Our long-term goal is to understand the molecular basis by which the potato cyst nematode (PCN), Globodera pallida, manipulates the physiological processes of host potato plants for successful colonization, and to eventually use the evolved knowledge to develop cultivars with improved resistance to G. pallida. Particularly, our research focuses on elucidating the biological significance of G. pallida effectors during establishment of the feeding site. Although several plant-parasitic nematode effectors have been shown to suppress plant defense signaling, the mechanistic basis by which effectors manipulate host defense is largely unknown, mainly due to lack of understanding of the biochemical characteristics of the effectors. We have recently identified the novel G. pallida effector RHA1B, which is the first E3 ubiquitin ligase effector found in eukaryotic pathogens. Significantly, RHA1B can suppress defense signaling and function in concert with three host ubiquitin E2s when ubiquitinating in vitro. These results suggest that the ability of RHA1B to exploit multiple host E2s could arm G. pallida with a unique advantage in parasitism, in which various RHA1B-E2 combinations provide the parasite with the ability to affect a wider range of host plant physiological processes via the manipulation of both proteolytic and non-proteolytic protein processes in infected hosts. Thus, to further investigate the mechanistic basis by which G. pallida manipulates host physiological processes for successful colonization and to identify the host susceptibility genes that are essential for G. pallida infection, with an ultimate goal of generation of G. pallida-resistant potatoes via loss of susceptibility, we propose three research objectives: 1) Determine the role of RHA1B as a potential metaeffector; 2) Determine the host targets of the RHA1B ubiquitin ligase; 3) Generate G. pallida-resistant potato via loss of susceptibility.