Submitted to: Critical Reviews in Biochemistry and Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 14, 1999
Publication Date: N/A
Interpretive Summary: Nematodes are microscopic soil worms that annually cause ten billion dollars of crop losses in the United States. Because safe methods for controlling nematodes are not always available, ARS scientists are looking for new control strategies. To solve the problem of developing safe control measures for nematodes, ARS scientists are looking at differences between the hormonal systems of nematodes and those of their animal and plant hosts, in order to logically design new ways of disrupting nematode hormone biochemistry or function. The present paper is a review article that summarizes this research. Specifically, the article focuses on hormone precursors called sterols. ARS scientists have shown that the chemical composition of nematode sterols is different from that of plants and mammals, and that nematodes must obtain sterols from their plant hosts. Moreover, some chemical compounds that disrupt sterol biochemistry in nematodes destroy the ability of nematodes to reproduce. These results indicate that it may be possible to selectively and safely interfere with the life cycles of nematodes by disrupting their ability to convert plant sterols to nematode sterols. Therefore, the results will be utilized by scientists interested in developing innovative strategies for managing plant- parasitic nematodes.
Nematodes do not biosynthesize sterols de novo and thus possess a nutritional requirement for sterol. This review focuses on the composition, metabolism and function of sterols and other steroids in nematodes. The sterol compositions of several species of plant- parasitic nematodes have been compared with those of their hosts. Saturation of the phytosterol nucleus is the major transformation in the root-knot nematodes Meloidogyne arenaria and M. incognita and the corn root lesion nematode, Pratylenchus agilis. In addition to saturation, the corn cyst nematode, Heterodera zeae, dealkylates its host sterols at C-24. Free-living nematodes have been successfully used as model organisms for investigation of sterol metabolism in plant-parasitic nematodes. Major pathways of phytosterol metabolism in Caenorhabditis elegans, Turbatrix aceti and Panagrellus redivivus include C-24 dealkylation and 4-methylation (a pathway unique to nematodes). C. elegans and T. aceti introduce double bonds at C-7, and T. aceti and P. redivivus saturate the sterol nucleus similarly to the plant-parasitic species examined. Several azasteroids and long chain dimethylalkylamines inhibit growth and development of C. elegans and also the delta-24-sterol reductase enzyme system involved in dealkylation.