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Journal of Bacteriology, June 2005, p. 4257-4269, Vol. 187, No. 12
0021-9193/05/$08.00+0     doi:10.1128/JB.187.12.4257-4269.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Pseudomonas syringae Type III Chaperones ShcO1, ShcS1, and ShcS2 Facilitate Translocation of Their Cognate Effectors and Can Substitute for Each Other in the Secretion of HopO1-1

Ming Guo,^1,2, Scott T. Chancey,^1,2,, Fang Tian,^1,3 Zhengxiang Ge,^1,4 Yashitola Jamir,^1,2 and James R. Alfano^1,2*

The Plant Science Initiative,¹ Department of Plant Pathology,² School of Biological Sciences,³ the Department of Agronomy, University of Nebraska, Lincoln, Nebraska 68588-0660⁴

Received 1 February 2005/ Accepted 14 March 2005

The Pseudomonas syringae type III secretion system (TTSS) translocates effector proteins into plant cells. Several P. syringae effectors require accessory proteins called type III chaperones (TTCs) to be secreted via the TTSS. We characterized the hopO1-1, hopS1, and hopS2 operons in P. syringae pv. tomato DC3000; these operons encode three homologous TTCs, ShcO1, ShcS1, and ShcS2. ShcO1, ShcS1, and ShcS2 facilitated the type III secretion and/or translocation of their cognate effectors HopO1-1, HopS1, and HopS2, respectively. ShcO1 and HopO1-1 interacted with each other in yeast two-hybrid and coimmunoprecipitation assays. Interestingly, ShcS1 and ShcS2 were capable of substituting for ShcO1 in facilitating HopO1-1 secretion and translocation and each TTC was able to bind the other's cognate effectors in yeast two-hybrid assays. Moreover, ShcO1, ShcS1, and ShcS2 all bound to the middle-third region of HopO1-1. The HopS2 effector possessed atypical P. syringae TTSS N-terminal characteristics and was translocated in low amounts. A site-directed HopS2 mutation that introduced a common N-terminal characteristic from other P. syringae type III secreted substrates increased HopS2 translocation, supporting the idea that this characteristic functions as a secretion signal. Additionally, hopO1-2 and hopT1-2 were shown to encode effectors secreted via the DC3000 TTSS. Finally, a DC3000 hopO1-1 operon deletion mutant produced disease symptoms similar to those seen with wild-type DC3000 but was reduced in its ability to multiply in Arabidopsis thaliana. The existence of TTCs that can bind to dissimilar effectors and that can substitute for each other in effector secretion provides insights into the nature of how TTCs function.

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* Corresponding author. Mailing address: Plant Science Initiative, The Beadle Center for Genetic Research, University of Nebraska, 1901 Vine St., Lincoln, NE 68588-0660. Phone: (402) 472-0395. Fax: (402) 472-3139. E-mail: jalfano2{at}unl.edu.

M.G. and S.T.C. contributed equally to this research.

Present address: Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322.

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Journal of Bacteriology, June 2005, p. 4257-4269, Vol. 187, No. 12
0021-9193/05/$08.00+0     doi:10.1128/JB.187.12.4257-4269.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

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