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Title: An oleic acid-mediated pathway induces constitutive defense signaling and enhanced resistance to multiple pathogens in soybean

Author
item KACHROO, AARDRA - UNIV OF KENTUCKY
item DA-QI, FU - UNIV OF KENTUCKY
item HAVENS, WENDY - UNIV OF KENTUCKY
item Navarre, Duroy - Roy
item KACHROO, PRADEEP - UNIV OF KENTUCKY
item GHABRIAL, SAID - UNIV OF KENTUCKY

Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/2008
Publication Date: 7/11/2008
Citation: Kachroo, A., Da-Qi, F., Havens, W., Navarre, D.A., Kachroo, P., Ghabrial, S.A. 2008. An oleic acid-mediated pathway induces constitutive defense signaling and enhanced resistance to multiple pathogens in soybean. Molecular Plant-Microbe Interactions. 21:564-575.

Interpretive Summary: Plant disease resistance is mediated by many different mechanisms. One of the more recently identified components of disease resistance involves lipid-mediated signaling. This work shows that lipid-mediated signaling is important not just in the model plant systems, but also in crop plants that may have different lipid biosynthetic pathways. Increasing the amounts of a certain type of plant lipid led to enhanced disease resistance against both bacterial and Phytophthora pathogens. Phytophthora species are oomycetes that are major pathogens of several of the most widely planted crops, including soybeans and potato. This work provides insight into how plants can be made to more effectively resist disease.

Technical Abstract: Lack of rapid phenotypical functional analyses systems for use in soybean has impeded the characterization of molecular mechanisms governing soybean development and physiology. This problem was alleviated by the recent development of a novel bean pod mottle virus (BPMV)-based vector for employing virus-induced gene silencing (VIGS) in soybean. Here, we demonstrate the efficacy of VIGS as a tool for functional genomics in soybean and show that silencing key endogenous sequences can result in physiologically relevant phenotypes in soybean. Stearoyl-acyl carrier protein-desaturase (SACPD)-catalyzed synthesis of oleic acid (18:1), is an essential step in fatty acid biosynthesis. Silencing soybean SACPD genes using the BPMV-based vector caused a reduction in 18:1 and increase in stearic acid. The silenced plants showed stunting, development of spontaneous cell death lesions on leaves, accumulation of increased levels of salicylic acid, and constitutive expression of several pathogenesis-related genes. These plants also expressed elevated levels of several resistance-like genes and were resistant to both bacterial and oomycete pathogens. Exogenous application of glycerol also reduced 18:1 levels and mimicked the phenotypes resulting from silencing of SACPD in soybean. Overexpression of soybean SACPD restored 18:1 levels as well as the altered morphological and defense-related phenotypes in the Arabidopsis SACPD mutant ssi2, but did not increase 18:1 beyond basal levels in wild-type plants. We show that although Arabidopsis and soybean differ significantly in their lipid biosynthetic pathways, they are both capable of recognizing similar 18:1-modulated cues that can induce a novel pathway conferring robust and broad-spectrum resistance in plants.