Mass spectrometry approaches to study plant endomembrane trafficking

Intracellular proteins reside in highly controlled microenvironments in which they perform context specific functions. Trafficking pathways have evolved that enable proteins to be precisely delivered to the correct location but also to re-locate in response to environmental perturbation. Trafficking of membrane proteins to their correct endomembrane location is especially important to enable them to carry out their function. Although a considerable amount of knowledge about membrane protein trafficking in plants has been delivered by years of dedicated research, there are still significant gaps in our understanding of this process. Further knowledge of endomembrane trafficking is dependent on thorough characterization of the subcellular components that constitute the endomembrane system. Such studies are challenging for a number of reasons including the complexity of the plant endomembrane system, inability to purify individual constituents, discrimination protein cargo for full time residents of compartments, and the fact that many proteins function at more than one location. In this review, we describe the components of the secretory pathway and focus on how mass spectrometry based proteomics methods have helped elucidation of this pathway. We demonstrate that the combination of targeted and untargeted approaches is allowing research into new areas of the secretory pathway investigation. Finally we describe new enabling technologies that will impact future studies in this area.