Rhamnogalacturonan II and plant growth


Principal investigator: Patrice Lerouge

Participants: Jean Claude Mollet, Arnaud Lehner


During the last four-year period, the investigation of RG-II role in the formation of the primary cell wall was mainly based on the analysis of plant mutants affected in the biosynthesis of RG-II constitutive monomers. In the project, we propose 1- to characterise new mutants affected in RG-II-specific glycosyltransferases and 2- to investigate the function of RG-II in the primary cell wall formation during plant growth. Concerning the identification of new RG-II mutants, we propose to select putative glycosyltransferases (GTs) involved in the Golgi-based synthesis of RG-II by searching Arabidopsis genes that are co-expressed with RG-II xylosyltransferase (RGXT1/2), the unique RG-II-specific GT identified so far (Egelund et al., 2006). A first investigation led to a list of 8 candidate genes encoding for type II proteins that are not predicted in CAZy (http://www.cazy.org). For each candidate GT, its intracellular localisation will be investigated using confocal microscopy of the corresponding GFP-fused proteins. Furthermore, the role of the putative GTs in RG-II biosynthesis will be carried out by analysing the Arabidopsis mutants or RNAi-silenced lines as well as through glycosyltransferase bioassays using GTs expressed in insect or plant cells. In addition, effects of their inactivation on RG-II dimerisation and plant growth will be investigated. Previous studies have shown that the inactivation of RG-II synthesis resulted in non viable null mutants (Delmas et al., 2008; Voxeur et al., 2011). In consequence, to investigate the function of RG-II in the primary cell wall formation and plant growth, we propose to inactivate RG-II biosynthesis at various developmental stages by utilising inducible gene knockout strategies targeting the RG-II specific GTs identified in the first part of this project or targeting the biosynthesis of specific monomers (Kdo, L-Gal). The organisation of the primary cell walls in the newly formed post-induction tissues will be investigated. RNAi directed against genes encoding RG-II GTs will also be utilised in order to generate plants with a range of developmental phenotypes due to the variation in efficiency of gene downregulation by RNAi in different transgenic plants.