Editing Self-incompatibility (section)

====The RNase-based SI mechanism====
In this mechanism, pollen tube elongation is halted when it has proceeded approximately one third of the way through the [[carpel|style]].<ref name="franklin-tong2003">{{cite journal | vauthors = Franklin-Tong VE, Franklin FC | title = The different mechanisms of gametophytic self-incompatibility | journal = Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences | volume = 358 | issue = 1434 | pages = 1025–1032 | date = June 2003 | pmid = 12831468 | pmc = 1693207 | doi = 10.1098/rstb.2003.1287 | name-list-style = amp }}</ref> The female component [[ribonuclease]] protein, termed '''S-RNase'''<ref name="mcclure">{{cite journal | vauthors = McClure BA, Haring V, Ebert PR, Anderson MA, Simpson RJ, Sakiyama F, Clarke AE | title = Style self-incompatibility gene products of Nicotiana alata are ribonucleases | journal = Nature | volume = 342 | issue = 6252 | pages = 955–957 | year = 1989 | pmid = 2594090 | doi = 10.1038/342955a0 | s2cid = 4321558 | doi-access =  | bibcode = 1989Natur.342..955M }}</ref> probably causes degradation of the [[ribosome|ribosomal]] [[RNA]] (rRNA) inside the pollen tube, in the case of identical male and female S alleles, and consequently pollen tube elongation is arrested, and the pollen grain dies.<ref name="franklin-tong2003"/>

Within a decade of the initial confirmation their role in GSI, proteins belonging to the same RNase gene family were also found to cause pollen rejection in species of [[Rosaceae]] and [[Plantaginaceae]]. Despite initial uncertainty about the common ancestry of RNase-based SI in these distantly related plant families, phylogenetic studies<ref name="igic2001">{{cite journal | vauthors = Igic B, Kohn JR | title = Evolutionary relationships among self-incompatibility RNases | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 98 | issue = 23 | pages = 13167–13171 | date = November 2001 | pmid = 11698683 | pmc = 60842 | doi = 10.1073/pnas.231386798 | name-list-style = amp | doi-access = free }}</ref> and the finding of shared male determinants ('''F-box proteins''')<ref name="qiao2004b">{{cite journal | vauthors = Qiao H, Wang F, Zhao L, Zhou J, Lai Z, Zhang Y, Robbins TP, Xue Y | display-authors = 6 | title = The F-box protein AhSLF-S2 controls the pollen function of S-RNase-based self-incompatibility | journal = The Plant Cell | volume = 16 | issue = 9 | pages = 2307–2322 | date = September 2004 | pmid = 15308757 | pmc = 520935 | doi = 10.1105/tpc.104.024919 | bibcode = 2004PlanC..16.2307Q }}</ref><ref name="ushijima">{{cite journal | vauthors = Ushijima K, Yamane H, Watari A, Kakehi E, Ikeda K, Hauck NR, Iezzoni AF, Tao R | display-authors = 6 | title = The S haplotype-specific F-box protein gene, SFB, is defective in self-compatible haplotypes of Prunus avium and P. mume | journal = The Plant Journal | volume = 39 | issue = 4 | pages = 573–586 | date = August 2004 | pmid = 15272875 | doi = 10.1111/j.1365-313X.2004.02154.x | doi-access = free }}</ref><ref name="sijacic">{{cite journal | vauthors = Sijacic P, Wang X, Skirpan AL, Wang Y, Dowd PE, McCubbin AG, Huang S, Kao TH | display-authors = 6 | title = Identification of the pollen determinant of S-RNase-mediated self-incompatibility | journal = Nature | volume = 429 | issue = 6989 | pages = 302–305 | date = May 2004 | pmid = 15152253 | doi = 10.1038/nature02523 | s2cid = 4427123 | bibcode = 2004Natur.429..302S }}</ref> strongly supported [[Homology (biology)|homology]] across [[eudicots]]. Therefore, this mechanism likely arose approximately 90 million years ago, and is the inferred ancestral state for approximately 50% of all plant species.<ref name="igic2001"/><ref name="steinbachs2002">{{cite journal | vauthors = Steinbachs JE, Holsinger KE | title = S-RNase-mediated gametophytic self-incompatibility is ancestral in eudicots | journal = Molecular Biology and Evolution | volume = 19 | issue = 6 | pages = 825–829 | date = June 2002 | pmid = 12032238 | doi = 10.1093/oxfordjournals.molbev.a004139 | name-list-style = amp | doi-access = free }}</ref>

In the past decade, the predictions about the wide distribution of this mechanism of SI have been confirmed, placing additional support of its single ancient origin. Specifically, a style-expressed T2/S-RNase gene and pollen-expressed F-box  genes are now implicated in causing SI among the members of [[Rubiaceae]],<ref name="asquini2011coffea">{{cite journal | vauthors =Asquini E, Gerdol M, Gasperini D, Igic B, Graziosi G, Pallavicini A |title=S-RNase-like Sequences in Styles of Coffea (Rubiaceae). Evidence for S-RNase Based Gametophytic Self-Incompatibility?|journal=Tropical Plant Biology |volume=4|pages=237–249|year=2011|issue=3–4|doi=10.1007/s12042-011-9085-2|s2cid=11092131}}</ref> [[Rutaceae]],<ref name="liang2020citrus">{{cite journal | vauthors = Liang M, Cao Z, Zhu A, Liu Y, Tao M, Yang H, Xu Q, Wang S, Liu J, Li Y, Chen C, Xie Z, Deng C, Ye J, Guo W, Xu Q, Xia R, Larkin RM, Deng X, Bosch M, Franklin-Tong VE, Chai L | display-authors = 6 | title = Evolution of self-compatibility by a mutant S<sub>m</sub>-RNase in citrus | journal = Nature Plants | volume = 6 | issue = 2 | pages = 131–142 | date = February 2020 | pmid = 32055045 | pmc = 7030955 | doi = 10.1038/s41477-020-0597-3 | bibcode = 2020NatPl...6..131L }}</ref> and [[Cactaceae]].<ref name="ramanauskas2021cacti">{{cite journal | vauthors = Ramanauskas K, Igić B | title = RNase-based self-incompatibility in cacti | journal = The New Phytologist | volume = 231 | issue = 5 | pages = 2039–2049 | date = September 2021 | pmid = 34101188 | doi = 10.1111/nph.17541 | name-list-style = amp | s2cid = 235370441 | doi-access = free }}</ref> Therefore, other mechanisms of SI are thought to be recently derived in eudicots plants, in some cases relatively recently. One particularly interesting case is the SI expressed in Prunus species, which functions through self-recognition<ref name="Matsumoto-The-Horticulture-Journal">{{Cite journal |vauthors=Matsumoto D, Tao R |date=2016 |title=Distinct Self-recognition in the Prunus S-RNase-based Gametophytic Self-incompatibility System |url=https://www.jstage.jst.go.jp/article/hortj/85/4/85_MI-IR06/_article |journal=The Horticulture Journal |language=en |volume=85 |issue=4 |pages=289–305 |doi=10.2503/hortj.MI-IR06 |issn=2189-0102 |doi-access=free |access-date=2022-09-28 |archive-date=2022-09-28 |archive-url=https://web.archive.org/web/20220928084909/https://www.jstage.jst.go.jp/article/hortj/85/4/85_MI-IR06/_article |url-status=live }}</ref> (the cytotoxic activity of the S-RNases is inhibited by default and selectively activated by the pollen partner S-haplotype-specific F-box protein (SFB) upon self-pollination), while SI in the other species with S-RNase functions through non-self recognition (the S-RNases are selectively detoxified upon cross-pollination).