Background and Aims Plant-synthesized sesquiterpenes play a pivotal role in chemotactic interactions with insects. profiling of sesquiterpenes. Aphid response to hyrdo-distillate extracts and head-space volatiles from transgenic plants was assessed using a bioassay. Key Results Either over-expression of in the cytosol or PD98059 targetting of its translated product to chlorplasts resulted in stimulatory growth responses of transgenic arabidopsis at early and late developmental stages. GC-MS analysis of hydro-distillate extracts from aerial parts of the plants revealed biosynthesis of several novel sesquiterpenes including E-β-farnesene an alarm pheromone of aphids. Both entrapped volatiles and hydro-distillate extracts of the transgenic leaves triggered agitation in aphids which was related to both time and dose of exposure. Conclusions Over-expression of in the cytosol and targeting of its translated product to chloroplasts in arabidopsis led to synthesis of several novel sesquiterpenes including E-β-farnesene and induced alarm responses in PD98059 (arabidopsis) (At5g47770.1) and (At4g17190) encoding cytosolic PD98059 FDP synthase showed differential expression patterns and have been implicated in the biosynthesis of FDP (Cunillera altered the profile of downstream sesquiterpenes and/or exerted any effect on the responses of the transgenic plants to biotic stress. Neither there is any report on the effects of over-expressing cytosolic and/or its targeting to the chloroplast in transgenic arabidopsis with respect to responses toward insect pests and in particular aphids. We report here on the generation of transgenic arabidopsis plants that either over-expressed in the cytosol or targeted the translated product to the chloroplast by a transit peptide. Compared with the wild-type both the transgenic plants showed enhanced growth responses and their GC-MS profiles revealed the presence of several novel sesquiterpenes including E-β-farnesene (E-β-f) which is an alarm pheromone for aphids. The consequent effects of an altered volatile profile of these transgenic plants on host-aphid interactions are discussed. MATERIALS AND METHODS ecotype Columbia (Col-0) and a green peach aphid (under PD98059 the constitutive promter (CaMV35S:sequence (At4g17190) was amplified from arabidopsis by PCR using gene-specific primers (FPS attB1_F and FPS attB2_R) on to which an ‘att’ sequence was added at their 5′ ends (Supplementary Data Table S1). The purified amplicon was introduced into pDONR 221 entry vector of the Gateway system (Invitrogen Carlsbad CA USA) and transformed into DH5α electrocompetent cells. Among several recombinant clones identified through PCR and for which their fidelity had been validated by sequencing one of them (hereafter the entry clone) was recombined into pEarleyGate100 destination vector (Earley For targeting (GenBank accession number: “type”:”entrez-nucleotide” attrs :”text”:”FJ154097″ term_id :”223885878″ term_text :”FJ154097″FJ154097) upstream of the coding sequence with a Several of these clones were sequenced to confirm the correct reading frame. The BioEdit program and SignalP 3.0 server were employed to validate the correct reading frame of the translation and the cleavage site of the transit peptide respectively. The two constructs (CaMV35S:and CaMV35S:Tp-(strain GV 3101) by electroporation. Floral dip transformation was carried out as described by Clough and Bent (1998). For selection of transgenic plants the transformed seeds (T0) of arabidopsis were sown on Petri dishes containing MS agar medium supplemented with glufosinate ammonium (6?μg?mL?1). Several transgenic plants were recovered with an average transformation efficiency of 5·8?%. Analyses of morphological characters Wild-type and transgenic plants grown for 2-3 weeks under controlled conditions were evaluated for their height numbers of branches and siliques per plant. For determination of dry weight 4 plants were uprooted and their roots were washed with water blot-dried and dried to a constant weight at 80?°C in hot air oven. For revealing root system architecture (RSA) seedlings were grown CTLA4 on vertically orientated Petri dishes containing full-strength MS medium?+?0·8?% (w/v) agar for 7?d. Roots were excised at the hypocotyl-root junction gently spread to PD98059 reveal RSA and scanned at 600?d.p.i. (HP Scanjet G2410). Rosette leaves were dissected from shoots and scanned at 600?d.p.i.; ImageJ (Collins 2007 http://rsb.info.nih.gov/ij) was used to measure total shoot area. Estimation of chlorophyll content Leaves (500?mg) from 2-week-old plants were.