SELECTABLE MARKERS

In order to quickly and easily identify which plant cells have incorporated the gene of interest, researchers piggy-back a gene referred to as a selectable marker. In practical plant improvement programs, selectable markers have been largely restricted to proteins providing resistance to herbicides or antibiotics. Putative transformants can be sprayed with, or grown on media containing the appropriate chemical. Transformed plants are identified as those that survive. For example, the antibiotic resistance gene for Kanamycin allows only transformed cells to grow in the presence of the selection agent Kanamycin. Other more exotic markers, such as GUS (a gene encoding ß-glucuronidase, identified in stained material by a blue colour) can also be used to screen transformants. Under the selective pressure of an antibiotic or herbicide and various plant growth promoters, transformed plant cells are gradually regenerated into plants. The new plants are "hardened off",transferred to soil and placed in a greenhouse environment. Plant and growth conditions are carefully monitored and controlled. The plants are used for analysis, seed production or are transplanted to the field.