Chen X, Naramoto S, Robert S, Tejos R, Löfke C, Lin D, Yang Z, Friml J
ABP1 and ROP6 GTPase Signaling Regulate Clathrin-Mediated Endocytosis in Arabidopsis Roots
Curr Biol. 2012, 22(14):1326-32

Abstract
The dynamic spatial and temporal distribution of the crucial plant signaling molecule auxin is achieved by feedback coordination of auxin signaling and intercellular auxin transport pathways [1,2]. Developmental roles of auxin have been attributed predominantly to its effect on transcription; however, an alternative pathway involving AUXIN BINDING PROTEIN1 (ABP1) has been proposed to regulate clathrin-mediated endocytosis in roots and Rho-like GTPase (ROP)-dependent pavement cell interdigitation in leaves [3,4]. In this study, we show that ROP6 and its downstream effector RIC1 regulate clathrin association with the plasma membrane for clathrin-mediated endocytosis, as well as for its feedback regulation by auxin. Genetic analysis revealed that ROP6/RIC1 acts downstream of ABP1 to regulate endocytosis. This signaling circuit is also involved in the feedback regulation of PIN-FORMED 1 (PIN1) and PIN2 auxin transporters activity (via its constitutive endocytosis) and corresponding auxin transport-mediated processes, including root gravitropism and leave vascular tissue patterning. Our findings suggest that the signaling module auxin–ABP1–ROP6/RIC1–clathrin–PIN1/PIN2 is a shared component of the feedback regulation of auxin transport during both root and aerial development.

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