Plant parasitic nematodes have evolved a complex relationship with their host plants. Sedentary endoparasitic nematodes, such as the soybean cyst nematode and the root-know nematode; alter plant cell development in order to form large plant cells that they feed upon throughout their life cycle.

Some generations of nematodes have the ability to feed on thousands of different plant species, suggesting they manipulate conserved plant pathways to form their feeding cells.

The discovery of a secreted plant parasite nematode chorismate mutase (CM), an enzyme found in the shikimate pathway of plants, suggests these nematodes directly alter this essential primary metabolic route.

Research Premise

It is the premise of this project that a thorough understanding of how nematode CMs alters plant metabolism will allow plants to be altered via transgenic strategies to counteract the nematode's own metabolic engineering.

The research will focus on CMs from the soybean cyst nematode (Heterodera glycines) and the root-knot nematode (Meliodogyne javanica), two types of nematodes that cause extensive damage to crop plants worldwide.

Objectives & Rationale

Specific goal is to identify the immediate down stream products of nematode CMs using a metabolomic-based approach. Preliminary work on transgenic soybean hairy roots has allowed the researchers to show the feasibility of the approach. However, more analysis is needed.

Since the shikimate pathway of plants is very complicated the PIs have devised a strategy to compare the metabolic aberrations caused by nematode CMs in both soybean hairy roots and E. coli. Both organisms have the shikimate pathway, but bacteria do not produce such an extensive array of secondary metabolites and will simplify the interpretation of data.

The next phase of the project is to design a transgenic approach to counteract what the nematode CM is doing to the plant's shikimate pathway. The rationale for this approach to engineer nematode resistance is based upon the observation that many shikimate derived compounds are toxic to nematodes. The nematode CM appear to lower the levels of some of these compounds thus facilitating plant parasitism.

If the primary role of the nematode CM is to lower toxic plant defense compounds or defense signaling compounds and the researchers can prevent this from occurring via metabolic engineering of the host plant, then significant nematode resistance should be imparted.

Methods

First, the researchers will complete an extensive analysis of downstream products produced by nematode CM expression in bacteria and plants. This will probably take the duration of the two-year project. However, at the end there should be a good metabolic engineering strategy devised to engineer nematode resistance.

Specific approaches:

1. Measure soluble aromatic metabolites by HPLC-MS metabolite profiling methods in hairy roots expressing nematode CM.
2. Determine rapid metabolic changes in tracer experiments with E. coli and soybean hairy roots expressing nematode CMs.

This project will identify a nematode CM diverted branch of the shikimate pathway and will identify the phenolic compounds that increase and decrease upon nematode CM expression in the plant cell. Since this new nematode induced branch of the plant's shikimate pathway should only be activated by the introduction of a nematode CM into the plant cell, the researchers should be able to use the nematode's own CM as a switch to trigger the synthesis of a plant defense signaling compound or a toxin to kill the nematode.

To accomplish this goal, biochemical information obtained from these studies will be used as a basis to choose phenolic metabolizing genes to insert into the plant to convert the nematode CM diverted phenolic compounds into metabolites detrimental to the nematode, thus allowing the generation of a new type of nematode resistant soybean.  Since this type of engineered nematode resistance will be activated solely by nematode CM biochemical activity, it should be effective against any nematode that uses a CM to aid it in plant parasitism, regardless of the DNA or protein sequence of the nematode CM.

The research strategy for generating nematode resistance has a distinct advantage over other approaches, such as RNAi based resistance that are highly sequence dependent, in that the proposed approach will generate a broad type of nematode resistance effective at controlling the most problematic sedentary endoparasitic nematode species.