Ubiquitin/Proteasome System In Plant Pathogen Responses

In eukaryotes, the ubiquitin/proteasome system plays crucial roles in the regulation of protein stability. These functions are largely mediated through the covalent attachment of ubiquitin to substrate proteins and their targeting to the 26S proteasome, a large multi-subunit protease. In the last three decades, the ubiquitin system has been shown to regulate essentially all processes in eukaryotes. In plants, it appears to play particularly important roles, perhaps as a result of the plants' sessile lifestyle and their need to adapt to rapidly changing environmental conditions. In particular, the ubiquitin system is key to the regulation of plant responses to pathogens, not only during interaction with a pathogen but also in the absence of infection to prevent the constitutive activation of defence responses that would have detrimental effects. In this article, we discuss the roles of the ubiquitin system in the regulation of different cellular pathways involved in plant defence responses, including the regulation of transmembrane and intracellular receptors, and the control of the signalling pathways that are activated downstream of pathogen detection. We also review how pathogens hijack the ubiquitin system to increase their virulence. Finally, we briefly discuss the emerging roles of autophagy in the regulation of plant/pathogen interactions.