Editing Self-incompatibility (section)

===Sporophytic self-incompatibility (SSI)===
In '''sporophytic self-incompatibility (SSI)''', the SI phenotype of the pollen is determined by the [[ploidity|diploid]] genotype of the [[anther]] (the [[sporophyte]]) in which it was created. This form of SI was identified in the families: [[Brassicaceae]], [[Asteraceae]], [[Convolvulaceae]], [[Betulaceae]], [[Caryophyllaceae]], [[Sterculiaceae]] and [[Polemoniaceae]].<ref>{{cite journal |doi=10.1038/hdy.1997.177 | vauthors = Goodwillie C |title=The genetic control of self-incompatibility in ''Linanthus parviflorus'' (Polemoniaceae) |journal=Heredity |volume=79 |pages=424–432 |year=1997 |issue=4|doi-access=free }}</ref> Up to this day, only one mechanism of SSI has been described in detail at the molecular level, in ''[[Brassica]]'' (Brassicaceae). {{cn|date=July 2024}}

Since SSI is determined by a diploid genotype, the pollen and pistil each express the translation products of two different alleles, i.e. two male and two female determinants. [[Dominance (genetics)|Dominance]] relationships often exist between pairs of alleles, resulting in complicated patterns of compatibility/self-incompatibility. These dominance relationships also allow the generation of individuals [[Zygosity|homozygous]] for a [[recessive]] S allele.<ref name="hiscock">{{cite journal | vauthors = Hiscock SJ, Tabah DA | title = The different mechanisms of sporophytic self-incompatibility | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 358 | issue = 1434 | pages = 1037–1045 | date = June 2003 | pmid = 12831470 | pmc = 1693206 | doi = 10.1098/rstb.2003.1297 | name-list-style = amp }}</ref>

Compared to a population in which all S alleles are [[co-dominance|co-dominant]], the presence of dominance relationships in the population raises the chances of compatible mating between individuals.<ref name="hiscock"/> The frequency ratio between recessive and dominant S alleles reflects a dynamic balance between [[reproductive assurance]] (favoured by recessive alleles) and avoidance of selfing (favoured by dominant alleles).<ref>{{cite journal | vauthors = Ockendon DJ |title=Distribution of self-incompatibility alleles and breeding structure of open-pollinated cultivars of Brussels sprouts |journal=Heredity |volume=32 |issue=2 |pages=159–171 |year=1974 |doi=10.1038/hdy.1974.84|doi-access=free }}</ref>

====The SI mechanism in ''Brassica''====
As previously mentioned, the SI phenotype of the pollen is determined by the diploid genotype of the anther. In ''[[Brassica]]'', the pollen coat, derived from the anther's [[tapetum (botany)|tapetum]] [[biological tissue|tissue]], carries the translation products of the two S alleles. These are small, [[cysteine]]-rich proteins. The male determinant is termed '''SCR''' or '''SP11''', and is expressed in the anther tapetum as well as in the [[microspore]] and pollen (i.e. sporophytically).<ref>{{cite journal | vauthors = Schopfer CR, Nasrallah ME, Nasrallah JB | title = The male determinant of self-incompatibility in ''Brassica'' | journal = Science | volume = 286 | issue = 5445 | pages = 1697–1700 | date = November 1999 | pmid = 10576728 | doi = 10.1126/science.286.5445.1697 }}</ref><ref>{{cite journal | vauthors = Takayama S, Shiba H, Iwano M, Shimosato H, Che FS, Kai N, Watanabe M, Suzuki G, Hinata K, Isogai A | display-authors = 6 | title = The pollen determinant of self-incompatibility in ''Brassica campestris'' | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 97 | issue = 4 | pages = 1920–1925 | date = February 2000 | pmid = 10677556 | pmc = 26537 | doi = 10.1073/pnas.040556397 | doi-access = free | bibcode = 2000PNAS...97.1920T }}</ref> There are possibly up to 100 polymorphs of the S-haplotype in ''Brassica'', and within these there is a dominance hierarchy. {{cn|date=July 2024}}

