Complex roles of Rabs and SNAREs in the secretory pathway and plant development: a never-ending story.

Membrane trafficking is critical for cell compartmentation which allows the maintenance of specialised environments required for specific cellular activities. To achieve this goal, cells need to tightly regulate vesicle transport between donor and acceptor compartments. Several different protein families are involved: among them the SNAREs (65 genes) and the small GTPases Rabs (57 genes) show the highest number of isoforms and will be in the spotlight. We will focus on the roles of these proteins in the ER-Golgi-plasma membrane pathway to illustrate how Rabs and SNAREs are involved to achieve specific set of functions. LAY DESCRIPTION: Protein and lipid transport between the different compartments inside cells are critical for many physiological functions of organisms. To achieve this goal, cells have developed several vesicular transport systems between these compartments. Numerous different protein families are involved in these processes among which two protein families are the focus of the review in plant cells: the SNAREs and the small GTPases Rabs. These proteins are essentially controlling the different steps of the transport processes to warrant that proteins and lipids will reach the right compartments. The SNAREs are encoded by 65 genes meaning that plant cells synthesise 65 different SNARE proteins, and the small GTPases Rabs are encoded by 57 genes meaning that plant cells synthesise 57 different GTPases Rabs proteins. This high number of proteins illustrates the complexity of the vesicular transport systems existing between plant cell compartments. The review discusses the different roles of these proteins in these processes and particularly in the functioning of the secretory pathway which contributes to transport proteins and lipids to the cell surface. The review describes how the Rabs and SNAREs proteins are involved to achieve their respective set of functions in the different transport pathways of plant cells, and illustrates the tremendous complexity of these mechanisms.