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Unformatted text preview: REVIEW Post-Golgi protein traffic in the plant secretory pathway Sally L. Hanton Æ Loren A. Matheson Æ Laurent Chatre Æ Marika Rossi Æ Federica Brandizzi Received: 24 April 2007 / Revised: 18 May 2007 / Accepted: 21 May 2007 / Published online: 6 June 2007 Ó Springer-Verlag 2007 Abstract The Golgi apparatus in plants is organized as a multitude of individual stacks that are motile in the cyto- plasm and in close association with the endoplasmic reticulum (ER) (Boevink et al. in Plant J 15:441–447, 1998 ). These stacks operate as a sorting centre for cargo molecules, providing modification and redirection to other organelles as appropriate. In the post-Golgi direction, these include vacuole and plasma membrane, and specialized transport routes to each are required to prevent mislocal- ization. Recent evidence in plant cells points to the exis- tence of post-Golgi organelles that function as intermediate stations for efficient protein traffic, as well as to the influence of small GTPases such as Rabs and ARFs on post-Golgi trafficking. This review focuses on the latest findings on post-Golgi trafficking routes and on the involvement of GTPases and their effectors on the traf- ficking of proteins in the plant secretory pathway. Keywords Golgi apparatus Á Protein secretion Á Plant secretory pathway Á Post-Golgi protein transport routes Post-Golgi protein transport in plant cells Protein transport beyond the Golgi apparatus is a complex field, made all the more so by the fact that our knowledge of the organelles involved is, in many cases, quite limited. For example, plant cells can contain two or more vacuole types in a single cell (Paris et al. 1996 ; Fig. 1 ). How pro- teins reach these vacuoles is not entirely clear. The route to the lytic vacuole involves a prevacuolar compartment (PVC) and is receptor-mediated, interaction of cargo molecules with the receptors apparently being dependent on the presence of a sequence-specific vacuolar sorting determinant in the cargo protein (Kirsch et al. 1994 , 1996 ; Ahmed et al. 2000 ). It is thought that proteins destined for the lytic vacuole are transported to the Golgi apparatus, where they can interact with receptors that mediate their sorting into clathrin-coated vesicles for transport to the PVC (Kirsch et al. 1994 ; Happel et al. 2004 ; daSilva et al. 2006 ). On arrival at the PVC, the receptors release their cargo and recycle to the Golgi apparatus to bind to further cargo molecules (Kirsch et al. 1994 ; daSilva et al. 2005 ). Whether the step of cargo release into the lytic vacuole involves maturation of the PVC into a fusion competent organelle or into an additional structure is yet unknown. An investigation into the response of the PVC to the drug brefeldin A, which prevents the activation of the GTPase ARF1 by sequestering its guanine nucleotide exchange factor (GEF) and causes the fusion of Golgi membranes with those in the ER (Driouich et al. 1993 ; Ritzenthaler et al. 2002 ), demonstrated that the PVC is slower to re-...
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