression of the N-terminal region of SS4 alone did not alter the ss4 mutant phenotype. Expression of the C-terminal region of SS4 alone increased granule initiation but did not rescue their aberrant round morphology. Expression of a self-priming GS from Agrobacterium tumefaciens also increased the number of round granules. Remarkably, fusion of the N-terminal region of SS4 to A. tumefaciens GS restored the development of wild-type-like lenticular starch granules. Interestingly, the N-terminal region of SS4 alone or when fused to GS conferred a patchy subchloroplastic localization similar to that of the full-length SS4 protein. Considered together, these data suggest that, while the glucosyltransferase activity of SS4 is important for granule initiation, the N-terminal part of SS4 serves to establish the correct granule morphology by properly localizing this activity., (© 2018 American Society of Plant Biologists. All Rights Reserved.)
- Published
- 2018
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21. Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day.
- Author
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Fernandez O, Ishihara H, George GM, Mengin V, Flis A, Sumner D, Arrivault S, Feil R, Lunn JE, Zeeman SC, Smith AM, and Stitt M
- Subjects
- Carbon Dioxide metabolism, Circadian Clocks radiation effects, Maltose metabolism, Mutation genetics, Photosynthesis radiation effects, Sucrose metabolism, Arabidopsis metabolism, Arabidopsis radiation effects, Light, Photoperiod, Plant Leaves metabolism, Plant Leaves radiation effects, Starch metabolism
- Abstract
We investigated whether starch degradation occurs at the same time as starch synthesis in Arabidopsis ( Arabidopsis thaliana ) leaves in the light. Starch accumulated in a linear fashion for about 12 h after dawn, then accumulation slowed and content plateaued. Following decreases in light intensity, the rate of accumulation of starch declined in proportion to the decline in photosynthesis if the decrease occurred <10 h after dawn, but accumulation ceased or loss of starch occurred if the same decrease in light intensity was imposed more than 10 h after dawn. These changes in starch accumulation patterns after prolonged periods in the light occurred at both high and low starch contents and were not related to time-dependent changes in either the rate of photosynthesis or the partitioning of assimilate between starch and Suc, as assessed from metabolite measurements and
14 CO2 pulse experiments. Instead, measurements of incorporation of13 C from13 CO2 into starch and of levels of the starch degradation product maltose showed that substantial starch degradation occurred simultaneously with synthesis at time points >14 h after dawn and in response to decreases in light intensity that occurred >10 h after dawn. Starch measurements in circadian clock mutants suggested that the clock influences the timing of onset of degradation. We conclude that the propensity for leaf starch to be degraded increases with time after dawn. The importance of this phenomenon for efficient use of carbon for growth in long days and for prevention of starvation during twilight is discussed., (© 2017 American Society of Plant Biologists. All Rights Reserved.)- Published
- 2017
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22. Molecular Genetic Analysis of Glucan Branching Enzymes from Plants and Bacteria in Arabidopsis Reveals Marked Differences in Their Functions and Capacity to Mediate Starch Granule Formation.
- Author
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Lu KJ, Streb S, Meier F, Pfister B, and Zeeman SC
- Subjects
- Escherichia coli genetics, Escherichia coli Proteins genetics, Escherichia coli Proteins metabolism, Gene Expression Regulation, Plant, Glucans chemistry, Plants, Genetically Modified, Solanum tuberosum genetics, Species Specificity, Starch chemistry, Zea mays genetics, Arabidopsis, Escherichia coli enzymology, Glucans biosynthesis, Solanum tuberosum enzymology, Starch biosynthesis, Zea mays enzymology
- Abstract
The major component of starch is the branched glucan amylopectin, the branching pattern of which is one of the key factors determining its ability to form semicrystalline starch granules. Here, we investigated the functions of different branching enzyme (BE) types by expressing proteins from maize (Zea mays BE2a), potato (Solanum tuberosum BE1), and Escherichia coli (glycogen BE [EcGLGB]) in Arabidopsis (Arabidopsis thaliana) mutant plants that are deficient in their endogenous BEs and therefore, cannot make starch. The expression of each of these three BE types restored starch biosynthesis to differing degrees. Full complementation was achieved using the class II BE ZmBE2a, which is most similar to the two endogenous Arabidopsis isoforms. Expression of the class I BE from potato, StBE1, resulted in partial complementation and high amylose starch. Expression of the glycogen BE EcGLGB restored only minimal amounts of starch production, which had unusual chain length distribution, branch point distribution, and granule morphology. Nevertheless, each type of BE together with the starch synthases and debranching enyzmes were able to create crystallization-competent amylopectin polymers. These data add to the knowledge of how the properties of the BE influence the final composition of starch and fine structure of amylopectin., (© 2015 American Society of Plant Biologists. All Rights Reserved.)
