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Science 15 August 2008:
Vol. 321. no. 5891, pp. 964 - 967
DOI: 10.1126/science.1159505
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Reports

Suppression of the MicroRNA Pathway by Bacterial Effector Proteins

Lionel Navarro,1 Florence Jay,1 Kinya Nomura,2 Sheng Yang He,2 Olivier Voinnet1*

Plants and animals sense pathogen-associated molecular patterns (PAMPs) and in turn differentially regulate a subset of microRNAs (miRNAs). However, the extent to which the miRNA pathway contributes to innate immunity remains unknown. Here, we show that miRNA-deficient mutants of Arabidopsis partly restore growth of a type III secretion-defective mutant of Pseudomonas syringae. These mutants also sustained growth of nonpathogenic Pseudomonas fluorescens and Escherichia coli strains, implicating miRNAs as key components of plant basal defense. Accordingly, we have identified P. syringae effectors that suppress transcriptional activation of some PAMP-responsive miRNAs or miRNA biogenesis, stability, or activity. These results provide evidence that, like viruses, bacteria have evolved to suppress RNA silencing to cause disease.

1 Institut de Biologie Moléculaire des Plantes, CNRS UPR 2353–Université Louis Pasteur, 12 Rue du Général Zimmer, 67084 Strasbourg Cedex, France.
2 Department of Energy Plant Research Laboratory, Michigan State University, East Lansing, MI 48824, USA.

* To whom correspondence should be addressed. E-mail: olivier.voinnet{at}ibmp-ulp.u-strasbg.fr

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