Physiological role of P4-ATPases in the plant secretory pathway

P4-ATPases belong to a family of cation-transporting proteins, the P-type ATPases, that are involved in relevant physiological functions, such as the generation of electrochemical gradients across membranes or cell detoxification. It is well-known that members of the P4-ATPase family in yeast are involved in formation of vesicles in the secretory and endocytic pathways. In fact, several of these proteins directly interact with small GTPases known to initiate vesicle formation. However, the concrete role of P4-ATPases in this process is still a matter of debate.

 

Lipid translocation from one leaflet of a bilayer to the other generates an imbalance in the lipid number that results in membrane bending. On the other hand, translocation of a specific lipid would result in its accumulation in a small area. This accumulation might be required for a correct interaction of the membrane with e.g. coat proteins necessary for vesicle formation.

The involvement of plant P4-ATPases in the formation of vesicles in vivo has been a research interest for the group in the past few years. For instance, Arabidopsis plants lacking the P4-ATPase ALA3 are unable to produce slime vesicles in the Golgi apparatus of root cells specialized in secretion. Another Arabidopsis P4-ATPase, ALA2, generates an enlargement of the prevacuolar compartment when transiently overexpressed in tobacco epidermal cells.

What is the role of plant P4-ATPases in formation of vesicles? What proteins do they interact with during this process? Is vesicle formation a direct consequence of lipid translocation or are there other factors involved?

 

Plants lacking ALA3 (right) do not produce vesicles in the Golgi while the wildtype (left) does. The arrows indicate vesicles (V), Golgi (G) and mitochondria (M).