Allelic Genealogies in Sporophytic Self-Incompatibility Systems in Plants

Abstract

Expectations for the time scale and structure of allelic genealogies in finite populations are formed under three models of sporophytic self-incompatibility. The models differ in the dominance interactions among the alleles that determine the self-incompatibility phenotype: In the SSIcod model, alleles act codominantly in both pollen and style, in the SSIdom model, alleles form a dominance hierarchy, and in SSIdomcod, alleles are codominant in the style and show a dominance hierarchy in the pollen. Coalescence times of alleles rarely differ more than threefold from those under gametophytic self-incompatibility, and transspecific polymorphism is therefore expected to be equally common. The previously reported directional turnover process of alleles in the SSIdomcod model results in coalescence times lower and substitution rates higher than those in the other models. The SSIdom model assumes strong asymmetries in allelic action, and the most recessive extant allele is likely to be the most recent common ancestor. Despite these asymmetries, the expected shape of the allele genealogies does not deviate markedly from the shape of a neutral gene genealogy. The application of the results to sequence surveys of alleles, including interspecific comparisons, is discussed.

Ancestral self-compatibility facilitates the establishment of allopolyploids in Brassicaceae

“…Self-recognition genes are multiallelic and extremely diverse, sharing high proportion of polymorphism between species and even between genera (Schierup et al 2001 ; Castric and Vekemans 2007 ). S -alleles are trans-specifically shared between the genera Arabidopsis, Crucihimalaya and Capsella (Schierup et al 1998 ; Paetsch et al 2006 ; Castric and Vekemans 2007 ; Busch et al 2008 ; Tedder et al 2011 ; Guo et al 2011 ; Leducq et al 2014 ; Zhang et al 2019 ), which had a common ancestor about 11–14 million years ago (Hohmann et al 2015 ; Mandáková et al 2017 ). However, while Leavenworthia alabamica evolved a secondary non-syntenic S -locus (Busch et al 2008 , 2011 ; Chantha et al 2013 , 2017 ), its close relative from the same tribe, Cardamine hirsuta , has a colinear S -locus to Arabidopsis and Brassica and the S-haplogroup of selfing C. hirsuta is orthologous to A. halleri and A. lyrata S -allele from S-haplogroup 1 (Gan et al 2016 ).…”

Sporophytic self-incompatibility genes and mating system variation in Arabis alpina

“…Within the Brassicaceae, the S-locus is comprised of a gene complex that encodes specific proteins involved in recognition and rejection of 'self' pollen (Suzuki et al, 1999;Kusaba et al, 2001;Shiba et al, 2003). These genes are highly polymorphic (Sims, 1993;Awadalla and Charlesworth, 1999;Nishio and Kusaba, 2000), due to negative frequencydependent selection, whereby rare alleles have a reproductive advantage in the population, which promotes the maintenance of extensive nucleotide and allelic diversity at the S-locus (Takahata, 1990;Vekemans and Slatkin, 1994;Schierup et al, 1998). The system is also subject to complex dominance interactions among alleles (Thompson and Taylor, 1966;Ockendon, 1975;Stevens and Kay, 1989;Hatakeyama et al, 1998;Prigoda et al, 2005), which affects both the male ( pollen) and female ( pistil) components (Thompson and Taylor, 1966;Visser et al, 1982;Shiba et al, 2002).…”

Genome-wide identification and characterization of SRLK gene family reveal their roles in self-incompatibility of Erigeron breviscapus

“…3 ). The polymorphism may be due to the strong negative frequency-dependent selection occurred at the S -locus [ 59 , 60 ]. In many plants, the S -locus alleles are highly polymorphic [ 61 – 64 ], such as in A. halleri and A. lyrate [ 65 ], and B. neustriaca [ 66 ] .…”