| Summary: | <p>Abstract</p> <p>Background</p> <p>The soil-borne fungal pathogen <it>Verticillium dahliae </it>Kleb causes <it>Verticillium </it>wilt in a wide range of crops including cotton (<it>Gossypium hirsutum</it>). To date, most upland cotton varieties are susceptible to <it>V. dahliae </it>and the breeding for cotton varieties with the resistance to <it>Verticillium </it>wilt has not been successful.</p> <p>Results</p> <p>Hpa1<sub>Xoo </sub>is a harpin protein from <it>Xanthomonas oryzae </it>pv. <it>oryzae </it>which induces the hypersensitive cell death in plants. When <it>hpa1</it><sub><it>Xoo </it></sub>was transformed into the susceptible cotton line Z35 through <it>Agrobacterium</it>-mediated transformation, the transgenic cotton line (T-34) with an improved resistance to <it>Verticillium dahliae </it>was obtained. Cells of the transgenic T-34, when mixed with the conidia suspension of <it>V. dahliae</it>, had a higher tolerance to <it>V. dahliae </it>compared to cells of untransformed Z35. Cells of T-34 were more viable 12 h after mixing with <it>V. dahliae </it>conidia suspension. Immunocytological analysis showed that Hpa1<sub>Xoo</sub>, expressed in T-34, accumulated as clustered particles along the cell walls of T-34. In response to the infection caused by <it>V. dahliae</it>, the microscopic cell death and the generation of reactive oxygen intermediates were observed in leaves of T-34 and these responses were absent in leaves of Z35 inoculated with <it>V. dahliae</it>. Quantitative RT-PCR analysis indicated that five defense-related genes, <it>ghAOX1, hin1, npr1, ghdhg-OMT</it>, and <it>hsr203J</it>, were up-regulated in T-34 inoculated with <it>V. dahliae</it>. The up-regulations of these defense-relate genes were not observed or in a less extent in leaves of Z-35 after the inoculation.</p> <p>Conclusions</p> <p>Hpa1<sub>Xoo </sub>accumulates along the cell walls of the transgenic T-34, where it triggers the generation of H<sub>2</sub>O<sub>2 </sub>as an endogenous elicitor. T-34 is thus in a primed state, ready to protect the host from the pathogen. The results of this study suggest that the transformation of cotton with <it>hpa1</it><sub><it>Xoo </it></sub>could be an effective approach for the development of cotton varieties with the improved resistance against soil-borne pathogens.</p>
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