The Rrop GTPase switch turns on polar growth in pollen.

Pollen-tube growth not only represents an essential stage of plant reproduction but also provides an attractive model for studying cell polarity and morphogenesis. For many years, pollen-tube growth has been known to require a tip-focused Ca2+ gradient and dynamic F actin, but the way that these are controlled remained a mystery until recently. Rop appears to be activated at growth sites by a tip-localized growth cue, acting as a central switch that controls the polar growth of pollen tubes, probably having its effect through phosphoinositides and Ca2+. These findings have begun to shed light on the molecular basis of pollen-tube growth and cell morphogenesis in plants.