Re: Primary endosymbiosis caught in the act

On 18/04/2024 19:04, Chris Thompson wrote:

Is it true that primary endosymbiosis is thought to have happened only twice? I'm a little dubious about that. But this is still cool.
 "Scientists have caught a once-in-a-billion-years evolutionary event in progress, as two lifeforms have merged into one organism that boasts abilities its peers would envy. Last time this happened, Earth got plants."
  https://newatlas.com/biology/life-merger-evolution-symbiosis-organelle/
 

One bit I'd found interesting that I didn't know when this article (or another one about the same paper) was posted earlier was that apparently symbioses of plants with N2-fixing bacteria date back to the Cretaceous - both for algae and land plants even though they do it completely differently!
I'm also dubious about it having happened twice, I thought plants had several plastids corresponding to more than one endosymbiotic event. But maybe they simplified things for effect, mitochondria and chloroplasts are the big ones everyone knows about. Of course (of course).
Checking that famous drawing of the tree of life with different endosymbiosis events that I thought included several, it does seem to only have the mitochondria and chloroplast one after all:
https://www.researchgate.net/figure/Schematic-Diagram-of-Symbiosis-in-the-Tree-of-Life-and-the-Union-of-the-Bacterial-and_fig1_332956942