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PLANTS INTERACTING WITH OTHER ORGANISMS

Effects of Endogenous Salicylic Acid on Nodulation in the Model Legumes Lotus japonicus and Medicago truncatula^1,[W]

Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996 (G.S., C.B.M.); Estación Experimental del Zaidin, Consejo Superior de Investigaciones Científicas, 18008 Granada, Spain (J.O., M.J.S.); and National Center for Soybean Biotechnology, Division of Plant Science (G.S., S.-Y.K.) and Division of Biochemistry, Department of Molecular Microbiology and Immunology (G.S.), University of Missouri, Columbia, Missouri 65211

The exogenous addition of salicylic acid (SA) was previously shown to inhibit indeterminate but not determinate-type nodulation. We sought to extend these results by modulating endogenous levels of SA through the transgenic expression of salicylate hydroxylase (NahG) in both stably transformed Lotus japonicus and composite Medicago truncatula plants. NahG expression in L. japonicus resulted in a marked reduction of SA levels. This reduction correlated with an increase in the number of infections and mean nodule number when compared to controls. However, a complicating factor was that NahG-expressing plants had greater root growth. Spot inoculations of NahG-expressing L. japonicus plants confirmed increased nodulation in these plants. Consistent with the reported inhibitory effects of exogenous SA on indeterminate-type nodulation, NahG expression in M. truncatula plants led to enhanced nodulation and infection. These data point to an important role for SA-mediated plant defense pathways in controlling nodule formation on both determinate and indeterminate nodule-forming hosts.

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: Gary Stacey (staceyg{at}missouri.edu).

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

Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.106.080986.

^* Corresponding author; e-mail staceyg{at}missouri.edu; fax 573–884–4752.

Received March 27, 2006; returned for revision June 13, 2006; accepted June 13, 2006.

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