The Role of the Ubiquitin-Proteasome System in Agrobacterium tumefaciens-Mediated Genetic Transformation of Plants

The ubiquitin-proteasome system (UPS) plays a pivotal role in diverse cellular and developmental processes of plants. Increasing evidence suggests that the UPS also regulates pathogen infection through degradation of the host or pathogen-derived proteins. Such involvement of the UPS in plant-pathogen interactions is particularly well exemplified by the Agrobacterium tumefaciens -encoded F-box protein VirF. It has been proposed that VirF targets a host protein for the UPS-mediated degradation, thereby facilitating Agrobacterium infection. Furthermore, a recent study elucidated that VirF itself is also targeted for proteasomal degradation presumably via the host defense system against Agrobacterium . The discovery of VirF spurred intensive research on the role of the UPS in the genetic transformation process, leading to identification of many more UPS-associated factors that may be involved in Agrobacterium -plant interaction. Here, we summarize the recent findings on such UPS-related factors and discuss their potential molecular functions in Agrobacterium infection and the resultant genetic modification of the host plant.