Просмотр кода страницы Triangle of U

{{Short description|Evolutionary history of Brassica genus}}
[[File:Triangle of U Simple1.PNG|thumb|right|360px|alt=Triangle of U|The "triangle of U" diagram, showing the genetic relationships among six species of the genus ''Brassica''. Chromosomes from each of the genomes A, B and C are represented by different colours.]]

The '''triangle of U''' ({{IPAc-en|uː}} {{respell|OO}}) is a theory about the evolution and relationships among the six most commonly known members of the plant genus ''[[Brassica]]''. The theory states that the [[genomes]] of three ancestral [[diploid]] species of ''Brassica'' combined to create three common [[tetraploid]] [[vegetable]]s and [[Vegetable fats and oils|oilseed]] crop species.<ref name=jules2009>{{cite book |title=Plant Breeding Reviews |last=Jules |first=Janick |year=2009 |volume=31 |publisher=Wiley |isbn=978-0-470-38762-7 |page=56 |url=http://as.wiley.com/WileyCDA/WileyTitle/productCd-0470387629.html}}</ref> It has been confirmed by studies of DNA and proteins.<ref name=pmid32595682>{{cite journal |last1=Xue |first1=JY |last2=Wang |first2=Y |last3=Chen |first3=M |last4=Dong |first4=S |last5=Shao |first5=ZQ |last6=Liu |first6=Y |title=Maternal Inheritance of U's Triangle and Evolutionary Process of ''Brassica'' Mitochondrial Genomes. |journal=Frontiers in Plant Science |date=2020 |volume=11 |article-number=805 |doi=10.3389/fpls.2020.00805 |doi-access=free |pmid=32595682 |pmc=7303332 |bibcode=2020FrPS...11..805X |quote=Comparative genomic analyses can assign the subgenomes of the allotetraploids, B. juncea and B. napus, with their diploid parental taxa, and the results were in agreement with U's triangle (Chalhoub et al., 2014; Yang et al., 2016a). [...] }}</ref>

The theory is summarized by a triangular diagram that shows the three ancestral genomes, denoted by AA, BB, and CC, at the corners of the triangle, and the three derived ones, denoted by AABB, AACC, and BBCC, along its sides.

The theory was first published in 1935 by [[Woo Jang-choon]],<ref name=woo1935>{{cite journal |author=Nagaharu U |year=1935 |title=Genome analysis in Brassica with special reference to the experimental formation of B. napus and peculiar mode of fertilization |journal=Japan. J. Bot |volume=7 |pages=389–452|author-link=Woo Jang-choon }}</ref> a [[Korean people|Korean]]-[[Japanese people|Japanese]] [[botanist]] (writing under the Japanized name "U Nagaharu").<ref>{{cite web |url=http://junior.sciencetimes.co.kr/data/article/7000/0000006890.jsp |title=인터넷 과학신문 사이언스 타임즈 |language=ko |archive-url=https://web.archive.org/web/20070927014758/http://junior.sciencetimes.co.kr/data/article/7000/0000006890.jsp |archive-date=2007-09-27 }}</ref> Woo made synthetic hybrids between the [[diploid]] and [[tetraploid]] species and examined how the chromosomes paired in the resulting triploids.

==Woo's theory==
The six species are

{| class = wikitable
! Genomes !! Chr. count !! Species !! Description
|-
| colspan=4 style="text-align:center;" | '''Diploid'''
|-
| '''AA''' || 2{{var|n}}=2{{var|x}}=20 || ''[[Brassica rapa]]'' || (syn. ''B. campestris'') [[turnip]], [[napa cabbage]], [[bok choi]]
|-
| '''BB''' || 2{{var|n}}=2{{var|x}}=16 || ''[[Brassica nigra]]'' || [[black mustard]]
|-
| '''CC''' || 2{{var|n}}=2{{var|x}}=18 || ''[[Brassica oleracea]]'' || [[cabbage]], [[kale]], [[broccoli]], [[Brussels sprouts]], [[cauliflower]], [[kohlrabi]]
|-
| colspan=4 style="text-align:center;" | '''Tetraploid'''
|-
| '''AABB''' || 2{{var|n}}=4{{var|x}}=36 || ''[[Brassica juncea]]'' || [[Brown mustard]]
|-
| '''AACC''' || 2{{var|n}}=4{{var|x}}=38 || ''[[Brassica napus]]'' || [[rapeseed]], [[rutabaga]]
|-
| '''BBCC''' || 2{{var|n}}=4{{var|x}}=34 || ''[[Brassica carinata]]'' || [[Ethiopian mustard]]
|}