- Published
- 2015
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23. Genetic Evidence That Chain Length and Branch Point Distributions Are Linked Determinants of Starch Granule Formation in Arabidopsis.
- Author
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Pfister B, Lu KJ, Eicke S, Feil R, Lunn JE, Streb S, and Zeeman SC
- Abstract
The major component of starch is the branched glucan amylopectin. Structural features of amylopectin, such as the branching pattern and the chain length distribution, are thought to be key factors that enable it to form semicrystalline starch granules. We varied both structural parameters by creating Arabidopsis (Arabidopsis thaliana) mutants lacking combinations of starch synthases (SSs) SS1, SS2, and SS3 (to vary chain lengths) and the debranching enzyme ISOAMYLASE1-ISOAMYLASE2 (ISA; to alter branching pattern). The isa mutant accumulates primarily phytoglycogen in leaf mesophyll cells, with only small amounts of starch in other cell types (epidermis and bundle sheath cells). This balance can be significantly shifted by mutating different SSs. Mutation of SS1 promoted starch synthesis, restoring granules in mesophyll cell plastids. Mutation of SS2 decreased starch synthesis, abolishing granules in epidermal and bundle sheath cells. Thus, the types of SSs present affect the crystallinity and thus the solubility of the glucans made, compensating for or compounding the effects of an aberrant branching pattern. Interestingly, ss2 mutant plants contained small amounts of phytoglycogen in addition to aberrant starch. Likewise, ss2ss3 plants contained phytoglycogen, but were almost devoid of glucan despite retaining other SS isoforms. Surprisingly, glucan production was restored in the ss2ss3isa triple mutants, indicating that SS activity in ss2ss3 per se is not limiting but that the isoamylase suppresses glucan accumulation. We conclude that loss of only SSs can cause phytoglycogen production. This is readily degraded by isoamylase and other enzymes so it does not accumulate and was previously unnoticed., (© 2014 American Society of Plant Biologists. All Rights Reserved.)
- Published
- 2014
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24. Plastidial NAD-dependent malate dehydrogenase is critical for embryo development and heterotrophic metabolism in Arabidopsis.
- Author
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Beeler S, Liu HC, Stadler M, Schreier T, Eicke S, Lue WL, Truernit E, Zeeman SC, Chen J, and Kötting O
- Subjects
- Arabidopsis enzymology, Arabidopsis genetics, Arabidopsis Proteins genetics, Arabidopsis Proteins metabolism, Autotrophic Processes genetics, Chlorophyll metabolism, Chloroplasts genetics, Chloroplasts ultrastructure, Circadian Rhythm genetics, DNA Transposable Elements genetics, Gene Expression Regulation, Developmental, Gene Expression Regulation, Plant, Gene Silencing, Genes, Plant genetics, Homozygote, Malate Dehydrogenase genetics, Metabolome genetics, Morphogenesis genetics, Mutagenesis, Insertional genetics, Photosynthesis, Protein Transport, Arabidopsis embryology, Arabidopsis metabolism, Chloroplasts enzymology, Heterotrophic Processes genetics, Malate Dehydrogenase metabolism, Seeds embryology, Seeds enzymology
- Abstract
In illuminated chloroplasts, one mechanism involved in reduction-oxidation (redox) homeostasis is the malate-oxaloacetate (OAA) shuttle. Excess electrons from photosynthetic electron transport in the form of nicotinamide adenine dinucleotide phosphate, reduced are used by NADP-dependent malate dehydrogenase (MDH) to reduce OAA to malate, thus regenerating the electron acceptor NADP. NADP-MDH is a strictly redox-regulated, light-activated enzyme that is inactive in the dark. In the dark or in nonphotosynthetic tissues, the malate-OAA shuttle was proposed to be mediated by the constitutively active plastidial NAD-specific MDH isoform (pdNAD-MDH), but evidence is scarce. Here, we reveal the critical role of pdNAD-MDH in Arabidopsis (Arabidopsis thaliana) plants. A pdnad-mdh null mutation is embryo lethal. Plants with reduced pdNAD-MDH levels by means of artificial microRNA (miR-mdh-1) are viable, but dark metabolism is altered as reflected by increased nighttime malate, starch, and glutathione levels and a reduced respiration rate. In addition, miR-mdh-1 plants exhibit strong pleiotropic effects, including dwarfism, reductions in chlorophyll levels, photosynthetic rate, and daytime carbohydrate levels, and disordered chloroplast ultrastructure, particularly in developing leaves, compared with the wild type. pdNAD-MDH deficiency in miR-mdh-1 can be functionally complemented by expression of a microRNA-insensitive pdNAD-MDH but not NADP-MDH, confirming distinct roles for NAD- and NADP-linked redox homeostasis.
