Transient Expression of DNA in Plant Cells

Abstract

Techniques for transferring DNA into cells often introduce much more DNA into the cell nucleus than the amount that becomes stably incorporated into the host’s chromosomes. If non-replicating, this extrachromosomal DNA is lost over a one to two week period as a result of dilution by cell division and susceptibility to intracellular degradation. During its transient existence in the cell, the extrachromosomal DNA is known to be transcriptionally active because typically 1 to 10% of the cells express the introduced DNA but only 0.01 to 0.1% of the cells stably integrate and maintain the introduced gene. This “transient expression” is extremely useful in studying gene structure and function relationships for a number of reasons. The most important is the speed with which results on gene expression can be obtained. The transfected cells are typically ready for analysis of gene expression 24 to 48 hours after DNA transfer. A second important aspect is the lack of host chromosomal flanking sequences that may influence gene expression. Quite often there is variation in gene expression in stable transformants depending on the site of insertion; such variation can be greater than the variation between the gene structures being compared (Odell et al., 1985; Velten et al., 1984). Transient DNA is free of host flanking sequences allowing a much simpler comparison of normal and altered gene structures.