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Resistance Enhancement of Transgenic Tomato to Bacterial Pathogens by the Heterologous Expression of Sweet Pepper Ferredoxin-I Protein

First, seventh, eighth, ninth, and tenth authors: Academia Sinica--Plant and Microbial Biology, Institute of Plant and Microbial Biology, Academia Sinica, Nankang, Taipei 115, Taiwan; second, fourth, and fifth authors: Biotechnology and Plant Physiology, Asian Vegetable Research and Development Center, P.O. Box 42, Shanhua, Tainan, 741 Taiwan - Republic of China; third author: Taiwan Seed Improvement and Propagation Station, Taichung, 426, Taiwan, and Department of Horticultural Sciences, National Taiwan University, Taipei, 106, Taiwan; and sixth author: Department of Life Science, National University of Kaohsiung, Kaohsiung, 811, Taiwan.

Expression of a foreign gene to enhance plant disease resistance to bacterial pathogens is a favorable strategy. It has been demonstrated that expressing sweet pepper ferredoxin-I protein (PFLP) in transgenic plants can enhance disease resistance to bacterial pathogens that infect leaf tissue. In this study, PFLP was applied to protect tomato (Lycopersicon esculentum cv. cherry Cln1558a) from the root-infecting pathogen, Ralstonia solanacearum. Independent R. solanacearum resistant T₁ lines were selected and bred to produce homozygous T₂ generations. Selected T₂ transgenic lines 24-18-7 and 26-2-1a, which showed high expression levels of PFLP in root tissue, were resistant to disease caused by R. solanacearum. In contrast, the transgenic line 23-17-1b and nontransgenic tomato, which showed low expression levels of PFLP in root tissue, were not resistant to R. solanacearum infection. The expansion of R. solanacearum populations in stem tissue of transgenic tomato line 24-18-7 was limited compared with the nontransgenic tomato Cln1558a. Using a detached leaf assay, transgenic line 24-18-7 was also resistant to maceration caused by E. carotovora subsp. carotovora; however, resistance to E. carotovora subsp. carotovora was less apparent in transgenic lines 26-2-1a and 23-17-1b. These results demonstrate that PFLP is able to enhance disease resistance at different levels to bacterial pathogens in individual tissue of transgenic tomato.