Editing Chloroplast (section)

=== Secondary and tertiary endosymbiosis ===

{{plain image with caption|File:Chloroplast secondary endosymbiosis.svg|Secondary endosymbiosis consisted of a [[eukaryote|eukaryotic]] [[Algae|alga]] being engulfed by another eukaryote, forming a chloroplast with three or four membranes.|600px|right|bottom|triangle|#71d7ff}}

Many other organisms obtained chloroplasts from the primary chloroplast lineages through secondary endosymbiosis—engulfing a red or green alga with a primary chloroplast. These chloroplasts are known as '''secondary plastids'''.<ref name="Wise-2006b" />

As a result of the secondary endosymbiotic event, secondary chloroplasts have additional membranes outside of the original two in primary chloroplasts.<ref name="Keeling-2004">{{cite journal |vauthors=Keeling PJ |date=October 2004 |title=Diversity and evolutionary history of plastids and their hosts |journal=American Journal of Botany |volume=91 |issue=10 |pages=1481–93 |doi=10.3732/ajb.91.10.1481 |pmid=21652304 |s2cid=17522125 |doi-access=free}}</ref> In secondary plastids, typically only the chloroplast, and sometimes its [[cell membrane]] and [[Cell nucleus|nucleus]] remain, forming a chloroplast with three or four membranes<ref name="Chaal-2005">{{cite journal |vauthors=Chaal BK, Green BR |date=February 2005 |title=Protein import pathways in 'complex' chloroplasts derived from secondary endosymbiosis involving a red algal ancestor |journal=Plant Molecular Biology |volume=57 |issue=3 |pages=333–42 |doi=10.1007/s11103-004-7848-y |pmid=15830125 |s2cid=22619029}}</ref>—the two cyanobacterial membranes, sometimes the eaten alga's cell membrane, and the [[phagosomal vacuole]] from the host's cell membrane.<ref name="Keeling-2004" />

The genes in the phagocytosed eukaryote's nucleus are often transferred to the secondary host's nucleus.<ref name="Keeling-2004" /> [[Cryptomonad]]s and [[chlorarachniophyte]]s retain the phagocytosed eukaryote's nucleus, an object called a [[nucleomorph]],<ref name="Keeling-2004" /> located between the second and third membranes of the chloroplast.<ref name="Kim-2009" /><ref name="McFadden-2001" />

All secondary chloroplasts come from [[green algae|green]] and [[red algae]]. No secondary chloroplasts from [[glaucophytes]] have been observed, probably because glaucophytes are relatively rare in nature, making them less likely to have been taken up by another eukaryote.<ref name="Keeling-2004" />

Still other organisms, including the dinoflagellates ''[[Karlodinium]]'' and ''[[Karenia (dinoflagellate)|Karenia]],'' obtained chloroplasts by engulfing an organism with a secondary plastid. These are called '''tertiary plastids'''.<ref name="Wise-2006b" />
[[File:Chloroplast Cladogram.svg|alt=Cladogram of chloroplast evolution|center|thumb|800x800px|'''Possible cladogram of chloroplast evolution'''<ref name="Keeling-2004" /><ref name="McFadden-2004">{{cite journal |last1=McFadden |first1=Geoffrey I. |last2=Van Dooren |first2=Giel G. |date=2004 |title=Evolution: Red Algal Genome Affirms a Common Origin of All Plastids |journal=Current Biology |volume=14 |issue=13 |pages=R514–R516 |bibcode=2004CBio...14.R514M |doi=10.1016/j.cub.2004.06.041 |pmid=15242632}}</ref><ref name="Keeling-2010" /> Circles represent [[endosymbiotic]] events. For clarity, [[dinophyte]] tertiary endosymbioses and many nonphotosynthetic lineages have been omitted.
----<small><sup>'''a'''</sup> It is now established that [[Chromalveolata]] is [[paraphyletic]] to [[Rhizaria]].<ref name="Keeling-2010" /></small>]]