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An Oleic Acid--Mediated Pathway Induces Constitutive Defense Signaling and Enhanced Resistance to Multiple Pathogens in Soybean

May 2008 , Volume 21 , Number  5
Pages  564 - 575

Aardra Kachroo,1 Da-Qi Fu,1 Wendy Havens,1 DuRoy Navarre,2 Pradeep Kachroo,1 and Said A. Ghabrial1

1Department of Plant Pathology, University of Kentucky, Lexington 40546, U.S.A.; 2Department of Plant Pathology, United States Department of Agriculture--Agricultural Research Service, Washington State University, Prosser 99350, U.S.A.


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Accepted 25 January 2008.

Stearoyl-acyl carrier protein-desaturase (SACPD)-catalyzed synthesis of oleic acid (18:1) is an essential step in fatty acid biosynthesis. Arabidopsis mutants (ssi2) with reduced SACPD activity accumulate salicylic acid (SA) and exhibit enhanced resistance to multiple pathogens. We show that reduced levels of 18:1 induce similar defense-related phenotypes in soybean. A Bean pod mottle virus (BPMV)-based vector was employed to effectively silence soybean SACPDs. The silenced plants contained reduced 18:1 and increased stearic acid, developed spontaneous cell death lesions, increased SA accumulation, and constitutively expressed pathogenesis-related genes. These plants also expressed elevated levels of resistance-like genes and showed resistance to bacterial and oomycete pathogens. Exogenous application of glycerol induced similar phenotypes, mimicking the effect of silencing SACPDs in healthy soybean plants. Overexpression of a soybean SACPD increased 18:1 levels in ssi2 but not in wild-type Arabidopsis plants, suggesting that the soybean enzyme was under feedback regulation similar to that of the Arabidopsis isozymes. These results suggest that soybean and Arabidopsis respond similarly to 18:1-derived cues by inducing a novel broad-spectrum resistance-conferring pathway, even though they differ significantly in their lipid biosynthetic pathways. We also demonstrate the efficacy of BPMV-induced gene silencing as a tool for functional studies in soybean.


Additional keywords:Phytophthora sojae, Pseudomonas syringae pv. glycinea, soybean defense.

© 2008 The American Phytopathological Society