title: Patterns of evolution at the gametophytic self-incompatibility Sorbus aucuparia (Pyrinae) S pollen genes support the non-self recognition by multiple factors model.
abstract: S-RNase-based gametophytic self-incompatibility evolved once before the split of the Asteridae and Rosidae. In Prunus (tribe Amygdaloideae of Rosaceae), the self-incompatibility S-pollen is a single F-box gene that presents the expected evolutionary signatures. In Malus and Pyrus (subtribe Pyrinae of Rosaceae), however, clusters of F-box genes (called SFBBs) have been described that are expressed in pollen only and are linked to the S-RNase gene. Although polymorphic, SFBB genes present levels of diversity lower than those of the S-RNase gene. They have been suggested as putative S-pollen genes, in a system of non-self recognition by multiple factors. Subsets of allelic products of the different SFBB genes interact with non-self S-RNases, marking them for degradation, and allowing compatible pollinations. This study performed a detailed characterization of SFBB genes in Sorbus aucuparia (Pyrinae) to address three predictions of the non-self recognition by multiple factors model. As predicted, the number of SFBB genes was large to account for the many S-RNase specificities. Secondly, like the S-RNase gene, the SFBB genes were old. Thirdly, amino acids under positive selection-those that could be involved in specificity determination-were identified when intra-haplotype SFBB genes were analysed using codon models. Overall, the findings reported here support the non-self recognition by multiple factors model.
authors.affiliation: Instituto de Biologia Molecular e Celular (IBMC), University of Porto, Rua do Campo Alegre 823, 4150-180 Porto, Portugal.
authors.forename: Bruno
authors.initials: B
authors.lastname: Aguiar
authors.forename: Jorge
authors.initials: J
authors.lastname: Vieira
authors.forename: Ana E
authors.initials: AE
authors.lastname: Cunha
authors.forename: Nuno A
authors.initials: NA
authors.lastname: Fonseca
authors.forename: David
authors.initials: D
authors.lastname: Reboiro-Jato
authors.forename: Miguel
authors.initials: M
authors.lastname: Reboiro-Jato
authors.forename: Florentino
authors.initials: F
authors.lastname: Fdez-Riverola
authors.forename: Olivier
authors.initials: O
authors.lastname: Raspé
authors.forename: Cristina P
authors.initials: CP
authors.lastname: Vieira
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D017343:Genes, Plant / Q000235:genetics* / Q000502:physiology; D006239:Haplotypes / Q000235:genetics; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D011058:Pollen / Q000235:genetics* / Q000502:physiology; D060436:Self-Incompatibility in Flowering Plants / Q000235:genetics* / Q000502:physiology; D031994:Sorbus / Q000235:genetics / Q000502:physiology*
keywords: S-RNase.; SFBB; Sorbus aucuparia; gametophytic self-incompatibility; molecular evolution; positively selected amino acid sites