ARMADILLO REPEAT ONLY proteins confine Rho GTPase signalling to polar growth sites

Arabidopsis pavement cell shape formation involves spatially confined ROPGAP regulators

“…Both PHGAPs displayed uniform distribution across most of the periclinal cell face, but were also distinctly aligning with microtubule subpopulations along anticlinal cell faces and across cell-face boundaries of indentation regions. Although PHGAPs also associated with phospholipids, 35 their striation accumulation on anticlinal faces relied on microtubules, but not on actin filaments. During pavement cell morphogenesis, actin and microtubule cytoskeleton fulfill different functions.…”

“…27 However, a potential role in cell polarity signaling, as established for their paralog REN1 in tip-growing cells, remained elusive. 20,27,35 Inspection of cotyledons of the established phgap1-1phgap2-1 double mutant and additional T-DNA allele combinations, phgap1-2phgap2-2 and phgap1-1phgap2-2, revealed differences in the aspect ratios of roundish wild type and lancet-shaped mutant cotyledons (Figures 1A, 1B, and S1A-S1D). 27 Rosette leaves presented a similar phenotype, implicating PHGAPs in leaf morphogenesis (Figure 1C).…”

“…27,34 Furthermore, REN1/PHGAP-interacting ARMADILLO REPEAT ONLY (ARO) scaffold ROP2-mediated cell polarity signaling modules, including REN1 during root hair growth in Arabidopsis. 35 Nevertheless, GAPs involved in ROP inactivation during pavement cell development were unknown.…”

Nanodomain-mediated lateral sorting drives polarization of the small GTPase ROP2 in the plasma membrane of root hair cells

“…Indeed, in epidermal cells of the root elongation zone, ROP6 was shown to be immobilized upon auxin treatment in PS-dependent nanodomains, which were required for inhibition of cell elongation and consequential gravitropic root bending (Platre et al, 2019). In a recent study on the maintenance of ROP polarization during root hair growth, ARMADILLO REPEAT ONLY (ARO) proteins were found to stabilize the interaction between ROP1 and the ROP1 enhancer GAP (REN-GAP) REN1 in PM nanodomains, thus confining ROP signaling to the polar growth site (Kulich et al, 2020). Although nanodomain association had not yet been considered in the Turing-like model by Payne and Grierson 2009, our findings are generally in line with a reaction-diffusion mechanism as we demonstrate that a mobility-regulating nanodomainassociation plays a role already during the initial steps of ROP polarization, driving the lateral sorting of GTPases and thereby leading to the formation of the RHID.…”

GTPase ROP6 negatively modulates phosphate deficiency through inhibition of PHT1;1 and PHT1;4 in Arabidopsis thaliana

“…The Rho of plant (ROP) GTPases act as molecular switches in various signaling pathways by cycling between their active GTP-bound and inactive GDP-bound form (Yang, 2002;Feiguelman et al, 2018). They participate in multiple cellular signaling processes, such as cell polarity establishment and maintenance (Fu et al, 2005;Hwang et al, 2005;Kulich et al, 2020), cytoskeletal dynamics and vesicle trafficking (Fu et al, 2009;Burkart et al, 2015), response to abscisic acid (ABA) and indoleacetic acid hormone signals (Xu et al, 2010;Lin et al, 2012;Li et al, 2012aLi et al, , 2018Yu et al, 2016;Platre et al, 2019), defense against pathogens (Poraty-Gavra et al, 2013; Venus and Oelmuller, 2013), H 2 O 2 production (Airica et al, 2002), guard cell opening and closing (Jeon et al, 2008;Hong et al, 2016), as well as cell wall growth (Sugiyama et al, 2019). Arabidopsis contains 11 ROP members, named ROP1-ROP11, which can be divided into four groups: type I (ROP8), type II (ROP9, ROP10, ROP11), type III (ROP7), and type IV (ROP1-ROP6) (Yang, 2002).…”