Protein secretion in plants: from the trans-Golgi network to the outer space

Functional analysis of exocytosis in yeast and animal cells has led to the identification of conserved elements and mechanisms of the trafficking machinery over the last decade. Although functional studies of protein secretion in plants are still fairly limited, the Arabidopsis genome sequence provides an opportunity to identify key players of vesicle trafficking that are conserved across the eukaryotic kingdoms. Here, we review and add to recent genome analyses of trafficking components and highlight some plant-specific modifications of the common eukaryotic machinery. Furthermore, we discuss the evidence for targeted, polarised secretion in plant cells, and speculate about possible underlying cargo sorting processes at the trans-Golgi network and endosomes, based on what is known in animals and yeast.