RPA, a Class II ARFGAP Protein, Activates ARF1 and U5 and Plays a Role in Root Hair Development in Arabidopsis

Abstract

The polar growth of plant cells depends on the secretion of a large amount of membrane and cell wall materials at the growing tip to sustain rapid growth. Small GTP-binding proteins, such as Rho-related GTPases from plants and ADP-ribosylation factors (ARFs), have been shown to play important roles in polar growth via regulating intracellular membrane trafficking. To investigate the role of membrane trafficking in plant development, a Dissociation insertion line that disrupted a putative ARF GTPase-activating protein (ARFGAP) gene, AT2G35210, was identified in Arabidopsis (Arabidopsis thaliana). Phenotypic analysis showed that the mutant seedlings developed isotropically expanded, short, and branched root hairs. Pollen germination in vitro indicated that the pollen tube growth rate was slightly affected in the mutant. AT2G35210 is specifically expressed in roots, pollen grains, and pollen tubes; therefore, it is designated as ROOT AND POLLEN ARFGAP (RPA). RPA encodes a protein with an N-terminal ARFGAP domain. Subcellular localization experiments showed that RPA is localized at the Golgi complexes via its 79 C-terminal amino acids. We further showed that RPA possesses ARF GTPase-activating activity and specifically activates Arabidopsis ARF1 and ARF1-like protein U5 in vitro. Furthermore, RPA complemented Saccharomyces cerevisiae glo3D gcs1D double mutant, which suggested that RPA functions as an ARFGAP during vesicle transport between the Golgi and the endoplasmic reticulum. Together, we demonstrated that RPA plays a role in root hair and pollen tube growth, most likely through the regulation of Arabidopsis ARF1 and ARF1-like protein U5 activity.

A Class I ADP-Ribosylation Factor GTPase-Activating Protein Is Critical for Maintaining Directional Root Hair Growth in Arabidopsis

“…It was shown recently that AGD10, a class II ARF-GAP, also is important for tip growth in Arabidopsis root hairs. The root hair phenotype of agd10, however, was different from that of agd1 in that agd10 had very short bulbous root hairs and also exhibited defects in pollen germination (Song et al, 2006). This indicates that some of the mechanisms by which AGD10 regulates tip growth in plants might be distinct from those of AGD1.…”

“…AGD10 is more closely related to the mammalian ARF-GAP1, which has a simpler domain organization than the AZAP class of ARF-GAPs to which AGD1 belongs. AGD10 and AGD7, another class II ARF-GAP, only contain a GAP domain and localize to Golgi stacks (Vernoud et al, 2003;Song et al, 2006;Min et al, 2007), in agreement with mammalian ARF-GAP1 localization . AGD1 and AGD3, on the other hand, partially localized to FM4-64-labeled endocytic vesicles and the trans-Golgi network ( Fig.…”

“…The differences in localization, domain organization, and possibly ARF substrate preference between AGD1 and AGD10 could likely explain the different nature of tip growth defects caused by their respective mutants. Whereas AGD10 activates the GTPase-hydrolyzing activity of plant ARF1 (Song et al, 2006), the precise plant ARF proteins that are substrates of the class I ARF-GAPs remain to be determined.…”

“…Similarly, expression of the GTP-locked form of ARF1 induced the formation of bulged root hairs, which occurred concomitantly with altered ROP localization (Xu and Scheres, 2005). Recently, an Arabidopsis mutant in a class II ARF-GAP displayed deformed root hairs and reduced growth of pollen tubes, further implicating ARFs in tip growth maintenance (Song et al, 2006).…”

A Small GTPase of the Rab Family Is Required for Root Hair Formation and Preinfection Stages of the Common Bean–RhizobiumSymbiotic Association

“…Several reports have shown that small G-proteins and their effectors play important roles in polar growth (e.g., Molendijk et al, 2001;Jones et al, 2002;Preuss et al, 2004;de Graaf et al, 2005;Carol et al, 2005;Gu et al, 2005Gu et al, , 2006Song et al, 2006;Nielsen et al, 2008). Rab11 proteins from mammals are localized in the recycling endosome of polarized epithelial cells.…”