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Saez-Aguayo S, Ralet MC, Berger A, Botran L, Ropartz D, Marion-Poll A, North HM. PECTIN METHYLESTERASE INHIBITOR6 promotes Arabidopsis mucilage release by limiting methylesterification of homogalacturonan in seed coat epidermal cells. THE PLANT CELL 2013; 25:308-23. [PMID: 23362209 PMCID: PMC3584544 DOI: 10.1105/tpc.112.106575] [Citation(s) in RCA: 99] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2012] [Revised: 12/20/2012] [Accepted: 01/03/2013] [Indexed: 05/17/2023]
Abstract
Imbibed seeds of the Arabidopsis thaliana accession Djarly are affected in mucilage release from seed coat epidermal cells. The impaired locus was identified as a pectin methylesterase inhibitor gene, PECTIN METHYLESTERASE INHIBITOR6 (PMEI6), specifically expressed in seed coat epidermal cells at the time when mucilage polysaccharides are accumulated. This spatio-temporal regulation appears to be modulated by GLABRA2 and LEUNIG HOMOLOG/MUCILAGE MODIFIED1, as expression of PMEI6 is reduced in mutants of these transcription regulators. In pmei6, mucilage release was delayed and outer cell walls of epidermal cells did not fragment. Pectin methylesterases (PMEs) demethylate homogalacturonan (HG), and the majority of HG found in wild-type mucilage was in fact derived from outer cell wall fragments. This correlated with the absence of methylesterified HG labeling in pmei6, whereas transgenic plants expressing the PMEI6 coding sequence under the control of the 35S promoter had increased labeling of cell wall fragments. Activity tests on seeds from pmei6 and 35S:PMEI6 transgenic plants showed that PMEI6 inhibits endogenous PME activities, in agreement with reduced overall methylesterification of mucilage fractions and demucilaged seeds. Another regulator of PME activity in seed coat epidermal cells, the subtilisin-like Ser protease SBT1.7, acts on different PMEs, as a pmei6 sbt1.7 mutant showed an additive phenotype.
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Pedersen HL, Fangel JU, McCleary B, Ruzanski C, Rydahl MG, Ralet MC, Farkas V, von Schantz L, Marcus SE, Andersen MCF, Field R, Ohlin M, Knox JP, Clausen MH, Willats WGT. Versatile high resolution oligosaccharide microarrays for plant glycobiology and cell wall research. J Biol Chem 2012; 287:39429-38. [PMID: 22988248 PMCID: PMC3501085 DOI: 10.1074/jbc.m112.396598] [Citation(s) in RCA: 175] [Impact Index Per Article: 14.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Revised: 09/10/2012] [Indexed: 12/13/2022] Open
Abstract
Microarrays are powerful tools for high throughput analysis, and hundreds or thousands of molecular interactions can be assessed simultaneously using very small amounts of analytes. Nucleotide microarrays are well established in plant research, but carbohydrate microarrays are much less established, and one reason for this is a lack of suitable glycans with which to populate arrays. Polysaccharide microarrays are relatively easy to produce because of the ease of immobilizing large polymers noncovalently onto a variety of microarray surfaces, but they lack analytical resolution because polysaccharides often contain multiple distinct carbohydrate substructures. Microarrays of defined oligosaccharides potentially overcome this problem but are harder to produce because oligosaccharides usually require coupling prior to immobilization. We have assembled a library of well characterized plant oligosaccharides produced either by partial hydrolysis from polysaccharides or by de novo chemical synthesis. Once coupled to protein, these neoglycoconjugates are versatile reagents that can be printed as microarrays onto a variety of slide types and membranes. We show that these microarrays are suitable for the high throughput characterization of the recognition capabilities of monoclonal antibodies, carbohydrate-binding modules, and other oligosaccharide-binding proteins of biological significance and also that they have potential for the characterization of carbohydrate-active enzymes.
