Why did chloroplasts and mitochondria transfer almost all their essential genes to the nucleus? I think economics had a part to play. TL;DR It is cheaper for the cell to encode organellar genes in the nucleus. I think I’m going to be Lynch’d...

1/8 https://www.biorxiv.org/content/10.1101/2020.10.01.322487v1

A typical eukaryotic cell contains two copies its nuclear genome and up to thousands of copies of its organellar genomes. Thus, it costs a cell more to encode a gene in the organellar genome than in the nuclear genome.

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For example, a 1kb gene costs 2kb of DNA in the nuclear genome and 5mb of DNA in mitochondrial genome of humans. Similarly, it would cost ~1.5mb of DNA in the chloroplast genome of plants.

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I thought that if the energy saved by transferring a gene from the organellar genome to the nuclear genome offset the cost of importing gene product (protein) back into the organelle, then this would provide an energetic advantage to any cell that managed to do it.

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I show for a wide range of estimates for host cell complexity, cellular investment in organelles, and organellar protein import costs, that it is more energy efficient for the cell to transfer the majority of organellar genes to the nuclear genome and re-import the proteins

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I then show that the energy saving for the nuclear transfer the majority of organellar genes is sufficient to impart a substantive selective advantage that would enable any such events to rapidly reach fixation

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Thus, I think organelles have surrendered the vast majority of their genes for the sake of the greater good of the cell.

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P.S. before you all try to kill me. I don’t think this discovery negates any other hypothesis for why genes transfer from the organellar to the nuclear genome. Biology is beautiful and complex. This helps us understand a bit more why endosymbiotic gene transfer is inevitable.
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