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In Vitro Translocation Experiments with RxLR-Reporter Fusion Proteins of Avr1b from Phytophthora sojae and AVR3a from Phytophthora infestans Fail to Demonstrate Specific Autonomous Uptake in Plant and Animal Cells

May 2013 , Volume 26 , Number  5
Pages  528 - 536

Stephan Wawra,1 Armin Djamei,2 Isabell Albert,3 Thorsten Nürnberger,3 Regine Kahmann,2 and Pieter van West1

1Aberdeen Oomycete Laboratory, University of Aberdeen, Institute of Medical Sciences, Foresterhill, Aberdeen, AB25 2ZD, U.K.; 2Department of Organismic Interactions, Max Planck Institute for Terrestrial Microbiology, Karl-von-Frisch-Straße 10, Marburg, 35043, Germany; 3Department of Plant Biochemistry, Center for Plant Molecular Biology, Eberhard Karls University, Auf der Morgenstelle 5, Tübingen, 72076, Germany

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Accepted 23 January 2013.

Plant-pathogenic oomycetes have a large set of secreted effectors that can be translocated into their host cells during infection. One group of these effectors are the RxLR effectors for which it has been shown, in a few cases, that the RxLR motif is important for their translocation. It has been suggested that the RxLR-leader sequences alone are enough to translocate the respective effectors into eukaryotic cells through binding to surface-exposed phosphoinositol-3-phosphate. These conclusions were primary based on translocation experiments conducted with recombinant fusion proteins whereby the RxLR leader of RxLR effectors (i.e., Avr1b from Phytophthora sojae) were fused to the green fluorescent protein reporter-protein. However, we failed to observe specific cellular uptake for a comparable fusion protein where the RxLR leader of the P. infestans AVR3a was fused to monomeric red fluorescent protein. Therefore, we reexamined the ability of the reported P. sojae AVR1b RxLR leader to enter eukaryotic cells. Different relevant experiments were performed in three independent laboratories, using fluorescent reporter fusion constructs of AVR3a and Avr1b proteins in a side-by-side comparative study on plant tissue and human and animal cells. We report that we were unable to obtain conclusive evidence for specific RxLR-mediated translocation.

© 2013 The American Phytopathological Society