VAN3 ARF–GAP-mediated vesicle transport is involved in leaf vascular network formation

Abstract

domains: a BAR (BIN/amphiphysin/RVS) domain, a pleckstrin homology (PH) domain, an ARF-GAP domain and an ankyrin (ANK)-repeat domain. Recombinant VAN3protein showed GTPase-activating activity and a specific affinity for phosphatidylinositols. This protein can selfassociate through the N-terminal BAR domain in the yeast two-hybrid system. Subcellular localization analysis by double staining for Venus-tagged VAN3 and several greenfluorescent-protein-tagged intracellular markers indicated that VAN3 is located in a subpopulation of the trans-Golgi network (TGN). Our results indicate that the expression of this gene is induced by auxin and positively regulated by VAN3 itself, and that a specific ACAP type of ARF-GAP functions in vein pattern formation by regulating auxin signaling via a TGN-mediated vesicle transport system.

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

“…AGD1 and AGD3, on the other hand, partially localized to FM4-64-labeled endocytic vesicles and the trans-Golgi network ( Fig. 8C; Koizumi et al, 2005). The partial localization of AGD1 to FM4-64-labeled bodies that we observed here is consistent with the endosomal localization of the closely related animal AZAPs (Jackson et al, 2000;Nie et al, 2002).…”

“…AGD3, which has similar domain organization to AGD1, has been shown to activate the GTPase-hydrolyzing activity of yeast ARF1p (Koizumi et al, 2005). Although we have yet to assay for AGD1 GAP activity, the possibility that the root hair phenotype of agd1 results from modified endogenous ARF function is evident from our results with BFA.…”

“…AGD1 encodes a class I ARF-GAP, which is closely related to the multidomain-containing mammalian AZAP-type ARFGAPs (Vernoud et al, 2003;Inoue and Randazzo, 2007). Among the Arabidopsis class I ARF-GAPs, only AGD3 has been demonstrated to function in plant development by affecting auxin-dependent vascular differentiation (Koizumi et al, 2005;Sieburth et al, 2006). Also, the overexpression of a rice (Oryza sativa) ARF-GAP (OsAGAP) hampered root development by interfering with the normal trafficking of auxin influx carriers (Zhuang et al, 2006).…”

“…Therefore, despite the absence of AGD1 activity, agd1 root hairs treated with BFA reverted to straight growth, because the opposing biochemical reaction triggered by a yet to be identified BFA-sensitive ARF-GEF in the cell was inhibited. In this regard, it is worth noting that AGD3 knockouts, which display discontinuous venation patterns (Koizumi et al, 2005;Sieburth et al, 2006), have roughly opposite phenotypes to mutants of the ARF-GEF, GNOM, which display extensive venation (Geldner et al, 2003). If the effect of BFA on agd1 root hairs is due to inhibited ARF-GEF activity counteracting the loss of AGD1, one would predict that overexpression of a constitutively active AGD1-dependent ARF will lead to similar wavy root hair phenotypes as agd1.…”

“…At5g61980 was designated AGD1 for ARF-GAP domain-containing protein 1 (Vernoud et al, 2003). Previously, a closely related class I ARF-GAP (AGD3) was shown to be involved in auxin efflux and vein patterning in Arabidopsis (Koizumi et al, 2005;Sieburth et al, 2006). Functional analyses of single mutants in the other class I ARF-GAPs, including mutations in the AGD1 gene, however, did not reveal any apparent phenotype (Sieburth et al, 2006).…”