Polar protein exocytosis: Lessons from plant pollen tube

Abstract

Exocytosis is a highly regulated outward secretion process which participates in multiple cellular events including membrane modeling, cell polarization, cell wall formation, and cell signaling. Pollen tube is regarded as an ideal model plant cell system to study the machinery and regulation of exocytosis. Vigorous exocytic vesicle fusion with the apical plasma membrane supports the rapid and polarized pollen tube growth. However, the molecular identities and regulations of these exocytic vesicles still remain largely unexplored. Recent discoveries of various exocytic markers and regulatory proteins of exocytic pathway have advanced this research field rapidly. Here, we review and summarize the recent development and progress of protein exocytic trafficking and regulation in pollen tube, with emphasize on the pertinent questions for future understanding the functional roles of exocytosis in cell polarization and polar cell wall formation.