Think of DNA and chances are the double helix structure comes to mind, but that's only one piece of the puzzle. Another major part is mitochondrial DNA, and in plants that's even more important – and so complex that scientists haven't yet been able to edit the genes in there. Now a team of Japanese researchers has managed to do just that, which could help improve the genetic diversity of crops.

Mitchondria are often called the "powerhouses" of cells, since they produce energy from nutrients. These regions contain their own DNA, separate from the nuclear DNA in the rest of the cell. While mitochondrial DNA in animals has a smaller and simpler genome, in plants it's the other way around.

"The plant mitochondrial genome is huge in comparison, the structure is much more complicated, the genes are sometimes duplicated, the gene expression mechanisms are not well-understood, and some mitochondria have no genomes at all – in our previous studies, we observed that they fuse with other mitochondria to exchange protein products and then separate again," says Shin-ichi Arimura, lead researcher on the study.

Because of that complexity, mitochondrial DNA had never been successfully edited in plants before. And that would be a useful ability – crops are regularly genetically modified to improve yields or make them hardier against disease and climate, but without access to large sections of their DNA, genetic diversity is somewhat limited.

And that can have devastating consequences. In 1970 a fungal disease called southern corn leaf blight decimated corn supplies in the US, made worse by a certain gene in the mitochondria that was common to many corn plants. Bananas are also vulnerable to similar threats thanks to limited genetic diversity.

"We still have a big risk now because there are so few plant mitochondrial genomes used in the world," says Arimura. "I would like to use our ability to manipulate plant mitochondrial DNA to add diversity."

To start with the team, made up of researchers from the Universities of Tokyo, Tohoku and Tamagawa, adapted a process used to edit mitochondrial DNA in animals. Named mitoTALENs, the technique uses a protein to cut and delete a specific gene from the mitochondrial genome.

The researchers used the modified mitoTALENs technique to snip out a mitochondrial gene that's thought to cause a condition called cytoplasmic male sterility (CMS), which leaves male plants infertile and unable to make pollen.

Using the method, the team created four new lines of rice and three new lines of canola. Sure enough, those plants that had their mitochondria edited appeared to be fertile, producing far more seeds than the unedited plants.

As useful as it is to improve yields like this, the team says that the real benefit of the work is adding genetic diversity to crops. More research will need to go into identifying which other mitochondrial genes could be edited for this goal.

The research was published in the journal Nature Plants.

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