Advances in transformation technology for vegetable brassica

Although transformation of Brassica vegetables has lagged behind similar work with rapeseed, transgenic cauliflower, broccoli, cabbage, and kale plants have been obtained by several methods. The most general approach is use of Agrobcicterium tumefaciens. A U.S. patent for A. tumefaciens-mediatcd transformation of Brassica; including B. oleracea, was recently granted to Calgene, Inc. Transformation via A. rhizogenes is another option, but the plants recovered may show abnormal phenotypes. Direct DNA update into protoplasts, induced either by polyethylene glycol or electroporation, has also succeeded. Biolistic approaches have not yet played an important role in vegetable Brassica transformation. Even the successful procedures are still not routine, and transgenic plants are usually recovered from fewer than 10% of explants transformed. Control of ethylene and moisture levels in culture plates are among the factors that can increase efficiency. Transformants are most often selected by resistance to kanamycin or hygromycin. Other genes introduced include B-glucuronidase, genes for resistance to herbicides, an S-locus gene, and insecticidal protein genes from Bacillus thuringiensis (Bt). When a modified CrylA(c) Bt gene was introduced into broccoli and cabbage, about 70% of ca. 250 transformants recovered were resistant to diamondback moths, a major pest of crucifers. Progeny of some of these transgenic plants are now being used in tests of insect resistance management strategies involving refuges. Additional transgenic vegetable Brassicas with enhanced resistances or other horticultural improvements are likely to be available soon, but regulatory issues will delay their commercial release.