OPINION article

Front. Bioeng. Biotechnol., 30 June 2025

Sec. Biosafety and Biosecurity

Volume 13 - 2025 | https://doi.org/10.3389/fbioe.2025.1600610

Naturally transgenic plants and the need to rethink regulatory triggers in biotechnology

  • 1. Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Asunción, San Lorenzo, Paraguay

  • 2. Doctorado en Ciencias Agrarias, Universidad San Carlos, Asunción, Paraguay

  • 3. Coordinación de Innovación y Biotecnología, Dirección Nacional de Bioeconomía, Subsecretaría de Producción Agropecuaria y Forestal, Secretaría de Agricultura, Ganadería y Pesca, Buenos Aires, Argentina

  • 4. Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones en Ciencias de la Salud, Universidad Nacional de Asunción, San Lorenzo, Paraguay

  • 5. Mycology Investigation and Safety Team, Centro Multidisciplinario de Investigaciones Tecnológicas, Universidad Nacional de Asunción, San Lorenzo, Paraguay

1 Introduction

Horizontal gene transfer (HGT) is a widespread phenomenon across all domains of life, and has been a driving force of evolution (; ; ). Viral sequences have been found in all eukaryotic (; ; ) and prokaryotic kingdoms (; ), and HGT has been found to occur in all directions between kingdoms of the same domain (; ; ).

Plant species have stably integrated foreign sequences into their genomes. This natural transgenesis has occurred repeatedly in the evolution of plants, affecting their biology and genetic diversification (). Some of the mechanisms of natural HGT have been characterized to sufficient extent to be used for genetic engineering applications, and the list of mechanisms of gene transfer mastered and applied to engineering might expand with the advancement of scientific knowledge. In order to make the case that natural HGT must be taken into account when designing regulatory frameworks for transgenic organisms, and in particular of transgenic crops, we will address the particular case of HGT from bacteria to plants.

The term “transgenic” usually refers in the literature to DNA constructs resulting from the process of gene transfer between species through genetic engineering (; ). Agrobacterium1-mediated transformation has established itself as the most widely used method for this purpose. In this procedure, a modified Agrobacterium plasmid transfers the desired DNA into the recipient cell, integrating it into its genome and allowing its hereditary transmission ().

2 Horizontal gene transfer in plants

For stable incorporation of a sequence into a host organism and its transmission to offspring, certain conditions must be met. First, the foreign sequence must be integrated into the host genome. Then, the incorporated sequence must not be lost in the genomic rearrangements during cell divisions. In addition, the transformed cell must be part of the germline, to ensure inheritance. Finally, the integrated sequence must persist throughout evolution ().

HGT is a process by which genes are transferred between unrelated organisms, as opposed to inheritance from parents. A clear example of gene acquisition by HGT is nitrogen fixation, a metabolic process present in certain bacteria of the genus Paenibacillus and regulated by the nif (nitrogen fixation) operon. These metabolic pathways are not specific to Paenibacillus, but have been acquired from phylogenetically distant organisms, including some of the Archaea domain and closely related bacterial phyla. HGT plays a key role in these changes, which has resulted in great diversity in the sequence and structure of nitrogen fixation regulatory elements, reflecting the multiplicity of such events from different donor organisms (). Although this phenomenon has been widely documented in Bacteria and Archaea, it has also been observed in eukaryotes, including plants (). In the latter, one of the most studied examples of HGT is the transfer of DNA from bacteria of the genus Agrobacterium to various plant species ().

Agrobacterium can transfer part of its DNA (T-DNA) to plant cells. Once incorporated, this T-DNA is integrated into the recipient genome, resulting in naturally occurring transgenic plants, or naturally occurring genetically modified plants (nGMs) (). These plants have sequences in their genomes called cellular T-DNA (cT-DNA), homologous to Agrobacterium T-DNAs ().

Most cT-DNAs identified to date appear to originate from Agrobacterium rhizogenes. However, cT-DNAs have also been found with previously unknown T-DNA sequences or unusual combinations thereof ().

T-DNA sequences naturally transferred by various Agrobacterium species contain two types of genes, both regulated by promoters compatible with expression in eukaryotic cells. The first group of genes, called “oncogenes”, encodes proteins that regulate the biosynthesis or response of plant cells to phytohormones, particularly auxins and cytokinins. Their expression causes uncontrolled cell division, leading to tissue proliferation and the formation of neoplastic growths, known as crown galls (; ). The second group of genes encodes enzymes involved in the synthesis of opines that can be used by Agrobacterium cells as a source of carbon and nitrogen (). It has been proposed that for the emergence of a natural transgenic plant, two conditions must be met: the naturally infected plant must be able to regenerate from tissues transformed upon infection; and the structure of the incorporated T-DNA must allow or favor such regeneration ().

