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A DUF-246 family glycosyltransferase-like gene affects male fertility and the biosynthesis of pectic arabinogalactans.

Stonebloom S, Ebert B, Xiong G, Pattathil S, Birdseye D, Lao J, Pauly M, Hahn MG, Heazlewood JL, Scheller HV - BMC Plant Biol. (2016)

Bottom Line: NbPAGR-silenced plants exhibited reduced internode and petiole expansion.Immunological and linkage analyses support that RG-I has reduced type-I arabinogalactan content and reduced branching of the RG-I backbone in NbPAGR-silenced plants.Together, results support a function for PAGR in the biosynthesis of RG-I arabinogalactans and illustrate the essential roles of these polysaccharides in vegetative and reproductive plant growth.

View Article: PubMed Central - PubMed

Affiliation: Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.

ABSTRACT

Background: Pectins are a group of structurally complex plant cell wall polysaccharides whose biosynthesis and function remain poorly understood. The pectic polysaccharide rhamnogalacturonan-I (RG-I) has two types of arabinogalactan side chains, type-I and type-II arabinogalactans. To date few enzymes involved in the biosynthesis of pectin have been described. Here we report the identification of a highly conserved putative glycosyltransferase encoding gene, Pectic ArabinoGalactan synthesis-Related (PAGR), affecting the biosynthesis of RG-I arabinogalactans and critical for pollen tube growth.

Results: T-DNA insertions in PAGR were identified in Arabidopsis thaliana and were found to segregate at a 1:1 ratio of heterozygotes to wild type. We were unable to isolate homozygous pagr mutants as pagr mutant alleles were not transmitted via pollen. In vitro pollen germination assays revealed reduced rates of pollen tube formation in pollen from pagr heterozygotes. To characterize a loss-of-function phenotype for PAGR, the Nicotiana benthamiana orthologs, NbPAGR-A and B, were transiently silenced using Virus Induced Gene Silencing. NbPAGR-silenced plants exhibited reduced internode and petiole expansion. Cell wall materials from NbPAGR-silenced plants had reduced galactose content compared to the control. Immunological and linkage analyses support that RG-I has reduced type-I arabinogalactan content and reduced branching of the RG-I backbone in NbPAGR-silenced plants. Arabidopsis lines overexpressing PAGR exhibit pleiotropic developmental phenotypes and the loss of apical dominance as well as an increase in RG-I type-II arabinogalactan content.

Conclusions: Together, results support a function for PAGR in the biosynthesis of RG-I arabinogalactans and illustrate the essential roles of these polysaccharides in vegetative and reproductive plant growth.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of the pectic polysaccharide rhamnogalacturonan-I (a) and the structure and expression of PAGR (b-d).a Rhamnogalacturonan-I has a backbone consisting of repeating [−α-d-GalpA-1,2-α-l-Rhap-1,4-] disaccharide units. Approximately half of the rhamnose residues are substituted with sidechains on the 4-position such as type-I and type-II arabinogalactans, α-(1,5)-linked arabinans or single arabinose or galactose residues. bpagr-1 is a T-DNA insertion in the 11th exon of PAGR; pagr-2 is an insertion in the 7th exon. cPAGR encodes a type-II membrane protein with an N-terminal disordered domain and a C-terminal O-fucosyltransferase-like DUF246 domain. d Quantitative RT-PCR analysis of PAGR expression in various Arabidopsis tissues. Results show PAGR expression is highest in reproductive tissues and roots. Error bars indicate standard deviation, n = 3
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Fig1: Schematic representation of the pectic polysaccharide rhamnogalacturonan-I (a) and the structure and expression of PAGR (b-d).a Rhamnogalacturonan-I has a backbone consisting of repeating [−α-d-GalpA-1,2-α-l-Rhap-1,4-] disaccharide units. Approximately half of the rhamnose residues are substituted with sidechains on the 4-position such as type-I and type-II arabinogalactans, α-(1,5)-linked arabinans or single arabinose or galactose residues. bpagr-1 is a T-DNA insertion in the 11th exon of PAGR; pagr-2 is an insertion in the 7th exon. cPAGR encodes a type-II membrane protein with an N-terminal disordered domain and a C-terminal O-fucosyltransferase-like DUF246 domain. d Quantitative RT-PCR analysis of PAGR expression in various Arabidopsis tissues. Results show PAGR expression is highest in reproductive tissues and roots. Error bars indicate standard deviation, n = 3

