Nematode Pheromones

Director: Fatma Kaplan, Ph.D.

Nematodes are present in every niche and parasitize nearly every animal and plant. When they infect insect, they can be used as biological control agents. When they infect plants, they cause biotic stress resulting in reduced yield and quality of crops leading great economic loss.

Currently, plant parasitic nematodes are manageable due to resistant varieties and nematicides, but the chemical landscape is changing and many toxic nematicides are being removed from the market. For example, methyl bromide, which is a broad spectrum biocide (kills insect pests, fungus, bacteria and nematodes), was used to control plant parasitic nematodes. Methyl bromide is now banned. Additionally, due to global warming, nematode survival will increase. We need newer, more environmentally friendly, methods to control plant parasitic nematodes.

Understanding small molecule mediated communication of nematodes with their environment may be the basis of chemical interventions to interfere with their colonization. Such discoveries may lead to crop treatment that deters colonization in the plant root zone and plants bred or engineered for resistance to nematodes and drugs that combat animal parasitic nematodes. These breakthroughs will improve human quality of life and agricultural production.

Pheromones are chemical factors that are secreted from one member and affect the physiology or a social behavior of other members of the same species. Pheromones have provided environmentally friendly plant insect pest control. For example, sex or mating pheromones are used to interfere with the reproduction of insect pests, by trapping males. They are effective in very low concentration and species specific, so they don’t kill nontarget organisms.

Nematode pheromones can be used for ecologically friendly control of 1- insect pests via improving efficacy of insect nematodes/entomopathogenic nematodes, EPNs and 2- of plant parasitic nematodes. Nematode pheromones were considered in the late 60s (Ann. Appl. Biol. (1966) 58:327-339, Nematologica (1970) 16:39-46, J. Exp. Zool. (1979) 208:311-318) to control plant parasitic nematodes. However, analytical chemistry instruments were not sensitive enough in the past (personal communication with Dr. Hammock). Particularly nuclear magnetic resonance (NMR) based structural elucidation required milligrams to grams of pure pheromone. Pheromones are very effective at low concentration and released in very small amounts which makes it difficult to collect enough material for NMR based structural identification. Since the 1960s, the sensitivity of analytical chemistry instrumentation has improved dramatically.

The first nematode pheromone was identified from Caenorhabditis elegans in 2005 (Jeong et al 2005 Nature 433:541-545). It was a single compound, named daumone, because it regulated entry of L1 larvae under stressful conditions into dauer or dispersal larvae. This is an alternative life stage resistant to stressful, adverse conditions and seeks food. In 2007, Dr. Kaplan in the Edison lab at the University of Florida and Dr. Srinivasan at the Sternberg lab at Caltech identified mate finding pheromone from C. elegans.  The same class of compounds were found to regulate both mate finding behavior and development (dauer/dispersal larvae formation) published this work in Nature in 2008 (Srinivasan and Kaplan et al. 2008, Nature 454: 1115–1118 and Kaplan et al. 2008, Mag Lab Reports 15: 14-15).

In January 2011, Dr. Kaplan prepared an application for The Schroth faces of the future, Nematology, award by American Phytopathological Society. She was one of the awardees. Dr. Kaplan followed that up with a 5 year vision essay for nematode pheromones in December 2013 that was selected for publication in the Genetics Society of America newsletter (The GSA Reporter 2014, Winter issue).