Editing ABC transporter (section)

=== Plant transporters ===
The genome of the model plant ''Arabidopsis thaliana'' is capable of encoding 120 ABC proteins compared to 50-70 ABC proteins that are encoded by the human genome and fruit flies (''[[Drosophila melanogaster]]'').  Plant ABC proteins are categorized in 13 subfamilies on the basis of size (full, half or quarter), orientation, and overall amino acid sequence similarity.<ref name="Rea_2007">{{cite journal | vauthors = Rea PA | title = Plant ATP-binding cassette transporters | journal = Annual Review of Plant Biology | volume = 58 | pages = 347–75 | year = 2007 | issue = 1 | pmid = 17263663 | doi = 10.1146/annurev.arplant.57.032905.105406 | bibcode = 2007AnRPB..58..347R }}</ref> Multidrug resistant (MDR) homologs, also known as P-glycoproteins, represent the largest subfamily in plants with 22 members and the second largest overall ABC subfamily. The B subfamily of plant ABC transporters (ABCBs) are characterized by their localization to the plasma membrane.<ref name="Bailly_Yang_2012">{{cite journal | vauthors = Bailly A, Yang H, Martinoia E, Geisler M, Murphy AS | title = Plant Lessons: Exploring ABCB Functionality Through Structural Modeling | journal = Frontiers in Plant Science | volume = 2 | pages = 108 | year = 2011 | pmid = 22639627 | pmc = 3355715 | doi = 10.3389/fpls.2011.00108 | doi-access = free }}</ref> Plant ABCB transporters are characterized by heterologously expressing them in ''Escherichia coli'', ''[[Saccharomyces cerevisiae]]'', ''[[Schizosaccharomyces pombe]]'' (fission yeast), and [[HeLa]] cells to determine substrate specificity. 
Plant ABCB transporters have shown to transport the phytohormone indole-3-acetic acid ( IAA),<ref name="Geisler_Murphy_2006">{{cite journal | vauthors = Geisler M, Murphy AS | title = The ABC of auxin transport: the role of p-glycoproteins in plant development | journal = FEBS Letters | volume = 580 | issue = 4 | pages = 1094–102 | date = Feb 2006 | pmid = 16359667 | doi = 10.1016/j.febslet.2005.11.054 | s2cid = 23368914 | doi-access =  | bibcode = 2006FEBSL.580.1094G }}</ref> also known as [[auxin]], the essential regulator for plant growth and development.<ref name="Yang_Murphy_2009">{{cite journal | vauthors = Yang H, Murphy AS | title = Functional expression and characterization of Arabidopsis ABCB, AUX 1 and PIN auxin transporters in Schizosaccharomyces pombe | journal = The Plant Journal | volume = 59 | issue = 1 | pages = 179–91 | date = Jul 2009 | pmid = 19309458 | doi = 10.1111/j.1365-313X.2009.03856.x | doi-access = free }}</ref><ref name="Blakeslee_Peer_2005">{{cite journal | vauthors = Blakeslee JJ, Peer WA, Murphy AS | title = Auxin transport | journal = Current Opinion in Plant Biology | volume = 8 | issue = 5 | pages = 494–500 | date = Oct 2005 | pmid = 16054428 | doi = 10.1016/j.pbi.2005.07.014 | bibcode = 2005COPB....8..494B }}</ref> The directional polar transport of auxin mediates plant environmental responses through processes such as phototropism and gravitropism.<ref name="Kretzschmar_Burla_2011">{{cite journal | vauthors = Kretzschmar T, Burla B, Lee Y, Martinoia E, Nagy R | title = Functions of ABC transporters in plants | journal = Essays in Biochemistry | volume = 50 | issue = 1 | pages = 145–60 | date = Sep 2011 | pmid = 21967056 | doi = 10.1042/bse0500145 | url = https://www.zora.uzh.ch/id/eprint/53838/1/Kretzschmar_EssaysBiochem_2011.pdf }}</ref> Two of the best studied auxin transporters, ABCB1 and ABCB19, have been characterized to be primary auxin exporters<ref name="Yang_Murphy_2009"/> Other ABCB transporters such as ABCB4 participate in both the export and import of auxin<ref name="Yang_Murphy_2009"/> At low intracellular auxin concentrations ABCB4 imports auxin until it reaches a certain threshold which then reverses function to only export auxin.<ref name="Yang_Murphy_2009"/><ref name="KubešYang2012">{{cite journal | vauthors = Kubeš M, Yang H, Richter GL, Cheng Y, Młodzińska E, Wang X, Blakeslee JJ, Carraro N, Petrášek J, Zažímalová E, Hoyerová K, Peer WA, Murphy AS | title = The Arabidopsis concentration-dependent influx/efflux transporter ABCB4 regulates cellular auxin levels in the root epidermis | journal = The Plant Journal | volume = 69 | issue = 4 | pages = 640–54 | date = Feb 2012 | pmid = 21992190 | doi = 10.1111/j.1365-313X.2011.04818.x }}</ref>