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. 2019 Jan 16;6:213. doi: 10.3389/fbioe.2018.00213

Table 1.

Genetic alterations and the proposed classification of organisms in the context of GMO regulatory oversight.

Organism Description of the alteration Does it occur in nature? Likeliness of occurrence Alteration beyond what does occur naturally by mating and/or natural recombination* Motivation
1 Any plant Single point mutation YES Very likely NO The mutation rate has been estimated in different plants to be on average 1 mutation per genome per generation, meaning that every single plant will contain, at least, one new mutation. See also the Appendix in supplementary material.
2 Any plant 2,000 point mutations Perhaps only in a nuclear fall-out Extremely unlikely YES This is the example of classical mutagenesis using a radioactive source to induce random mutations. The organisms resulting from this intervention are exempted from the scope of the EU GMO directive on the condition that no recombinant nucleic acid molecules or GMOs have been used.
3 Any plant Short deletions (a few bp) YES Very likely NO Such one base pair deletions occur on a regular basis. Mostly after the occurrence of a double-strand break.
4 Any plant Larger deletions (a few kbp) YES It does happen NO Larger deletions also do occur, but with a lower frequency. In viruses such deletions occur rather frequently during processes of attenuation.
5 Any plant Short insertions (a few bp) YES Very likely NO Small insertions also occur on a regular basis. Similar as with small deletions such insertions may occur, for example after a double-strand break.
6 Maize 50 kb exogenous DNA insertion YES Very unlikely YES Such size of insertions do occur in very rare occasions, but the larger the insertion the more unlikely they become.
7 Any plant 2 kb exogenous DNA insertion from a non-related source (a transgene) YES Very unlikely YES Even though there are rare events of horizontal gene transfer, it is very unlikely that such an event occurs. This is also what the legislation truly intended to have covered by the GMO legislation.
8 Any plant A cisgene flanked by the T-DNA left and right borders NO Extremely unlikely YES? There are no known examples of such types of alterations occurring in nature. Where T-DNA has been introduced spontaneously, it was with sequences stemming from A.tumefaciens in between.
9 Any plant An allele swap YES It does happen NO Allele swaps do occur, especially as a result of recombination during meiosis.
10 Any plant Cisgene addition YES It does happen NO/YES The difference with an allele swap is that the cisgene may be present anywhere in the genome, not necessarily on its 'natural' location. It is known however that in plants genes on a regular basis get duplicated, resulting in an extra copy of the gene being inserted at another location in the genome, away from its original ‘natural' location.
11 Any plant Intragene addition ? Extremely unlikely YES The rearrangement of regulatory sequences does occur in nature and is actually important in evolutionary terms. But it is extremely unlikely to occur within a few generations in the context of plant breeding.
12 Plants that cannot naturally be infected by A. tumefaciens T-DNA insertion NO Extremely unlikely YES When a plant cannot naturally be infected by A. tumefaciens, then the insertion of T-DNA cannot occur.
13 Plants that can be naturally infected by A. tumefaciens such as Nicotiana spp., sweet potato and Linaria spp T-DNA insertion YES Unlikely, but it has happened NO A. tumefaciens can naturally infect a wide variety of plants, but this usually is a local infection resulting in the formation of crown galls, without the T-DNA being inserted into the reproductive DNA. However, this has happened during evolution of for example sweet potato.
14 Any plant Genome duplication YES It does happen NO Genome duplications do spontaneously happen in nature but have even more been exploited by man to strengthen certain characteristics of crops.
15 Any plant Transposon insertion YES It does happen NO Transposons mobile genetic elements that account for an important fraction of all plant genomes. Its movement generates mutations that are at the origin of many traits selected by humans to domesticate wild plants of breed new varieties.
*

As proposed in the article organisms should only be considered as GMO subject to specific regulatory oversight when they fulfill two criteria: (1) the alteration must have been achieved by means of a technical intervention that does not occur naturally, and (2) the genetic combination formed must be beyond what does occur naturally by mating and/or natural recombination.