A DUF-246 family glycosyltransferase-like gene affects male fertility and the biosynthesis of pectic arabinogalactans.
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.
Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.|Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, C 1871, Copenhagen, Denmark.
Solomon
S
Stonebloom
Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.|Department of Plant and Environmental Sciences, Faculty of Science, University of Copenhagen, C 1871, Copenhagen, Denmark.
Berit
B
Ebert
Energy Biosciences Institute, University of California, Berkeley, CA, 94720, USA.|Department of Plant and Microbial Biology, University of California, Berkeley, CA, 94720, USA.
Guangyan
G
Xiong
Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602-4712, USA.|BioEnergy Science Center, University of Georgia, Athens, GA, 30602-4712, USA.
Sivakumar
S
Pattathil
Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Devon
D
Birdseye
Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.
Jeemeng
J
Lao
Energy Biosciences Institute, University of California, Berkeley, CA, 94720, USA.|Department of Plant and Microbial Biology, University of California, Berkeley, CA, 94720, USA.
Markus
M
Pauly
Complex Carbohydrate Research Center, University of Georgia, Athens, GA, 30602-4712, USA.|BioEnergy Science Center, University of Georgia, Athens, GA, 30602-4712, USA.|Department of Plant Biology, University of Georgia, Athens, GA, 30602-4712, USA.
Michael G
MG
Hahn
Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA.|ARC Centre of Excellence in Plant Cell Walls, School of Botany, The University of Melbourne, 3010, Melbourne, Victoria, Australia.
Joshua L
JL
Heazlewood
Joint BioEnergy Institute and Biological Systems and Engineering, Lawrence Berkeley National Laboratory, Berkeley, CA, 94720, USA. hscheller@lbl.gov.|Department of Plant and Microbial Biology, University of California, Berkeley, CA, 94720, USA. hscheller@lbl.gov.
Henrik Vibe
HV
Scheller
D017360:Arabidopsis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D005298:Fertility / Q000235:genetics; D005685:Galactans / Q000096:biosynthesis; D018506:Gene Expression Regulation, Plant; D020868:Gene Silencing; D005838:Genotype; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D015151:Immunoblotting; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D018613:Microscopy, Confocal; D009154:Mutation; D010368:Pectins / Q000096:biosynthesis*; D010641:Phenotype; D030821:Plants, Genetically Modified; D011058:Pollen / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D053205:Pollen Tube / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014026:Nicotiana / Q000166:cytology / Q000235:genetics / Q000378:metabolism
D029681:Arabidopsis Proteins; D005685:Galactans; D008164:Luminescent Proteins; C042491:rhamnogalacturonan I; D010368:Pectins; D016695:Glycosyltransferases; C000612484:PAGR protein, Arabidopsis; C005653:arabinogalactan
Arabidopsis thaliana; Cell wall; Nicotiana benthamiana; Pectin; Pollen tube; Rhamnogalacturonan-I