title: Apple S locus region represents a large cluster of related, polymorphic and pollen-specific F-box genes.
abstract: Gametophytic self-incompatibility (GSI) of Rosaceae, Solanaceae and Plantaginaceae is controlled by a complex S locus that encodes separate proteins for pistil and pollen specificities, extracellular ribonucleases (S-RNases) and F-box proteins SFB/SLF, respectively. SFB/SLFs of Prunus (subfamily Prunoideae of Rosaceae), Solanaceae and Plantaginaceae are single copy in each S haplotype, while recently identified pollen S candidates SFBBs of subfamily Maloideae of Rosaceae, apple and Japanese pear, are multiple; two and three related SFBBs were isolated from each S haplotype of apple and Japanese pear, respectively. Here, we show that apple (Malus x domestica) SFBBs constitute a gene family that is much larger than initially thought. Twenty additional SFBB-like genes/alleles were isolated by screening of a BAC library derived from S (3) S (9) genotype, and tentatively named MdFBX1-20. All but one MdFBX showed S haplotype-specific polymorphisms. All the polymorphic MdFBXs were completely linked to S-RNase in 239 segregants. In addition, FISH revealed that the monomorphic gene MdFBX11 is also located near S-RNase, and the S locus is located in a subtelomeric region of a chromosome and is not close to the centromere. All MdFBXs were specifically expressed in pollen, except for a pseudogene MdFBX4 that showed no expression in any organs analyzed. Phylogenetic analysis revealed that the closest relatives of most MdFBXs were from a different S haplotype, suggesting that proliferation of MdSFBB/FBXs predates diversification of the S haplotypes.
authors.affiliation: Chiba University, Matsudo, Japan.
authors.forename: Mai
authors.initials: M
authors.lastname: Minamikawa
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Kakui
authors.forename: Sanhong
authors.initials: S
authors.lastname: Wang
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Kotoda
authors.forename: Shinji
authors.initials: S
authors.lastname: Kikuchi
authors.forename: Takato
authors.initials: T
authors.lastname: Koba
authors.forename: Hidenori
authors.initials: H
authors.lastname: Sassa
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D022202:Chromosomes, Artificial, Bacterial / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D019143:Evolution, Molecular; D044783:F-Box Proteins / Q000235:genetics; D015723:Gene Library; D017343:Genes, Plant; D008040:Genetic Linkage; D006239:Haplotypes; D017404:In Situ Hybridization, Fluorescence; D027845:Malus / Q000235:genetics*; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D020161:Physical Chromosome Mapping; D010940:Plant Proteins / Q000235:genetics; D011058:Pollen / Q000235:genetics; D011110:Polymorphism, Genetic; D012260:Ribonucleases / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D017931:DNA Primers; D044783:F-Box Proteins; D010940:Plant Proteins; D012260:Ribonucleases