The female determinant of the SI response in ''Brassica'', is a transmembrane protein termed '''SRK''', which has an intracellular [[kinase]] domain, and a variable extracellular domain.<ref>{{cite journal | vauthors = Stein JC, Howlett B, Boyes DC, Nasrallah ME, Nasrallah JB | title = Molecular cloning of a putative receptor protein kinase gene encoded at the self-incompatibility locus of ''Brassica oleracea'' | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 88 | issue = 19 | pages = 8816–8820 | date = October 1991 | pmid = 1681543 | pmc = 52601 | doi = 10.1073/pnas.88.19.8816 | doi-access = free | bibcode = 1991PNAS...88.8816S }}: .</ref><ref>{{cite journal | vauthors= Nasrallah JB, Nasrallah ME |title=Pollen–stigma signalling in the sporophytic self-incompatibility response |journal=Plant Cell |volume=5 |issue=10  |pages=1325–35 |year=1993 |doi=10.2307/3869785|jstor=3869785  |bibcode=1993PlanC...5.1325N }}</ref> SRK is expressed in the stigma, and probably functions as a receptor for the SCR/SP11 protein in the pollen coat. Another stigmatic protein, termed '''SLG''', is highly similar in [[sequence (biology)|sequence]] to the SRK protein, and seems to function as a [[co-receptor]] for the male determinant, amplifying the SI response.<ref>{{cite journal | vauthors = Takasaki T, Hatakeyama K, Suzuki G, Watanabe M, Isogai A, Hinata K | title = The S receptor kinase determines self-incompatibility in ''Brassica'' stigma | journal = Nature | volume = 403 | issue = 6772 | pages = 913–916 | date = February 2000 | pmid = 10706292 | doi = 10.1038/35002628 | s2cid = 4361474 | bibcode = 2000Natur.403..913T }}</ref>

The interaction between the SRK and SCR/SP11 proteins results in [[autophosphorylation]] of the intracellular kinase domain of SRK,<ref>{{cite journal | vauthors = Schopfer CR, Nasrallah JB | title = Self-incompatibility. Prospects for a novel putative peptide-signaling molecule | journal = Plant Physiology | volume = 124 | issue = 3 | pages = 935–940 | date = November 2000 | pmid = 11080271 | pmc = 1539289 | doi = 10.1104/pp.124.3.935 | name-list-style = amp }}</ref><ref>{{cite journal | vauthors = Takayama S, Shimosato H, Shiba H, Funato M, Che FS, Watanabe M, Iwano M, Isogai A | display-authors = 6 | title = Direct ligand-receptor complex interaction controls ''Brassica'' self-incompatibility | journal = Nature | volume = 413 | issue = 6855 | pages = 534–538 | date = October 2001 | pmid = 11586363 | doi = 10.1038/35097104 | s2cid = 4419954 | bibcode = 2001Natur.413..534T }}</ref> and a signal is transmitted into the [[wikt:papilla|papilla]] cell of the stigma. Another protein essential for the SI response is '''MLPK''', a [[serine]]-[[threonine]] kinase, which is anchored to the [[plasma membrane]] from its intracellular side.<ref>{{cite journal | vauthors = Murase K, Shiba H, Iwano M, Che FS, Watanabe M, Isogai A, Takayama S | title = A membrane-anchored protein kinase involved in ''Brassica'' self-incompatibility signaling | journal = Science | volume = 303 | issue = 5663 | pages = 1516–1519 | date = March 2004 | pmid = 15001779 | doi = 10.1126/science.1093586 | s2cid = 29677122 | bibcode = 2004Sci...303.1516M }}</ref> A downstream signaling cascade leads to proteasomal degradation that produces an SI response.<ref>{{citation |journal = Nature Plants |volume = 1 |issue = 12 |doi=10.1038/nplants.2015.185 |title=Degradation of glyoxalase I in ''Brassica napus'' stigma leads to self-incompatibility response |author=Subramanian Sankaranarayanan, Muhammad Jamshed, and Marcus A. Samuel |date = 2015 |page = 15185 |pmid = 27251720 |bibcode = 2015NatPl...115185S }}</ref>