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PLANTS INTERACTING WITH OTHER ORGANISMS

Salicylic Acid and Systemic Acquired Resistance Play a Role in Attenuating Crown Gall Disease Caused by Agrobacterium tumefaciens^1,[W],[OA]

Plant Biology Division, Samuel Roberts Noble Foundation, Ardmore, Oklahoma 73401

We investigated the effects of salicylic acid (SA) and systemic acquired resistance (SAR) on crown gall disease caused by Agrobacterium tumefaciens. Nicotiana benthamiana plants treated with SA showed decreased susceptibility to Agrobacterium infection. Exogenous application of SA to Agrobacterium cultures decreased its growth, virulence, and attachment to plant cells. Using Agrobacterium whole-genome microarrays, we characterized the direct effects of SA on bacterial gene expression and showed that SA inhibits induction of virulence (vir) genes and the repABC operon, and differentially regulates the expression of many other sets of genes. Using virus-induced gene silencing, we further demonstrate that plant genes involved in SA biosynthesis and signaling are important determinants for Agrobacterium infectivity on plants. Silencing of ICS (isochorismate synthase), NPR1 (nonexpresser of pathogenesis-related gene 1), and SABP2 (SA-binding protein 2) in N. benthamiana enhanced Agrobacterium infection. Moreover, plants treated with benzo-(1,2,3)-thiadiazole-7-carbothioic acid, a potent inducer of SAR, showed reduced disease symptoms. Our data suggest that SA and SAR both play a major role in retarding Agrobacterium infectivity.

² Present address: Systems Microbiology Research Center, KRIBB, Daejon 305–333, South Korea.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Kirankumar S. Mysore (ksmysore{at}noble.org).

^[W] The online version of this article contains Web-only data.

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.111302

^* Corresponding author; e-mail ksmysore{at}noble.org.

Received October 18, 2007; accepted December 14, 2007; published December 21, 2007.