A circulatory system useful both for long-term somatic embryogenesis and genetic transformation in Vitis vinifera L. cv. Thompson Seedless

To establish an efficient regeneration protocol for functional validation and variety resistance improvement, a long-term system that useful for embryogenic culture maintenance and transformation was developed through recurrent cycles of secondary embryogenesis from Vitis vinifera L. cv. Thompson Seedless. Three media and five types of somatic embryo in secondary embryogenesis were evaluated. Somatic embryos (SE) in the torpedo and mid-cotyledonary stages gave the best embryogenic responses with re-induction rates of about 80 %. Embryogenic callus, proembryonic masses and SE produced in the system, could be propagated for over 3 years and all proved competent for Agrobacterium-mediated transformation. Based on this system, different transgenic selection regimes were compared. Addition of kanamycin at 4 weeks after co-cultivation was optimal for embryo recovery. Plant conversion was improved by alternating culture on two media: one containing 0.2 mg l−1 BA and the other 0.25 mg l−1 kinetin. To further test the efficiency of the system, a ubiquitin ligase gene (VpPUB23) from Chinese wild Vitis pseudoreticulata was transferred into Thompson Seedless for functional evaluation. Of the 351 transgenic plants obtained, those overexpressing VpPUB23 exhibited decreased resistance to powdery mildew compared with non-transgenic plants.