title: Sequence divergence and loss-of-function phenotypes of S locus F-box brothers genes are consistent with non-self recognition by multiple pollen determinants in self-incompatibility of Japanese pear (Pyrus pyrifolia).
abstract: The S-RNase-based gametophytic self-incompatibility (SI) of Rosaceae, Solanaceae, and Plantaginaceae is controlled by at least two tightly linked genes located at the complex S locus; the highly polymorphic S-RNase for pistil specificity and the F-box gene (SFB/SLF) for pollen. Self-incompatibility in Prunus (Rosaceae) is considered to represent a 'self recognition by a single factor' system, because loss-of-function of SFB is associated with self-compatibility, and allelic divergence of SFB is high and comparable to that of S-RNase. In contrast, Petunia (Solanaceae) exhibits 'non-self recognition by multiple factors'. However, the distribution of 'self recognition' and 'non-self recognition' SI systems in different taxa is not clear. In addition, in 'non-self recognition' systems, a loss-of-function phenotype of pollen S is unknown. Here we analyze the divergence of SFBB genes, the multiple pollen S candidates, of a rosaceous plant Japanese pear (Pyrus pyrifolia) and show that intrahaplotypic divergence is high and comparable to the allelic diversity of S-RNase while interhaplotypic divergence is very low. Next, we analyzed loss-of-function of the SFBB1 type gene. Genetic analysis showed that pollen with the mutant haplotype S(4sm)  lacking SFBB1-S(4)  is rejected by pistils with an otherwise compatible S(1)  while it is accepted by other non-self pistils. We found that the S(5)  haplotype encodes a truncated SFBB1 protein, even though S(5)  pollen is accepted normally by pistils with S(1)  and other non-self haplotypes. These findings suggest that Japanese pear has a 'non-self recognition by multiple factors' SI system, although it is a species of Rosaceae to which Prunus also belongs.
authors.affiliation: Graduate School of Horticulture, Chiba University, 648 Matsudo, Matsudo, Chiba 271-8510, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kakui
authors.forename: Masaki
authors.initials: M
authors.lastname: Kato
authors.forename: Koichiro
authors.initials: K
authors.lastname: Ushijima
authors.forename: Miyoko
authors.initials: M
authors.lastname: Kitaguchi
authors.forename: Shu
authors.initials: S
authors.lastname: Kato
authors.forename: Hidenori
authors.initials: H
authors.lastname: Sassa
mesh_terms: D001483:Base Sequence; D044783:F-Box Proteins / Q000235:genetics*; D035264:Flowers; D017343:Genes, Plant; D006239:Haplotypes; D008969:Molecular Sequence Data; D010802:Phylogeny; D011058:Pollen / Q000235:genetics*; D031989:Pyrus / Q000235:genetics*; D060436:Self-Incompatibility in Flowering Plants / Q000235:genetics*
chemical_list: D044783:F-Box Proteins