Two evolutionary distinct effectors from a nematode and virus target RanGAP1 and 2 via the WPP domain to promote disease

The Gpa2 and Rx1 intracellular immune receptors are canonical CC-NB-LRR proteins belonging to the same R gene cluster in potato. Despite sharing high sequence homology, they have evolved to provide defence against unrelated pathogens. Gpa2 detects Gp-RBP-1 effectors secreted by the potato cyst nematode Globodera pallida whereas Rx1 recognizes the viral coat protein (CP) of Potato Virus X (PVX). How Gpa2 and Rx1 perceive their matching effectors remains unknown. Using a combination of in planta Co-Immunoprecipitation and cellular imaging, we show that both Gp-RBP-1 and PVX-CP physically interact with RanGAP2 and RanGAP1 in the cytoplasm of plant cells. Interestingly, this was also demonstrated for the eliciting variants of Gp-RBP-1 and PVX-CP indicating a role for RanGAP1 and RanGAP2 in pathogenicity independent from Gpa2 and Rx1 recognition. Indeed, knocking down both RanGAP homologs reduce cyst nematode and PVX infection. These findings show that RanGAP1/2 act as common host targets of evolutionary distinct effectors from two plant pathogens with different lifestyles. The involvement of RanGAP1/2 to pathogen virulence is a novel role not yet reported for these key host cell components and as such, their possible role in cyst nematode parasitism and viral pathogenicity are discussed. Moreover, from these findings a model emerges for their possible role as co-factor in pathogen recognition by the potato immune receptors Gpa2/Rx1

The effector GpRbp-1 of Globodera pallida targets a nuclear HECT E3 ubiquitin ligase to modulate gene expression in the host

Plant-parasitic nematodes secrete effectors that manipulate plant cell morphology and physiology to achieve host invasion and establish permanent feeding sites. Effectors from the highly expanded SPRYSEC (SPRY domain with a signal peptide for secretion) family in potato cyst nematodes have been implicated in activation and suppression of plant immunity, but the mechanisms underlying these activities remain largely unexplored. To study the host mechanisms used by SPRYSEC effectors, we identified plant targets of GpRbp-1 from the potato cyst nematode Globodera pallida. Here, we show that GpRbp-1 interacts in yeast and in planta with a functional potato homologue of the Homology to E6-AP C-Terminus (HECT)-type ubiquitin E3 ligase UPL3, which is located in the nucleus. Potato lines lacking StUPL3 are not available, but the Arabidopsis mutant upl3-5 displaying a reduced UPL3 expression showed a consistently small but not significant decrease in susceptibility to cyst nematodes. We observed a major impact on the root transcriptome by the lower levels of AtUPL3 in the upl3-5 mutant, but surprisingly only in association with infections by cyst nematodes. To our knowledge, this is the first example that a HECT-type ubiquitin E3 ligase is targeted by a pathogen effector and that a member of this class of proteins specifically regulates gene expression under biotic stress conditions. Together, our data suggest that GpRbp-1 targets a specific component of the plant ubiquitination machinery to manipulate the stress response in host cells.</p

SIZ1 is a nuclear host target of the nematode effector GpRbp1 from Globodera pallida that acts as a negative regulator of basal plant defense to cyst nematodes

Soil-borne cyst nematodes are obligatory sedentary parasites that cause severe losses to cultivation of major crops such as potato and soybean. Cyst nematodes establish specialised permanent feeding sites within the roots of their host by manipulating plant morphology and physiology through secreted effectors. Here we identified host targets of effector GpRbp-1 and studied their roles in plant-nematode interactions. GpRbp-1 was found to interact in yeast and in planta with the potato and Arabidopsis homologues of Siz/PIAS-type E3 SUMO ligase SIZ1. Our results show that a pathogen effector targets the master regulator SIZ1 in plant cells, which has not been demonstrated earlier to our knowledge. The interaction of GpRbp-1 and SIZ1 localizes to the plant nucleus, suggesting that the nuclear functions of SIZ1 as regulator of plant immunity and physiology may be modulated by GpRbp-1. Furthermore, nematode infection assays and transcriptomic profiling indicate that SIZ1 is required for susceptibility to cyst nematodes. So, these data indicate that E3 SUMO ligases may play an important role in plant-nematode interactions. Based on the prediction of SUMO acceptor and interaction sites in GpRbp-1, a model is proposed in which the effector may recruit SIZ1 to be SUMOylated for full functionality in host cells