title: Evolutionary genetics of an S-like polymorphism in Papaveraceae with putative function in self-incompatibility.
abstract: BACKGROUND
  Papaver rhoeas possesses a gametophytic self-incompatibility (SI) system not homologous to any other SI mechanism characterized at the molecular level. Four previously published full length stigmatic S-alleles from the genus Papaver exhibited remarkable sequence divergence, but these studies failed to amplify additional S-alleles despite crossing evidence for more than 60 S-alleles in Papaver rhoeas alone.
  
  
  RESULTS
  Using RT-PCR we identified 87 unique putative stigmatic S-allele sequences from the Papaveraceae Argemone munita, Papaver mcconnellii, P. nudicuale, Platystemon californicus and Romneya coulteri. Hand pollinations among two full-sib families of both A. munita and P. californicus indicate a strong correlation between the putative S-genotype and observed incompatibility phenotype. However, we also found more than two S-like sequences in some individuals of A. munita and P. californicus, with two products co-segregating in both full-sib families of P. californicus. Pairwise sequence divergence estimates within and among taxa show Papaver stigmatic S-alleles to be the most variable with lower divergence among putative S-alleles from other Papaveraceae. Genealogical analysis indicates little shared ancestral polymorphism among S-like sequences from different genera. Lack of shared ancestral polymorphism could be due to long divergence times among genera studied, reduced levels of balancing selection if some or all S-like sequences do not function in incompatibility, population bottlenecks, or different levels of recombination among taxa. Preliminary estimates of positive selection find many sites under selective constraint with a few undergoing positive selection, suggesting that self-recognition may depend on amino acid substitutions at only a few sites.
  
  
  CONCLUSIONS
  Because of the strong correlation between genotype and SI phenotype, sequences reported here represent either functional stylar S-alleles, tightly linked paralogs of the S-locus or a combination of both. The considerable complexity revealed in this study shows we have much to learn about the evolutionary dynamics of self-incompatibility systems.
authors.affiliation: College of Biological Sciences, University of Minnesota, St. Paul, Minnesota, United States of America. paap0008@umn.edu
authors.forename: Timothy
authors.initials: T
authors.lastname: Paape
authors.forename: Takashi
authors.initials: T
authors.lastname: Miyake
authors.forename: Naoki
authors.initials: N
authors.lastname: Takebayashi
authors.forename: Diana
authors.initials: D
authors.lastname: Wolf
authors.forename: Joshua R
authors.initials: JR
authors.lastname: Kohn
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D004171:Diploidy; D019143:Evolution, Molecular; D006239:Haplotypes / Q000235:genetics; D006824:Hybridization, Genetic; D008969:Molecular Sequence Data; D009928:Organ Specificity; D028101:Papaveraceae / Q000235:genetics* / Q000502:physiology*; D010641:Phenotype; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics; D054817:Pollination / Q000235:genetics; D011110:Polymorphism, Genetic / Q000235:genetics*; D012641:Selection, Genetic; D060436:Self-Incompatibility in Flowering Plants / Q000235:genetics*; D013045:Species Specificity; D057891:Tetraploidy
chemical_list: D010940:Plant Proteins