Organization of transport from endoplasmic reticulum to Golgi in higher plants

Abstract

In plant cells, the organization of the Golgi apparatus and its interrelationships with the endoplasmic reticulum differ from those in mammalian and yeast cells. Endoplasmic reticulum and Golgi apparatus can now be visualized in plant cells in vivo with green fluorescent protein (GFP) specifically directed to these compartments. This makes it possible to study the dynamics of the membrane transport between these two organelles in the living cells. The GFP approach, in conjunction with a considerable volume of data about proteins participating in the transport between endoplasmic reticulum and Golgi in yeast and mammalian cells and the identification of their putative plant homologues, should allow the establishment of an experimental model in which to test the involvement of the candidate proteins in plants. As a first step towards the development of such a system, we are using Sar1, a small G-protein necessary for vesicle budding from the endoplasmic reticulum. This work has demonstrated that the introduction of Sar1 mutants blocks the transport from endoplasmic reticulum to Golgi in vivo in tobacco leaf epidermal cells and has therefore confirmed the feasibility of this approach to test the function of other proteins that are presumably involved in this step of endomembrane trafficking in plant cells.

Dual Fatty Acyl Modification Determines the Localization and Plasma Membrane Targeting of CBL/CIPK Ca2+ Signaling Complexes in Arabidopsis

“…In addition, we coexpressed a dominant negative mutant of the tobacco (Nicotiana tabacum) Sar1 protein (H74L), which has been reported to block vesicle trafficking between the ER and the Golgi (Andreeva et al, 2000). As shown in Figure 8B, targeting of GFP:TM23 was severely affected when Nt Sar1H74L was coexpressed, leading to strong fluorescence, especially surrounding the nucleus, which we identified as representing the ER.…”

Membrane Protein Transport between the Endoplasmic Reticulum and the Golgi in Tobacco Leaves Is Energy Dependent but Cytoskeleton Independent

“…However, some indication of COPII-independent transport in plants has been reported (Hara-Nishimura et al, 1998;Chrispeels and Herman, 2000;Toyooka et al, 2000;Törmäkangas et al, 2001). ER-to-Golgi transport of membrane proteins, such as ST-GFP and AtERD2-GFP, secretory, and vacuole-targeted forms of GFP, is compromised by the expression of nonfunctional Sar1p and AtRab1 mutants (Andreeva et al, 2000, Batoko et al, 2000, Takeuchi et al, 2000, Phillipson et al, 2001). Thus, in vivo evidence supports the idea that the COPII machinery, but not necessarily COPII vesicles, may be a prerequisite for exit from the ER.…”

“…Genome analysis (Andreeva et al, 1997) and biochemical/immunological studies (Pimpl et al, 2000;Phillipson et al, 2001;Ritzenthaler et al, 2002) have shown that components of the COPI and COPII coat systems (Schekman and Orci, 1996;Barlowe, 2000), which are proposed to function in vesicle transport in animal cells (Rothman and Wieland, 1996), operate in protein trafficking steps in plant cells. For example, GTPase-deficient mutants of Sar1, Rab1, and ARF1 have been shown in plant cells to act as trans -dominant negative inhibitors of protein transport (Andreeva et al, 2000;Batoko et al, 2000;Takeuchi et al, 2000;Phillipson et al, 2001). Moreover, immunogold labeling of cryosections has shown that COPI and ARF1 are localized to small vesicles surrounding or budding from cisternae at the cis face of the Golgi apparatus in plant cells and that the binding of these proteins is sensitive to brefeldin A (BFA) (Pimpl et al, 2000;Ritzenthaler et al, 2002).…”

Diacidic Motifs Influence the Export of Transmembrane Proteins from the Endoplasmic Reticulum in Plant Cells

“…Anterograde ER-Golgi transport of soluble proteins occurs via a passive bulk-flow mechanism (Denecke et al, 1990;Phillipson et al, 2001), but the selectivity of the ER export of transmembrane proteins is subject to considerable debate. It is generally assumed that transmembrane proteins are exported via a COPII-mediated mechanism similar to that of soluble proteins (Andreeva et al, 2000;Takeuchi et al, 2000;Phillipson et al, 2001;daSilva et al, 2004), although a Golgi-independent route for the sorting of a-TIP has also been suggested (Hofte and Chrispeels, 1992;Gomez and Chrispeels, 1993;Jiang and Rogers, 1998). It has been shown that the transmembrane domain alone is sufficient to dictate protein export from the ER in plants (Hofte and Chrispeels, 1992;Brandizzi et al, 2002a).…”