Slow integration
Thousands of genes of mitochondria and chloroplasts have found their way into the genome of the plant. A process that is still going on, regardless of that mitochondria and chloroplasts are nested inside plant cells for millions of years. The process is purposely slow German researchers show in Nature Plants.
There are different advantages for a gen to be located in the genome of a plant. Sexual recombination for example, something that does not happen with genes located in the mitochondrial or chloroplast genome. In addition, a plant can regulate the genes that are located in its genome in a more energy efficient way. Nevertheless, genes coming from mitochondria or chloroplast don’t enter the genome easy.
There are three things that need to happen for the translocation of genes from the chloroplast genome to that of the plant. First the DNA of the chloroplast need to find a wat into the cytosol. For example, through rupture of the chloroplast. Secondly, the DNA needs to find a way to the nucleus. Where, thirdly, it needs to integrate into the genome. Whereas researchers have a reasonably good idea how this works for the first and second step, they haven’t for the last step. Therefor the researchers of the article decided to investigate.
Without DSBR-system the plant is integrating more chloroplast and mitochondria DNA in its genome
Double strand breaks give chloroplast and mitochondrial DNA a chance to sneak into the genome. By this process the double strand repair system (also called DSBR-system) is involved. The researchers made two mutants, who each inactivated of one of the two DSBR-systems of the plant, in order to find out if the DSBR-system is also involved in the integration of mitochondrial or chloroplast DNA.
Through combining this with a system that stimulates the rupture of chloroplasts the researchers could see the effect of missing one of the two DSBR-systems. They noticed that when plants missed one of the two DSBR-systems that the plants were integrating more chloroplast DNA in the genome.
This occurred at a very high frequency, which in turn increased the chance of influencing the workings of other genes. And this is something the plant wants to prevent as much as possible. From that prospective it is not strange that DSBR-systems don’t allow the integration of mitochondrial or chloroplast DNA into the genome to be to fast.
Literature
Gonzalez-Duran, E., Kroop, X., Schadach, A. et al. Suppression of plastid-to-nucleus gene transfer by DNA double-strand break repair. Nat. Plants (2025). https://doi.org/10.1038/s41477-025-02005-w
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