Localization of a Rho GTPase Implies a Role in Tip Growth and Movement of the Generative Cell in Pollen Tubes

Abstract

The Rho family GTPases function as key molecular switches, controlling a variety of actin-dependent cellular processes, such as the establishment of cell polarity, cell morphogenesis, and movement in diverse eukaryotic organisms. A novel subfamily of Rho GTPases, Rop, has been identified in plants. Protein gel blot and RNA gel blot hybridization analyses indicated that one of these plant Rho GTPases, Rop1, is expressed predominantly in the male gametophyte (pollen and pollen tubes). Cell fractionation analysis of pollen tubes showed that Rop is partitioned into soluble and particulate fractions. The particulate Rop could be solubilized with detergents but not with salts, indicating that it is tightly bound to membranes. The membrane association appears to result from membrane anchoring via a geranylgeranyl group because an in vitro isoprenylation assay demonstrated that Rop1Ps is geranylgeranylated. Subcellular localization, using indirect immunofluorescence and confocal microscopy, showed that Rop is highly concentrated in the cortical region of the tube apex and in the periphery of the generative cell. The cortical Rop protein at the apex forms a gradient with decreasing concentration from tip to base and appears to be associated with the plasma membrane. These results suggest that the apical Rop GTPase may be involved in the signaling mechanism that controls the actin-dependent tip growth of pollen tubes. Localization of the Rop GTPase to the periphery of the generative cell is analogous to that of myosin, suggesting that the Rop GTPase plays an important role in the modulation of an actomyosin motor system involved in the movement of the generative cell.

Inhibition of Geranylgeranylation Mediates the Effects of 3-Hydroxy-3-methylglutaryl (HMG)-CoA Reductase Inhibitors on Microglia

“…51 for a recent review). It is possible that the pathways leading to cytoskeletal versus gene regulation diverge at the very beginning of the isoprenylation step and that different members of the Rho family initiate different cascades (52)(53)(54)(55)(56)(57)(58)(59)(60)(61).…”

Protein Geranylgeranyltransferase I Is Involved in Specific Aspects of Abscisic Acid and Auxin Signaling in Arabidopsis

“…org/ptmdb/results.htm). These include eight Rop GTPases, which regulate actin organization (Fu et al, 2001(Fu et al, , 2002Gu et al, 2003), pollen tube tip growth (Lin et al, 1996;Fu et al, 2001;Gu et al, 2003), ABA and auxin signaling (Lemichez et al, 2001;Li et al, 2001;Tao et al, 2002), and other processes; AIG1, which is involved in RPS2-and avrRpt2-dependent responses to Pseudomonas infection (Reuber and Ausubel, 1996); Aux2-11, a negative regulator of auxin signaling (Wyatt et al, 1993;Caldelari et al, 2001;Dharmasiri and Estelle, 2002); and other proteins. Thus, it is surprising that era1, ggb, and plp phenotypes are not more severe.…”

Tansley Review No. 108

“…Farnesylation by Era1 of racand rho-type GTPases may be important for cytosolic traffic or transcriptional functions (Bonetta & McCourt, 1998) as well as protein-protein interactions mediated by ras and related GTPases (Bokoch & Der, 1993 ;Casey, 1995 ;Zerial & Huber, 1995 ;Martin, 1997). In fact, a rho-like GTPase, Rop1, that is localized to the apex of Pisum pollen tubes (Lin et al, 1996) has been implicated in microfilament-based intracellular transport of vesicles. Intriguingly, actin organization has been implicated also in the regulation of guard cell ion channels and stomatal function (Kim et al, 1995).…”