title: S locus genes and the evolution of self-fertility in Arabidopsis thaliana.
abstract: Loss of self-incompatibility (SI) in Arabidopsis thaliana was accompanied by inactivation of genes required for SI, including S-LOCUS RECEPTOR KINASE (SRK) and S-LOCUS CYSTEINE-RICH PROTEIN (SCR), coadapted genes that constitute the SI specificity-determining S haplotype. Arabidopsis accessions are polymorphic for PsiSRK and PsiSCR, but it is unknown if the species harbors structurally different S haplotypes, either representing relics of ancestral functional and structurally heteromorphic S haplotypes or resulting from decay concomitant with or subsequent to the switch to self-fertility. We cloned and sequenced the S haplotype from C24, in which self-fertility is due solely to S locus inactivation, and show that this haplotype was produced by interhaplotypic recombination. The highly divergent organization and sequence of the C24 and Columbia-0 (Col-0) S haplotypes demonstrate that the A. thaliana S locus underwent extensive structural remodeling in conjunction with a relaxation of selective pressures that once preserved the integrity and linkage of coadapted SRK and SCR alleles. Additional evidence for this process was obtained by assaying 70 accessions for the presence of C24- or Col-0-specific sequences. Furthermore, analysis of SRK and SCR polymorphisms in these accessions argues against the occurrence of a selective sweep of a particular allele of SCR, as previously proposed.
authors.affiliation: Department of Plant Biology, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Sue
authors.initials: S
authors.lastname: Sherman-Broyles
authors.forename: Nathan
authors.initials: N
authors.lastname: Boggs
authors.forename: Agnes
authors.initials: A
authors.lastname: Farkas
authors.forename: Pei
authors.initials: P
authors.lastname: Liu
authors.forename: Julia
authors.initials: J
authors.lastname: Vrebalov
authors.forename: Mikhail E
authors.initials: ME
authors.lastname: Nasrallah
authors.forename: June B
authors.initials: JB
authors.lastname: Nasrallah
mesh_terms: D000483:Alleles; D017360:Arabidopsis / Q000145:classification / Q000235:genetics / Q000502:physiology*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics*; D002874:Chromosome Mapping; D032461:Chromosomes, Plant; D004251:DNA Transposable Elements; D019143:Evolution, Molecular; D005298:Fertility / Q000235:genetics; D017353:Gene Deletion; D020440:Gene Duplication; D015321:Gene Rearrangement; D006239:Haplotypes; D008969:Molecular Sequence Data; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics*; D011110:Polymorphism, Genetic; D011494:Protein Kinases / Q000737:chemistry / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D029681:Arabidopsis Proteins; D004251:DNA Transposable Elements; D010940:Plant Proteins; C100978:SCR protein, Arabidopsis; D011494:Protein Kinases; C079832:S-receptor kinase