Inter-species Interaction by Semiochemicals
— Elucidation of Inter-species Interaction and Expression Mechanisms of Ecological Functions by Semiochemicals —

Background and Objectives

In an agricultural ecosystem, a large variety of living organisms live interacting with each other. For sound management of agricultural ecosystems, the accumulation of knowledge about the interactions among the species that constitute is indispensable. It has been made clear that various semiochemicals play important roles in inter-species interaction. With respect to plants, for example, juglone glycoside produced by black walnut is transformed to juglone in the environment by the action of microorganisms and inhibits growth of other plants. A cis-cinnamic acid derivative produced by Thunberg's meadowsweet (Spiraea thunbergii) (Fig. 1) is known to possess the most potent plant growth regulating activity among all naturally produced substances. With respect to insects, semiochemicals that function as carriers of inter-individual communications were first identified in 1959 in the silkworm (Bombyx mori), followed by the discovery and structure identification of a large number of sex pheromones. Many microorganisms, which had been considered to act as single cell, have been proven to move in concert by the working of semiochemicals.

This research project is aimed to elucidating the inter-species interaction of plants, insects and microorganisms through the semiochemicals they produce, thus contributing to a wide array of technological development in many fields.

Expected Outcomes

The plant growth regulating mechanism of the family Rosaceae will be elucidated, and the causal substance extracted from the plant and its chemical structure will also be identified. The behavior and changes in biological activity in soil of such plant growth-regulating substances will be analyzed, and the functions they have in soil will be clarified. With respect to insects, the sex pheromones of Crambidae Pyraustinae will be identified with the aim of elucidating the genetic background of sex pheromone mutation, and the mutation of reactivity to male sex pheromones. In the field of microorganisms, we seek to determine the substances involved in the expression of gene clusters that function to decompose persistent chemicals, and to identify substances that are involved in the expression of such gene clusters in the environment. Outcomes of these research projects will provide the base for the development of novel weeding techniques, insect control techniques or technologies for the removal of environmental contaminants.

Relevant Outcomes to Date

Discovery of a high-activity plant growth-regulating substance in Thunberg's meadowsweet

As for the methods to specifically detect plant growth-regulating activity associated with allelopathy, we have successfully developed the plant box method, the sandwich method, the dish pack method and the rhizospheric soil method. With regard to new techniques to separate and identify plant semiochemicals, we have successfully developed a method based on the index of total activity which takes into account not only the specific activity, but also the content in the plant body. In Thunberg's meadowsweet, which belongs to the rose family known for strong allelopathic activity, we have discovered new cis-cinnamic acid derivatives which are believed to be the source of the activity (Fig. 1).

Elucidation of possible communication in insects through sex pheromones

We investigated the constituent substances of the insect sex pheromones of Ostrinia scapulalis (Fig. 2) and Adoxophyes orana, as well as the biosynthesis route in adult females, and have clarified that the mutation of a very small number of enzymes involved in fatty acid decomposition and other major metabolic routes alters the composition of sex pheromones considerably. We have also discovered that the problem of reduced susceptibility (acquisition of resistance) of Tortricidae to a communication disrupter based on sex pheromones is due to a short-term evolutionary function expansion in the sex pheromone reception and recognition mechanism of adult males. This finding suggests that interactions via sex pheromones and other semiochemicals is more variable and complex than has been assumed, and it represents an important step forward in the future improvement and development of techniques for insect monitoring and communication disruption.

Elucidation of substrate-specific site determination in dioxygenase enzymes that decompose persistent chloroaromatic compounds.

Chlorocatechols are a major intermediate in the chloroaromatic decomposition process by microorganisms. With respect to chlorocatechol dioxynase, which is a chlorocatechol decomposition enzyme in Burkholderia bacteria, we have successfully identified the site that determines its substrate specificity. We have also discovered that the expression of gene clusters of these decomposition enzymes is regulated by LysR-type expression-regulating factors, which are induced in the presence of inducing substances. For the first time in the world, we have successfully determined the steric structure of expression-regulating factor CbnR in the chlorocatechol decomposition gene cluster of Ralstonia eutropha NH9 strain, which is a LysR-type transcription regulating factor.