Agrobacterium tumefaciens-Mediated Transformation of Recalcitrant Crops

The most widely used technique for the introduction of new genetic information into plant cells is based on the natural gene transfer capacity of Agrobacterium tumefaciens. Currently, this technique is routinely applicable in just a few model species, like tobacco and petunia. Thus far, the numerous efforts to apply the technique to crop species have had limited success. In this review, an attempt is made to survey all the research experience on Agrobacterium tumefaciens-mediated transformation of recalcitrant crops and to highlight the problems generally encountered. The main difficulty appears to be directing the gene transfer towards those plant cells that are amenable to regeneration. The various ways to reduce stress during the transformation and regeneration process are often beneficial. The influence of the developmental stage of the plant material and the host range of the Agrobacterium strain depends largely on the plant species used, which hampers the formulation of common procedures. However, some general guidelines for the development of a transformation protocol are discussed.