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Key Words fatty acid, hypersensitive response, oxylipin, plant defense, systemic acquired resistance (SAR)
Abstract Lipids and lipid metabolites influence pathogenesis and resistance mechanisms associated with plant-microbe interactions. Some microorganisms sense their presence on a host by perceiving plant surface waxes, whereas others produce toxins that target plant lipid metabolism. In contrast, plants have evolved to recognize microbial lipopolysaccharides (LPSs), sphingolipids, and lipid-binding proteins as elicitors of defense response. Recent studies have demonstrated that the plasma membrane provides a surface on which some plant resistance (R) proteins perceive pathogen-derived effectors and thus confer race-specific resistance. Plant cell membranes also serve as reservoirs from which biologically active lipids and precursors of oxidized lipids are released. Some of these oxylipins, for example jasmonic acid (JA), are important signal molecules in plant defense. Arabidopsis thaliana is an excellent model plant to elucidate the biosynthesis and metabolism of lipids and lipid metabolites, and the characterization of signaling mechanisms involved in the modulation of plant defense responses by phytolipids. This review focuses on recent studies that highlight the involvement of lipids and lipid metabolites, and enzymes involved in lipid metabolism and modification in plant disease resistance.
INTRODUCTION
Lipids are critical components of plant cell membranes and provide energy for metabolic activities. They are also important for photosynthesis, provide a physical barrier on the surface of epidermal cells that protects the plant from environmental assaults, and serve as second messengers in signal transduction mechanisms that influence plant growth, development, and response to stress (94, 203, 204). The endoplasmic reticulum and plastid provide the two major sites for lipid biosynthesis in plants (169, 199). The hydrophobic nature of lipids and the relative instability of some products of lipid metabolism have constrained our efforts to understand the involvement of lipids in plant-microbe interactions. With the advent of highly sensitive and quantitative analytical technology utilizing mass-spectrometry, gas chromatography, and high-pressure liquid chromatography studies to elucidate the role of lipids in plant-microbe interaction are rapidly advancing (141, 210-212). In addition, studies with the model plant Arabidopsis thaliana have expedited efforts to understand the role of lipids and proteins involved in lipid metabolism and signaling in plant-microbe interactions (13, 39, 46, 187, 203, 204).
Plant-Microbe Interaction
The interaction between a plant and a microbial pathogen...