Plastid evolution

A plastid is a membrane-bound organelle found in plants, algae and other eukaryotic organisms that contribute to the production of pigment molecules.

Endosymbiosis is reputed to have led to the evolution of eukaryotic organisms today, although the timeline is highly debated.

[1] The first plastid is highly accepted within the scientific community to be derived from the engulfment of cyanobacteria ancestor into a eukaryotic organism.

When the cyanobacteria became engulfed, the bacterium avoided digestion and led to the double membrane found in primary plastids.

[4] However, in order to live in symbiosis, the eukaryotic cell that engulfed the cyanobacterium must now provide proteins and metabolites to maintain the functions of the bacteria in exchange for energy.

Thus, an engulfed cyanobacterium must give up some of its genetic material to allow for endosymbiotic gene transfer to the eukaryote, a phenomenon that is thought to be extremely rare due to the "learned nature" of the interactions that must occur between the cells to allow for processes such as; gene transfer, protein localization, excretion of highly reactive metabolites, and DNA repair.

[6][7][8] Separately, somewhere about 90–140 million years ago, primary endosymbiosis happened again in the amoeboid Paulinella with a cyanobacterium in the genus Prochlorococcus.

Although the cyanobacterium had not been completely engulfed in the eukaryotic organism, the relationship is thought to demonstrate the precursor to endosymbiotic primary plastids.

[13] Roughly 1 in every 5 million cells on the tobacco leaves highly expressed spectinomycin and kanamycin resistant genes.

Further, they only encode atpA, atpB, petB, perD, psaA, psaB, psbA-E, psbI, 16S and 23S rRNA.

[20][21] Two previously undescribed dinoflagellates ("MGD" and "TGD") contain a green algal endosymbioant that has a nucleus, most closely related to Pedinomonas.