title: The genetic architecture of tristyly and its breakdown to self-fertilization.
abstract: The floral polymorphism tristyly involves three style morphs with a reciprocal arrangement of stigma and anther heights governed by two diallelic loci (S and M). Tristyly functions to promote cross-pollination, but modifications to stamen position commonly cause transitions to selfing. Here, we integrate whole-genome sequencing and genetic mapping to investigate the genetic architecture of the M locus and the genetic basis of independent transitions to selfing in tristylous Eichhornia paniculata. We crossed independently derived semi-homostylous selfing variants of the long- and mid-styled morph fixed for alternate alleles at the M locus (ssmm and ssMM, respectively), and backcrossed the F1to the parental ssmm genotype. We phenotyped and genotyped 462 backcross progeny using 1450 genotyping-by-sequencing (GBS) markers and performed composite interval mapping to identify quantitative trait loci (QTL) governing style-length and anther-height variation. A QTL associated with the primary style-morph differences (style length and anther height) mapped to linkage group 5 and spanned ~13-27.5 Mbp of assembled sequence. Bulk segregant analysis identified 334 genes containing SNPs potentially linked to the M locus. The stamen modifications characterizing each selfing variant were governed by loci on different linkage groups. Our results provide an important step towards identifying the M locus and demonstrate that transitions to selfing have originated by independent sets of mating-system modifier genes unlinked to the M locus, a pattern inconsistent with a recombinational origin of selfing variants at a putative supergene.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada, M5S 3B2.
authors.forename: Ramesh
authors.initials: R
authors.lastname: Arunkumar
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada, M5S 3B2.
authors.forename: Wei
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada, M5S 3B2.
authors.forename: Stephen I
authors.initials: SI
authors.lastname: Wright
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada, M5S 3B2.
authors.forename: Spencer C H
authors.initials: SC
authors.lastname: Barrett
mesh_terms: D002874:Chromosome Mapping; D003433:Crosses, Genetic; D031806:Eichhornia / Q000235:genetics* / Q000502:physiology*; D035264:Flowers / Q000502:physiology*; D008040:Genetic Linkage; D005819:Genetic Markers; D005838:Genotype; D054817:Pollination; D020641:Polymorphism, Single Nucleotide; D040641:Quantitative Trait Loci; D057945:Self-Fertilization
chemical_list: D005819:Genetic Markers
keywords: M locus; QTL mapping; bulk segregant analysis; modifier genes; self-fertilization; tristyly