Re-targeting of a plant defense protease by a cyst nematode effector.

Plants mount defense responses during pathogen attacks, and robust host defense suppression by pathogen effector proteins is essential for infection success. 4E02 is an effector of the sugar beet cyst nematode Heterodera schachtii. Arabidopsis thaliana lines expressing the effector-coding sequence showed altered expression levels of defense response genes, as well as higher susceptibility to both the biotroph H. schachtii and the necrotroph Botrytis cinerea, indicating a potential suppression of defenses by 4E02. Yeast two-hybrid analyses showed that 4E02 targets A. thaliana vacuolar papain-like cysteine protease (PLCP) 'Responsive to Dehydration 21A' (RD21A), which has been shown to function in the plant defense response. Activity-based protein profiling analyses documented that the in planta presence of 4E02 does not impede enzymatic activity of RD21A. Instead, 4E02 mediates a re-localization of this protease from the vacuole to the nucleus and cytoplasm, which is likely to prevent the protease from performing its defense function and at the same time, brings it in contact with novel substrates. Yeast two-hybrid analyses showed that RD21A interacts with multiple host proteins including enzymes involved in defense responses as well as carbohydrate metabolism. In support of a role in carbohydrate metabolism of RD21A after its effector-mediated re-localization, we observed cell wall compositional changes in 4E02 expressing A. thaliana lines. Collectively, our study shows that 4E02 removes RD21A from its defense-inducing pathway and repurposes this enzyme by targeting the active protease to different cell compartments.

A parasitic nematode releases cytokinin that controls cell division and orchestrates feeding site formation in host plants.

Sedentary plant-parasitic cyst nematodes are biotrophs that cause significant losses in agriculture. Parasitism is based on modifications of host root cells that lead to the formation of a hypermetabolic feeding site (a syncytium) from which nematodes withdraw nutrients. The host cell cycle is activated in an initial cell selected by the nematode for feeding, followed by activation of neighboring cells and subsequent expansion of feeding site through fusion of hundreds of cells. It is generally assumed that nematodes manipulate production and signaling of the plant hormone cytokinin to activate cell division. In fact, nematodes have been shown to produce cytokinin in vitro; however, whether the hormone is secreted into host plants and plays a role in parasitism remained unknown. Here, we analyzed the spatiotemporal activation of cytokinin signaling during interaction between the cyst nematode, Heterodera schachtii, and Arabidopsis using cytokinin-responsive promoter:reporter lines. Our results showed that cytokinin signaling is activated not only in the syncytium but also in neighboring cells to be incorporated into syncytium. An analysis of nematode infection on mutants that are deficient in cytokinin or cytokinin signaling revealed a significant decrease in susceptibility of these plants to nematodes. Further, we identified a cytokinin-synthesizing isopentenyltransferase gene in H. schachtii and show that silencing of this gene in nematodes leads to a significant decrease in virulence due to a reduced expansion of feeding sites. Our findings demonstrate the ability of a plant-parasitic nematode to synthesize a functional plant hormone to manipulate the host system and establish a long-term parasitic interaction.

Activity profiling reveals changes in the diversity and activity of proteins in Arabidopsis roots in response to nematode infection.

Cyst nematodes are obligate, sedentary endoparasites with a highly specialised biology and a huge economic impact in agriculture. Successful parasitism involves morphological and physiological modifications of the host cells which lead to the formation of specialised syncytial feeding structures in roots. The development of the syncytium is aided by a cocktail of nematode effectors that manipulate the host plant activities in a complex network of interactions through post-translational modifications. Traditional transcriptomic and proteomic approaches cannot display this functional proteomic information. Activity-based protein profiling (ABPP) is a powerful technology that can be used to investigate the activity of the proteome through activity-based probes. To better understand the functional proteomics of syncytium, ABPP was conducted on syncytia induced by the beet cyst nematode Heterodera schachtii in Arabidopsis roots. Our results demonstrated that the activity of several enzymes is differentially regulated in the syncytium compared to the control roots. Among those specifically activated in the syncytium are a putative S-formyl-glutathione hydrolase (SFGH), a putative methylesterase (MES) and two unidentified enzymes. In contrast, the activities of vacuolar processing enzymes (VPEs) are specifically suppressed in the syncytium. Competition labelling, quantitative gene expression and T-DNA knock-out mutants were used to further characterise the roles of the differentially regulated enzymes during plant-nematode interaction. In conclusion, our study will open the door to generate a comprehensive and integrated view of the host-pathogen warfare that results in the formation of long-term feeding sites for pathogens.