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Microbe-Independent Entry of Oomycete RxLR Effectors and Fungal RxLR-Like Effectors Into Plant and Animal Cells Is Specific and Reproducible

June 2013 , Volume 26 , Number  6
Pages  611 - 616

Brett M. Tyler,1 Shiv D. Kale,2 Qunqing Wang,1 Kai Tao,1 Helen R. Clark,2 Kelly Drews,2 Vincenzo Antignani,2 Amanda Rumore,2 Tristan Hayes,2 Jonathan M. Plett,3 Isabelle Fudal,4 Biao Gu,2,5 Qinghe Chen,2 Katharyn J. Affeldt,6 Erwin Berthier,6 Gregory J. Fischer,6 Daolong Dou,2,7 Weixing Shan,5 Nancy P. Keller,6 Francis Martin,3 Thierry Rouxel,4 and Christopher B. Lawrence2

1Center for Genome Research and Biocomputing, and Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, U.S.A.; 2Virginia Bioinformatics Institute, Virginia Tech, Blacksburg, VA 24061, U.S.A.; 3Lab of Excellence ARBRE, UMR INRA/UHP 1136, Interactions Arbres/Micro-organismes, Centre INRA de Nancy, 54280 Champenoux, France; 4INRA-Bioger, Campus AgroParisTech, 78850 Thiverval-Grignon, France; 5College of Plant Protection and State Key Laboratory of Crop Stress Biology in Arid Areas, Northwest A&F University, Yangling, Shaanxi 712100, China; 6Department of Medical Microbiology and Immunology, University of Wisconsin, Madison, WI 53706, U.S.A.; 7Department of Plant Pathology, Nanjing Agricultural University, Nanjing 210095, China

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Accepted 25 February 2013.

A wide diversity of pathogens and mutualists of plant and animal hosts, including oomycetes and fungi, produce effector proteins that enter the cytoplasm of host cells. A major question has been whether or not entry by these effectors can occur independently of the microbe or requires machinery provided by the microbe. Numerous publications have documented that oomycete RxLR effectors and fungal RxLR-like effectors can enter plant and animal cells independent of the microbe. A recent reexamination of whether the RxLR domain of oomycete RxLR effectors is sufficient for microbe-independent entry into host cells concluded that the RxLR domains of Phytophthora infestans Avr3a and of P. sojae Avr1b alone are NOT sufficient to enable microbe-independent entry of proteins into host and nonhost plant and animal cells. Here, we present new, more detailed data that unambiguously demonstrate that the RxLR domain of Avr1b does show efficient and specific entry into soybean root cells and also into wheat leaf cells, at levels well above background nonspecific entry. We also summarize host cell entry experiments with a wide diversity of oomycete and fungal effectors with RxLR or RxLR-like motifs that have been independently carried out by the seven different labs that coauthored this letter. Finally we discuss possible technical reasons why specific cell entry may have been not detected by Wawra et al. (2013).

© 2013 The American Phytopathological Society