Gene Transfer Technique in Plant Callus and Selection of Transformants

Abstract

The desired trait to a crop of a foreign gene encoding the trait must be inserted into plant cells along with a cassette
of additional genetic material. The cassette includes a DNA sequence called a promoter which determines where and
when the foreign gene is expressed in the host and a marker gene that allows breeders to determine which plants
contain the inserted gene by screening. The marker genes render plants resistant to antibiotics that are not used
medically or tolerant to certain herbicides. Two methods are used to transfer foreign genes into plants. The first
method involves the use of a plant pathogen called Agrobacterium tumefaciens which causes crown gall disease in
many species. This bacterium has a plasmid that contains tumor inducing genes (T-DNA) along with additional
genes that help the T-DNA integrate into the host genome. This is done by removing most of the T-DNA while
leaving the left and right border sequences which integrate a foreign gene into the genome of cultured plant cells.
The second delivery method is a gene gun which fires gold particles carrying the foreign DNA into plant cells. These
particles pass through the plant cell wall and enter the cell nucleus where the transgene integrates itself into the
plant chromosome. The both methods of gene transfer are fairly random and must screen for the plant cells that
contain the foreign gene.