Genome-wide expression analysis shows significant differences in root and shoot-induced jasmonic acid responses in a feral Brassica species

Jasmonic acid (JA) is commonly used to mimic herbivore induced responses in plants. In previous studies, we found that belowground JA application to a feral Brassica species resulted in a different metabolomic shoot profi le than when the JA was applied aboveground. Moreover, shoot-feeding caterpillars on aboveground induced (AGI) plants grew signifi cantly slower than those on belowground induced (BGI) plants. To identify when and where these differences in plant responses arise, we analysed expression profi les of plants that received 500 ìg JA either aboveground or belowground. At 6, 18 and 30 h after JA application, the roots and shoots of these plants were harvested separately. The expression profi les were analyzed using 70 -mer Arabidopis oligonucleotide microarrays (Arizona University, Arizona USA) and compared to expression levels of control plants. Of the 2637 shoot genes responding to JA-treatment, 58% were unique to aboveground application and 11% to belowground application. Interestingly, in BGI shoot samples, genes involved in aliphatic glucosinolate biosynthesis were more expressed, whereas in AGI plants indole glucosinolate genes were highly expressed. Roots also specifi cally responded: monoterpene biosynthetic genes strongly responded in BGI plants. This indicates that both local and systemic responses to JA depend on which organ is induced. These differences may cause -unexpected- interactions between shoot and root herbivores feeding on the same plan