The Cell Wall Pectic Polymer rhamnogalacturonan-II Is Required for Proper Pollen Tube Elongation: Implications of a Putative Sialyltransferase-Like Protein

Ann Bot. 2014 Oct;114(6):1177-88. doi: 10.1093/aob/mcu093. Epub 2014 May 13.

Abstract

Background and aims: 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.

Key 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.

Keywords: Arabidopsis thaliana; Dha; Kdo; RG-II; Rhamnogalacturonan-II; pectin motif; plant cell wall; pollen tube; sialyltransferase-like protein.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / enzymology*
  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism
  • Cell Wall / metabolism
  • Gene Expression Regulation, Plant*
  • Genes, Reporter
  • Mutation
  • Organ Specificity
  • Pectins / metabolism*
  • Phenotype
  • Pollen / enzymology
  • Pollen / genetics
  • Pollen / growth & development
  • Pollen Tube / enzymology*
  • Pollen Tube / genetics
  • Pollen Tube / growth & development
  • Polymers / metabolism
  • Sialyltransferases / genetics*
  • Sialyltransferases / metabolism
  • Sugar Acids / chemistry
  • Sugar Acids / metabolism

Substances

  • Arabidopsis Proteins
  • Polymers
  • Sugar Acids
  • rhamnogalacturonan II
  • 2-keto-3-deoxyoctonate
  • Pectins
  • SIA2 protein, Arabidopsis
  • Sialyltransferases