Combining one of the most advanced DNA modification techniques with one of the oldest methods of plant manipulation, grafting: this is the idea presented on January 2 in the journal Nature Biotechnology by a team from the Max Planck Institute for Molecular Plant Physiology in Potsdam (Germany). Friedrich Kragler and his colleagues describe how they used Crispr-Cas9, a 2020 “nobel” genome editing tool, to modify the lady’s cress, a model plant, before grafting a stem onto it. wild”, unmodified. They then found that some of the seeds produced by the graft carried the desired genetic changes.
“The fact that a message goes from roots to flowers is fascinating in itself”, notes Friedrich Kragler, who has been working for twenty years on the mobility of ribonucleic acids (RNA) in plants. RNAs are key molecules, particularly in the transport, regulation and translation of genetic information carried by DNA in cells and between tissues. In plants, their long-distance circulation passes through the phloem, a vascular system used by the sap, but also by viruses carrying a molecular conformation similar to transfer ribonucleic acids (tRNA) − we speak of « tRNA-like sequences »or TLS.
In 2016, the Potsdam team showed that TLS-like structures allow long-distance transport of RNA molecules, from one side of grafted plant tissue to the other. “The idea then came to us that we could use this technique to make genetically modified organisms”says Friedrich Kragler, who recalls that grafting has been used for millennia − and not only in the vine, to save it from the phylloxera aphid, but also on many fruit trees.
Holy Grail of varietal selection…
Let’s go into the detail of the “molecular cuisine” of the German team. She first genetically modified the Arabis so that it synthesizes molecules intended to fulfill three functions: to transport these molecules from the roots to the leaves and the flowers thanks to the passport constituted by the TLS; cut the DNA of the cells of the aerial part of the plant using the Cas9 protein; and insert genetic information carried by an RNA serving as a guide. It remained to be seen whether this molecule produced in the transgenic rootstock was going to circulate well and be expressed in the “natural” graft. This is what has been observed, infrequently, including when a related plant, rapeseed, was grafted onto the root of the arabian beet.
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