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Cell Microbiol. 2012 May;14(5):669-81. doi: 10.1111/j.1462-5822.2012.01749.x. Epub 2012 Feb 15.

A bacterial cysteine protease effector protein interferes with photosynthesis to suppress plant innate immune responses.

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Centro de Biotecnología y Genómica de Plantas (CBGP). Universidad Politécnica de Madrid-Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria., Parque Científico y Tecnológico de la UPM. Campus de Montegancedo. 28223 Pozuelo de Alarcón, Madrid, Spain.


The bacterial pathogen Pseudomonas syringae pv tomato DC3000 suppresses plant innate immunity with effector proteins injected by a type III secretion system (T3SS). The cysteine protease effector HopN1, which reduces the ability of DC3000 to elicit programmed cell death in non-host tobacco, was found to also suppress the production of defence-associated reactive oxygen species (ROS) and callose when delivered by Pseudomonas fluorescens heterologously expressing a P. syringae T3SS. Purified His(6) -tagged HopN1 was used to identify tomato PsbQ, a member of the oxygen evolving complex of photosystem II (PSII), as an interacting protein. HopN1 localized to chloroplasts and both degraded PsbQ and inhibited PSII activity in chloroplast preparations, whereas a HopN1(D299A) non-catalytic mutant lost these abilities. Gene silencing of NtPsbQ in tobacco compromised ROS production and programmed cell death by DC3000. Our data reveal PsbQ as a contributor to plant immunity responses and a target for pathogen suppression.

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