© 2008 The Author(s).
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RESEARCH PAPER |
Expression analysis of Arabidopsis vacuolar sorting receptor 3 reveals a putative function in guard cells
1Center for Plant Cell Biology, University of California, Riverside, CA 92521, USA
2Centre for Research in Plant Science, Genomics Research Institute, University of the West of England, Bristol BS16 1QY, UK
To whom correspondence should be addressed. E-mail: natasha.raikhel{at}ucr.edu
Vacuolar sorting receptors (VSRs) are responsible for the proper targeting of soluble cargo proteins to their destination compartments. The Arabidopsis genome encodes seven VSRs. In this work, the spatio-temporal expression of one of the members of this gene family, AtVSR3, was determined by RT-PCR and promoter::reporter gene fusions. AtVSR3 was expressed specifically in guard cells. Consequently, a reverse genetics approach was taken to determine the function of AtVSR3 by using RNA interference (RNAi) technology. Plants expressing little or no AtVSR3 transcript had a compressed life cycle, bolting 
1 week earlier and senescing up to 2 weeks earlier than the wild-type parent line. While the development and distribution of stomata in AtVSR3 RNAi plants appeared normal, stomatal function was altered. The guard cells of mutant plants did not close in response to abscisic acid treatment, and the mean leaf temperatures of the RNAi plants were on average 0.8 °C lower than both wild type and another vacuolar sorting receptor mutant, atvsr1-1. Furthermore, the loss of AtVSR3 protein caused the accumulation of nitric oxide and hydrogen peroxide, signalling molecules implicated in the regulation of stomatal opening and closing. Finally, proteomics and western blot analyses of cellular proteins isolated from wild-type and AtVSR3 RNAi leaves showed that phospholipase D
, which may play a role in abscisic acid signalling, accumulated to higher levels in AtVSR3 RNAi guard cells. Thus, AtVSR3 may play an important role in responses to plant stress.
Key words:
Abscisic acid, expression analysis, guard cells, hydrogen peroxide, nitric oxide, phospholipase D1, protein trafficking, vacuolar sorting receptor
* Present address: Department of Biology, Chaffey College, 5885 Haven Avenue, Rancho Cucamonga, CA 91737-3002, USA.
Present address: Division of Biology. Imperial College London, South Kensington, London SW7 2AZ, UK.
Received 12 December 2007; Revised 14 January 2008 Accepted 17 January 2008