Mentions: Pectins are an important group of structural cell wall polysaccharides in plants and are major constituents of primary cell walls. Pectins are also important components of many foods and food products. Along with the hemicelluloses, pectins form a matrix into which cellulose microfibrils are embedded. Pectins comprise several types of acidic polysaccharide domains: homogalacturonan, xylogalacturonan, rhamnogalacturonan-I (RG-I) and rhamnogalacturonan-II (RG-II), that may be interconnected to one another as well as to other polysaccharides and glycoproteins including hemicelluloses and arabinogalactan proteins (AGPs) [1, 2]. Homogalacturonan consists of linear chains of α-1-4-linked d-galacturonic acid residues and can account for 60 % or more of pectin. Galacturonic acid residues are methyl esterified to varying degrees and can be acetylated at O-2 or O-3 in both homogalacturonan and RG-I. In some plants or tissues homogalacturonan is substituted with xylose or apiose making xylogalacturonan and apiogalacturonan, respectively. RG-I (diagrammed in Fig. 1a) is a distinct class of pectic polysaccharides with a backbone consisting of repeating [−α-d-GalpA-1,2-α-l-Rhap-1,4-] disaccharide units [3]. Approximately half of the rhamnose residues are elaborated with sidechains on the 4-position, including β-1,4-linked d-Galp chains, α-(1,5)-linked l-Araf chains as well as type I and II–arabinogalactans. Type-I arabinogalactans consist of β-1,4-linked d-Galp backbones with arabinan sidechains, while type-II arabinogalactans possess a backbone of β-1,3-, β-1,6-and β-1,3,6- linked d-Galp similar to the arabinogalactans of AGPs. Rhamnogalacturonan-II is a form of homogalacturonan substituted with four characteristic types of elaborate side chains with distinctive structures made up of 13 different types of monosaccharides and containing the rare sugars l-Aceric acid, d-Apiose, 2-keto-3-deoxy-d-Lyxo-heptulosaric acid (Dha) and 2-keto-3-deoxy-d-Manno-octulosonic acid (Kdo) [4, 5]. RG-II forms dimers through boron di-ester bonds and is a ubiquitous component of plant cell walls, highlighting its importance. Given its structural complexity, as many as 67 different transferase activities are thought to be necessary for the biosynthesis of pectin [1].Fig. 1


A DUF-246 family glycosyltransferase-like gene affects male fertility and the biosynthesis of pectic arabinogalactans.

Stonebloom S, Ebert B, Xiong G, Pattathil S, Birdseye D, Lao J, Pauly M, Hahn MG, Heazlewood JL, Scheller HV - BMC Plant Biol. (2016)

Schematic representation of the pectic polysaccharide rhamnogalacturonan-I (a) and the structure and expression of PAGR (b-d).a Rhamnogalacturonan-I has a backbone consisting of repeating [−α-d-GalpA-1,2-α-l-Rhap-1,4-] disaccharide units. Approximately half of the rhamnose residues are substituted with sidechains on the 4-position such as type-I and type-II arabinogalactans, α-(1,5)-linked arabinans or single arabinose or galactose residues. bpagr-1 is a T-DNA insertion in the 11th exon of PAGR; pagr-2 is an insertion in the 7th exon. cPAGR encodes a type-II membrane protein with an N-terminal disordered domain and a C-terminal O-fucosyltransferase-like DUF246 domain. d Quantitative RT-PCR analysis of PAGR expression in various Arabidopsis tissues. Results show PAGR expression is highest in reproductive tissues and roots. Error bars indicate standard deviation, n = 3
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4836069&req=5

