Conclusions
Since the identification of Agrobacterium tumefaciens as the causitive agent of Crown Gall disease, the interaction of this species with the host plant has been of great fascination to many botanists. However, it was nut until recently when it was apparant just how useful A. tumefaciens could be as a gene delivery system. During the last 15 years, improvements in biotechnology have come a long way since the realisation that plants can be genetically modified to give desirable phoentypic variations. Now that we are able to make transgenic plants, the main questions facing plant scientists are how to regulate gene expression, how can transformation be made more efficient and consistent, and perhaps most importantly, what are the environmental implications of this technology.
There has been much speculation in the past as to whether the world is able to increase food production to cope with the projected population increase. In the past, this increase has been met by a combination of growers gain through breeding for high-yielding varieties, and by improvements in growing technology and crop protection. However, the gap between food production and demand is narrowing much faster, and already there are civil wars breaking out between countries in Africa over the right to use land for food production.
One of the main drawbacks of A. tumefaciens is its inability to effectively transform many monocotyledons, although current research by Ke et al. (2001) suggest that genetically engineered "supervirulent" strains may be effective in transforming many different plant species.
In a study carried out in 1994 by Hiei et al., it was found that almost all of the transgenic Japonica rice plants had normal morphology, and 70% were fully fertile. Similar results were found when Indica varieties were also investigated. Delivery of foreign DNA into rice by A. tumefaciens is becoming standard practice in a growing number of laboratories, thus allowing the genetic improvement of many ovarieties of this fundamentally important crop plant.
Important problems facing plant transformation which still remain to be solved include regulation of the DNA integration, and achieving the holy grail of plant transformation technology, that is targeted gene disruption and gene replacement hy homologous recombination. Recent reports of efficient targeting in Arabidopsis thaliana suggest that this breakthrough is closer than we might think (Gelvin, 1998).
It seems probable that Agrobacterium mediated transfer techniques will soon be extended to other recalcitrant species of commercially important plants as soon as the methodologies are optimized.