The code in the "Chr.count" column specifies the total number of chromosomes in each somatic cell, and how it relates to the number {{var|n}} of [[chromosome]]s in each full genome set (which is also the number found in the pollen or [[ovule]]), and the number {{var|x}} of chromosomes in each component genome. For example, each somatic cell of the tetraploid species ''Brassica napus'', with letter tags AACC and count "2{{var|n}}=4{{var|x}}=38", contains two copies of the A genome, each with 10 chromosomes, and two copies of the C genome, each with 9 chromosomes, which is 38 chromosomes in total. That is two full genome sets (one A and one C), hence "2{{var|n}}=38" which means "{{var|n}}=19" (the number of chromosomes in each [[gamete]]). It is also four component genomes (two A and two C), hence "4{{var|x}}=38".<ref name=pmid32595682/>

The three diploid species exist in nature, but can easily interbreed because they are closely related.  This [[interspecific breeding]] allowed for the creation of three new species of tetraploid ''Brassica''.<ref name=woo1935/> (Critics, however, consider the geological separation too large.)  These are said to be [[allotetraploid]] (containing four genomes from two or more different species); more specifically, [[amphidiploid]] (with two genomes each from two diploid species).<ref name=pmid32595682/>

== Further relationships ==
The framework proposed by Woo, although backed by modern studies, leaves open questions about the time and place of hybridization and which species is the maternal or paternal parent. ''B. napus'' (AACC) is dated to have originated about 8,000<ref name=pmid25146293/> or 38,000&ndash;51,000<ref name=pmid27595476>{{cite journal |last1=Yang |first1=J |last2=Liu |first2=D |last3=Wang |first3=X |last4=Ji |first4=C |last5=Cheng |first5=F |last6=Liu |first6=B |last7=Hu |first7=Z |last8=Chen |first8=S |last9=Pental |first9=D |last10=Ju |first10=Y |last11=Yao |first11=P |last12=Li |first12=X |last13=Xie |first13=K |last14=Zhang |first14=J |last15=Wang |first15=J |last16=Liu |first16=F |last17=Ma |first17=W |last18=Shopan |first18=J |last19=Zheng |first19=H |last20=Mackenzie |first20=SA |last21=Zhang |first21=M |title=The genome sequence of allopolyploid Brassica juncea and analysis of differential homoeolog gene expression influencing selection. |journal=Nature Genetics |date=October 2016 |volume=48 |issue=10 |pages=1225–32 |doi=10.1038/ng.3657 |pmid=27595476 |doi-access=free}}</ref> years ago. The homologous part of its constituent chromosomes has [[Chromosomal crossover|crossed over]] in many cultivars.<ref name=pmid25146293>{{cite journal |last1=Chalhoub |first1=B |last2=Denoeud |first2=F |last3=Liu |first3=S |last4=Parkin |first4=IA |last5=Tang |first5=H |last6=Wang |first6=X |last7=Chiquet |first7=J |last8=Belcram |first8=H |last9=Tong |first9=C |last10=Samans |first10=B |last11=Corréa |first11=M |last12=Da Silva |first12=C |last13=Just |first13=J |last14=Falentin |first14=C |last15=Koh |first15=CS |last16=Le Clainche |first16=I |last17=Bernard |first17=M |last18=Bento |first18=P |last19=Noel |first19=B |last20=Labadie |first20=K |last21=Alberti |first21=A |last22=Charles |first22=M |last23=Arnaud |first23=D |last24=Guo |first24=H |last25=Daviaud |first25=C |last26=Alamery |first26=S |last27=Jabbari |first27=K |last28=Zhao |first28=M |last29=Edger |first29=PP |last30=Chelaifa |first30=H |last31=Tack |first31=D |last32=Lassalle |first32=G |last33=Mestiri |first33=I |last34=Schnel |first34=N |last35=Le Paslier |first35=MC |last36=Fan |first36=G |last37=Renault |first37=V |last38=Bayer |first38=PE |last39=Golicz |first39=AA |last40=Manoli |first40=S |last41=Lee |first41=TH |last42=Thi |first42=VH |last43=Chalabi |first43=S |last44=Hu |first44=Q |last45=Fan |first45=C |last46=Tollenaere |first46=R |last47=Lu |first47=Y |last48=Battail |first48=C |last49=Shen |first49=J |last50=Sidebottom |first50=CH |last51=Wang |first51=X |last52=Canaguier |first52=A |last53=Chauveau |first53=A |last54=Bérard |first54=A |last55=Deniot |first55=G |last56=Guan |first56=M |last57=Liu |first57=Z |last58=Sun |first58=F |last59=Lim |first59=YP |last60=Lyons |first60=E |last61=Town |first61=CD |last62=Bancroft |first62=I |last63=Wang |first63=X |last64=Meng |first64=J |last65=Ma |first65=J |last66=Pires |first66=JC |last67=King |first67=GJ |last68=Brunel |first68=D |last69=Delourme |first69=R |last70=Renard |first70=M |last71=Aury |first71=JM |last72=Adams |first72=KL |last73=Batley |first73=J |last74=Snowdon |first74=RJ |last75=Tost |first75=J |last76=Edwards |first76=D |last77=Zhou |first77=Y |last78=Hua |first78=W |last79=Sharpe |first79=AG |last80=Paterson |first80=AH |last81=Guan |first81=C |last82=Wincker |first82=P |title=Plant genetics. Early allopolyploid evolution in the post-Neolithic Brassica napus oilseed genome. |journal=Science |date=22 August 2014 |volume=345 |issue=6199 |pages=950–3 |doi=10.1126/science.1253435 |pmid=25146293 |s2cid=206556986 |url=https://www.researchgate.net/publication/267755510}}</ref> ''B. juncea'' (AABB) is estimated to have originated 39,000&ndash;55,000 years ago.<ref name=pmid27595476/> As of 2020, research on organellar genomes shows that ''B. nigra'' (BB) is likely the "mother" of ''B. carinata'' (BBCC) and that ''B. rapa'' (AA) likely mothered ''B. juncea''. The situation with ''B. napus'' (AACC) is more complex: some specimens have a ''rapa''-like organellar genome, while the rest indicate an ancient, unidentified maternal plant.<ref name=pmid32595682/>

Data from molecular studies indicate the three diploid species are themselves [[paleopolyploid|paleohexaploid]]s.<ref>{{cite journal
 |author1=Martin A. Lysak |author2=Kwok Cheung |author3=Michaela Kitschke |author4=Petr Bu  |name-list-style=amp |date= October 2007
 | title = Ancestral Chromosomal Blocks Are Triplicated in Brassiceae Species with Varying Chromosome Number and Genome Size
 | journal = Plant Physiology
 | pmid = 17720758
 | volume = 145
 | issue = 2
 | pmc = 2048728| pages = 402–10
 | doi = 10.1104/pp.107.104380
 | url = http://www.plantphysiol.org/cgi/reprint/145/2/402
 | format = PDF
 | access-date = 2010-08-22
 }}</ref><ref>{{cite journal |last1=Murat |first1=Florent |last2=Louis |first2=Alexandra |last3=Maumus |first3=Florian |last4=Armero |first4=Alix |last5=Cooke |first5=Richard |last6=Quesneville |first6=Hadi |last7=Crollius |first7=Hugues Roest |last8=Salse |first8=Jerome |title=Understanding Brassicaceae evolution through ancestral genome reconstruction |journal=Genome Biology |date=December 2015 |volume=16 |issue=1 |page=262 |doi=10.1186/s13059-015-0814-y |pmid=26653025 |pmc=4675067 |doi-access=free}}</ref>