Fig1: Schematic representation of the pectic polysaccharide rhamnogalacturonan-I (a) and the structure and expression of PAGR (b-d).a Rhamnogalacturonan-I has a backbone consisting of repeating [−α-d-GalpA-1,2-α-l-Rhap-1,4-] disaccharide units. Approximately half of the rhamnose residues are substituted with sidechains on the 4-position such as type-I and type-II arabinogalactans, α-(1,5)-linked arabinans or single arabinose or galactose residues. bpagr-1 is a T-DNA insertion in the 11th exon of PAGR; pagr-2 is an insertion in the 7th exon. cPAGR encodes a type-II membrane protein with an N-terminal disordered domain and a C-terminal O-fucosyltransferase-like DUF246 domain. d Quantitative RT-PCR analysis of PAGR expression in various Arabidopsis tissues. Results show PAGR expression is highest in reproductive tissues and roots. Error bars indicate standard deviation, n = 3
Mentions: Pectins are an important group of structural cell wall polysaccharides in plants and are major constituents of primary cell walls. Pectins are also important components of many foods and food products. Along with the hemicelluloses, pectins form a matrix into which cellulose microfibrils are embedded. Pectins comprise several types of acidic polysaccharide domains: homogalacturonan, xylogalacturonan, rhamnogalacturonan-I (RG-I) and rhamnogalacturonan-II (RG-II), that may be interconnected to one another as well as to other polysaccharides and glycoproteins including hemicelluloses and arabinogalactan proteins (AGPs) [1, 2]. Homogalacturonan consists of linear chains of α-1-4-linked d-galacturonic acid residues and can account for 60 % or more of pectin. Galacturonic acid residues are methyl esterified to varying degrees and can be acetylated at O-2 or O-3 in both homogalacturonan and RG-I. In some plants or tissues homogalacturonan is substituted with xylose or apiose making xylogalacturonan and apiogalacturonan, respectively. RG-I (diagrammed in Fig. 1a) is a distinct class of pectic polysaccharides with a backbone consisting of repeating [−α-d-GalpA-1,2-α-l-Rhap-1,4-] disaccharide units [3]. Approximately half of the rhamnose residues are elaborated with sidechains on the 4-position, including β-1,4-linked d-Galp chains, α-(1,5)-linked l-Araf chains as well as type I and II–arabinogalactans. Type-I arabinogalactans consist of β-1,4-linked d-Galp backbones with arabinan sidechains, while type-II arabinogalactans possess a backbone of β-1,3-, β-1,6-and β-1,3,6- linked d-Galp similar to the arabinogalactans of AGPs. Rhamnogalacturonan-II is a form of homogalacturonan substituted with four characteristic types of elaborate side chains with distinctive structures made up of 13 different types of monosaccharides and containing the rare sugars l-Aceric acid, d-Apiose, 2-keto-3-deoxy-d-Lyxo-heptulosaric acid (Dha) and 2-keto-3-deoxy-d-Manno-octulosonic acid (Kdo) [4, 5]. RG-II forms dimers through boron di-ester bonds and is a ubiquitous component of plant cell walls, highlighting its importance. Given its structural complexity, as many as 67 different transferase activities are thought to be necessary for the biosynthesis of pectin [1].Fig. 1

Bottom Line: NbPAGR-silenced plants exhibited reduced internode and petiole expansion.Immunological and linkage analyses support that RG-I has reduced type-I arabinogalactan content and reduced branching of the RG-I backbone in NbPAGR-silenced plants.Together, results support a function for PAGR in the biosynthesis of RG-I arabinogalactans and illustrate the essential roles of these polysaccharides in vegetative and reproductive plant growth.

View Article: PubMed Central - PubMed

Affiliation: Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.

ABSTRACT

Background: Pectins are a group of structurally complex plant cell wall polysaccharides whose biosynthesis and function remain poorly understood. The pectic polysaccharide rhamnogalacturonan-I (RG-I) has two types of arabinogalactan side chains, type-I and type-II arabinogalactans. To date few enzymes involved in the biosynthesis of pectin have been described. Here we report the identification of a highly conserved putative glycosyltransferase encoding gene, Pectic ArabinoGalactan synthesis-Related (PAGR), affecting the biosynthesis of RG-I arabinogalactans and critical for pollen tube growth.

Results: T-DNA insertions in PAGR were identified in Arabidopsis thaliana and were found to segregate at a 1:1 ratio of heterozygotes to wild type. We were unable to isolate homozygous pagr mutants as pagr mutant alleles were not transmitted via pollen. In vitro pollen germination assays revealed reduced rates of pollen tube formation in pollen from pagr heterozygotes. To characterize a loss-of-function phenotype for PAGR, the Nicotiana benthamiana orthologs, NbPAGR-A and B, were transiently silenced using Virus Induced Gene Silencing. NbPAGR-silenced plants exhibited reduced internode and petiole expansion. Cell wall materials from NbPAGR-silenced plants had reduced galactose content compared to the control. Immunological and linkage analyses support that RG-I has reduced type-I arabinogalactan content and reduced branching of the RG-I backbone in NbPAGR-silenced plants. Arabidopsis lines overexpressing PAGR exhibit pleiotropic developmental phenotypes and the loss of apical dominance as well as an increase in RG-I type-II arabinogalactan content.

Conclusions: Together, results support a function for PAGR in the biosynthesis of RG-I arabinogalactans and illustrate the essential roles of these polysaccharides in vegetative and reproductive plant growth.

No MeSH data available.


Related in: MedlinePlus