3 Evidence of natural transgenesis in plants

HGT in plants was initially identified in species of the genus Nicotiana, in whose genomes the presence of Agrobacterium T-DNA was detected (). Studies in N. glauca and N. sylvestris showed that bacterial DNA insertion was not an isolated event ().

The identification of new cT-DNA sequences in several plant species has been possible thanks to whole genome sequencing databases. The evidence suggests that HGT from bacteria to plants is a more common phenomenon than previously thought and that it has occurred in multiple plant lineages () (Table 1).

TABLE 1

FamilySpeciesReferences
ApocynaceaeApocynum venetum
BurseraceaeBoswellia sacra
CaprifoliaceaeLonicera japonica
Lonicera maackii
CaryophyllaceaeSilene noctiflora
Silene uniflora
ConvolvulaceaeCuscuta australis
Cuscuta campestris
Cuscuta gronovii
Cuscuta suaveolens
Ipomoea batatas
Ipomoea trifida
EbenaceaeDiospyros lotus
ElaeagnaceaeElaeagnus angustifolia
EricaceaeVaccinium corymbosum
Vaccinium macrocarpon
Vaccinium microcarpum
Vaccinium oxycoccos
ErythroxylaceaeErythroxylum cataractarum
Erythroxylum daphnites
Erythroxylum densum
Erythroxylum havanense
EuphorbiaceaeTriadica sebifera
FabaceaeAeschynomene evenia
Arachis appressipila
Arachis macedoi
Arachis magna
Arachis monticola
Arachis paraguariensis
Arachis pintoi
Arachis pusilla
Arachis rigonii
Arachis stenophylla
Arachis stenosperma
Arachis trinitensis
Arachis valida
Arachis villosa
Eperua falcata
KewaceaeKewa caespitosa
MyrtaceaeEucalyptus cloeziana
MolluginaceaePharnaceum exiguum
NyssaceaeNyssa sinensis
PaulowniaceaePaulownia fortunei
PlantaginaceaeLinaria acutiloba
Linaria dalmatica
Linaria genistifolia subsp. dalmatica
Linaria vulgaris
RhizophoraceaeCeriops decandra
SalicaceaePopulus alba × Populus glandulosa
SolanaceaeNicotiana glauca
Nicotiana noctiflora
Nicotiana otophora
Nicotiana sylvestris
Nicotiana tabacum
Nicotiana tomentosa
Nicotiana tomentosiformis
TheaceaeCamellia oleifera

Examples of nGM plants reported in the literature.

Genes acquired by HGT can retain their functionality in recipient plants and influence their traits. An example of this is Ipomoea batatas, where a cT-DNA has been identified with functional Agrobacterium genes which have remained stable over time (). In addition, such genes can affect certain phenotypic traits, such as the rol genes, associated with root development ().

Unlike transgenics obtained through genetic engineering, in which genes are inserted in a targeted manner in the laboratory, nGMs acquired foreign DNA through natural infections (). Between 5%–10% of dicotyledonous species are estimated to contain cT-DNAs (). With approximately 200 million species in this class, about 10,000 species would be nGM plants (). The existence of nGM plants challenges the separation between “natural” and “artificial” made by regulatory triggers when determining which types of plants should be subjected to biosafety assessments, by showing that transgenics are not only the result of human manipulation, but also a naturally occurring phenomenon.

4 Discussion

The natural presence of Agrobacterium sequences in plant organisms questions the logic of strictly regulating transgenics obtained through genetic engineering, while exempting organisms that are similar, but obtained through conventional methods (; ). cT-DNA evidence suggests that regulation focused on the method of production may be inadequate (). In many regulatory frameworks, a transgenic organism is one that contains deliberately altered genetic material which does not occur “naturally” through breeding or selection (). This inconsistency becomes more evident when considering that the same trait can be obtained both by genetic engineering techniques and by conventional breeding, creating different regulatory thresholds for products with the same traits.

