title: Self-incompatibility (S) alleles of the Rosaceae encode members of a distinct class of the T2/S ribonuclease superfamily.
abstract: Stylar ribonucleases (RNases) are associated with gametophytic self-incompatibility in two plant families, the Solanaceae and the Rosaceae. The self-incompatibility-associated RNases (S-RNases) of both the Solanaceae and the Rosaceae were recently reported to belong to the T2 RNase gene family, based on the presence of two well-conserved sequence motifs. Here, the cloning and characterization of S-RNase genes from two species of Rosaceae, apple (Malus x domestica) and Japanese pear (Pyrus serotina) is described and these sequences are compared with those of other T2-type RNases. The S-RNases of apple specifically accumulated in styles following maturation of the flower bud. Two cDNA clones for S-RNases from apple, and PCR clones encoding a further two apple S-RNases as well as two Japanese pear S-RNases were isolated and sequenced. The deduced amino acid sequences of the rosaceous S-RNases contained two conserved regions characteristic of the T2/S-type RNases. The sequences showed a high degree of diversity, with similarities ranging from 60.4% to 69.2%. Interestingly, some interspecific sequence similarities were higher than those within a species, possibly indicating that diversification of S-RNase alleles predated speciation in the Rosaceae. A phylogenetic tree of members of the T2/S-RNase superfamily in plants was obtained. The rosaceous S-RNases formed a new lineage in the tree that was distinct from those of the solanaceous S-RNases and the S-like RNases. The findings suggested that self-incompatibility mechanisms in Rosaceae and Solanaceae are similar but arose independently in the course of evolution.
authors.affiliation: Faculty of Horticulture, Chiba University, Matsudo, Chiba, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Sassa
authors.forename: T
authors.initials: T
authors.lastname: Nishio
authors.forename: Y
authors.initials: Y
authors.lastname: Kowyama
authors.forename: H
authors.initials: H
authors.lastname: Hirano
authors.forename: T
authors.initials: T
authors.lastname: Koba
authors.forename: H
authors.initials: H
authors.lastname: Ikehashi
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence; D017931:DNA Primers; D004722:Endoribonucleases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D004926:Escherichia coli; D017343:Genes, Plant; D014644:Genetic Variation; D008969:Molecular Sequence Data; D005810:Multigene Family; D009838:Oligodeoxyribonucleotides; D010802:Phylogeny; D010944:Plants / Q000201:enzymology / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000302:isolation & purification / Q000378:metabolism; D012260:Ribonucleases / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D011198:Solanum tuberosum / Q000201:enzymology / Q000235:genetics
chemical_list: D017931:DNA Primers; D009838:Oligodeoxyribonucleotides; D011994:Recombinant Proteins; D004722:Endoribonucleases; D012260:Ribonucleases; C022543:ribonuclease T(2); C022542:ribonuclease S