===Allohexaploid species===
In 2011 and 2018, novel [[wikt:allohexaploid|allohexaploid]]s (AABBCC) located at the "center" of the triangle of U were created by different means,<ref>{{Cite journal| doi = 10.1080/07352689.2011.615700| issn = 0735-2689| volume = 30| issue = 6| pages = 524–547| last1 = Chen| first1 = Sheng| last2 = Nelson| first2 = Matthew N.| last3 = Chèvre| first3 = Anne-Marie| last4 = Jenczewski| first4 = Eric| last5 = Li| first5 = Zaiyun| last6 = Mason| first6 = Annaliese S.| last7 = Meng| first7 = Jinling| last8 = Plummer| first8 = Julie A.| last9 = Pradhan| first9 = Aneeta| last10 = Siddique| first10 = Kadambot H. M.| last11 = Snowdon| first11 = Rod J.| last12 = Yan| first12 = Guijun| last13 = Zhou| first13 = Weijun| last14 = Cowling| first14 = Wallace A.| title = Trigenomic Bridges for Brassica Improvement| journal = Critical Reviews in Plant Sciences| date = 2011-11-01| bibcode = 2011CRvPS..30..524C| s2cid = 84504896}}</ref><ref>{{Cite journal| doi = 10.3389/fpls.2018.01161| issn = 1664-462X| volume = 9| article-number = 1161| last1 = Yang| first1 = Su| last2 = Chen| first2 = Sheng| last3 = Zhang| first3 = Kangni| last4 = Li| first4 = Lan| last5 = Yin| first5 = Yuling| last6 = Gill| first6 = Rafaqat A.| last7 = Yan| first7 = Guijun| last8 = Meng| first8 = Jinling| last9 = Cowling| first9 = Wallace A.| last10 = Zhou| first10 = Weijun| title = A High-Density Genetic Map of an Allohexaploid Brassica Doubled Haploid Population Reveals Quantitative Trait Loci for Pollen Viability and Fertility| journal = Frontiers in Plant Science| date = 2018-08-28| pmid = 30210508| pmc = 6123574| bibcode = 2018FrPS....9.1161Y| doi-access = free}}</ref><ref name=s2c91439428>{{Cite journal| doi = 10.1080/07352689.2018.1517143| issn = 0735-2689| volume = 37| issue = 5| pages = 422–437| last1 = Gaebelein| first1 = Roman| last2 = Mason| first2 = Annaliese S.| title = Allohexaploids in the Genus Brassica| journal = Critical Reviews in Plant Sciences| date = 2018-09-03| bibcode = 2018CRvPS..37..422G| s2cid = 91439428}}</ref> for example by crossing ''B. rapa'' (AA) with ''B. carinata'' (BBCC), or ''B. nigra'' (BB) with ''B. napus'' (AACC), or ''B. oleracea'' (CC) with ''B. juncea'' (AABB), followed by chromosome duplication of the triploid (ABC) offspring to generate [[doubled haploid]] (AABBCC) offspring.<ref name=s2c91439428/>

In addition, two stable allohexaploid (AABBSS) intergeneric hybrids between Indian mustard (''B. juncea'', AABB) and [[white mustard]] (''Sinapis alba'', SS) were created in 2020 by [[protoplast fusion]].<ref name="pmid33329636">{{cite journal| author=Kumari P, Singh KP, Kumar S, Yadava DK| title=Development of a Yellow-Seeded Stable Allohexaploid Brassica Through Inter-Generic Somatic Hybridization With a High Degree of Fertility and Resistance to Sclerotinia sclerotiorum. | journal=Front Plant Sci | year= 2020 | volume= 11 | issue=  | article-number= 575591 | pmid=33329636 | doi=10.3389/fpls.2020.575591 | pmc=7732669| bibcode=2020FrPS...1175591K | doi-access=free }}</ref>

==See also==
* [[Cultivar]]
* [[Hybrid (biology)|Hybridisation]]

==References==

<references/>

{{Brassica}}

[[Category:Genetics]]
[[Category:Brassica]]
[[Category:Hybrid plants]]