The Membrane Dynamics of Root Hair Morphogenesis
Root hair elongation requires the delivery of cell wall materials and new membrane to the growing tip. This occurs via polarized secretion, a process mediated by proteins called SNARES (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) on vesicle and target membranes. Although the Arabidopsisgenome encodes an unprecedented number of SNARES, none have thus far been specifically implicated in root hair growth. Forward and reverse genetic approaches, however, have identified a Sec1 protein and a Rab GTPase implicated in root hair morphogenesis. Such proteins gate SNARE interactions and ensure the specificity and fidelity of membrane fusion. ARF GTPases, involved in the sorting of cargo upon vesicle formation, have also been implicated in root hair morphogenesis. In addition to a role in tip growth, polarized secretion may play a role in the establishment or maintenance of polarity, or both. Plasma membrane microdomains enriched in sterols or phosphatidylinositol phosphates may act as anchors for the polarization of the trafficking apparatus. In this chapter I discuss models whereby plant homologues of RHO GTPases (ROPs), master choreographers of cellular polarity, target plasma membrane domains for vesicle delivery and fusion, and how polarity, once established, is maintained.
KeywordsRoot Hair Lipid Raft Membrane Fusion Membrane Traffic Golgi Stack
I am very grateful to Erik Nielsen, Shaul Yalovsky, Hyung-Taeg Cho, Anne Mie Emons, Tijs Ketelaar, and J.E. Rothman for their stimulating discussions and images. Research in my laboratory is supported by grant AS110/4–3 from the DFG.
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