-Plant virus delivers Cas9 to plant cells to cause the target mutation-
The National Agriculture and Food Research Organization (NARO) established a viral vector-mediated plant genome editing method using a plant virus. Most of the conventional genome-editing methods for plants require crossbreeding and selection processes. However, the newly developed method does not involve this step. Thus, it can be applied to vegetative propagation crops such as potatoes, making the genome-editing process of the crops much simple. Since the plant virus adopted as a vector is pathogenic to a wide range of plants in the family Solanaceae, it is expected to expand the possibility of genome editing of wider crop varieties.
Genome-editing technology is highly expected to unlock the potential of various crops and contribute to realizing sustainable agriculture. The common genome-editing method using genome editing enzymes such as "CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9)" requires incorporating genome editing enzymes into the cells. However, for the genome editing of plants, the enzymes are difficult to be directly introduced into the cells, as the cell walls stand as an obstacle. Therefore, a gene that produces the genome-editing enzymes needs to be introduced first into the plant cells. The final genome-edited plant does not include the DNA that expresses genome-editing enzymes. This is because individuals with exogenous DNA will be taken out during the crossbreeding process. However, this method cannot be applied to vegetative propagation crops such as potatoes for their regeneration styles.
The development of the viral vector-mediated plant genome editing method had been long-awaited. In this method, a plant virus with RNA genome is used as a vector for delivering the genome-editing enzyme "Cas9" to plant cells. Plant cells infected with the viral vectors will reproduce Cas9 within the cell, which leads to the target mutation. In June 2020, a Chinese research team had announced the establishment of the plant genome-editing method using a plant virus vector. But the virus used in the project could infect only the limited range of plants, most of which are in the Compositae family, and the application of their method to crops was impractical.
However, the recent accomplishment of NARO researchers proved to be a gamechanger. NARO succeeded in establishing the viral vector-mediated plant genome editing method using a Potato Virus X (PVX) vector. PVX is infectious to a wide range of crops in the family Solanaceae. The newly established method has realized an accurate target mutation that no one else had succeeded in the past.
An additional advantage of the viral vector-mediated plant genome editing method is that crossbreeding is not required in the process. The new method has a large potential to make contributions to genome editing of wider plant varieties.
Ariga H, Toki S, Ishibashi K, Potato Virus X Vector-Mediated DNA-Free Genome Editing in Plants. Plant and Cell Physiology 61: 1946-1953. https://doi.org/10.1093/pcp/pcaa123
Fig. Flowchart for the viral vector-mediated plant genome editing method
(1) The conventional method temporally incorporates a gene that expresses genome-editing enzymes to the plant genes. After the shoot regeneration, a genome-edited individual with foreign DNA is selected by antibiotic resistance, etc. In the final genome-edited plant, foreign DNA, such as Cas9, will not exist because of the crossbreeding process.
(2) The viral vector-mediated plant genome editing method inoculates virions to the plant. In this method, highly efficient target mutation occurs through the genome-editing enzymes expressed by PVX vectors with an RNA genome. The genome-edited foreign DNA-free plants will be obtained through conducting tissue culture of the mutated plant.