The main focus of research has been the role of plant hydroxyproline-rich proteoglycans known as arabinogalactan proteins, in particular regarding the development and guidance of the pollen tube, as well as other phenomena related to plant reproduction. Main methodological approaches include gene expression analyses, promoter analyses, and Arabidopsis null mutant studies. Lectin-receptor kinases is another protein family whose members are being scrutinized for their role in pollen development.