Advances in Genetic Transformation of Plants

Many plant species, including both dicots and monocots, can now be genetically engineered with individual genes isolated from any source. Methods for delivery of foreign DNA into plant cells or protoplasts utilise Agrobacterium tumefaciens (and A. gazogenes), micro­injection, polyethylene glycol, electroporation and particle guns. Advantages and disadvantages of each system are discussed. At present, all systems involve i11 vitra cell or tissue culture lo some extent, and this is the most difficult and variable aspect of plant genetic engineering. In addition, all systems suffer from random insertions of the foreign DNA into the plant genome. This requires Southern blot screening of DNA from many transgenic plants in order to identify plants having a single gene insertion or at least only a few copies of the gene of interest. Several pasture crops such as Medicago satlva and Medicago vara A2 (alfalfa or lucerne), Trifolium repens L. (white clover), Brassica sp., Dactylis glomerata L. (orchardgrass), Lotus cornicaltus (birdsfoot trefoil) and Fest11ca anmdinacea Schreb. (tall fescue) have now been genetically transformed with foreign genes. With the variety of methods now available for plant transformation, the number of transformed pasture species should expand rapidly. The challenge now is to extend the number of grassland species and cultivars that can be genetically engineered, and to identify and isolate genes of unique importance for incorporation into these species.