ScienceDaily (May 15, 2007) — Thale cress has a complicated defence technique against insects and microorganisms that use the plant as a source of food. The plant hormone jasmonic acid plays a major role during the immune response against insects and pathogens. Dutch researcher Vivian van Oosten has demonstrated that this does not necessarily lead to the control of the same genes during the various interactions.

Van Oosten exposed thale cress to five different plant pests with various attack strategies: aphids, thrips, caterpillars, bacteria and fungi. The composition and quantity of the plant hormones jasmonic acid, ethylene, and salicylic acid that the plant produces as a response, was specific for each pest. Analysis of the activated genes made it clear that every hormone composition in the plant led to an extremely complex expression file.

Four pests mainly stimulated the production of the plant hormone jasmonic acid, which is involved in the regulation of the immune response to insects as well as some pathogens. Although the hormone produced was always the same, there was little overlap in the expression of the genes that are responsive to jasmonic acid. This revealed that the immune response of the plant to a certain pest was also influenced by other signals.

This was surprising, as other studies into various plant pests had shown that jasmonic acid played a key role in the immune response against insects and some plant pathogens. By studying the immune response of a large range of pests on a single plant species, it became clear that even the jasmonic acid dependent immune mechanism of thale cress is attacker-specific.

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