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Ralet MC, Williams MAK, Tanhatan-Nasseri A, Ropartz D, Quéméner B, Bonnin E. Innovative enzymatic approach to resolve homogalacturonans based on their methylesterification pattern. Biomacromolecules 2012; 13:1615-24. [PMID: 22520025 DOI: 10.1021/bm300329r] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Three series of model homogalacturonans (HGs) covering a large range of degree of methylesterification (DM) were prepared by chemical and/or enzymatic means. Randomly demethylesterified HGs, HGs containing a few long demethylesterified galacturonic acid stretches, and HGs with numerous but short demethylesterified blocks were recovered. The analysis of the degradation products generated by the action of a purified pectin lyase allowed the definition of two new parameters, the degree of blockiness, and the absolute degree of blockiness of the highly methylesterified stretches (DBMe and DB(abs)Me, respectively). By combining this information with that obtained by the more traditional endopolygalacturonase digestion, the total proportion of degradable zones for a given DM was measured and was shown to permit a clear differentiation of the three types of HG series over a large range of DM. This double enzymatic approach will be of interest to discriminate industrial pectin samples exhibiting different functionalities and to evaluate pectin fine structure dynamics in vivo in the plant cell wall, where pectin plays a key mechanical role.
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Morris GA, Ralet MC. A copolymer analysis approach to estimate the neutral sugar distribution of sugar beet pectin using size exclusion chromatography. Carbohydr Polym 2012. [DOI: 10.1016/j.carbpol.2011.08.077] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Koubala BB, Kansci G, Garnier C, Thibault JF, Ralet MC. Physicochemical Properties of Dietary Fibres Prepared from Ambarella (Spondias cytherea) and Mango (Mangifera indica) Peels. FOOD BIOPROCESS TECH 2011. [DOI: 10.1007/s11947-011-0660-1] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Tanhatan-Nasseri A, Crépeau MJ, Thibault JF, Ralet MC. Isolation and characterization of model homogalacturonans of tailored methylesterification patterns. Carbohydr Polym 2011. [DOI: 10.1016/j.carbpol.2011.06.019] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Sullivan S, Ralet MC, Berger A, Diatloff E, Bischoff V, Gonneau M, Marion-Poll A, North HM. CESA5 is required for the synthesis of cellulose with a role in structuring the adherent mucilage of Arabidopsis seeds. PLANT PHYSIOLOGY 2011; 156:1725-39. [PMID: 21705653 PMCID: PMC3149949 DOI: 10.1104/pp.111.179077] [Citation(s) in RCA: 88] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2011] [Accepted: 06/22/2011] [Indexed: 05/17/2023]
Abstract
Imbibed Arabidopsis (Arabidopsis thaliana) seeds are encapsulated by mucilage that is formed of hydrated polysaccharides released from seed coat epidermal cells. The mucilage is structured with water-soluble and adherent layers, with cellulose present uniquely in an inner domain of the latter. Using a reverse-genetic approach to identify the cellulose synthases (CESAs) that produce mucilage cellulose, cesa5 mutants were shown to be required for the correct formation of these layers. Expression of CESA5 in the seed coat was specific to epidermal cells and coincided with the accumulation of mucilage polysaccharides in their apoplast. Analysis of sugar composition showed that although total sugar composition or amounts were unchanged, their partition between layers was different in the mutant, with redistribution from adherent to water-soluble mucilage. The macromolecular characteristics of the water-soluble mucilage were also modified. In accordance with a role for CESA5 in mucilage cellulose synthesis, crystalline cellulose contents were reduced in mutant seeds and birefringent microfibrils were absent from adherent mucilage. Although the mucilage-modified5 mutant showed similar defects to cesa5 in the distribution of sugar components between water-soluble and adherent mucilage, labeling of residual adherent mucilage indicated that cesa5 contained less cellulose and less pectin methyl esterification. Together, the results demonstrate that CESA5 plays a major and essential role in cellulose production in seed mucilage, which is critical for the establishment of mucilage structured in layers and domains.
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Louvet R, Rayon C, Domon JM, Rusterucci C, Fournet F, Leaustic A, Crépeau MJ, Ralet MC, Rihouey C, Bardor M, Lerouge P, Gillet F, Pelloux J. Major changes in the cell wall during silique development in Arabidopsis thaliana. PHYTOCHEMISTRY 2011; 72:59-67. [PMID: 21051061 DOI: 10.1016/j.phytochem.2010.10.008] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2010] [Revised: 10/12/2010] [Accepted: 10/13/2010] [Indexed: 05/08/2023]
Abstract
Fruit development is a highly complex process, which involves major changes in plant metabolism leading to cell growth and differentiation. Changes in cell wall composition and structure play a major role in modulating cell growth. We investigated the changes in cell wall composition and the activities of associated enzymes during the dry fruit development of the model plant Arabidopsis thaliana. Silique development is characterized by several specific phases leading to fruit dehiscence and seed dispersal. We showed that early phases of silique growth were characterized by specific changes in non-cellulosic sugar content (rhamnose, arabinose, xylose, galactose and galacturonic acid). Xyloglucan oligosaccharide mass profiling further showed a strong increase in O-acetylated xyloglucans over the course of silique development, which could suggest a decreased capacity of xyloglucans to be associated with each other or to cellulose. The degree of methylesterification, mediated by the activity of pectin methylesterases (PMEs), decreased over the course of silique growth and dehiscence. The major changes in cell wall composition revealed by our analysis suggest that it could be major determinants in modulating cell wall rheology leading to growth or growth arrest.
