Figure 3.
A possible model of auxin-ROP signaling in pollen tube and root hair growth. Auxin may be the polarizing signal that initiates the ROP-dependent tip growth. ROP signaling can be modulated by various upstream regulators and downstream effectors. Tip-localized activated ROP regulates the Ca2+ gradient, actin dynamic as well as exocytic trafficking during tip growth. RLK, receptor-like kinases; GAP, GTPase activating proteins; GEF, guanine nucleotide exchange factor; RIC, Rop-interacting CRIB-containing proteins; ICR, interactor of constitutively active ROPs; ROS, reactive oxygen species