volicitin and methyl-jasmonate

Plants synthesize many fatty acid derivatives, several of which play important regulatory roles. Jasmonates are the best characterized examples. Jasmonate-insensitive mutants and mutants with a constitutive jasmonate response have given us new insights into jasmonate signalling. The jasmonate biosynthesis mutant opr3 allowed the dissection of cyclopentanone and cyclopentenone signalling, thus defining specific roles for these molecules. Jasmonate signalling is a complex network of individual signals and recent findings on specific activities of methyl jasmonate and (Z)-jasmone add to this picture. In addition, there are keto, hydroxy and hydroperoxy fatty acids that might be involved in cell death and the expression of stress-related genes. Finally, there are bruchins and volicitin, signal molecules from insects that are perceived by plants in the picomole to femtomole range. They highlight the importance of fatty acid-derived molecules in interspecies communication and in plant defence.

Topics: Acetates; alpha-Linolenic Acid; Animals; Arabidopsis; Arabidopsis Proteins; Chloroplasts; Cyclopentanes; Fatty Acids; Fatty Acids, Volatile; Glutamine; Lipid Peroxides; Lipoxygenase; Models, Chemical; Mutation; Oxidoreductases; Oxylipins; Peroxisomes; Plant Proteins; Signal Transduction

Volicitin (17-hydroxylinolenoyl-l-Gln) present in the regurgitant of Spodoptera exigua (beet armyworm caterpillars) activates the emission of volatile organic compounds (VOCs) when in contact with damaged Zea mays cv Delprim (maize) leaves. VOC emissions in turn serve as a signaling defense for the plant by attracting female parasitic wasps that prey on herbivore larvae. A tritiated form of volicitin was synthesized and shown to induce volatiles in the same fashion as the biological form. [(3)H]-l-volicitin rapidly, reversibly, and saturably bound to enriched plasma membrane fractions isolated from Z. mays leaves with an apparent K(d) of 1.3 nM and a Hill coefficient of 1.07. Analog studies showed that the l-Gln and hydroxy moieties of volicitin play an important role in binding. Treatment of plants with methyl jasmonate (MeJA) increased the total binding of [(3)H]-l-volicitin to the enriched plasma membrane more than threefold, suggesting that MeJA activates transcription of the gene encoding the binding protein. S. exigua feeding also increased total binding fourfold. Cycloheximide pretreatment of plants significantly decreased binding of radiolabeled volicitin to the enriched plasma membrane. These data provide the first experimental evidence that initiation of plant defenses in response to herbivore damage can be mediated by a binding protein-ligand interaction.

Topics: Acetates; alpha-Linolenic Acid; Animals; Binding Sites; Cyclopentanes; Glutamine; Immunity, Innate; Insect Control; Membrane Proteins; Molecular Structure; Oxylipins; Plant Diseases; Plant Growth Regulators; Plant Leaves; Protein Binding; Signal Transduction; Spodoptera; Transcription, Genetic; Tritium; Volatilization; Wasps; Zea mays

The indole-3-glycerol phosphate lyase Igl is the structural gene of volatile indole biosynthesis in the tritrophic interaction in maize. The gene is activated on transcriptional level with the same kinetics and to the same level by the fatty acid-amino acid conjugates (FAC's) volicitin (17S)-(N-(17-hydroxylinolenoyl)-L-glutamine) and N-linolenoyl-L-glutamine. Both conjugates are present in the regurgitates of herbivorous caterpillars. Modifications of the fatty acid moiety of the FACs greatly reduces the elicitation of Igl and only the L-stereo-isomer of the FACs shows biological activity in the system. Volicitin treatment leads to a fast increase of AOS and AOC transcription levels and methyl jasmonate application induces Igl transcription. Hence, the induction of jasmonate biosynthesis appears to be an integral part of the elicitor mediated increase of Igl gene transcription.

Topics: Acetates; alpha-Linolenic Acid; Amino Acids, Cyclic; Animals; Aristolochic Acids; Aspirin; Cyclooxygenase Inhibitors; Cyclopentanes; Genes, Plant; Glutamine; Indole-3-Glycerol-Phosphate Synthase; Indoles; Intramolecular Oxidoreductases; Lepidoptera; Linolenic Acids; Oxylipins; Pyrazoles; Stereoisomerism; Structure-Activity Relationship; Transcriptional Activation; Zea mays