Engineering the plant genome: Prospects of selection systems using nonantibiotic marker genes

In the past two to three decades, great progress has been achieved in the field of plant genetic manipulation. This progress is based on fine-tuning gene transfer methods, selection of transformed cells and regulation of transgene expression. Transgenic plant production requires selectable marker genes that enable the selection of transformed cells, tissue and plants. The most used are those that exhibit resistance to antibiotics or herbicides. Although this type of selection is routinely practiced, there are perceived risks in the deployment of transgenic plants containing these markers. A number of strategies have emerged on the development of alternate selection systems referred to as positive selection and marker-free systems. Transgenes that permit plant cells to utilize new carbon sources are being employed in transformation research. Current research on development of novel selection methods in transgenics is growing rapidly and its application is being tested in different plant species.