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Morris GA, Ralet MC, Bonnin E, Thibault JF, Harding SE. Physical characterisation of the rhamnogalacturonan and homogalacturonan fractions of sugar beet (Beta vulgaris) pectin. Carbohydr Polym 2010. [DOI: 10.1016/j.carbpol.2010.06.049] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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Habrant A, Gaillard C, Ralet MC, Lairez D, Cathala B. Relation between chemical structure and supramolecular organization of synthetic lignin-pectin particles. Biomacromolecules 2010; 10:3151-6. [PMID: 19894766 DOI: 10.1021/bm900950r] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Valentin R, Cerclier C, Geneix N, Aguié-Béghin V, Gaillard C, Ralet MC, Cathala B. Elaboration of extensin-pectin thin film model of primary plant cell wall. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2010; 26:9891-8. [PMID: 20222720 DOI: 10.1021/la100265d] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
With the aim of mimicking the plant cell wall, a layer by layer approach was used to build a thin film consisting of successive adsorption of pectin and extensin. Elaboration of the thin film was monitored by surface plasmon resonance, quartz crystal microbalance, and ellipsometry. All data indicate that formation of the film was successful and that growth occurred according to a nonuniform growth. It is likely that diffusion of the polymers occurred within the multilayer structure and that the final structure is not constituted by layered individual pectin and extensin films. Polymer rearrangements were also supported by the atomic force microscopy images that show a smoother surface after extensin adsorption than after pectin deposition.
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Williams MAK, Cucheval A, Nasseri AT, Ralet MC. Extracting Intramolecular Sequence Information from Intermolecular Distributions: Highly Nonrandom Methylester Substitution Patterns in Homogalacturonans Generated by Pectinmethylesterase. Biomacromolecules 2010; 11:1667-75. [DOI: 10.1021/bm1003527] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Lopez M, Bizot H, Chambat G, Marais MF, Zykwinska A, Ralet MC, Driguez H, Buléon A. Enthalpic Studies of Xyloglucan−Cellulose Interactions. Biomacromolecules 2010; 11:1417-28. [DOI: 10.1021/bm1002762] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Normand J, Ralet MC, Thibault JF, Rogniaux H, Delavault P, Bonnin E. Purification, characterization, and mode of action of a rhamnogalacturonan hydrolase from Irpex lacteus, tolerant to an acetylated substrate. Appl Microbiol Biotechnol 2009; 86:577-88. [PMID: 19862512 DOI: 10.1007/s00253-009-2310-3] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2009] [Revised: 10/13/2009] [Accepted: 10/13/2009] [Indexed: 11/29/2022]
Abstract
A novel rhamnogalacturonase (RGase) acting on an acetylated substrate was detected in the commercial preparation Driselase, an enzymatic mixture derived from the basidiomycete Irpex lacteus. The activity was isolated by hydrophobic interaction chromatography, gel filtration, and preparative isoelectric focusing, resulting in the isolation of five different rhamnogalacturonan hydrolases exhibiting various isoelectric points from 6.2 to 7.7. Sodium dodecyl sulfate polyacrylamide gel electrophoresis and mass spectrometry analyses after trypsin cleavage of the five fractions revealed that the five rhamnogalacturonases have a molar mass of 55 kDa without any divergences in the identified peptides. The RGase with a pI of 7.2 exhibited a pH optimum between 4.5 and 5 and a temperature optimum between 40 degrees C and 50 degrees C. Its mode of action was analyzed by mass spectrometry of the oligosaccharides produced after hydrolysis of acetylated and nonacetylated rhamnogalacturonan. Oligomers esterified by an acetyl group on the reducing galacturonic acid residue or fully acetylated were detected in the hydrolysate showing that the novel enzyme is able to bind acetylated galacturonic acid in its active site.
