Rapid tip growth: Insights from pollen tubes

Pollen tubes extend rapidly in an oscillatory manner by the extreme form of polarized growth, tip growth, and provide an exciting system for studying the spatiotemporal control of polarized cell growth. The Rho-family ROP GTPase is a key signaling molecule in this growth control and is periodically activated at the apical plasma membrane to spatially define the apical growth region and temporally precede the burst of growth. The spatiotemporal dynamics of ROP GTPase is interconnected with actin dynamics and polar exocytosis that is required for tip-targeted membrane and wall expansion. Recent advances in the study of the mechanistic interlinks between ROP-centered signaling and spatiotemporal dynamics of cell membrane and wall remodeling will be discussed.

• Pollen tubes, which extend rapidly by polarized growth in an oscillatory manner, provide an excellent model system for investigating the mechanism behind sustained rapid tip growth.
• The conserved Rho-family ROP GTPase controls this polarized and oscillatory growth.
• ROP GTPase signaling is intertwined with actin dynamics and polar exocytosis, which are essential for tip growth, and may also be linked to cell wall mechanics that also regulate tip growth.
• Comparison of the mechanisms for tip growth pollen tubes and other tip growth systems is emphasized.