Engineering Plants for Stress Tolerance via Organelle Genomes

Abstract

Most common strategies for gene transfer derive from the fact that Agrobacterium tumefaciens contains Ti plasmids which facilitate transfer of T-DNA from the plasmid genome into plant cells with attendant integration of the T-DNA region into the plant nuclear genome (Binns,1990). Alternatively, DNA may be introduced into protoplasts using various chemical agents (Jenes et al, 1993) or by electroporation (Fromm et al., 1987) or microinjection (Neuhans and Spangenberg, 1990). In all these approaches foreign DNA is introduced into the nuclear genome. Sanford and coworkers (1990) have developed a transformation technique that relies on bombardment of recipient cells or tissues with high velocity tungsten microprojectiles coated with foreign DNA. Using this delivery system several groups have demonstrated stable transformation of foreign genes into nuclear genomes of higher plants, mitochondrial genomes of yeast, and chloroplast genomes of Chlamydomonas and higher plants (Sanford, 1990). Microprojectile bombardment is replacing traditional methods of transformation because of the use of simple vectors and unlimited host range. DNA delivery by the Gene Gun into cultured tissues or the scutellum of immature embryos of several cereal crops is generally followed by selection for transformed tissues. Regenerated transgenic plants have been obtained from maize, rice, wheat, oat and numerous dicots (Guerin and Guerin, 1993), demonstrating the broad applicability of the Gene Gun. The Gene Gun is also routinely used in studies on transient foreign gene expression and is a reliable method to deliver foreign DNA into organelles (Daniell, 1993).