Genetic Modification of Grapevine Embryogenic Cultures.

Precision breeding is an approach to grapevine genetic improvement that transfers only specific traits among sexually compatible species via the relatively stable mitotic cell division pathway in order to avoid the significant disruption imposed upon conventional breeding by meiosis. Factors enabling precision breeding include the availability of the Vitis genome sequence combined with highly optimized gene insertion and plant regeneration protocols. A protocol for the production of grapevine embryogenic cultures and their genetic transformation is described. Embryogenic cultures are produced from either leaf or floral explants. Somatic embryos at the cotyledonary stage of development are used for Agrobacterium-mediated transformation. Following co-cultivation with Agrobacterium containing the genes of interest, modified embryos are selected on the basis of anthocyanin pigmentation and antibiotic resistance. Somatic embryos are then germinated to produce modified plants that are hardened and transferred to a greenhouse. The presence of the genes of interest is confirmed by PCR.

Agrobacterium-mediated transformation of embryogenic cultures and plant regeneration in Vitis rotundifolia Michx. (muscadine grape).

A method to produce transgenic plants of Vitis rotundifolia was developed. Embryogenic cultures were initiated from leaves of in vitro grown shoot cultures and used as target tissues for Agrobacterium-mediated genetic transformation. A green fluorescent protein/neomycin phosphotransferase II (gfp/nptII) fusion gene that allowed for simultaneous selection of transgenic cells based on GFP fluorescence and kanamycin resistance was used to optimize parameters influencing genetic transformation. It was determined that both proembryonal masses (PEM) and mid-cotyledonary stage somatic embryos (SE) were suitable target tissues for co-cultivation with Agrobacterium as evidenced by transient GFP expression. Kanamycin at 100 mg l(-1) in the culture medium was effective in suppression of non-transformed tissue and permitting the growth and development of transgenic cells, compared to 50 or 75 mg l(-1), which permitted the proliferation of more non-transformed cells. Transgenic plants of "Alachua" and "Carlos" were recovered after secondary somatic embryogenesis from primary SE explants co-cultivated with Agrobacterium. The presence and stable integration of transgenes in transgenic plants was confirmed by PCR and Southern blot hybridization. Transgenic plants exhibited uniform GFP expression in cells of all plant tissues and organs including leaves, stems, roots, inflorescences and the embryo and endosperm of developing berries.

Transgenic plants from shoot apical meristems of Vitis vinifera L. "Thompson Seedless" via Agrobacterium-mediated transformation.

Shoot apical meristem explants of Vitis vinifera "Thompson Seedless" were used for Agrobacterium-mediated genetic transformation. It was determined that the meristems had to be subjected to a dark growth phase then wounded to obtain transgenic plants. Morphological and histological studies illustrated the role of wounding to expose apical meristem cells for transformation. A bifunctional egfp/nptII fusion gene was used to select kanamycin resistant plants that expressed green fluorescent protein (GFP). Kanamycin at a concentration of 16 mg L(-1) in selection medium resulted in recovery of non-chimeric transgenic plants that uniformly expressed GFP, whereas 8 mg L(-1) kanamycin allowed non-transgenic and/or chimeric plants to develop. Polymerase chain reaction (PCR) and Southern blot analyses confirmed the presence of transgenes and their stable integration into the genome of regenerated plants. Up to 1% of shoot tips produced stable transgenic cultures within 6 weeks of treatment, resulting in a total of 18 independent lines.