Editing Photosynthesis (section)

===Symbiosis and the origin of chloroplasts===
[[File:Plagiomnium affine laminazellen.jpeg|thumb|left|Plant cells with visible chloroplasts (from a moss, ''[[Plagiomnium affine]]'')]]

Several groups of [[animal]]s have formed [[symbiosis|symbiotic]] relationships with photosynthetic [[algae]]. These are most common in [[coral]]s, [[sponge]]s, and [[sea anemone]]s. [[Scientist]]s presume that this is due to the particularly simple [[body plan]]s and large [[surface area]]s of these animals compared to their [[volume]]s.<ref>{{cite journal |vauthors= Venn AA, Loram JE, Douglas AE |title= Photosynthetic symbioses in animals |journal= Journal of Experimental Botany |volume= 59 |issue= 5 |pages= 1069–1080 |year= 2008 |pmid= 18267943 |doi= 10.1093/jxb/erm328 |doi-access= free }}</ref> In addition, a few marine [[mollusks]], such as ''[[Elysia viridis]]'' and ''[[Elysia chlorotica]],'' also maintain a symbiotic relationship with [[chloroplast]]s they capture from the algae in [[Mollusca#Eating, digestion, and excretion|their diet]] and then store in their bodies (see [[Kleptoplasty]]). This allows the mollusks to survive solely by photosynthesis for several months at a time.<ref>{{cite journal |vauthors= Rumpho ME, Summer EJ, Manhart JR |date= May 2000 |title= Solar-powered sea slugs. Mollusc/algal chloroplast symbiosis |journal= Plant Physiology |volume= 123 |issue= 1 |pages= 29–38 |doi= 10.1104/pp.123.1.29 |pmc= 1539252 |pmid= 10806222 }}</ref><ref>{{Cite book |vauthors= Muscatine L, Greene RW |year= 1973 |title= Chloroplasts and Algae as Symbionts in Molluscs |series= International Review of Cytology |volume= 36 |pages= 137–169 |isbn= 978-0-12-364336-0 |pmid= 4587388 |doi= 10.1016/S0074-7696(08)60217-X }}</ref> Some of the [[gene]]s from the plant [[cell nucleus]] have even been transferred to the [[slug]]s, so that the chloroplasts can be supplied with [[protein]]s they need to survive.<ref>{{cite journal |vauthors= Rumpho ME, Worful JM, Lee J, Kannan K, Tyler MS, Bhattacharya D, Moustafa A, Manhart JR |date= November 2008 |title= Horizontal gene transfer of the algal nuclear gene psbO to the photosynthetic sea slug Elysia chlorotica |journal= Proceedings of the National Academy of Sciences of the United States of America |volume= 105 |issue= 46 |pages= 17867–17871 |bibcode= 2008PNAS..10517867R |doi= 10.1073/pnas.0804968105 |doi-access= free |pmc= 2584685 |pmid= 19004808 }}</ref>

An even closer form of symbiosis may explain the origin of chloroplasts. Chloroplasts have many similarities with photosynthetic [[bacteria]], including a circular [[chromosome]], prokaryotic-type [[ribosome]], and similar [[Photosynthetic reaction centre protein family|proteins in the photosynthetic reaction center]].<ref>{{cite journal |vauthors= Douglas SE |date= December 1998 |title= Plastid evolution: origins, diversity, trends |journal= Current Opinion in Genetics & Development |volume= 8 |issue= 6 |pages= 655–661 |doi= 10.1016/S0959-437X(98)80033-6 |pmid= 9914199 }}</ref><ref>{{cite journal |vauthors=Reyes-Prieto A, Weber AP, Bhattacharya D |year=2007 |title=The origin and establishment of the plastid in algae and plants |journal=Annual Review of Genetics |volume=41 |pages=147–168 |doi=10.1146/annurev.genet.41.110306.130134 |pmid=17600460 |s2cid=8966320}}</ref> The [[endosymbiotic theory]] suggests that photosynthetic bacteria were acquired (by [[endocytosis]]) by early [[eukaryotic]] cells to form the first plant cells. Therefore, chloroplasts may be photosynthetic bacteria that adapted to life inside plant cells. Like [[mitochondria]], chloroplasts possess their own [[DNA]], separate from the [[nuclear DNA]] of their plant host cells and the genes in this chloroplast DNA resemble those found in [[cyanobacteria]].<ref>{{cite journal |vauthors= Raven JA, Allen JF |year= 2003 |title= Genomics and chloroplast evolution: what did cyanobacteria do for plants? |journal= Genome Biology |volume= 4 |issue= 3 |page= 209 |doi= 10.1186/gb-2003-4-3-209 |doi-access= free |pmc= 153454 |pmid= 12620099 }}</ref> DNA in chloroplasts codes for [[redox]] proteins such as those found in the photosynthetic reaction centers. The [[CoRR Hypothesis]] proposes that this co-location of genes with their gene products is required for redox regulation of [[gene expression]], and accounts for the persistence of DNA in bioenergetic [[organelle]]s.<ref>{{cite journal |vauthors= Allen JF |date= December 2017 |title= The CoRR hypothesis for genes in organelles |journal= Journal of Theoretical Biology |volume= 434 |pages= 50–57 |bibcode= 2017JThBi.434...50A |doi= 10.1016/j.jtbi.2017.04.008 |doi-access= free |pmid= 28408315 }}</ref>