- Published
- 2014
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25. Callose synthase GSL7 is necessary for normal phloem transport and inflorescence growth in Arabidopsis.
- Author
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Barratt DH, Kölling K, Graf A, Pike M, Calder G, Findlay K, Zeeman SC, and Smith AM
- Subjects
- Arabidopsis genetics, Arabidopsis ultrastructure, Arabidopsis Proteins genetics, Biological Transport drug effects, Carbohydrate Metabolism drug effects, Carbon Isotopes, Gene Expression Regulation, Plant drug effects, Genes, Plant genetics, Glucans metabolism, Glucosyltransferases genetics, Inflorescence anatomy & histology, Inflorescence genetics, Inflorescence ultrastructure, Mutation genetics, Phloem cytology, Phloem drug effects, Phloem ultrastructure, Plant Leaves drug effects, Plant Leaves metabolism, Plant Roots drug effects, Plant Roots metabolism, Plant Roots ultrastructure, Plant Stems anatomy & histology, Plant Stems drug effects, Plant Stems metabolism, Plant Stems ultrastructure, Sucrose pharmacology, Transcription, Genetic drug effects, Arabidopsis enzymology, Arabidopsis growth & development, Arabidopsis Proteins metabolism, Glucosyltransferases metabolism, Inflorescence growth & development, Phloem metabolism
- Abstract
One isoform of callose synthase, Glucan Synthase-Like7 (GSL7), is tightly coexpressed with two isoforms of sucrose synthase (SUS5 and SUS6) known to be confined to phloem sieve elements in Arabidopsis (Arabidopsis thaliana). Investigation of the phenotype of gsl7 mutants of Arabidopsis revealed that the sieve plate pores of stems and roots lack the callose lining seen in wild-type plants. Callose synthesis in other tissues of the plant appears to be unaffected. Although gsl7 plants show only minor phenotypic alterations during vegetative growth, flowering stems are reduced in height and all floral parts are smaller than those of wild-type plants. Several lines of evidence suggest that the reduced growth of the inflorescence is a result of carbohydrate starvation. Levels of sucrose, hexoses, and starch are lower in the terminal bud clusters of gsl7 than in those of wild-type plants. Transcript levels of "starvation" genes expressed in response to low sugars are elevated in the terminal bud clusters of gsl7 plants, at the end of the night, and during an extended night. Pulse-chase experiments with (14)CO(2) show that transport of assimilate in the flowering stem is much slower in gsl7 mutants than in wild-type plants. We suggest that the callose lining of sieve plate pores is essential for normal phloem transport because it confers favorable flow characteristics on the pores.
- Published
- 2011
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26. Loss of cytosolic phosphoglucomutase compromises gametophyte development in Arabidopsis.
- Author
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Egli B, Kölling K, Köhler C, Zeeman SC, and Streb S
- Subjects
- Arabidopsis enzymology, Genes, Plant, Germination, Mutation, Phosphoglucomutase genetics, Phylogeny, Pollen, Arabidopsis growth & development, Cytosol enzymology, Germ Cells, Plant growth & development, Phosphoglucomutase metabolism
- Abstract
Cytosolic phosphoglucomutase (cPGM) interconverts glucose-6-phosphate and glucose-1-phosphate and is a key enzyme of central metabolism. In this study, we show that Arabidopsis (Arabidopsis thaliana) has two cPGM genes (PGM2 and PGM3) encoding proteins with high sequence similarity and redundant functions. Whereas pgm2 and pgm3 single mutants were undistinguishable from the wild type, loss of both PGM2 and PGM3 severely impaired male and female gametophyte function. Double mutant pollen completed development but failed to germinate. Double mutant ovules also developed normally, but approximately half remained unfertilized 2 d after pollination. We attribute these phenotypes to an inability to effectively distribute carbohydrate from imported or stored substrates (e.g. sucrose) into the major biosynthetic (e.g. cell wall biosynthesis) and respiratory pathways (e.g. glycolysis and the oxidative pentose phosphate pathway). Disturbing these pathways is expected to have dramatic consequences for germinating pollen grains, which have high metabolic and biosynthetic activities. We propose that residual cPGM mRNA or protein derived from the diploid mother plant is sufficient to enable double mutant female gametophytes to attain maturity and for some to be fertilized. Mature plants possessing a single cPGM allele had a major reduction in cPGM activity. However, photosynthetic metabolism and growth were normal, suggesting that under standard laboratory conditions cPGM activity provided from one wild-type allele is sufficient to mediate the photosynthetic and respiratory fluxes in leaves.
