Development of a Transformation System for Woods

Abstract

We have developed a new vector system for repeated transformation (called MAT for multi-auto-transformation) in which a chimeric ipt gene, inserted into the yeast site-specific-recombination system pSR 1 (pNPI 132), is used a selectable marker (called “hit and run cassette”) for transformation. Selectable marker genes conferring antibiotic or herbicide resistance, used to introduce economically valuable genes into crop plants, have three major problems:(1) the selective agents have negative effects on proliferation and differentiation of plant cells;(2) there is uncertainyty regarding the environmental impact of many selectable maker genes;(3) it is difficult to repeat transformation using the same selectable marker in order to pryamaid desirable genes. The MAT vector system in designed to overcome these difficulties. When tabacco leaf segments where transformed and selected, excision of the “hit and run casstte” successfully produced marker-free tansgenic tobacco plants withhout sexual crosses or seed production. In addition, the chimeric ipt gene could be visually used as a selectable marker for transformation of hybrid aspen (Populus Sieboldii x P. grandidentata). The chimeric ipt gene, therefore, is an attactive alternative to the most widely used selectable marker genes. The MAT vector system enables us to produce environmentally safe transgenic plants without sexual corsses and seed production, and pyramid multiple genes into a vegetably propagated crop by repeated transformation. This method could be particularly valuable for fruit and forest trees where long generation times are a more significant barrier to breeding and genetic analysis.