Genomic stability and stability of expression in genetically modified plants

Abstract

SUMMARY This review provides a survey of those factors that might influence genetic stability of genetically modified organisms and somatic hybrids in breeding programmes. In this respect several aspects may be distinguished: (i) host genomic factors that might influence genetic stability, (ii) events related to the introduction of new DNA into the genome and their effect on genetic stability, (iii) stability of gene expression of newly introduced DNA, and (iv) stability of the modified genome. In our view a gene is defined as being stable if it inherits according to Mendelian laws. Obviously, this can be valid only for nuclear genes. Non‐Mendelian inheritance may be caused by intrinsic genomic factors or be the result of skewed segregation during meiosis. Newly introduced DNA may be stably integrated into the genome, yet data on its site of integration is limited. The level of expression and, thus, the strength of the related trait, may vary. Variation in expression may depend on the construct, such as the promoter or additional sequences such as MAR elements or the coding sequence itself, the site of integration and the species used. Another, and undesired, phenomenon is the silencing of expression of introduced genes. The kinds of silencing described depend on the relative position in the genome of the genes involved, cis vs. trans and whether only one or all genes are silenced. Instability of expression generally becomes visible within a few generations, but once expression is stable it is supposed to remain so provided the environment does not change dramatically. Although the production of somatic hybrids seems to be a promising technique to obtain new genetic material and even though numerous hybrids have been made, only a few follow‐up studies have been published. Therefore the use of somatic hybrids in breeding programmes is limited.

Interactions betweenBt-expressing tomato and non-target insects: the aphidMacrosiphum euphorbiaeand its natural enemies

“…However, it remains to assess the effect of a long-term exposure to Cry proteins on each component of the trophic chain, at least for a period (months) compatible with the current cultivation procedures. Among the possible effects of a genetic transformation, they must be considered either the pleiotropic effects or insertional mutagenesis (Maessen 1997), leading to an alteration of the volatile profile that affect the foraging behavior of insect antagonists. For example, the overexpression of a protein involved in the plant response to wounding resulted in a higher attractiveness of transformed tomato plants toward the parasitoid A. ervi (Corrado et al 2007).…”

Environmental release of transgenic trees in Canada — potential benefits and assessment of biosafety

“…As the transfer of DNA using the biolistic method occurs in a nonpreferential way, the stability of organelle transformation may be questioned (Suzuki et al 1997). However, as chloroplast and mitochondria are usually maternally inherited, transforming these organelles would, in many species, offer assurance that gene flow via pollen will not occur (Maessen 1997).…”

“…To further complicate matters, the lack of a reliable method for tissue culture regeneration of conifer species has further delayed the application of recombinant technology to this taxon (Tsang et al 1995;Maessen 1997). While transformation and expression have been confirmed in many species, relatively few have been regenerated and confirmed as stable, and most of these are angiosperm species.…”

“…It is well documented that transformations are not always stable during the life cycle of the plant (see review by Maessen 1997). Many developmental processes will influence the expression of the reporter gene (and the new transgene), together with environmental stresses.…”

“…Testing transgenic sterility of most forest tree species will take rather a long time, as stability must be demonstrated over many years, through dormancy cycles and during times of various environmental stresses (Strauss et al 1995). Another approach to restricting gene flow might be to transform chloroplast DNA which is expressed by the transformed plant but only maternally inherited (Maessen 1997).…”