Editing Plant hormone (section)

===Brassinosteroids===
[[File:Brassinolide.png|thumb|Brassinolide, a major brassinosteroid|155px]]
[[Brassinosteroid]]s (BRs) are a class of polyhydroxysteroids, the only example of steroid-based hormones in plants. Brassinosteroids control cell elongation and division, [[gravitropism]], resistance to stress, and [[xylem]] differentiation. They inhibit root growth and leaf abscission. [[Brassinolide]] was the first brassinosteroid to be identified and was isolated from extracts of rapeseed (''[[Brassica napus]]'') pollen in 1979.<ref>{{cite journal | vauthors = Grove MD, Spencer GF, Rohwedder WK, Mandava N, Worley JF, Warthen JD, Steffens GL, Flippen-Anderson JL, Cook JC | display-authors = 6 |year=1979|title=Brassinolide, a plant growth-promoting steroid isolated from Brassica napus pollen|journal=Nature|volume=281|issue=5728|pages=216–217|bibcode=1979Natur.281..216G|doi=10.1038/281216a0| s2cid = 4335601 }}</ref> Brassinosteroids are a class of steroidal phytohormones in plants that regulate numerous physiological processes. This plant hormone was identified by Mitchell et al. who extracted ingredients from Brassica pollen only to find that the extracted ingredients’ main active component was [[Brassinolide]].<ref name="Tang 113">{{cite journal | vauthors = Tang J, Han Z, Chai J | title = Q&A: what are brassinosteroids and how do they act in plants? | journal = BMC Biology | volume = 14 | issue = 1 | pages = 113 | date = December 2016 | pmid = 28007032 | pmc = 5180403 | doi = 10.1186/s12915-016-0340-8 | doi-access = free }}</ref> This finding meant the discovery of a new class of plant hormones called Brassinosteroids. These hormones act very similarly to animal steroidal hormones by promoting growth and development.

In plants these steroidal hormones play an important role in cell elongation via BR signaling.<ref>{{cite journal | vauthors = Yamagami A, Saito C, Nakazawa M, Fujioka S, Uemura T, Matsui M, Sakuta M, Shinozaki K, Osada H, Nakano A, Asami T, Nakano T | display-authors = 6 | title = Evolutionarily conserved BIL4 suppresses the degradation of brassinosteroid receptor BRI1 and regulates cell elongation | journal = Scientific Reports | volume = 7 | issue = 1 | pages = 5739 | date = July 2017 | pmid = 28720789 | pmc = 5515986 | doi = 10.1038/s41598-017-06016-2 | bibcode = 2017NatSR...7.5739Y }}</ref> The brassinosteroids receptor brassinosteroid insensitive 1 (BRI1) is the main receptor for this signaling pathway. This BRI1 receptor was found by Clouse et al. who made the discovery by inhibiting BR and comparing it to the wildtype in Arabidopsis. The BRI1 mutant displayed several problems associated with growth and development such as [[dwarfism]], reduced cell elongation and other physical alterations.<ref name="Tang 113" /> These findings mean that plants properly expressing brassinosteroids grow more than their mutant counterparts. Brassinosteroids bind to BRI1 localized at the plasma membrane<ref>{{cite journal | vauthors = Yamagami A, Nakazawa M, Matsui M, Tujimoto M, Sakuta M, Asami T, Nakano T | title = Chemical genetics reveal the novel transmembrane protein BIL4, which mediates plant cell elongation in brassinosteroid signaling | journal = Bioscience, Biotechnology, and Biochemistry | volume = 73 | issue = 2 | pages = 415–421 | date = February 2009 | pmid = 19202280 | doi = 10.1271/bbb.80752 | s2cid = 35568960 | doi-access = free }}</ref> which leads to a signal cascade that further regulates cell elongation. This signal cascade however is not entirely understood at this time. What is believed to be happening is that BR binds to the BAK1 complex which leads to a [[Phosphorylation cascade|phosphorylation]] cascade.<ref name="Planas-Riverola dev151894">{{cite journal | vauthors = Planas-Riverola A, Gupta A, Betegón-Putze I, Bosch N, Ibañes M, Caño-Delgado AI | title = Brassinosteroid signaling in plant development and adaptation to stress | journal = Development | volume = 146 | issue = 5 | pages = dev151894 | date = March 2019 | pmid = 30872266 | pmc = 6432667 | doi = 10.1242/dev.151894 }}</ref> This phosphorylation cascade then causes BIN2 to be deactivated which causes the release of [[transcription factor]]s.<ref name="Planas-Riverola dev151894" /> These released transcription factors then bind to DNA that leads to growth and developmental processes<ref name="Planas-Riverola dev151894" /> and allows plants to respond to [[abiotic stress]]ors.<ref>{{Cite journal| vauthors = Ahammed GJ, Li X, Liu A, Chen S |date=19 March 2020|title=Brassinosteroids in Plant Tolerance to Abiotic Stress|url=http://link.springer.com/10.1007/s00344-020-10098-0|journal=Journal of Plant Growth Regulation|language=en|volume=39|issue=4|pages=1451–1464|doi=10.1007/s00344-020-10098-0|s2cid=213166792|issn=0721-7595|url-access=subscription}}</ref>