Transformation of Rhododendron through microprojectile bombardment

Abstract.

A method for producing transgenic Rhododendron plants via microprojectile bombardment was developed. Leaves from in vitro microshoots of R. catawbiense cv. Album Michx. were bombarded with the marker gene uidA (coding for β-glucuronidase, GUS) or smGFP (green fluorescent protein, GFP) in combination with nptII (neomycin phosphotransferase). Transgenic plants were regenerated under a biphasic selection strategy with initial selection on 50 mg/l kanamycin followed by stringent selection on 100 mg/l kanamycin. GFP expression was detected in leaf callus from transgenic plants. Histochemical GUS assays of transformed tissues indicated uniform expression throughout the transgenic plant, including leaves, stems, and roots. GUS expression was stable during all stages of plant development over 2 years, as demonstrated by characteristic blue staining of vegetative and floral buds. Molecular characterization of the transformants indicated that the transgenes were stably integrated into the Rhododendron genome through ten vegetative generations.