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IN BRIEF

An Exocyst Vesicle Tethering Complex in Plants

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Tethering factors are a large group of proteins that function in secretory membrane trafficking (reviewed in Sztul and Lupashin, 2006; Cai et al., 2007). Animal cells contain two types of tethering factors: proteins with extensive coiled-coil domains and large multisubunit complexes. Both types interact with SNAREs and small GTPases involved in vesicular trafficking, and they appear to form connections between vesicles and endomembrane compartments and to play a role in vesicle targeting and docking. The exocyst complex is one of eight types of multisubunit tethering complexes that have been described, and it functions preferentially in plasma membrane trafficking of vesicles carrying cargo involved in polarized cell growth. Other complexes have functions in transport between the ER and Golgi, within the Golgi, or between the Golgi and vacuolar membrane.

The exocyst complex consists of eight subunits (sec3, sec5 s6, sec8, sec10, sec15, exo70, and exo84), which are conserved in eukaryotes, including plants. The Arabidopsis genome contains as many as 23 homologs of exo70, but information on possible function is limited (Synek et al., 2006). Recent studies have implicated homologs of the exocyst subunits in polarized cell growth in plants, including such processes as root hair elongation, hypocotyl elongation, and pollen tube growth (reviewed in Cole and Fowler, 2006). Hála et al. (pages 1330–1345) now show that exocyst subunits in Arabidopsis interact and function as a bona fide exocyst complex in vivo and play an important role in plant morphogenesis.

The authors found that mutations in different exocyst subunits displayed a synergistic effect on hypocotyl elongation, indicating a functional relationship in vivo between subunits (see figure ). Chromatographic fractionation of an Arabidopsis cell suspension extract revealed the presence of a complex containing the SEC3, SEC5, SEC6, SEC8, SEC10, SEC15, and EXO70 subunits. In addition, yeast two-hybrid assays demonstrated interactions between a number of the subunits, and complexes containing several of the subunits could be isolated through native gel electrophoresis. This work provides genetic, biochemical, and cell biological evidence that the predicted exocyst subunits function together in a complex in vivo in Arabidopsis.

View larger version (81K): [in this window] [in a new window] [as a PowerPoint slide]   Arabidopsis wild-type and exocyst subunit single and double mutant seedlings.

www.plantcell.org/cgi/doi/10.1105/tpc.108.200511

REFERENCES

Cai, H., Reinisch, K., and Ferro-Novick, S. (2007). Coats, tethers, Rabs, and SNAREs work together to mediate the intracellular destination of a transport vesicle. Dev. Cell 12: 671–682.[CrossRef][ISI][Medline]

Cole, R.A., and Fowler, J.E. (2006). Polarized growth: Maintaining focus on the tip. Curr. Opin. Plant Biol. 9: 579–588.[CrossRef][ISI][Medline]

Hála, M., Cole, R., Synek, L., Drdová, E., Peenková, T., Nordheim, A., Lamkemeyer, T., Madlung, J., Hochholdinger, F., Fowler, J.E., and ársk, V. (2008). An exocyst complex functions in plant cell growth in Arabidopsis and tobacco. Plant Cell 20: 1330–1345.[Abstract/Free Full Text]

Synek, L., Schlager, N., Elias, M., Quentin, M., Hauser, M.T., and Zarsky, V. (2006). At EXO70A1, a member of a family of putative exocyst subunits specifically expanded in land plants, is important for polar growth and plant development. Plant J. 48: 54–72.[CrossRef][ISI][Medline]

Sztul, E., and Lupashin, V. (2006). Role of tethering factors in secretory membrane traffic. Am. J. Physiol. Cell Physiol. 290: 11–26.

Related articles in Plant Cell:

An Exocyst Complex Functions in Plant Cell Growth in Arabidopsis and Tobacco

Michal Hála, Rex Cole, Lukás Synek, Edita Drdová, Tamara Pecenková, Alfred Nordheim, Tobias Lamkemeyer, Johannes Madlung, Frank Hochholdinger, John E. Fowler, and Viktor Zársky
Plant Cell 2008 20: 1330-1345. [Abstract] [Full Text]  

This Article Full Text (PDF) All Versions of this Article: 20/5/1188    most recent tpc.108.200511v1 Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Plant Cell Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via CrossRef Citing Articles via Google Scholar Google Scholar Articles by Eckardt, N. A. Search for Related Content PubMed PubMed Citation Articles by Eckardt, N. A. Agricola Articles by Eckardt, N. A.