Ability to edit plant mitochondrial DNA may lead to a more secure food supply

Nuclear DNA was first edited in the early 1970s, chloroplast DNA was first edited in 1988, and animal mitochondrial DNA was edited in 2008. However, until now, no tool has successfully edited plant mitochondrial DNA. The University of Japan researchers, who have published their results in Nature Plants, hope to use the technique to address the current lack of mitochondrial genetic diversity in crops, a potentially devastating weak point in our food supply.

The mitochondria contain DNA separate from the cell’s main DNA, which is stored in the nucleus. Nuclear DNA is the long double-helix genetic material inherited from both parents. The mitochondrial genome is circular, contains far fewer genes, and is primarily inherited only from mothers. The animal mitochondrial genome is a relatively small molecule contained in a single circular structure with remarkable conservation between species. Plant mitochondrial genomes are a different story.

“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,” said Shin-ichi Arimura, associate professor in plant molecular genetics at the University of Tokyo.

To find a way to manipulate the complex plant mitochondrial genome, Arimura turned to collaborators familiar with the cytoplasmic male sterility (CMS) systems in rice and rapeseed (canola). Prior research strongly suggested that in both plants, the cause of CMS was a single, evolutionarily unrelated mitochondrial gene in rice and in rapeseed (canola): clear targets in the perplexing maze of plant mitochondrial genomes.

Arimura’s team adapted a technique that had previously edited mitochondrial genomes of animal cells growing in a dish. The technique, called mitoTALENs, uses a single protein to locate the mitochondrial genome, cut the DNA at the desired gene, and delete it. “While deleting most genes creates problems, deleting a CMS gene solves a problem for plants. Without the CMS gene, plants are fertile again,” said Arimura.

The fully fertile four new lines of rice and three new lines of rapeseed (canola) that researchers created are a proof of concept that the mitoTALENs system can successfully manipulate even the complex plant mitochondrial genome.

Researchers will study the mitochondrial genes responsible for plant male infertility in more detail and identify potential mutations that could add much-needed diversity.

Abstract