A putative serine protease, SpSsp1, from Saprolegnia parasitica is recognised by sera of rainbow trout, Oncorhynchus mykiss

Acknowledgements Our work was supported by the BBSRC (BB/C518457/1, BB/G012075/1, BB/J018333/1) (K.L.M., C.J.S., J.S.C., K.S.D., and P.v.W.), the University of Aberdeen (V.L.A., C.J.S., and P.v.W.), MSD Animal Health (J.S.C., K.S.D., and A.H.v.d.B), and The Royal Society (P.v.W.). This work was also supported by a Marie Curie Initial Training Networks with the SAPRO (sustainable approaches to reduce Oomycete (Saprolegnia) infections in aquacultures) grant PITN-GA-2009-238550 (A.H.v.d.B., L.L., C.J.S., P.v.W.). We would like to acknowledge Aberdeen Proteomics for carrying out LC–MS/MS and Laura Grenville-Briggs for valuable discussion and technical help. We are grateful to the Broad Institute (Carsten Russ, Rays Jiang, Brian Haas, and Chad Nusbaum), Brett Tyler (VBI), and P.v.W. for early release of draft supercontigs of the genome sequence of isolate CBS233.65, which helped us identify SpSsp1.Peer reviewedPublisher PD

Cell entry of a host-targeting protein of oomycetes requires gp96

The animal-pathogenic oomycete Saprolegnia parasitica causes serious losses in aquaculture by infecting and killing freshwater fish. Like plant-pathogenic oomycetes, S. parasitica employs similar infection structures and secretes effector proteins that translocate into host cells to manipulate the host. Here, we show that the host-targeting protein SpHtp3 enters fish cells in a pathogen-independent manner. This uptake process is guided by a gp96-like receptor and can be inhibited by supramolecular tweezers. The C-terminus of SpHtp3 (containing the amino acid sequence YKARK), and not the N-terminal RxLR motif, is responsible for the uptake into host cells. Following translocation, SpHtp3 is released from vesicles into the cytoplasm by another host-targeting protein where it degrades nucleic acids. The effector translocation mechanism described here, is potentially also relevant for other pathogen-host interactions as gp96 is found in both animals and plants.This work is supported by the [European Community’s] Seventh Framework Programme [FP7/2007–2013] under grant agreement no. [238550] (L.L., J.D.-U., C.J.S., P.v.W.); BBSRC [BBE007120/1, BB/J018333/1 and BB/G012075/1] (F.T., I.d.B., C.J.S., S.W., P.v.W.); Newton Global Partnership Award [BB/N005058/1] (F.T., P.v.W.), the University of Aberdeen (A.D.T., T.R., C.J.S., P.v.W.) and Deutsche Forschungsgemeinschaft [CRC1093] (P.B., T.S.). We would like to acknowledge the Ministry of Higher Education Malaysia for funding INA. We would like to thank Brian Haas for his bioinformatics support. We would like to acknowledge Neil Gow and Johannes van den Boom for critical reading of the manuscript. We would like to acknowledge Svetlana Rezinciuc for technical help with pH-studies