Are Mutations in Genetically Modified Plants Dangerous?

Latham et al. [1] and Wilson et al. [2] reviewed the long known phenomenon that plant transformation may cause mutations. Mutations can occur at any position in the genome, due to the tissue culture phase or other factors. Furthermore , insertion mutations may be induced by Agrobac-terium-mediated transformation or particle bombardment. The authors focus in particular on mutations and chro-mosomal rearrangements flanking the insertion of the T-DNA. In their view, these mutations pose a risk regarding biosafety. The transgenic plant should in their opinion be as identical to its parent as possible. Therefore, they recommend extended backcrossing for elimination of genome-wide mutations, and sequencing of flanking DNA of 50 kbp at each side of the insertion, and discarding of plants that show any mutation in the flanking DNA compared to the parent plant. These and other precautions should ensure that transformation-induced mutations will not impact on biosafety. Apparently, the authors suggest that in addition to the inserted transgene, mutations have their own contribution to uncertainties regarding biosafety. If the transgenic plant was to be released in the environment, genotypes with mutations should be discarded. The authors do not mention mutation breeding of plants. Since the discovery of X-ray induced mutations in barley nearly 80 years ago (Stadler [3]), plant breeders and geneti-cists have realized how DNA mutations can be induced for widening the genetic variation in their germplasm. During the past seventy years, mutation breeding led to more than 2250 plant varieties (Maluszynski et al. [4]; Ahloowalia et al. [5]). 70% of these varieties were released as directly induced mutants, and the other 30% from crosses with induced mutants. The use of chemical treatments was relatively infrequent , but gamma rays were frequently used (64%), followed by X-rays (22%) (Ahloowalia et al. [5]). The freely accessible FAO/IAEA website contains a database of plant varieties derived from induced mutations list has been composed on the basis of official information from plant breeders and authorities. The composers of the database mention that the list is far from complete, as frequently it is not published how new varieties have been obtained. In spite of that, the list contains now (August 2007) already 2543 released plant varieties. In reality, the number of induced mutant varieties is much larger. If spontaneous mutants would also be included, the list would further expand strongly. The induced mutant varieties have been developed in 175 plant species, including rice, …