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BackgroundThe soil-borne fungal pathogen Verticillium dahliae Kleb causes Verticillium wilt in a wide range of crops including cotton (Gossypium hirsutum). To date, most upland cotton varieties are susceptible to V. dahliae and the breeding for cotton varieties with the resistance to Verticillium wilt has not been successful.ResultsHpa1Xoo is a harpin protein from Xanthomonas oryzae pv. oryzae which induces the hypersensitive cell death in plants. When hpa1Xoo was transformed into the susceptible cotton line Z35 through Agrobacterium-mediated transformation, the transgenic cotton line (T-34) with an improved resistance to Verticillium dahliae was obtained. Cells of the transgenic T-34, when mixed with the conidia suspension of V. dahliae, had a higher tolerance to V. dahliae compared to cells of untransformed Z35. Cells of T-34 were more viable 12 h after mixing with V. dahliae conidia suspension. Immunocytological analysis showed that Hpa1Xoo, expressed in T-34, accumulated as clustered particles along the cell walls of T-34. In response to the infection caused by V. dahliae, 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 V. dahliae. Quantitative RT-PCR analysis indicated that five defense-related genes, ghAOX1, hin1, npr1, ghdhg-OMT, and hsr203J, were up-regulated in T-34 inoculated with V. dahliae. The up-regulations of these defense-relate genes were not observed or in a less extent in leaves of Z-35 after the inoculation.ConclusionsHpa1Xoo accumulates along the cell walls of the transgenic T-34, where it triggers the generation of H2O2 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 hpa1Xoo could be an effective approach for the development of cotton varieties with the improved resistance against soil-borne pathogens.

Fusarium wilt of watermelon commonly occurs in locations where the crop has been grown for many seasons. Its occurrence results in a severely decreased watermelon crop. The goal of this study was to assess the capability of a new product (bio-organic fertilizer) to control the wilt in Fusarium-infested soil. Pot experiments were conducted under growth chamber and greenhouse conditions. The results showed that the fertilizer controlled the wilt disease. Compared with control pots, the incidence rates of Fusarium wilt at 27 and 63 days following treatment of the plants with the bio-organic fertilizer at a rate of 0.5% (organic fertilizer + antagonistic microorganisms, including 3 9 10 9 CFU g -1 Paenibacillus polymyxa and 5 910 7 CFU g -1 Trichoderma harzianum) were reduced by 84.9 and 75.0%, respectively, in both the growth chamber and greenhouse settings. The activities of antioxidases (catalase, superoxide dismutase and peroxidase) in watermelon leaves increased by 38.9, 150 and 250%, respectively. In the roots, stems and leaves, the activity of b-1,3-glucanase (pathogenesis-related proteins) increased by 80, 1140 and 100% and that of chitinase increased by 240, 80, and 20%, respectively, while the contents of malondialdehyde fell by 56.8, 42.1 and 45.9%, respectively. These results indicate that this new fertilizer formula is capable of protecting watermelon from Fusarium oxysporum f.sp. niveum. The elevated levels of defense-related enzymes are consistent with the induction and enhancement of systemic acquired resistance of plant.

Harpins encoded by many gram-negative phytopathogenic bacterial hrp genes induce hypersensitive response (HR) and associated defense responses on nonhost plants. Hpa1(Xoo) and Hpa1(Xoc), two harpin proteins from Xanthomonas oryzae pathovars, induce HR when infiltrated into tobacco leaves. N- and C-terminal mutations of Hpa1(Xoo) and Hpa1(Xoc), respectively, were tested for their ability to elicit HR on tobacco. Deletion of codons for 12 highly hydrophilic amino acids (H(2)N-QGISEKQLDQLL-COOH) that partially overlap the N-terminal alpha-helical regions of respective proteins was found to be critical for the elicitation of HR in tobacco. Furthermore, two single missense mutants Hpa1(Xoo) (L51P) and Hpa1(Xoc) (L53P) that are predicted to destroy the coiled-coil integrity and inhibit the dimer formation eliminated HR elicitation activity in tobacco. However, both wild-type proteins and derivative mutants retained the ability to induce systemic acquired resistance in tobacco against tobacco mosaic virus. Accumulations of npr1 (nonexpressor of pathogenesis-related protein 1), hsr515 (hypersensitivity-related protein 515), and pr2 (pathogenesis-related protein 2) transcripts were found in tobacco plants infiltrated with wild-type or mutated proteins.