The complex structures of arabinogalactan-proteins and the journey towardsunderstanding function

Arabinogalactan-proteins (AGPs) are a family of complex proteoglycans found in all higher plants. Although the precise function(s) of any single AGP i s unknown, they are implicated in diverse developmental roles such as diffe rentiation, cell-cell recognition, embryogenesis and programmed cell death. DNA sequencing projects have made possible the identification of the genes encoding a large number of putative AGP protein backbones. In contrast, ou r understanding of how AGPs undergo extensive post-translational modificati on is poor and it is important to understand these processes since they are likely to be critical for AGP function. Genes believed to be responsible f or post-translational modification of an AGP protein backbone, include prol yl hydroxylases, glycosyl transferases, proteases and glycosylphosphatidyli nositol-anchor synthesising enzymes. Here we examine models for proteoglyca n function in animals and yeast to highlight possible strategies for determ ining the function(s) of individual AGPs in plants.