Transcriptional activation of Igl, the gene for indole formation in Zea mays: a structure–activity study with elicitor-active N-acyl glutamines from insects

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.