Nematode MDH-like sequences

Details Nematode MDH-like sequences Nematode MDH-like sequences

2002-01-30

2004-06-01

Saidha, Tekchand (Department: 1652)

Chemistry: molecular biology and microbiology

Enzyme , proenzyme; compositions thereof; process for...

Oxidoreductase

C435S440000, C536S023200

Reexamination Certificate

active

06743612

ABSTRACT:

BACKGROUND
Nematodes (derived from the Greek word for thread) are active, flexible, elongate, organisms that live on moist surfaces or in liquid environments, including films of water within soil and moist tissues within other organisms. While only 20,000 species of nematode have been identified, it is estimated that 40,000 to 10 million actually exist. Some species of nematodes have evolved as very successful parasites of both plants and animals and are responsible for significant economic losses in agriculture and livestock and for morbidity and mortality in humans (Whitehead (1998)
Plant Nematode Control.
CAB International, New York).
Nematode parasites of plants can inhabit all parts of plants, including roots, developing flower buds, leaves, and stems. Plant parasites are classified on the basis of their feeding habits into the broad categories: migratory ectoparasites, migratory endoparasites, and sedentary endoparasites. Sedentary endoparasites, which include the root knot nematodes (Meloidogyne) and cyst nematodes (Globodera and Heterodera) induce feeding sites and establish long-term infections within roots that are often very damaging to crops (Whitehead, supra). It is estimated that parasitic nematodes cost the horticulture and agriculture industries in excess of $78 billion worldwide a year, based on an estimated average 12% annual loss spread across all major crops. For example, it is estimated that nematodes cause soybean losses of approximately $3.2 billion annually worldwide (Barker et al. (1994)
Plant and Soil Nematodes: Societal Impact and Focus for the Future.
The Committee on National Needs and Priorities in Nematology. Cooperative State Research Service, US Department of Agriculture and Society of Nematologists). Several factors make the need for safe and effective nematode controls urgent. Continuing population growth, famines, and environmental degradation have heightened concern for the sustainability of agriculture, and new government regulations may prevent or severely restrict the use of many available agricultural anthelmintic agents.
The situation is particularly dire for high value crops such as strawberries and tomatoes where chemicals have been used extensively to control soil pests. The soil fumigant methyl bromide has been used effectively to reduce nematode infestations in a variety of these specialty crops. It is however regulated under the U.N. Montreal Protocol as an ozone-depleting substance and is scheduled for elimination in 2005 in the US (Carter (2001)
California Agriculture,
55(3):2). It is expected that strawberry and other commodity crop industries will be significantly impacted if a suitable replacement for methyl bromide is not found. Presently there are a very small array of chemicals available to control nematodes and they are frequently inadequate, unsuitable, or too costly for some crops or soils (Becker (1999)
Agricultural Research Magazine
47(3):22-24; U.S. Pat. Nos. 6,048,714). The few available broad-spectrum nematicides such as Telone (a mixture of 1,3-dichloropropene and chloropicrin) have significant restrictions on their use because of toxicological concerns (Carter (2001)
California Agriculture,
Vol. 55(3):12-18).
Fatty acids are a class of natural compounds that have been investigated as alternatives to the toxic, non-specific organophosphate, carbamate and fumigant pesticides (Stadler et al. (1994)
Planta Medica
60(2):128-132; U.S. Pat. Nos. 5,192,546; 5,346,698; 5,674,897; 5,698,592; 6,124,359). It has been suggested that fatty acids derive their pesticidal effects by adversely interfering with the nematode cuticle or hypodermis via a detergent (solubilization) effect, or through direct interaction of the fatty acids and the lipophilic regions of target plasma membranes (Davis et al. (1997)
Journal of Nematology
29(4S):677-684). In view of this general mode of action it is not surprising that fatty acids are used in a variety of pesticidal applications including as herbicides (e.g., SCYTHE by Dow Agrosciences is the C9 saturated fatty acid pelargonic acid), as bactericides and fungicides (U.S. Pat. Nos. 4,771,571; 5,246,716) and as insecticides (e.g., SAFER INSECTICIDAL SOAP by Safer, Inc.).
The phytotoxicity of fatty acids has been a major constraint on their general use in agricultural applications (U.S. Pat. No. 5,093,124) and the mitigation of these undesirable effects while preserving pesticidal activity is a major area of research. The esterification of fatty acids can significantly decrease their phytotoxicity (U.S. Pat. Nos. 5,674,897; 5,698,592; 6,124,359). Such modifications can however lead to dramatic loss of nematicidal activity as is seen for linoleic, linolenic and oleic acid (Stadler et al. (1994)
Planta Medica
60(2):128-132) and it may be impossible to completely decouple the phytotoxicity and nematicidal activity of pesticidal fatty acids because of their non-specific mode of action. Perhaps not surprisingly, the nematicidal fatty acid pelargonic acid methyl ester (U.S. Pat. Nos. 5,674,897; 5,698,592; 6,124,359) shows a relatively small “therapeutic window” between the onset of pesticidal activity and the observation of significant phytotoxicity (Davis et al. (1997)
J Nematol
29(4S):677-684). This is the expected result if both the phytotoxicity and the nematicidial activity derive from the non-specific disruption of plasma membrane integrity. Similarly the rapid onset of pesticidal activity seen with many nematicidal fatty acids at therapeutic concentrations (U.S. Pat. Nos. 5,674,897; 5,698,592; 6,124,359) suggests a non-specific mechanism of action, possibly related to the disruption of membranes, action potentials and neuronal activity.
Ricinoleic acid, the major component of castor oil, provides another example of the unexpected effects esterification can have on fatty acid activity. Ricinoleic acid has been shown to have an inhibitory effect on water and electrolyte absorption using everted hamster jejunal and ileal segments (Gaginella et al. (1975)
J Pharmacol Exp Ther
195(2):355-61) and to be cytotoxic to isolated intestinal epithelial cells (Gaginella et al. (1977)
J Pharmacol Exp Ther
201(1):259-66). These features are likely the source of the laxative properties of castor oil which is given as a purgative in humans and livestock. In contrast, the methyl ester of ricinoleic acid is ineffective at suppressing water absorption in the hamster model (Gaginella et al. (1975)
J Pharmacol Exp Ther
195(2):355-61). (N.B. Castor oil is a component of some de-worming protocols because of its laxative properties.)
The macrocyclic lactones (e.g., avermectins and milbemycins) and delta-toxins from
Bacillus thuringiensis
(Bt) are chemicals that in principle provide excellent specificity and efficacy and should allow environmentally safe control of plant parasitic nematodes. Unfortunately, in practice, these two approaches have proven less effective for agricultural applications against root pathogens. Although certain avermectins show exquisite activity against plant parasitic nematodes these chemicals are hampered by poor bioavailability due to their light sensitivity, degradation by soil microorganisms and tight binding to soil particles (Lasota & Dybas (1990)
Acta Leiden
59(1-2):217-225; Wright & Perry (1998) Musculature and Neurobiology. In: The Physiology and Biochemistry of Free-Living and Plant-parasitic Nematodes (eds R. N. Perry & D. J. Wright), CAB International 1998). Consequently despite years of research and extensive use against animal parasitic nematodes, mites and insects (plant and animal applications), macrocyclic lactones (e.g., avernectins and milbemycins) have never been commercially developed to control plant parasitic nematodes in the soil.
Bt delta toxins must be ingested to affect their target organ the brush border of midgut epithelial cells (Marroquin et al. (2000)
Genetics.
155(4):1693-1699). Consequently they are not anticipated to be effective against the dispersal, non-feeding, juvenile stages of plant parasitic nematodes in the field. These

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