Regulation of stem biomechanics by Fasciclin-like arabinogalactan proteins in Arabidopsis thaliana

E Liu1, C Macmillan2, K Ford1, A Bacic1 and K Johnson1

  1. ARC Centre of Excellence in Plant Cell Walls, School of BioSciences, University of Melbourne, Parkville, Vic 3010, Australia
  2. CSIRO Agriculture, GPO Box 1600, Canberra, ACT 2601, Australia

Our natural and plantation forests not only provide aesthetic beauty, they contribute to vegetative biomass that represents 90% of the captured carbon and is our most renewable bio-resource. The bulk of the biomass consists of secondary cell walls, which are thick, rigid and deposited on the inner side of the primary walls in specialized tissues. Secondary cell wall development is an area of intense interest given its importance for plant growth, water conductance and human applications such as biofuels, bio-inspired materials/bio-composites, construction and paper. Secondary cell walls are composed of roughly equal proportions of cellulose, hemicelluloses, lignin and some proteins. A group of plant cell wall glycoproteins, the Fasciclin-Like Arabinogalactan proteins (FLAs) have been implicated in regulating secondary cell wall development and influencing their biomechanical properties (MacMillan et al., 2010). FLAs are a sub-class of the arabinogalactan-proteins (AGPs), glycoproteins implicated in cell wall sensing and signalling and proposed to cross-link to pectins in the wall (Tan et al., 2013). The fasciclin (FAS) domain has been shown to be involved in cell adhesion and development in mammals, insects and algae. Glycoproteins such as FLAs are therefore fascinating ‘chimeric’ molecules with a number of interesting properties; being able to potentially form protein-protein, protein-carbohydrate and carbohydrate-carbohydrate interactions in the wall. Using Arabidopsis as a model system, we have focussed on a subset FLAs (FLA11, FLA12 and FLA16) that are expressed in cells undergoing secondary cell wall development. Preliminary evidence suggests these FLAs influence the amount and angle of cellulose deposition, the most abundant cell wall polymer that forms the structural basis for all cell walls. Through mutant studies, biomechanical analysis and examination of FLA location we are gaining insight into the function(s) of these complex glycoproteins. MacMillan et al. (2010) Plant J: 62, 689-703 Tan et al. (2013) Plant Cell: 25, 270-287.