Intracellular trafficking and proteolysis of the Arabidopsis auxin-efflux facilitator PIN2 are involved in root gravitropism

Abstract

Root gravitropism describes the orientation of root growth along the gravity vector and is mediated by differential cell elongation in the root meristem. This response requires the coordinated, asymmetric distribution of the phytohormone auxin within the root meristem, and depends on the concerted activities of PIN proteins and AUX1 - members of the auxin transport pathway. Here, we show that intracellular trafficking and proteasome activity combine to control PIN2 degradation during root gravitropism. Following gravi-stimulation, proteasome-dependent variations in PIN2 localization and degradation at the upper and lower sides of the root result in asymmetric distribution of PIN2. Ubiquitination of PIN2 occurs in a proteasome-dependent manner, indicating that the proteasome is involved in the control of PIN2 turnover. Stabilization of PIN2 affects its abundance and distribution, and leads to defects in auxin distribution and gravitropic responses. We describe the effects of auxin on PIN2 localization and protein levels, indicating that redistribution of auxin during the gravitropic response may be involved in the regulation of PIN2 protein.

COP1 mediates the coordination of root and shoot growth by light through modulation of PIN1- and PIN2-dependent auxin transport in Arabidopsis

“…As previously reported using MG132 (Abas et al, 2006;Laxmi et al, 2008), specific inhibition of proteasome activity using lactacystin blocked PIN2-GFP targeting to the vacuole in darkness (supplementary material Fig. S11).…”

“…5G,H). Because auxin can modulate PIN intracellular localization and stability (Paciorek et al, 2005;Sauer et al, 2006;Abas et al, 2006;Sieberer et al, 2000;Vieten et al, 2005), we wondered whether reduced shoot-to-root PAT in darkness could cause these changes. To 3407 RESEARCH ARTICLE COP1 regulates root growth test this, we inhibited shoot-to-root PAT in light-grown DR5:GUS, DR5rev:GFP , PIN1:PIN1-GFP and PIN2:PIN2-GFP seedlings using local NPA application to the hypocotyl (Fig.…”

“…Given that PIN2 degradation is also essential for root gravitropism (Abas et al, 2006), we reasoned that a role for COP1 in the regulation of this developmental response would provide independent evidence for its involvement in the regulation of PIN2 stability. cop1 mutants indeed demonstrated a reduced capacity to reorientate root growth in response to a change in the gravity vector (Fig.…”

“…7A). In addition, cop1 mutations also interfered with the degradation of PIN2-GFP on the upper side of gravistimulated roots (Abas et al, 2006) (Fig. 7B-D).…”

Internaliser pour diriger, ou comment l’endocytose régule les flux d’auxine chez les plantes

“…Le transporteur d'auxine PIN2 est impliqué dans la réo-rientation de la croissance racinaire en fonction de la gravité. Récemment, il a été démontré que PIN2 est internalisée et dégradée après gravistimulation, au niveau de la face supérieure de la racine mais pas de la face inférieure (Figure 2) [10]. L'auxine s'accumule ainsi vers la face inférieure de la racine permettant la réorientation de sa croissance.…”