On the discovery of an endomembrane compartment in plants

To maintain homeostasis and to react to external stimuli, eukaryotic cells have evolved a complex internal membrane system. Among them, lytic compartments are hallmarks of eukaryotic cells: Animals possess lysosomes, whereas fungi and plants build up vacuoles. Although largely molecularly conserved, the plant endomembrane system displays unique features, among them the presence of large vacuoles. The central vacuole can occupy up to 90% of the cellular volume in mature vegetative tissues and is involved in numerous essential functions. These include degradation of cellular waste, storage of ions and proteins, plant growth, defense against pathogens, and intracellular pH homeostasis. Given the importance of vacuoles for plants, it is not surprising that trafficking to this compartment has been intensively studied. Despite significant progress toward the identification of different trafficking routes, the underlying molecular machinery is far from being understood and is, in part, controversially discussed in the field. In PNAS, Delgadillo et al. (1) elegantly identify and characterize a set of mutants impaired in vacuolar transport. Most identified mutant alleles were known trafficking factors, but subsequent localization analysis proposes the identification of a previously unknown plant compartment. Soluble vacuolar cargoes require positive sorting mechanisms … [↵][1]1To whom correspondence may be addressed. Email: scheurin{at}rhrk.uni-kl.de. [1]: #xref-corresp-1-1