These inconsistencies also extend to relevant aspects of risk assessment, given that HGT represents an important topic in the evaluation of GM plants. In regulatory practice, HGT is typically evaluated using a pathway-to-harm approach (). However, to date, no empirical evidence supports HGT from GM plants to soil bacteria under field conditions (; ; ). Similarly, while humans and animals routinely ingest DNA from multiple biological sources, the likelihood of HGT from GM plant-derived DNA to gut microbiota or host tissues remains extremely low (; ; ; ). A detailed assessment of the potential for HGT from GM plants to microorganisms is beyond the scope of this work. For further information, readers are encouraged to consult for a detailed review.

Given these complexities, the existence of nGM plants highlights the need for a product-based regulatory trigger in which biosafety assessment focuses on the traits and phenotype of the final organism rather than the process by which it was obtained (). This approach offers several important advantages over traditional process-based frameworks, particularly in the context of emerging breeding techniques. Focusing on the characteristics and potential risks of the final product ensures regulatory coherence and risk assessment proportionality, avoiding inconsistencies where crops with similar traits are subject to different oversight (; ). Not all GMOs pose the same level of risk; some have well-characterized, low-risk profiles; just as not all conventionally bred crops are inherently safe. Conventional methods such as wide crosses, mutagenesis, or spontaneous mutations can also result in traits with biosafety implications, including increased toxicity, allergenicity, or invasiveness (). While these products are generally not subject to a complete risk assessment, they are often regulated at various stages of the production chain (registration for the crop, safety assessment for the byproducts).

A product-based approach enables regulators to focus their efforts on the actual risk presented by a crop rather than presuming risk based on the technique employed (). This logic has already been adopted in the case of NBTs by countries such as Argentina, Brazil and Canada, that exclude certain products developed through NBTs from GMO regulations when no novel combination of genetic material is present in the final product (; ; ). This aligns with risk assessment principles that prioritize the traits of the crop. It also allows for the inclusion of conventionally bred crops in biosafety assessments when they present novel or potentially hazardous traits, which process-based systems tend to overlook (). Altogether, adopting a product-based perspective would contribute to building a coherent, adaptable, and science-driven regulatory framework for novel organisms.

Statements

Author contributions

DF: Conceptualization, Data curation, Formal Analysis, Funding acquisition, Investigation, Methodology, Project administration, Resources, Supervision, Validation, Visualization, Writing – original draft, Writing – review and editing. NB: Data curation, Formal Analysis, Investigation, Methodology, Validation, Writing – review and editing. SQ: Formal Analysis, Investigation, Methodology, Writing – original draft. MG: Data curation, Methodology, Validation, Writing – review and editing. EN: Data curation, Methodology, Validation, Writing – review and editing. AA: Data curation, Methodology, Validation, Writing – review and editing. AC: Data curation, Investigation, Methodology, Project administration, Supervision, Writing – original draft, Writing – review and editing.

Funding

The author(s) declare that financial support was received for the research and/or publication of this article. This work was supported by the projects “Regulatory sciences in agricultural biotechnology” (PIC-45–2023), and “Innovation in Regulatory Science” (PIC-01–2024) from the Faculty of Exact and Natural Sciences, National University of Asunción.

Acknowledgments

The authors express their sincere appreciation to Rocío Riveros, Marcos Florentín, Samuel Gabaglio, and Vitor Pinoti for their kind contributions of scientific references.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Generative AI statement

The author(s) declare that no Generative AI was used in the creation of this manuscript.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Footnotes

1.^The collective term Agrobacterium is used in recognition of tradition and due to the impossibility of precisely identifying the bacterium responsible for the plant transformation that occurred millions of years ago. The T-DNA fragments present in plant genomes are insufficient for this determination (). The classification of the genus is still evolving, as the taxonomic affiliation of five Agrobacterium genomospecies has not yet been determined, suggesting a possible increase in the number of species in the future ().

References

Summary

Keywords

naturally transgenic plants, horizontal gene transfer (HGT), cellular T-DNA (cT-DNA), Agrobacterium, regulatory triggers

Citation

Fernández Ríos D, Benítez Candia N, Quintana SA, Goberna MF, Nara Pereira E, Arrúa AA and Castro Alegría A (2025) Naturally transgenic plants and the need to rethink regulatory triggers in biotechnology. Front. Bioeng. Biotechnol. 13:1600610. doi: 10.3389/fbioe.2025.1600610

Received

26 March 2025

Accepted

16 May 2025

Published

30 June 2025

Volume

13 - 2025

Edited by

Monica Garcia-Alonso, Estel Consult Ltd., United Kingdom

Reviewed by

Paul Keese, University of Ghana, Ghana

Updates

Copyright

*Correspondence: Danilo Fernández Ríos, ; Andrés Castro Alegría,

Disclaimer

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

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