Submitted to: Journal of Chemical Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/9/2010
Publication Date: 2/27/2010
Citation: Yoshinaga, N., Alborn, H.T., Nakanishi, T., Suckling, D.M., Nishida, R., Tumlinson, J.H., Mori, N. 2010. Fatty acid-amino acid conjugates diversification in Lepidopteran caterpillars. Journal of Chemical Ecology. 36:319-325. Interpretive Summary: Fatty acid amino acid conjugates (FACs) that have been found in oral secretions of Noctuid as well as Sphingid caterpillar of agricultural importance are known to affect defensive responses in the insect host plants. Consequently, the role of FACs in induced plants defense is the subject of intense research. However, the role of FACs in the insect is still virtually unknown. In this investigation a scientist at USDA ARS CMAVE in Gainesville Florida in co-operation with scientists at Kyoto University, and Penn State University conducted FAC screening of a diverse group of lepidopteran species and found FACs in approximately 2/3 of these species, thus, FACs are commonly synthesized through a broad range of lepidopteran caterpillars. In a previous study we found FAC to be beneficial to Lepidopteran larvae by having a positive role in nitrogen assimilation. Despite that, in this investigation we found no clear indication of developmental disadvantage for lepidopteran larvae free of FACs. Comparing the diversity of FACs with lepidopteran phylogeny indicates that the glutamine based conjugates are the evolutionary oldest FACs. Glutamic acid conjugates can also be synthesized by relatively primitive species, while hydroxylation of fatty acids is mostly limited to larger and more developed Macrolepidopteran species. This paper has highlighted the need to intensify our studies of FACs role not only in plants but in Lepidoptera as well as other insects in order to obtain an understanding of the multifaceted functions of FACs in the insect world and to explore if we can utilize this knowledge to control pest insects.
Technical Abstract: Fatty acid amino acid conjugates (FACs) have been found in Noctuid as well as Sphingid caterpillar oral secretions and especially volicitin [N-(17-hydroxylinolenoyl)-L-Glutamine] and its biochemical precursor, N-linolenoyl-L-glutamine, are known elicitors of induced volatile emissions in corn plants. These induced volatiles in turn attract natural enemies of the caterpillars. In a previous study we showed that N-linolenoyl-L-glutamine in larval Spodoptera litura plays an important role in nitrogen assimilation which might be a strong incentive for caterpillars to synthesize FACs despite an increased risk of attracting natural enemies. However, the presence of FACs in lepidopteran species outside these families of agricultural interest is not well known. We conducted FAC screening of 29 lepidopteran species and found FACs in 19 of these species. Thus, FACs are quite commonly synthesized through a broad range of lepidopteran caterpillars. Since all FAC containing species had Nlinolenoyl-L-glutamine and/or N-linoleoyl-L-glutamine in common and the evolutionarily earliest species among them had only these two FACs, these glutamine conjugates might be evolutionary older FACs. Some species further had glutamic acid conjugates and some had hydroxylated FACs. Comparing the diversity of FACs with lepidopteran phylogeny indicates that glutamic acid conjugates can be synthesized by relatively primitive species, while hydroxylation of fatty acids is mostly limited to larger and more developed Macrolepidopteran species.