The cell wall pectic polymer rhamnogalacturonan-II is required for proper pollen tube elongation: implications of a putative sialyltransferase-like protein.
OBJECTIVE
Rhamnogalacturonan-II (RG-II) is one of the pectin motifs found in the cell wall of all land plants. It contains sugars such as 2-keto-3-deoxy-d-lyxo-heptulosaric acid (Dha) and 2-keto-3-deoxy-d-manno-octulosonic acid (Kdo), and within the wall RG-II is mostly found as a dimer via a borate diester cross-link. To date, little is known regarding the biosynthesis of this motif. Here, after a brief review of our current knowledge on RG-II structure, biosynthesis and function in plants, this study explores the implications of the presence of a Golgi-localized sialyltransferase-like 2 (SIA2) protein that is possibly involved in the transfer of Dha or Kdo in the RG-II of Arabidopsis thaliana pollen tubes, a fast-growing cell type used as a model for the study of cell elongation.


METHODS
Two heterozygous mutant lines of arabidopsis (sia2-1+/- and qrt1 × sia2-2+/-) were investigated. sia2-2+/- was in a quartet1 background and the inserted T-DNA contained the reporter gene β-glucuronidase (GUS) under the pollen-specific promoter LAT52. Pollen germination and pollen tube phenotype and growth were analysed both in vitro and in vivo by microscopy.


RESULTS
Self-pollination of heterozygous lines produced no homozygous plants in the progeny, which may suggest that the mutation could be lethal. Heterozygous mutants displayed a much lower germination rate overall and exhibited a substantial delay in germination (20 h of delay to reach 30 % of pollen grain germination compared with the wild type). In both lines, mutant pollen grains that were able to produce a tube had tubes that were either bursting, abnormal (swollen or dichotomous branching tip) or much shorter compared with wild-type pollen tubes. In vivo, mutant pollen tubes were restricted to the style, whereas the wild-type pollen tubes were detected at the base of the ovary.


CONCLUSIONS
This study highlights that the mutation in arabidopsis SIA2 encoding a sialyltransferase-like protein that may transfer Dha or Kdo on the RG-II motif has a dramatic effect on the stability of the pollen tube cell wall.
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA4358, Normandy University, University of Rouen, Institut de Recherche et d'Innovation Biomédicale, 76821 Mont-Saint-Aignan, France.
Marie
M
Dumont
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA4358, Normandy University, University of Rouen, Institut de Recherche et d'Innovation Biomédicale, 76821 Mont-Saint-Aignan, France.
Arnaud
A
Lehner
Laboratoire Biologie des Plantes & Innovation (BIOPI) EA3900, University of Picardie Jules Verne, 80039 Amiens, France.
Sophie
S
Bouton
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA4358, Normandy University, University of Rouen, Institut de Recherche et d'Innovation Biomédicale, 76821 Mont-Saint-Aignan, France.
Marie Christine
MC
Kiefer-Meyer
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA4358, Normandy University, University of Rouen, Institut de Recherche et d'Innovation Biomédicale, 76821 Mont-Saint-Aignan, France Institut Jean-Pierre Bourgin UMR1318 INRA-AgroParisTech, 78026 Versailles Cedex, France.
Aline
A
Voxeur
Laboratoire Biologie des Plantes & Innovation (BIOPI) EA3900, University of Picardie Jules Verne, 80039 Amiens, France.
Jérôme
J
Pelloux
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA4358, Normandy University, University of Rouen, Institut de Recherche et d'Innovation Biomédicale, 76821 Mont-Saint-Aignan, France.
Patrice
P
Lerouge
Laboratoire de Glycobiologie et Matrice Extracellulaire Végétale (Glyco-MEV) EA4358, Normandy University, University of Rouen, Institut de Recherche et d'Innovation Biomédicale, 76821 Mont-Saint-Aignan, France jean-claude.mollet@univ-rouen.fr.
Jean-Claude
JC
Mollet
D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002473:Cell Wall / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D009154:Mutation; D009928:Organ Specificity; D010368:Pectins / Q000378:metabolism*; D010641:Phenotype; D011058:Pollen / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D053205:Pollen Tube / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D011108:Polymers / Q000378:metabolism; D012799:Sialyltransferases / Q000235:genetics* / Q000378:metabolism; D013400:Sugar Acids / Q000737:chemistry / Q000378:metabolism
D029681:Arabidopsis Proteins; D011108:Polymers; D013400:Sugar Acids; C042492:rhamnogalacturonan II; C002532:2-keto-3-deoxyoctonate; D010368:Pectins; C000598696:SIA2 protein, Arabidopsis; D012799:Sialyltransferases
Arabidopsis thaliana; Dha; Kdo; RG-II; Rhamnogalacturonan-II; pectin motif; plant cell wall; pollen tube; sialyltransferase-like protein