Genetic Engineering of Crop Plants

Abstract

Crop improvement was, so far, based on selection of naturally occurring variation within a given species. Induced mutations increased the available genetic variation only moderately. Techniques that permitted rescue of offspring from interspecific crosses and that favored introgression of chromosome segments allowed the limited combination of characters between species. The technique of gene transfer to plants has changed the situation dramatically. In principle, the plant breeder can from now on use any given character, from any given organism, in any given species. And he can decide in which organ the novel character should be expressed, at which strength, and in response to which external trigger or endogenous signal. Gene transfer also offers the opportunity to inactivate endogenous genes. This is all true in theory. In reality, however, there are still numerous problems interfering with too easy a construction of novel miracle crop plants. Genes of agronomic importance are often not easy to identify and to isolate. Expression of the genes often depends more on the (random) integration into the host genome than on the appropriate expression signals. Gene transfer techniques that yield thousands of transgenic plants with laboratory model species might require an enormous investment in manpower and persistence when the production of just a few transgenic plants from a specific commercial variety is needed for some important crop species. However, in the short time between the recovery of the first transgenic “model plant” in 1983 [1] and now, it has been possible to develop the state-of-the-art of gene transfer to plants to a level at which many of the major crop plants are accessible to the technique and for which we have good reason to believe there is no basic biological principle that will prevent gene transfer to a specific crop plant. Three gene-transfer techniques have been developed to such a stage of reproducibility and practical applicability that they can be recommended for future practical work. These are Agrobacterium-mediated gene transfer, ballistic gene transfer, and direct gene transfer to protoplasts. These techniques are described in some detail in the following chapter, and Table 1 summarizes which crop plants have been transformed with which of these techniques. There