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Scott Schaefer, Ksenija Gasic, and Schuyler Korban

Peach shoots were grown in vitro for 0, 6, 12, 24, and 48 h on a basal medium containing one of several phytohormones or chemical elicitors, including abscisic acid (ABA), indolebutyric acid (IBA), indoleacetic acid (IAA), kinetin, gibberellic acid (GA3), aminocyclopropane-1-carboxylic acid (ACC), methyl jasmonate (MeJ), and salicylic acid (SA). Northern blot analysis was conducted using the 3' end of a peach-1,3-glucanase gene, PpGns1, used as a probe. Variations in levels of PpGns1 expression patterns were observed for each of the treatments. Shoots treated with ABA displayed high levels of transcripts at 12 and 24 h, followed by a sharp decline at 48 h. Shoots treated with ACC displayed a steady increase in transcripts throughout the 48 h period. The synthetic auxin IBA displayed a steady increase in mRNA accumulation for the first 24 h followed by a sharp decline at 48 h. Shoots treated with kinetin displayed low levels of transcripts after 24 h, while GA3 did not induce any accumulation of PpGns1 transcripts. Both SA and MeJA induced steady mRNA accumulation in peach shoots over the entire 48-h period. Induction of PpGns1 in response to SA, MeJ, and ACC also resulted in observed necrotic lesions on peach shoots, thus suggesting a different defense mechanism response.

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Scott C. Schaefer, Ksenija Gasic, and Schuyler S. Korban

Several plant defense genes, including an iris ribosomal-inactivating protein (I-RIP) and a maize β-glucanase (M-GLU) as well as a small antimicrobial peptide (5 kd) from Mirabilisjalapa(Mj-AMP) were separately introduced into tomato (Lycopersiconesculentum) cv. Sweet Chelsea using Agrobacteriumtumefaciens-mediated transformation. Transgenic lines carrying each of the transgenes were confirmed for integration into the tomato genome using Southern blot hybridization. Transcription of I-RIP, M-GLU, and Mj-AMP genes in various transgenic lines was determined using Northern blot analysis. Plants of some transgenic lines were inoculated with a 2 × 104 to 3 × 104 conidial spores/mL suspension of the fungal pathogen Alternariasolani, the causal agent of tomato early blight disease. Several transgenic lines carrying either a M-GLU or Mj-AMP transgene showed a higher level of resistance to early blight than control (nontransgenic) plants. The implications of this approach on developing disease resistance in tomato will be discussed.