A Novel ROP/RAC Effector Links Cell Polarity, Root-Meristem Maintenance, and Vesicle Trafficking

Abstract

ROP/RAC GTPases are master regulators of cell polarity in plants, implicated in the regulation of diverse signaling cascades including cytoskeleton organization, vesicle trafficking, and Ca(2+) gradients [1-8]. The involvement of ROPs in differentiation processes is yet unknown. Here we show the identification of a novel ROP/RAC effector, designated interactor of constitutive active ROPs 1 (ICR1), that interacts with GTP-bound ROPs. ICR1 knockdown or silencing leads to cell deformation and loss of root stem-cell population. Ectopic expression of ICR1 phenocopies activated ROPs, inducing cell deformation of leaf-epidermis-pavement and root-hair cells [3, 5, 6, 9]. ICR1 is comprised of coiled-coil domains and forms complexes with itself and the exocyst vesicle-tethering complex subunit SEC3 [10-13]. The ICR1-SEC3 complexes can interact with ROPs in vivo. Plants overexpressing a ROP- and SEC3-noninteracting ICR1 mutant have a wild-type phenotype. Taken together, our results show that ICR1 is a scaffold-mediating formation of protein complexes that are required for cell polarity, linking ROP/RAC GTPases with vesicle trafficking and differentiation.

The Modified Flavonol Glycosylation Profile in the Arabidopsis rol1 Mutants Results in Alterations in Plant Growth and Cell Shape Formation

“…This may be due to overlapping expression patterns of the (assumed) functionally redundant genes RHM1 (i.e., ROL1) to RHM3 (Reiter and Vanzin, 2001). A very similar pavement cell phenotype is restricted spatially to the adaxial side of cotyledons in the ROP-interacting protein mutant icr1 (Lavy et al, 2007), suggesting a coordinated regulation of this process. It is an attractive hypothesis that, under natural conditions, plants have the potential to modify the flavonol glycosylation profile as a means to modulate growth and development.…”

EXO70C2 Is a Key Regulatory Factor for Optimal Tip Growth of Pollen

“…Sekereš et al (2017) Genevestigator). Especially, a co-operation with ROP GTPases, major regulators of cell 519 polarity, is highly probable, because their interaction with exocyst subunits EXO70B1 and 520 SEC3 has been already documented (Hong et al, 2016;Lavy et al, 2007). Future 521 experimental work will likely reveal additional functional interactions of EXO70C2 and 522 EXO70C1 with other players involved in tip growth and elucidate the precise mechanism of 523 their action.…”

Interdependence of Endomembrane Trafficking and Actin Dynamics during Polarized Growth of Arabidopsis Pollen Tubes

“…Plausible candidates for such signaling proteins are ROP GTPases. ROP GTPases regulate dynamic actin polymerization in pollen tubes (Fu et al, 2001), and both in pollen tubes and in sporophytic cells they also regulate membrane trafficking through actin dynamics and/or their effectors (Lavy et al, 2007;Lee et al, 2008). ROP-GTP is spatiotemporally restricted to the apical plasma membrane ) by the coordinated function of a receptor kinase (PRK2a) and a ROP guanine nucleotide exchange factor (Zhang and McCormick, 2007), suggesting that ROP-mediated signaling is a convergence point for actin dynamics and endomembrane trafficking in pollen tubes.…”