Arabinogalactan proteins in plant sexual reproduction

Arabinogalactan proteins (AGPs) are a class of plant extracellular-matrix proteins believed to participate in a broad range of processes involving the plant cell surface. They are extremely abundant in female reproductive tissues and in pollen tubes, the haploid male structures that traverse the diploid female reproductive tissues to deliver sperms to the egg cells. The prevalence of AGPs in reproductive tissues has led to speculations that they play significant functional roles ranging from serving as nutrient resources to cell-cell recognition in plant reproduction. Recent research from several laboratories demonstrated functional participation by AGPs in reproductive processes and began to examine the mechanisms underlying these functional roles. An overview of these recent studies will be discussed with a historical perspective as well as with a view towards future studies in establishing the significance of AGPs that, as a class, they have prominent roles in plant sexual reproduction in multiple and diverse ways.