Specificity of syntaxin action in membrane fusion

The Arabidopsis genome encodes 18 syntaxins, which represent 5 families (SYP1, 2, 3, 4 and 8) that are evolutionarily conserved among eukaryotes. The SYP1 family comprises 8 plasma membrane-localised members and a unique plant-specific syntaxin named KNOLLE, which is exclusively required for membrane fusion during cytokinesis (Fig. 1, 2b; Müller et al., 2003).

Figure 1 SYP1 family of plasma-membrane syntaxins The 3 subgroups are highlighted. Prevacuolar syntaxin PEP12 (SYP2 family) represents the outgroup.

KNOLLE is only expressed during G2/M-phase, specifically targeted from the trans-Golgi network (TGN) to the plane of cell division during cytokinesis, subsequently endocytosed from the cell plate and degraded in the vacuole (Fig. 2a; Reichardt et al., 2007).

Figure 2 Role of KNOLLE in cytokinesis (a) KNOLLE (green) trafficking from TGN (trans-Golgi network; early mitosis) to the plane of cell division (CP, cell plate) followed by endocytosis and trafficking via the PVC (prevacuolar compartment; late) to the vacuole for degradation. Red signals represent compartment-specific markers. (b) Membrane fusion during cytokinesis is impaired in knolle mutants, resulting in the accumulation of unfused vesicles (top; n, nucleus).

Our research addresses mechanisms underlying the specificity of action of syntaxins in cytokinesis and secretion. To this end, we analyse how KN and other SYP1 syntaxins are targeted to their site of action, attempt to identify their endogenous interactors including SM proteins such as KEULE and other SNAREs, and analyse syntaxin dynamics and turnover.