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First published online July 22, 2005; 10.1104/pp.105.062273 Plant Physiology 138:2005-2018 (2005) © 2005 American Society of Plant Biologists SEC8, a Subunit of the Putative Arabidopsis Exocyst Complex, Facilitates Pollen Germination and Competitive Pollen Tube Growth1,[w]Department of Botany and Plant Pathology and Center for Gene Research and Biotechnology, Oregon State University, Corvallis, Oregon 97331 (R.A.C., J.E.F.); Department of Plant Physiology, Charles University, Praha 2, CZ–128 44, Czech Republic (L.S., V.Z.); and Laboratory of Cell Biology, Institute of Experimental Biology, Academy of Sciences of the Czech Republic, Praha 6, CZ–165 02, Czech Republic (L.S., V.Z.)
The exocyst, a complex of eight proteins, contributes to the morphogenesis of polarized cells in a broad range of eukaryotes. In these organisms, the exocyst appears to facilitate vesicle docking at the plasma membrane during exocytosis. Although we had identified orthologs for each of the eight exocyst components in Arabidopsis (Arabidopsis thaliana), no function has been demonstrated for any of them in plants. The gene encoding one exocyst component ortholog, AtSEC8, is expressed in pollen and vegetative tissues of Arabidopsis. Genetic studies utilizing an allelic series of six independent T-DNA mutations reveal a role for SEC8 in male gametophyte function. Three T-DNA insertions in SEC8 cause an absolute, male-specific transmission defect that can be complemented by expression of SEC8 from the LAT52 pollen promoter. Microscopic analysis shows no obvious abnormalities in the microgametogenesis of the SEC8 mutants, and the mutant pollen grains appear to respond to the signals that initiate germination. However, in vivo assays indicate that these mutant pollen grains are unable to germinate a pollen tube. The other three T-DNA insertions are associated with a partial transmission defect, such that the mutant allele is transmitted through the pollen at a reduced frequency. The partial transmission defect is only evident when mutant gametophytes must compete with wild-type gametophytes, and arises in part from a reduced pollen tube growth rate. These data support the hypothesis that one function of the putative plant exocyst is to facilitate the initiation and maintenance of the polarized growth of pollen tubes.
1 This work was supported by the National Science Foundation (grant nos. IBN–0111078 and IBN–0420226 to J.E.F.), and by Grantová Agentura AV (Czech Republic grant no. A6038410 and EU–HPRN–CT–2002–002656 TIPNET to V.Z.). [w] The online version of this article contains Web-only data. Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.062273. * Corresponding author; e-mail fowlerj{at}science.oregonstate.edu; fax 541–737–3573. Received March 4, 2005; returned for revision May 11, 2005; accepted May 17, 2005. Related articles in Plant Physiol.:
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