Molecular characterization of nucleus-associated virulence targets of effector GpRbp-1 from Globodera pallida

Soil-borne cyst nematodes are obligatory sedentary parasites that induce extraordinary modifications in the roots of their hosts, thereby causing severe losses to cultivation of major crops. The alterations of plant morphology and physiology are required for the establishment of specialised permanent feeding sites, which solely support the sedentary life style of the nematodes. Nematodes secrete effectors which target host proteins to mediate this drastic cellular reprogramming of the plant. GpRbp-1 from the largely expanded family of SPRYSEC effectors in the potato cyst nematode Globodera pallida acts as an avirulence factor in the presence of potato immune receptor Gpa2. Nevertheless, its virulence function in plants in the absence of the receptor remains undescribed. In this thesis, we determined and characterised the plant targets of GpRbp-1 to elucidate its function in virulence. We used a combination of protein-protein interaction methods, in vivo assays, and transcriptomics to demonstrate that GpRbp-1 targets the SUMO E3-ligase SIZ1, the Ubiquitin E3-ligase UPL3, and a Gpa2 recognition co-factor the Ran-activating GTPase RanGAP. Our findings suggest that GpRbp-1 may function by modulating plant immunity mediated by salicylic acid and the Ran cycle to promote susceptibility to nematodes. Finally, we propose mechanistic models for the activity of GpRbp-1 and discuss them in the wider context of plant-pathogen interactions.