Background: Inserting DNA at a defined site in plant genomes

A study reports targeted insertion of DNA several kilobases long into plant ribosomal DNA (rDNA) using an optimized avian R2 protein. The researchers reported full-length cargo insertions ranging from 2.2–5 kb in Arabidopsis protoplasts, leaves of Nicotiana benthamiana, a plant in the tobacco genus, and tomato seedlings. In N. benthamiana leaves, the measured insertion efficiency was 30-fold higher than with Cas9-based homology-directed repair (HDR).

In conventional plant transformation using Agrobacterium tumefaciens, introduced DNA integrates randomly into the genome. The researchers explained that newer approaches based on nucleases, prime editors, transposases, and recombinases still face limitations such as low efficiency, off-target insertion, or cargo-size constraints. The alternative examined in this study uses an R2 protein to insert DNA several kilobases long at a specific genomic target.

Key findings: Optimizing R2Tg and RNA cargo design

The protein used was R2Tg, derived from the bird Taeniopygia guttata. The researchers designed an R2Tg expression cassette and RNA cargo, and optimized the rDNA homology arms and untranslated regions. The RNA cargo reportedly contained a reporter interrupted by introns. Homology arms are sequence regions corresponding to the target rDNA, while untranslated regions are portions that are not translated into protein.

The editing system was tested in Arabidopsis thaliana protoplasts, N. benthamiana leaves, and tomato (Solanum lycopersicum) seedlings. The reported size range for full-length cargo was 2.2–5 kb. However, the provided abstract does not make clear whether every size in this range was tested in each of the three experimental systems.

The quantitative comparison was reported for N. benthamiana leaves. In this setting, the insertion amount averaged one copy per genome, and the researchers reported 30-fold higher insertion efficiency than with Cas9 HDR. Average copy number is distinct from the proportion of cells in which insertion succeeded. The evidence does not support interpreting this result as exactly one copy being inserted into every cell or the same efficiency being achieved in other plants.

Significance and outlook: Using multicopy rDNA as a gene-insertion target

The researchers presented an R2Tg ribonucleoprotein platform that uses the multicopy rDNA locus to add genes several kilobases long to plant genomes. The available archived publisher description specifies 25S rDNA as the target. The abstract describes this locus as a “safe harbor” for gene insertion, but that label alone does not establish long-term safety or stable expression.

The study reports targeted insertion of full-length cargo in plant experimental systems and provides a quantitative comparison with Cas9 HDR under specific experimental conditions in leaves. Application in crop development should be accompanied by evaluations of insertion structure in regenerated plants, transmission to subsequent generations, maintenance of expression, and effects on growth. These are validation tasks for subsequent applications; their mention does not mean that the paper did not experimentally assess them.

The available evidence is limited to bibliographic information, the abstract, and a brief description. Sample sizes, statistical uncertainty, and detailed results on off-target insertion and stability across generations could not be confirmed from the provided materials. The study design and quantitative results are based on the Europe PMC bibliographic record and abstract.