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Ralet MC, Lerouge P, Quéméner B. Mass spectrometry for pectin structure analysis. Carbohydr Res 2009; 344:1798-807. [DOI: 10.1016/j.carres.2008.08.036] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Revised: 08/27/2008] [Accepted: 08/29/2008] [Indexed: 01/01/2023]
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Koubala BB, Kansci G, Garnier C, Mbome IL, Durand S, Thibault JF, Ralet MC. Rheological and high gelling properties of mango (Mangifera indica) and ambarella (Spondias cytherea) peel pectins. Int J Food Sci Technol 2009. [DOI: 10.1111/j.1365-2621.2009.02003.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Williams MAK, Cucheval A, Ström A, Ralet MC. Electrophoretic Behavior of Copolymeric Galacturonans Including Comments on the Information Content of the Intermolecular Charge Distribution. Biomacromolecules 2009; 10:1523-31. [DOI: 10.1021/bm900119u] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Zykwinska A, Thibault JF, Ralet MC. Modelling of xyloglucan, pectins and pectic side chains binding onto cellulose microfibrils. Carbohydr Polym 2008. [DOI: 10.1016/j.carbpol.2008.01.011] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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Ralet MC, Crépeau MJ, Bonnin E. Evidence for a blockwise distribution of acetyl groups onto homogalacturonans from a commercial sugar beet (Beta vulgaris) pectin. PHYTOCHEMISTRY 2008; 69:1903-1909. [PMID: 18448141 DOI: 10.1016/j.phytochem.2008.03.008] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/25/2008] [Revised: 03/17/2008] [Accepted: 03/18/2008] [Indexed: 05/26/2023]
Abstract
Commercial acid-extracted sugar beet pectin was extensively hydrolysed using an endo-polygalacturonase (AnPGI from Aspergillus niger or AnPGII from A. niger or FmPG from Fusarium moniliforme) in combination with Aspergillus aculeatus pectin methyl-esterase (AaPME). The homogalacturonan-derived oligogalacturonates released were quantified by high-performance anion-exchange chromatography and their structure determined by mass spectrometry. The different endo-polygalacturonases exhibited variable tolerance towards acetyl groups. AnPGI was the most active and FmPG the less. A hypothetical homogalacturonan was constructed using the AnPGI-recovered oligogalacturonates as building blocks and the validity of the model was checked taking into account FmPG observed requirements and hydrolysis products. A blockwise repartition of the acetyl groups onto sugar beet pectin homogalacturonan is proposed.
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Ralet MC, Crépeau MJ, Lefèbvre J, Mouille G, Höfte H, Thibault JF. Reduced Number of Homogalacturonan Domains in Pectins of an Arabidopsis Mutant Enhances the Flexibility of the Polymer. Biomacromolecules 2008; 9:1454-60. [DOI: 10.1021/bm701321g] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Ropers MH, Meister A, Blume A, Ralet MC. Pectin−Lipid Assembly at the Air–Water Interface: Effect of the Pectin Charge Distribution. Biomacromolecules 2008; 9:1306-12. [DOI: 10.1021/bm7013685] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Macquet A, Ralet MC, Loudet O, Kronenberger J, Mouille G, Marion-Poll A, North HM. A naturally occurring mutation in an Arabidopsis accession affects a beta-D-galactosidase that increases the hydrophilic potential of rhamnogalacturonan I in seed mucilage. THE PLANT CELL 2007; 19:3990-4006. [PMID: 18165330 PMCID: PMC2217647 DOI: 10.1105/tpc.107.050179] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
The Arabidopsis thaliana accession Shahdara was identified as a rare naturally occurring mutant that does not liberate seed mucilage on imbibition. The defective locus was found to be allelic to the mum2-1 and mum2-2 mutants. Map-based cloning showed that MUCILAGE-MODIFIED2 (MUM2) encodes the putative beta-D-galactosidase BGAL6. Activity assays demonstrated that one of four major beta-D-galactosidase activities present in developing siliques is absent in mum2 mutants. No difference was observed in seed coat epidermal cell structure between wild-type and mutant seed; however, weakening of the outer tangential cell wall by chemical treatment resulted in the release of mucilage from mum2 seed coat epidermal cells, and the mum2 mucilage only increased slightly in volume, relative to the wild type. Consistent with the absence of beta-D-galactosidase activity in the mutant, the inner layer of mucilage contained more Gal. The allocation of polysaccharides between the inner and outer mucilage layers was also modified in mum2. Mass spectrometry showed that rhamnogalacturonan I in mutant mucilage had more branching between rhamnose and hexose residues relative to the wild type. We conclude that the MUM2/BGAL6 beta-D-galactosidase is required for maturation of rhamnogalacturonan I in seed mucilage by the removal of galactose/galactan branches, resulting in increased swelling and extrusion of the mucilage on seed hydration.
