AtSYP51/52 Functions Diverge in the Post-Golgi Traffic and Differently Affect Vacuolar Sorting

Abstract

Plant sensitive factor attachment protein receptors (SNAREs) encoded by genes of the same sub-family are generally considered as redundant in promoting vesicle-associated membrane fusion events. Nonetheless, the application of innovative experimental approaches highlighted that members of the same gene sub-family often have different functional specificities. In this work, two closely related Qc-SNAREs--the AtSYP51 and the AtSYP52--are compared in their ability to influence different secretory pathways. Their role in the vesicle sorting to the central vacuole has been revised and they were found to have a novel inhibitory function. When transiently overexpressed, the SYP51 and the SYP52 distributed between the TGN and the tonoplast. Our data demonstrate that these SYPs (syntaxin of plants) act as t-SNARE when present on the membrane of TGN/PVC, whereas they behave as inhibitory or interfering SNAREs (i-SNAREs) when they accumulate on the tonoplast. Moreover, the performed functional analysis indicated that the AtSYP51 and the AtSYP52 roles differ in the traffic to the vacuole. The findings are a novel contribution to the functional characterization of plant SNAREs that reveals additional non-fusogenic roles.

The Plant Trans-Golgi Network: Not Just a Matter of Distinction

“…The Arabidopsis SYP5 family of SNAREs consists of two members, SYP51 and SYP52, which localize to tonoplast and TGN (Sanderfoot et al, 2001;Carter et al, 2004;De Benedictis et al, 2013). Both SYP5s mediate traffic to the vacuole, although they seem to differ in cargo selectivity.…”

“…Intriguingly, SYP5s appear to inhibit homotypic fusion (SNARE interfering or i-SNARE) when accumulated at the tonoplast. Such an i-SNARE function could provide a control for cargo delivery to the vacuole (De Benedictis et al, 2013).…”

Vacuolar Sorting Mechanisms are Differently Influenced by Detoxification Processes

“…Several studies proved that the two reporters are sorted to vacuoles by different sorting machineries [4,6,12]. GFPChi contains the ctVSD of tobacco chitinase A [13] while AleuGFP harbors the N-terminal ssVSD from barley aleurain, containing the specific conserved sequence NPIR [6].…”

“…As for secondary metabolites, such as anthocyanins [1,2], specific compartmentalization adaptations could be observed and the sequence of traffic events remains unclear [3]. Here we investigated the alteration induced by GST overexpression and/or glyphosate treatment on the vacuolar sorting pathway using two known vacuolar markers: AleuGFP (Sar1 dependent sorting) and GFPChi (Sar1 independent sorting) [4]. These reporter proteins follow two different and independent routes to the vacuole [4][5][6] and can be used to monitor independent mechanisms during glyphosate induced stress.…”

“…Here we investigated the alteration induced by GST overexpression and/or glyphosate treatment on the vacuolar sorting pathway using two known vacuolar markers: AleuGFP (Sar1 dependent sorting) and GFPChi (Sar1 independent sorting) [4]. These reporter proteins follow two different and independent routes to the vacuole [4][5][6] and can be used to monitor independent mechanisms during glyphosate induced stress. We observed an adaptive reaction of tobacco protoplasts evidenced by alterations in the fluorescent labeling of the vacuolar complex.…”