RopGEF1 Plays a Critical Role in Polar Auxin Transport in Early Development

Abstract

Polar auxin transport, facilitated by the combined activities of auxin influx and efflux carriers to maintain asymmetric auxin distribution, is essential for plant growth and development. Here, we show that Arabidopsis (Arabidopsis thaliana) RopGEF1, a guanine nucleotide exchange factor and activator of Rho GTPases of plants (ROPs), is critically involved in polar distribution of auxin influx carrier AUX1 and differential accumulation of efflux carriers PIN7 and PIN2 and is important for embryo and early seedling development when RopGEF1 is prevalently expressed. Knockdown or knockout of RopGEF1 induces embryo defects, cotyledon vein breaks, and delayed root gravity responses. Altered expression from the auxin response reporter DR5rev:GFP in the root pole of RopGEF1-deficient embryos and loss of asymmetric distribution of DR5rev:GFP in their gravistimulated root tips suggest that auxin distribution is affected in ropgef1 mutants. This is reflected by the polarity of AUX1 being altered in ropgef1 embryos and roots, shifting from the normal apical membrane location to a basal location in embryo central vascular and root protophloem cells and also reduced PIN7 accumulation at embryos and altered PIN2 distribution in gravistimulated roots of mutant seedlings. In establishing that RopGEF1 is critical for AUX1 localization and PIN differential accumulation, our results reveal a role for RopGEF1 in cell polarity and polar auxin transport whereby it imapcts auxin-mediated plant growth and development.

FERONIA regulates auxin‐mediated lateral root development and primary root gravitropism

“…In leaf pavement cells, the auxin-activated interaction of ROP2 with RIC4 inhibits PIN endocytosis by stabilizing cortical actin filaments, whereas the RIC4-dependent assembly of cortical F-actin promotes lobe outgrowth [53]. Recently, we showed that a Rho of plants (Rop)-guanine nucleotide exchange factor, RopGEF1, regulates the polarized localization of AUX1 and affects the distribution of PIN7 and PIN2 [27]. Recently, we showed that a Rho of plants (Rop)-guanine nucleotide exchange factor, RopGEF1, regulates the polarized localization of AUX1 and affects the distribution of PIN7 and PIN2 [27].…”

“…F3 seedlings were subjected to further experimentation, with the marker plants as controls. Quantification of the seedling F-actin density was performed as described by Liu et al [27] and according to the methods of Dyachok et al [28] and Higaki et al [29]. The density of F-actin was defined as the ratio of the filament occupancy and cell area, as described by Dyachok et al [28].…”

“…In root cells, the SPK1-ROP6-RIC1 pathway inhibits PIN2 internalization by stabilizing actin filaments [26]. Recently, we showed that a Rho of plants (Rop)-guanine nucleotide exchange factor, RopGEF1, regulates the polarized localization of AUX1 and affects the distribution of PIN7 and PIN2 [27]. Interestingly, ropgef1 mutants showed impaired actin filament accumulation in root cells, suggesting that RopGEF1 participates in PAT by modulating actin filaments [27].…”

“…Recently, we showed that a Rho of plants (Rop)-guanine nucleotide exchange factor, RopGEF1, regulates the polarized localization of AUX1 and affects the distribution of PIN7 and PIN2 [27]. Interestingly, ropgef1 mutants showed impaired actin filament accumulation in root cells, suggesting that RopGEF1 participates in PAT by modulating actin filaments [27]. Acting as an upstream regulator of GEF-RAC/ROPs, FER probably affects actin stability through downstream signaling components.…”

Genome-wide analysis of RopGEF gene family to identify genes contributing to pollen tube growth in rice (Oryza sativa)

“…Arabidopsis has 14 RopGEFs in its genome, with a high degree of sequence similarity [8,9]. Functional studies showed that AtRopGEF1 and AtRopGEF4 specifically regulate ROP11 in abscisic acid (ABA)-mediated stomatal closure [10], and that AtRopGEF1 plays a role in controlling lateral root growth [11] and polar auxin transport to achieve cell polarity during early plant development [12]. Among them, seven members are specifically or highly expressed in pollen tubes and function redundantly [8,13].…”