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Macquet A, Ralet MC, Kronenberger J, Marion-Poll A, North HM. In situ, chemical and macromolecular study of the composition of Arabidopsis thaliana seed coat mucilage. PLANT & CELL PHYSIOLOGY 2007; 48:984-99. [PMID: 17540691 DOI: 10.1093/pcp/pcm068] [Citation(s) in RCA: 130] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
A comprehensive analysis was carried out of the composition of seed coat mucilage from Arabidopsis thaliana using the Columbia-0 accession. Pectinaceous mucilage is released from myxospermous seeds upon imbibition, and in Arabidopsis consists of a water-soluble, outer layer and an adherent, inner layer. Analysis of monosaccharide composition in conjunction with digestion with pectolytic enzymes conclusively demonstrated that the principal pectic domain of both layers was rhamnogalacturonan I, and that in the outer layer this was unbranched. The macromolecular characteristics of the water-soluble mucilage indicated that the rhamnogalacturonan molecules in the outer layer were in a slightly expanded random-coil conformation. The inner, adherent layer remained attached to the seed, even after extraction with acid and alkali, suggesting that its integrity was maintained by covalent bonds. Confocal microscopy and monosaccharide composition analyses showed that the inner layer can be separated into two domains. The internal domain contained cellulose microfibrils, which could form a matrix with RGI and bind it to the seed. In effect, in the mum5-1 mutant where most of the inner and outer mucilage layers were water soluble, cellulose remained attached to the seed coat. Immunolabeling with anti-pectin antibodies indicated the presence of galactan and arabinan in the inner layer, with the latter only present in the non-cellulose-containing external domain. In addition, JIM5 and JIM7 antibodies labeled different domains of the inner layer, suggesting the presence of stretches of homogalacturonan with different levels of methyl esterification.
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Yapo BM, Lerouge P, Thibault JF, Ralet MC. Pectins from citrus peel cell walls contain homogalacturonans homogenous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II. Carbohydr Polym 2007. [DOI: 10.1016/j.carbpol.2006.12.024] [Citation(s) in RCA: 148] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Mouille G, Ralet MC, Cavelier C, Eland C, Effroy D, Hématy K, McCartney L, Truong HN, Gaudon V, Thibault JF, Marchant A, Höfte H. Homogalacturonan synthesis in Arabidopsis thaliana requires a Golgi-localized protein with a putative methyltransferase domain. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2007; 50:605-14. [PMID: 17425712 DOI: 10.1111/j.1365-313x.2007.03086.x] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
Pectins are a family of complex cell-wall polysaccharides, the biosynthesis of which remains poorly understood. We identified dwarf mutants with reduced cell adhesion at a novel locus, QUASIMODO2 (QUA2). qua2-1 showed a 50% reduction in homogalacturonan (HG) content compared with the wild type, without affecting other cell-wall polysaccharides. The remaining HG in qua2-1 showed an unaltered degree of methylesterification. Positional cloning and GFP fusions showed that QUA2, consistent with a role in HG synthesis, encodes a Golgi-localized protein. In contrast to QUA1, another Golgi-localized protein required for HG-synthesis, QUA2 does not show sequence similarity to glycosyltransferases, but instead contains a putative methyltransferase (MT) domain. The Arabidopsis genome encodes 29 QUA2-related proteins. Interestingly, the transcript profiles of QUA1 and QUA2 are correlated and other pairs of QUA1 and QUA2 homologues with correlated transcript profiles can be identified. Together, the results lead to the hypothesis that QUA2 is a pectin MT, and that polymerization and methylation of homogalacturonan are interdependent reactions.
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