Editing Plastid (section)

==Origin==
Plastids are thought to be descended from [[endosymbiosis|endosymbiotic]] [[cyanobacteria]]. The primary endosymbiotic event of the Archaeplastida is hypothesized to have occurred around 1.5 billion years ago<ref>{{cite journal | vauthors = Ochoa de Alda JA, Esteban R, Diago ML, Houmard J | title = The plastid ancestor originated among one of the major cyanobacterial lineages | journal = Nature Communications | volume = 5 | pages = 4937 | date = September 2014 | pmid = 25222494 | doi = 10.1038/ncomms5937 | bibcode = 2014NatCo...5.4937O | doi-access = free }}</ref> and enabled eukaryotes to carry out [[Carbon fixation#Oxygenic photosynthesis|oxygenic photosynthesis]].<ref>{{cite journal | vauthors = Hedges SB, Blair JE, Venturi ML, Shoe JL | title = A molecular timescale of eukaryote evolution and the rise of complex multicellular life | journal = BMC Evolutionary Biology | volume = 4 | pages = 2 | date = January 2004 | pmid = 15005799 | pmc = 341452 | doi = 10.1186/1471-2148-4-2 | doi-access = free }}</ref> Three evolutionary lineages in the Archaeplastida have since emerged in which the plastids are named differently: chloroplasts in [[green algae]] and/or plants, [[rhodoplast]]s in [[red algae]], and [[muroplast]]s in the glaucophytes. The plastids differ both in their pigmentation and in their ultrastructure. For example, chloroplasts in plants and green algae have lost all [[phycobilisomes]], the [[light harvesting complex]]es found in cyanobacteria, red algae and glaucophytes, but instead contain [[Stroma (fluid)|stroma]] and grana [[thylakoid]]s. The glaucocystophycean plastid—in contrast to chloroplasts and rhodoplasts—is still surrounded by the remains of the cyanobacterial cell wall. All these primary plastids are surrounded by two membranes.

The plastid of photosynthetic ''[[Paulinella]]'' species is often referred to as the 'cyanelle' or chromatophore, and had a much more recent endosymbiotic event about 90–140 million years ago; it is the only known primary endosymbiosis event of cyanobacteria outside of the Archaeplastida.<ref name="Nature 2019"/><ref name="Gabr Grossman Bhattacharya pp. 837–843"/> The plastid belongs to the "PS-clade" (of the cyanobacteria genera ''[[Prochlorococcus]]'' and ''[[Synechococcus]]''), which is a different sister clade to the plastids belonging to the Archaeplastida.<ref name="Marin Nowack Glöckner Melkonian 2021 p. "/><ref name="Ochoa de Alda-2014" />

In contrast to primary plastids derived from primary endosymbiosis of a prokaryoctyic cyanobacteria, complex plastids originated by secondary [[endosymbiosis]] in which a eukaryotic organism engulfed another eukaryotic organism that contained a primary plastid.<ref>{{Cite journal|title = The Origin of Plastids |url = http://www.nature.com/scitable/topicpage/the-origin-of-plastids-14125758|journal=Nature Education|page=84|volume=3|issue=9|year=2010| vauthors = Chan CX, Bhattachary D }}</ref> When a [[eukaryote]] engulfs a red or a green alga and retains the algal plastid, that plastid is typically surrounded by more than two membranes. In some cases these plastids may be reduced in their metabolic and/or photosynthetic capacity. Algae with complex plastids derived by secondary endosymbiosis of a red alga include the [[heterokont]]s, [[haptophyte]]s, [[cryptomonads]], and most [[dinoflagellate]]s (= rhodoplasts). Those that endosymbiosed a green alga include the [[euglenid]]s and [[chlorarachniophyte]]s (= chloroplasts). The [[Apicomplexa]], a phylum of [[Obligate parasite|obligate parasitic]] [[alveolates]] including the causative agents of [[malaria]] (''[[Plasmodium]]'' spp.), [[toxoplasmosis]] (''[[Toxoplasma gondii]]''), and many other human or animal diseases also harbor a complex plastid (although this organelle has been lost in some apicomplexans, such as ''[[Cryptosporidium parvum]]'', which causes [[cryptosporidiosis]]). The '[[apicoplast]]' is no longer capable of photosynthesis, but is an essential organelle, and a promising [[drug target|target]] for [[antiparasitic drug]] development.

Some [[dinoflagellates]] and [[sea slug]]s, in particular of the genus ''[[Elysia (gastropod)|Elysia]]'', take up algae as food and keep the plastid of the digested alga to profit from the photosynthesis; after a while, the plastids are also digested. This process is known as [[kleptoplasty]], from the Greek, ''kleptes'' ({{wikt-lang|grc|κλέπτης}}), thief.