title: Multiple features that distinguish unilateral incongruity and self-incompatibility in the tomato clade.
abstract: Wild tomato species in Solanum Section Lycopersicon often exhibit two types of reproductive barriers: self-incompatibility (SI) and unilateral incompatibility or incongruity (UI), wherein the success of an inter-specific cross depends on the direction of the cross. UI pollen rejection often follows the 'SI × SC' rule, i.e. pistils of SI species reject the pollen of SC (self-compatible) species but not vice versa, suggesting that the SI and UI pollen rejection mechanisms may overlap. In order to address this question, pollen tube growth was measured after inter-specific crosses using wild tomato species as the female parents and pollen from cultivated tomato (Solanum lycopersicum). Two modes of UI pollen rejection, early and late, were observed, and both differed from SI pollen rejection. The structure and expression of known stylar SI genes were evaluated. We found that S-RNase expression is not required for either the early or late mode of UI pollen rejection. However, two HT family genes, HT-A and HT-B, map to a UI QTL. Surprisingly, we found that a gene previously implicated in SI, HT-B, is mutated in both SI and SC S. habrochaites accessions, and no HT-B protein could be detected. HT-A genes were detected and expressed in all species examined, and may therefore function in both SI and UI. We conclude that there are significant differences between SI and UI in the tomato clade, in that pollen tube growth differs between these two rejection systems, and some stylar SI factors, including S-RNase and HT-B, are not required for UI.
authors.affiliation: Department of Biology, Colorado State University, Fort Collins, CO 80523-1878, USA.
authors.forename: Paul A
authors.initials: PA
authors.lastname: Covey
authors.forename: Katsuhiko
authors.initials: K
authors.lastname: Kondo
authors.forename: Lilli
authors.initials: L
authors.lastname: Welch
authors.forename: Eric
authors.initials: E
authors.lastname: Frank
authors.forename: Shelley
authors.initials: S
authors.lastname: Sianta
authors.forename: Aruna
authors.initials: A
authors.lastname: Kumar
authors.forename: Reynaldo
authors.initials: R
authors.lastname: Nuñez
authors.forename: Gloria
authors.initials: G
authors.lastname: Lopez-Casado
authors.forename: Esther
authors.initials: E
authors.lastname: van der Knaap
authors.forename: Jocelyn K C
authors.initials: JK
authors.lastname: Rose
authors.forename: Bruce A
authors.initials: BA
authors.lastname: McClure
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Bedinger
mesh_terms: D000595:Amino Acid Sequence; D002874:Chromosome Mapping; D017343:Genes, Plant; D006824:Hybridization, Genetic; D018551:Solanum lycopersicum / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D053205:Pollen Tube / Q000254:growth & development / Q000502:physiology*; D054817:Pollination; D040641:Quantitative Trait Loci; D012098:Reproduction; D012260:Ribonucleases / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D010940:Plant Proteins; D012260:Ribonucleases; C022542:ribonuclease S