How Agrobacterium, a Natural Genetic Engineer, Became a Tool for Modern Agriculture

Agrobacterium is well known for its capacity to transfer specific fragments of DNA (transferred DNA or T-DNA) into plant cells, leading to the formation of tumours (crown galls) by A. tumefaciens and to abundant root growth (hairy roots) by A. rhizogenes. The T-DNA contains genes which change the growth of plant cells in various ways and lead to the production of special metabolites (called opines) used by the bacterium for its growth. The discovery of this natural plant transformation system started about one hundred years ago, and the adaptation of A. tumefaciens as a vector to stably introduce foreign DNA into plants has led to a revolution in plant research and in agriculture. The potential of A. rhizogenes is not yet fully exploited and much remains to be learnt about its root-inducing properties. Recent research has shown that apart from tumours and hairy roots, Agrobacterium can also produce transgenic plants in at least three different plant genera (Nicotiana, Linaria and Ipomoea), with stable transmission of T-DNA genes across species. In the case of Nicotiana tabacum, some cultivars express the TB-mas2' T-DNA gene to high levels in roots and produce the corresponding opine. The possible growth-modifying role of T-DNA genes in natural transformants remains to be studied.