This may indicate that the induced responses, although weaker than in wt, were strong enough to keep the same level of resistance. Alternatively, responses were mainly induced locally, so that the aphids could benefit from frequent changes of feeding places. In the fou2 mutant, several genes involved in defence Imatinib against B. brassicae were induced in non challenged plants. As a consequence, the transcriptional profile of non challenged fou2 resembled the aphid induced profile of wt. Although additional B. brassicae mediated regulation of already induced genes was limited, the aphids reproduction rate was negatively influenced by the fou2 mutation. As an array of defensive responses is constitutively activated in fou2 plants, the feeding aphids could not move to a leaf area where the response was not induced, as they could in the case of wt plants.

Our results indicate that JA regulated responses are important in defining susceptibility of a plant to infesta tion with aphids. As shown in this study, JA derived compounds are powerful regulators of a range of defen sive responses exhibited by plants attacked by aphids. Methods Plant material The Arabidopsis thaliana Columbia 0 ecotype single seeds line used in the experiment has been derived from seeds produced by Lehle Seeds. The aos mutant was the one described in. The fou2 mutant was kindly donated by Prof. Edward Farmer. Both mutants are in Col 0 background. Seeds were ster ilized according to standard procedures and plants were initially grown aseptically on agar medium containing MS basal salt mixture, 3% sucrose, and 0.

7% agar to assure uniform germination. After 15 days, seedlings were moved to 6 cm diameter pots filled with a sterile soil mix. Plants were kept in growth chambers V?tsch VB 1514 under the following conditions, a 8 16 h photoperiod at 22 C 18 C, 40% 70% relative humidity, and 70 0 umol m 2s 1 light intensity. A short time day was applied to prevent plants from bolting. For aphid fitness experiments, plants were sown directly to pots with soil and kept in chambers under a 16 8 h photoperiod. Insects Brevicoryne brassicae was reared on Brassica napus or Brassica oleracea plants in a growth chamber with a 16 8 h photoperiod at 22 C 18 C, 40% 70% relative humidity, and 70 0 umol m 2s 1 light intensity. Infestation experiments Thirty two day old plants had 8 fully developed leaves.

Each plant was infested with 32 wingless aphids, which were trans ferred to leaves with a fine paintbrush. Infested plants and aphid free controls were kept in plexiglass cylinders Anacetrapib as described in. Plants were harvested 72 h after infesta tion between the 6th and 8th hour of the light photoper iod. Four biological replicates were run, each sampled from 15 individual plants. Whole rosettes were cut at the hypocotyls and aphids were removed by washing with Milli Q filtered water. Harvested material was immediately frozen in liquid nitrogen.