Gene editing in plants is usually achieved by modifying the genome of cultured cells and then regenerating whole plants by exposing the modified cultured cells to growth hormones. This method is inefficient, limited to a few species, and can also lead to undesired genome aberrations. Maher et al. now report that it is possible to overcome the tissue culture bottleneck by modifying somatic cells in whole plants and inducing the formation of shoot meristems — the plant stem cell niches that give rise to all the above-ground organs of the plant.
First, the authors developed a protocol (a high-throughput platform) to generate de novo meristems on the leaves of Nicotiana benthamiana in vitro-grown seedlings by expressing the developmental regulators Wus2 and STM using Agrobacterium-mediated transient transformation. This transient expression led to the formation of callus-like growths. Even though many calli remained undifferentiated, some formed meristem-like structures that then differentiated into small shoots that could be transferred to a rooting medium, and then soil, to obtain full flowering plants (from which seeds could be harvested). Using a similar method on tomato seedlings, transient expression of Wus2, ipt and STM enabled the regeneration of whole tomato plants.
This protocol was repeated using transgenic seedlings that constitutively expressed the nuclease Cas9. But in addition to developmental regulators, a single guide RNA (sgRNA, which targets the Cas9 nuclease to a specific sequence) was also expressed transiently to induce targeted mutations. This led to the generation of target gene-edited shoot meristems that developed into whole plants.
The authors could then show that it is possible to apply the same method to generate gene-edited shoots by transiently transforming stems of soil-grown plants. Moreover, they could modify agronomically important species such as potato and grape.
it is possible … to generate gene-edited shoots by transiently transforming stems of soil-grown plants
Thus, this study reports the successful generation of gene-edited plants without the need for time-consuming and inefficient sterile culture methods. Importantly, the developed high-throughput platform will enable the method to be tested on different plant species.
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Maher, M. F. et al. Plant gene editing through de novo induction of meritems. Nat. Biotechnol. https://doi.org/10.1038/s41587-019-0337-2 (2019)
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Baumann, K. Plant gene editing improved. Nat Rev Mol Cell Biol 21, 66 (2020). https://doi.org/10.1038/s41580-019-0207-2
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DOI: https://doi.org/10.1038/s41580-019-0207-2