Setting SNAREs in a Different Wood

Abstract

Vesicle traffic is essential for cell homeostasis, growth and development in plants, as it is in other eukaryotes, and is facilitated by a superfamily of proteins known as soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors (SNAREs). Although SNAREs are well-conserved across phylla, genomic analysis for two model angiosperm species available to date, rice and Arabidopsis, highlights common patterns of divergence from other eukaryotes. These patterns are associated with the expansion of some gene subfamilies of SNAREs, the absence of others and the appearance of new proteins that show no significant homologies to SNAREs of mammals, yeast or Drosophila. Recent findings indicate that the functions of these plant SNAREs also extend beyond the conventional 'housekeeping' activities associated with vesicle trafficking. A number of SNAREs have been implicated in environmental responses as diverse as stomata movements and gravisensing as well as sensitivity to salt and drought. These proteins are essential for signal transduction and response and, in most cases, appear also to maintain additional roles in membrane trafficking. One common theme to this added functionality lies in control of non-SNARE proteins, notably ion channels. Other examples include interactions between the SNAREs and scaffolding or other structural components within the plant cell.

Selective Regulation of Maize Plasma Membrane Aquaporin Trafficking and Activity by the SNARE SYP121

“…In plants, sequence comparison allowed the identification of rice orthologs for most of the Arabidopsis Q-SNAREs (Sutter et al, 2006a). Our observation that SYP121-Sp2 fragments from Arabidopsis and maize decreased the plasma membrane trafficking of mYFP:ZmPIP2;5 in tobacco epidermal cells and maize mesophyll protoplasts demonstrates that the mechanism of SYP121-mediated plasma membrane anchoring of PIP2 aquaporins is conserved between monocots and dicots.…”

“…Genome analysis showed that the SNARE family is larger in plants than in other eukaryotes (Sanderfoot, 2007). Indeed, more than 60 SNARE isoforms have been identified in the Arabidopsis genome, and orthologs are found in rice (Oryza sativa) for most of them, supporting the idea that they are conserved between monocots and dicots (Sutter et al, 2006a). Syntaxins belong to the Q-SNARE subfamily and, in Arabidopsis, seven of them localize to the plasma membrane and are involved in traffic at this membrane .…”

“…It was previously shown that the delivery of Np-PMA2 to the plasma membrane was not affected by AtSYP121-Sp2 in tobacco epidermal cells (Sutter et al, 2006a). When coexpressed with mYFP:ZmSYP121-Sp2 in maize protoplasts, no modification in mCFP:NpPMA2 plasma membrane localization and intensity was detected ( Figures 1E and 1F).…”

An Elaborate Classification of SNARE Proteins Sheds Light on the Conservation of the Eukaryotic Endomembrane System

“…Thus, it remains unclear how the remarkable morphological diversity of eukaryotes is reflected in their SNARE repertoires. For example, so far the highest number of SNARE proteins was discovered in green plants (Sanderfoot et al, 2000;Sutter et al, 2006;Sanderfoot, 2007), but it is unclear so far whether the additional SNAREs mediate novel trafficking steps or whether they are simply variations in the given repertoire. This calls for an exhaustive comparison of SNARE repertoires in different organisms.…”

“…In addition, the original classification of SNARE proteins (Bock et al, 2001) was based on only ϳ100 sequences from only few organisms and did not include some more diverged SNARE types (Lewis et al, 1997;Lewis and Pelham, 2002;Burri et al, 2003;Dilcher et al, 2003). In the subsequent years, additional complete genomes shed more light onto the conservation of the SNARE machinery, yet some SNAREs, in particular from protists, appeared to be rather atypical (Sanderfoot et al, 2000; Doolittle, 2002, 2004;Gupta and Brent Heath, 2002;Uemura et al, 2004;Besteiro et al, 2006;Schilde et al, 2006;Sutter et al, 2006;Ayong et al, 2007;Kissmehl et al, 2007;Sanderfoot, 2007). These studies, however, did not provide a universal classification scheme, as usually only a subset of sequences was examined.…”