To deliver or to degrade - an interplay of the ubiquitin-proteasome system, autophagy and vesicular transport in plants

The efficient utilization and subsequent reuse of cell components is a key factor in determining the proper growth and functioning of all cells under both optimum and stress conditions. The process of intracellular and intercellular recycling is especially important for the appropriate control of cellular metabolism and nutrient management in immobile organisms, such as plants. Therefore, the accurate recycling of amino acids, lipids, carbohydrates or micro- and macronutrients available in the plant cell becomes a critical factor that ensures plant survival and growth. Plant cells possess two main degradation mechanisms: a ubiquitin-proteasome system and autophagy, which, as a part of an intracellular trafficking system, is based on vesicle transport. This review summarizes knowledge of both the ubiquitin-proteasome system and autophagy pathways, describes the cross-talk between the two and discusses the relationships between autophagy and the vesicular transport systems.