Genetically modified plants and the 35S promoter: assessing the risks and enhancing the debate

Abstract

The 35S promoter, derived from the common plant virus, cauliflower mosaic virus (CaMV), is a component of transgenic constructs in more than 80% of genetically modified (GM) plants. Alarming reports have suggested that the 35S promoter might cause accidental activation of plant genes or endogenous viruses, promote horizontal gene transfer, or might even recombine with mammalian viruses such as HIV, with unexpected consequences. In this article, we discuss the properties of CaMV and the 35S promoter and the potential risks associated with the use of the promoter in GM plants, concluding that any risks are no greater than those encountered in conventional plant breeding. IntroductionIn a recent article, Ho et al. (1999) suggested that the widespread use of the 35S promoter of cauliflower mosaic virus (CaMV) in transgenic plants is "a recipe for disaster". Ho et al. (1999) base their arguments on three considerations, a) that the CaMV 35S promoter has a hotspot for recombination (Kohli et al., 1999); b) that the 35S promoter has several domains with different tissue specificities and c) that the 35S promoter is very efficient and can function in a wide range of organisms, not only plants but also bacteria and animals. From this they deduce that the 35S promoter could recombine to activate dormant viruses, create new viruses and "cause cancer by the overexpression of normal genes". As scientists who have worked on CaMV for up to 25 years and have contributed much to the understanding of its molecular biology we wish to put these scenarios in the correct context.

The Cauliflower Mosaic Virus 35S Promoter Extends into the Transcribed Region

“…Note that, in the case of the S1 probe, the GTA present at position 53-55 (which derives from a Bst11071 cloning site present in the expression constructs) is replaced with the wild-type sequence TAA. The annealed products were digested with NcoI and labeled with 32 P. Competitor DNA fragments were prepared by directly annealing two synthetic complementary oligonucleotides.…”

Opinion of the Scientific Panel on genetically modified organisms [GMO] related to the safeguard clause invoked by Greece according to Article 23 of Directive 2001/18/EC and to Article 18 of Directive 2002/53/EC

“…It has been suggested (Ho et al, 1999) that the CaMV 35S promoter could result in an inadvertent activation of plant genes or endogenous viruses, promote horizontal gene transfer, or might even recombine with mammalian viruses with unexpected consequences. Arguments for the safety of the promoter in GM crops are provided by Hull et al (2000). Greece is concerned about accepting that safety studies of CRY proteins are performed with proteins produced in bacteria, as the nucleotide sequence of the corresponding genes integrated into GM crops may not be precisely the same as the nucleotide sequence of the bacterial gene.…”

Cloning and Characterization of Alcohol Dehydrogenase (Adh) Promoter Region for Expression Under Submergence and Salinity Stress

“…Genetic engineering allows control of the timing, tissuespecificity, and expression level of the introduced genes for their optimal function. CaMV35S is frequently used as a constitutive promoter to control the gene expression in conventional transgenic approaches (Hull et al 2000, Kasuga et al 2004). This, however, frequently results in suboptimal growth and yield penalty under normal conditions (Wang et al 2003).…”