Plant cell walls are intricate structures comprised largely of polysaccharides, including a network of cellulose microfibrils-xyloglucans, pectins, and highly glycosylated hydroxyproline-rich O-glycoproteins (HRGPs), such as extensins (EXTs) and arabinogalactan proteins (AGPs). Pollen tubes are single cells that require intensive cell-wall amendments to accommodate apical cell expansion in a process known as tip growth. Pollen tube growth is essential for successful fertilization in plants and they constitute an excellent model to understand plant biology at a single cell level. We propose to functionally dissect the signaling feedback loop that allows for polarized growth of pollen tubes in Arabidopsis thaliana. The present project pursues the identification of key genes with roles in protein O-glycosylation that are crucial for pollen tube growth. We have employed transcriptional modular networks to identify components necessary for polarized growth of pollen tubes. We explored the biological function of HRGPs and proline-rich extensin-like receptor kinase (PERK) involved in tip growth. Our results suggest that PERK receptors and O-glycosilation of HRGPs are required for pollen tube growth. We plan to continue targeting these processes by biochemical inhibition and by different modes of reverse genetics, and assess blockage of polarized growth. In this project I proposed to use the yeast two hybrid system to isolate genes that encode proteins which interact with the cytoplasmic domain of PERKs. Using knowledge gained from model systems like Arabidopsis thaliana, we will investigate in the future the regulation of pollen tube growth in crop plants. The results obtained in these experimental lines could be applicable to the polarized cell growth and expansion in many other plant cell types.