Marker Free Transgenic Plants
Abstract
Selectable marker genes are widely used for efficient transformation of crop plants. In most cases, selection is based on antibiotic or herbicide resistance. Due mainly to consumer concern, a suite of strategies have been developed to eliminate the marker gene from the nuclear or chloroplast genome after selection. Current efforts concentrate on systems where marker genes are eliminated efficiently soon after the transformation. Alternatively, transgenic plants are produced by the use of marker genes that do not relay on antibiotic or herbicide resistance but instead promote regeneration after transformation.
Co-transformations of two different constructs can result in transgenic lines that have integrated both transgene. As alternative to co-transformation, several transposable element systems and site specific recombination systems have been employed for marker removal. A less complicated approach to induce DNA deletions is based on Intrachromosomal homologous recombination between two homologous sequences.
A luciferase gene was introduced into the tobacco genome by using the hygromysin phototransferase gene (hpt) as a linked selectable marker. Flanked by recombination sites from the bacteriophage P1 Cre / lox recombination system, the hpt gene was subsequently excised from the plant genome by the Cre recombination. The dhlA marker provides haloalkane dehalogenase reporter activity and substrate dependant negative selection in transgenic plants. The gus gene codes for β-glucuronidase enzyme and was isolated from Escherichia coli is widely used as a reporter gene in positive selection of transgenic plants.
Keywords : Marker free transgenics, Clean gene technology, transposable elements, selectable marker, co-transformation and site specific recombination
Authors : *M.B. Boranayaka1 and R.Gnanam2
* For Correspondence : E mail : aamaravian@gmail.com
