Principle of MAT Vector System

Plant transformation is a core technology in the genetic engineering of plants, which is composed of three processes; 1) introduction of genes into plant cells, 2) selection of transgenic cells, 3) regeneration of intact plants. Plant transformation systems using an Agrobacterium-infection or a direct gene transfer (particle bombardment, electroporation, etc.) have been developed and widely used to introduce a foreign DNA into plant cells [1] . However, the introduced DNA is integrated to plant genome in only a minor fraction of the treated cells during these treatments. It is, therefore, generally essential to select a small number of these transgenic cells from a large excess of non-transgenic cells, and to regenerate intact plants from them. Commonly selective agents (antibiotic, herbicide etc.) and the corresponding resistance genes (selectable marker genes) are used for the selection of transgenic cells [2] . In these selection systems, resistant genes are introduced along with desirable genes, and these treated cells containing both non-transgenic and transgenic cells are placed on culture media with selective agents. The non-transgenic cells are killed, while the transgenic cells survive and are selected (negative selection) . During this selection process, exogenous plant hormones (auxin, cytokinin, etc.) are added into the media to stimulate regeneration of transgenic plants. However these current transformation systems have three major problems: 1) the selective agents decrease the activity of plant cells to proliferate and differentiate; 2) there is uncertainty regarding the environmental impact of many selectable marker genes; 3) it is difficult to perform repeated transformations in the step-wise process using the same selectable marker to pyramid desirable genes [3-5] . In this review, we describe a new plant vector system (called MATVS for multi-auto-transformation vector system) to overcome these difficulties [7-9]. 2. Principle of MATVS