The mechanisms underpinning lateral gene transfer between grasses

Societal Impact Statement Lateral gene transfer (LGT) refers to the transmission of genetic material without sexual reproduction. LGT is widespread in a number of plant species, including grasses. But how these genes of foreign origin got there is presently unknown. In this review, we show that transformation techniques used to genetically modify organisms could occur in the wild and be responsible for the frequently observed grass-to-grass LGTs. The distinction between natural evolutionary processes and genetic engineering might be arbitrary, and its validity will be further debated as agricultural biotechnology becomes more widely used and examples of “natural genetic engineering” through LGT increase.

Summary Lateral gene transfer (LGT) is the transmission of genetic material among species without sexual reproduction. LGT was initially thought to be restricted to prokaryotes, but it has since been reported in a wide range of eukaryotes, including plants. Grasses seem to be particularly prone to LGT and frequently exchange genes among species. However, the mechanism(s) facilitating these transfers in this economically and ecologically important group of plants are debated. Here, we review vector-mediated, direct tissue-to-tissue contact, wide-crossing and reproductive contamination LGT mechanisms and discuss the likelihood of each in light of recent studies. Of particular relevance are transformation approaches that require minimal human intervention to transfer DNA among grasses in the lab that could mimic the mechanisms facilitating grass-to-grass LGT in the wild. These approaches include relatively simple techniques, such as pollen tube pathway-mediated transformation, that take advantage of the permeability of the reproductive process to introduce alien genetic material from a third individual into an embryo. This process could be easily mirrored in the wild where pollen from one species lands on the stigma of another, acting as a source of alien DNA that can ultimately contaminate the reproductive process. This contamination is likely to be prevalent in wind pollinated species such as grasses, where the rates of illegitimate pollination will be high. In conclusion, plant transformation methods requiring minimal intervention are likely paralleled in the wild where they act as the mechanism underpinning LGT between distantly related grass species.