抄録
Arabinogalactan-proteins (AGPs) are a class of proteoglycans found at the surface of plant cells and in plant gums and secretions. Their functions in these locations are far from clear although various studies involving genetic, inhibitor and immunochemical analyses are indicating roles in cell expansion and the mediation of local cell interactions that underpin developmental events. AGPs are structurally diverse within a plant: Arabidopsis thaliana has at least 40 genes encoding AGP core proteins. Proline-rich domains that carry AGP glycans can be associated with a range of other protein motifs including fasciclin domains. AGP glycan components are decorated arabino-3,6-galactans and are highly heterogeneous. Monoclonal antibodies to AGP glycan epitopes indicate extensive regulation of glycan structure in relation to developmental events in meristems and that the precise developmental occurrence of an AGP epitope can vary between species. The relationship between AGP glycans and core protein diversity has not been fully elucidated and understanding the precise biochemical/cell biological functions of individual AGPs remains a challenge. A chemical disruptor of AGPs, a synthetic phenyl glycoside, known as β-glucosyl Yariv reagent (βGlcY) is a useful tool for the functional analysis of AGPs. The application βGlcY to living cells can result in the disruption of cell proliferation, disruption of cell expansion or modified cell development. In the Arabidopsis seedling root the application of βGlcY blocks the final stage of accelerated cell elongation and also disrupts a staged occurrence of pectin-associated 1,4-galactan. Analysis of the moss Physcomitrella patens indicates the presence of several classes of AGP core protein sequences and the presence of AGP glycan epitopes at all plasma membranes. Physcomitrella grows by tip-extending apical cells and this cell expansion is sensitive to βGlcY application. Genetic and experimental tractability makes this a suitable system for the structural and functional analysis of AGPs as well as providing an evolutionary perspective.
