Transgenic Crops by Direct Treatment of Exogenous DNA without Agrobacierium tumefaciens Plasmid and Tissue Culture

摘要

Gene transfer methods are developing quickly recently, but each method has its limitations. We introduce a new gene transfer technique in this paper, which is simple, effective, and easy to operate, but docs not get enough attention from scientists. This technique is used to transform plants by injecting exogenous DNA to stigma, style, ovary, young fruit or meristcm of the recipient, or soaking the recipient's seeds in exogenous DNA solution. Lots of heritable variations were found in many charactersof many crops. It may be use to create new germplasms or realize gene exchange between different species, genera, or families, even between animals and plants. A brief discussion was given to the mechanism of exogenous DNA introduction, integration intoand expression in the recipient. We also discussed the merits and limitations of the technique. Currently there are two successful approaches that can be used to transform plants genetically, but each method has its limitations that are delaying the application of the techniques to certain commercially important crops. The first technique exploits a natural genetic cngineer,Agrobacterlum tumefaciens, which contains a tumor-inducing (T_i) plasmid that transfers a DNA segment (the T—DNA) from the plasmid to the nuclear genome of infected plants (or in vitro to plant tissue). The method is restricted to dicotyledenous plants; monocotyledenous plants are usually not susceptible to agrobacterial infection. The second technique involves direct transfer ofDNA to plant protoplast, prepared by enzymatic digestion of cell walls, for example by chemically stimulated uptake using polyethylene glycol or a high voltage pulse, generating transient 'holes' in the protoplast membrane. This technique depends on a tissue culture system that allows regeneration of mature plants from protoplasts. But so far it is impossible to achieve plant regeneration from protoplasts in many crops. Both techniques use dominant selectable markers (for example, kanamycin resistance)to select for the transformed tissue or plant which can then be screened for expression of co-transferred but unselected genes (Lichenstcin, 1987). Now there is a new successful method which can transform various crops, regardless of dicots or monocots,cereals or legumes. It doesn't need Agrobacterium tumefaciens and plasmid, doesn't depend 00 the tissue culture system that allows regeneration of mature plants from protoplasts. Comple and advance equipments are not necessary. It is very simple., but very effective. Next is a review about the technique, its application in several crops, the mechanism of transformation, and its merits and limitations.