AtSNX1 defines an endosome for auxin-carrier trafficking in Arabidopsis

Abstract

Polarized cellular distribution of the phytohormone auxin and its carriers is essential for normal plant growth and development. Polar auxin transport is maintained by a network of auxin influx (AUX) and efflux (PIN) carriers. Both auxin transport and PIN protein cycling between the plasma membrane and endosomes require the activity of the endosomal GNOM; however, intracellular routes taken by these carriers remain largely unknown. Here we show that Arabidopsis thaliana SORTING NEXIN 1 (AtSNX1) is involved in the auxin pathway and that PIN2, but not PIN1 or AUX1, is transported through AtSNX1-containing endosomes. We demonstrate that the snx1-null mutant exhibits multiple auxin-related defects and that loss of function of AtSNX1 severely enhances the phenotype of a weak gnom mutant. In root cells, we further show that AtSNX1 localizes to an endosomal compartment distinct from GNOM-containing endosomes, and that PIN2 accumulates in this compartment after treatment with the phosphatidylinositol-3-OH kinase inhibitor wortmannin or after a gravity stimulus. Our data reveal the existence of a novel endosomal compartment involved in PIN2 endocytic sorting and plant development.

Rice SCAMP1 Defines Clathrin-Coated,trans-Golgi–Located Tubular-Vesicular Structures as an Early Endosome in Tobacco BY-2 Cells

“…Despite the many caveats in working with wortmannin (Roth et al, 2004), which also probably apply to plants, it will be interesting to determine whether the effects of wortmannin as described here in tobacco BY-2 cells can be confirmed in other plant cells. Indeed, an endosome as defined by labeling with At SNX1-GFP in Arabidopsis cells was recently shown to form small vacuoles in response to wortmannin treatment (Jaillais et al, 2006).…”

Evidence for a sorting endosome in Arabidopsis root cells

“…The contradiction regarding the localization of RABF1 and RABF2b, which is probably due to the various model systems employed, precludes the use of these proteins as specific markers to distinguish between early and late endosomes/PVC. However, both proteins have been used in several studies as general endosomal markers (Dettmer et al, 2006;Dhonukshe et al, 2006;Geldner et al, 2003;Grebe et al, 2003;Jaillais et al, 2006;Takano et al, 2005). Recently, we demonstrated the existence of at least two distinct endosomal compartments in Arabidopsis root cells, depending on the presence of either the GNOM or AtSNX1 protein (Jaillais et al, 2006).…”

“…However, both proteins have been used in several studies as general endosomal markers (Dettmer et al, 2006;Dhonukshe et al, 2006;Geldner et al, 2003;Grebe et al, 2003;Jaillais et al, 2006;Takano et al, 2005). Recently, we demonstrated the existence of at least two distinct endosomal compartments in Arabidopsis root cells, depending on the presence of either the GNOM or AtSNX1 protein (Jaillais et al, 2006). GNOM is a GDP/GTP exchange factor for small G-proteins (ARF-GEF) that is required for cycling of some auxin transporters (Geldner et al, 2003).…”

Salt Modulates Gravity Signaling Pathway to Regulate Growth Direction of Primary Roots in Arabidopsis

“…Although the mechanosensing receptors and/or channels that sense amyloplast movement are still unknown, evidence suggests that cytosolic ions such as Ca 21 and rapid cytoplasmic alkalization may be involved in gravity signal transduction (Legue et al, 1997;Scott and Allen, 1999;Fasano et al, 2001;Johannes et al, 2001;Plieth and Trewavas, 2002;Hou et al, 2004). Asymmetric distribution of auxin in roots caused by basipetal transport mainly through the auxin efflux carrier PIN-FORMED2 (PIN2), which is distributed asymmetrically within the cells, results in gravitropic root response of the root elongation zone (Muller et al, 1998;Friml and Palme, 2002;Moore, 2002;Morita and Tasaka, 2004;Abas et al, 2006;Jaillais et al, 2006). This is the well-known Cholodny-Went hypothesis, which has been strongly supported by recent molecular genetic and biochemical evidence.…”