- Published
- 2010
- Full Text
- View/download PDF
27. The Laforin-like dual-specificity phosphatase SEX4 from Arabidopsis hydrolyzes both C6- and C3-phosphate esters introduced by starch-related dikinases and thereby affects phase transition of alpha-glucans.
- Author
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Hejazi M, Fettke J, Kötting O, Zeeman SC, and Steup M
- Subjects
- Phosphorylation, Arabidopsis enzymology, Arabidopsis Proteins metabolism, Dual-Specificity Phosphatases metabolism, Glucans metabolism, Starch metabolism
- Abstract
The biochemical function of the Laforin-like dual-specific phosphatase AtSEX4 (EC 3.1.3.48) has been studied. Crystalline maltodextrins representing the A- or the B-type allomorph were prephosphorylated using recombinant glucan, water dikinase (StGWD) or the successive action of both plastidial dikinases (StGWD and AtPWD). AtSEX4 hydrolyzed carbon 6-phosphate esters from both the prephosphorylated A- and B-type allomorphs and the kinetic constants are similar. The phosphatase also acted on prelabeled carbon-3 esters from both crystalline maltodextrins. Similarly, native starch granules prelabeled in either the carbon-6 or carbon-3 position were also dephosphorylated by AtSEX4. The phosphatase did also hydrolyze phosphate esters of both prephosphorylated maltodextrins when the (phospho)glucans had been solubilized by heat treatment. Submillimolar concentrations of nonphosphorylated maltodextrins inhibited AtSEX4 provided they possessed a minimum of length and had been solubilized. As opposed to the soluble phosphomaltodextrins, the AtSEX4-mediated dephosphorylation of the insoluble substrates was incomplete and at least 50% of the phosphate esters were retained in the pelletable (phospho)glucans. The partial dephosphorylation of the insoluble glucans also strongly reduced the release of nonphosphorylated chains into solution. Presumably, this effect reflects fast structural changes that following dephosphorylation occur near the surface of the maltodextrin particles. A model is proposed defining distinct stages within the phosphorylation/dephosphorylation-dependent transition of alpha-glucans from the insoluble to the soluble state.
- Published
- 2010
- Full Text
- View/download PDF
28. A putative phosphatase, LSF1, is required for normal starch turnover in Arabidopsis leaves.
- Author
-
Comparot-Moss S, Kötting O, Stettler M, Edner C, Graf A, Weise SE, Streb S, Lue WL, MacLean D, Mahlow S, Ritte G, Steup M, Chen J, Zeeman SC, and Smith AM
- Subjects
- Arabidopsis genetics, Arabidopsis Proteins genetics, Chloroplasts enzymology, DNA, Bacterial genetics, Glucans metabolism, Mutagenesis, Insertional, Mutation, Oligonucleotide Array Sequence Analysis, Phosphorylation, Plant Leaves genetics, RNA, Plant genetics, Arabidopsis enzymology, Arabidopsis Proteins metabolism, Plant Leaves metabolism, Starch metabolism
- Abstract
A putative phosphatase, LSF1 (for LIKE SEX4; previously PTPKIS2), is closely related in sequence and structure to STARCH-EXCESS4 (SEX4), an enzyme necessary for the removal of phosphate groups from starch polymers during starch degradation in Arabidopsis (Arabidopsis thaliana) leaves at night. We show that LSF1 is also required for starch degradation: lsf1 mutants, like sex4 mutants, have substantially more starch in their leaves than wild-type plants throughout the diurnal cycle. LSF1 is chloroplastic and is located on the surface of starch granules. lsf1 and sex4 mutants show similar, extensive changes relative to wild-type plants in the expression of sugar-sensitive genes. However, although LSF1 and SEX4 are probably both involved in the early stages of starch degradation, we show that LSF1 neither catalyzes the same reaction as SEX4 nor mediates a sequential step in the pathway. Evidence includes the contents and metabolism of phosphorylated glucans in the single mutants. The sex4 mutant accumulates soluble phospho-oligosaccharides undetectable in wild-type plants and is deficient in a starch granule-dephosphorylating activity present in wild-type plants. The lsf1 mutant displays neither of these phenotypes. The phenotype of the lsf1/sex4 double mutant also differs from that of both single mutants in several respects. We discuss the possible role of the LSF1 protein in starch degradation.
- Published
- 2010
- Full Text
- View/download PDF
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