title: Self-incompatibility of Prunus tenella and evidence that reproductively isolated species of Prunus have different SFB alleles coupled with an identical S-RNase allele.
abstract: Many species of Prunus display an S-RNase-based gametophytic self-incompatibility (SI), controlled by a single highly polymorphic multigene complex termed the S-locus. This comprises tightly linked stylar- and pollen-expressed genes that determine the specificity of the SI response. We investigated SI of Prunus tenella, a wild species found in small, isolated populations on the Balkan peninsula, initially by pollination experiments and identifying stylar-expressed RNase alleles. Nine P. tenella S-RNase alleles (S(1)-S(9)) were cloned; their sequence analysis showed a very high ratio of non-synonymous to synonymous nucleotide substitutions (K(a)/K(s)) and revealed that S-RNase alleles of P. tenella, unlike those of Prunus dulcis, show positive selection in all regions except the conserved regions and that between C2 and RHV. Remarkably, S(8)-RNase, was found to be identical to S(1)-RNase from Prunus avium, a species that does not interbreed with P. tenella and, except for just one amino acid, to S(11) of P. dulcis. However, the corresponding introns and S-RNase-SFB intergenic regions showed considerable differences. Moreover, protein sequences of the pollen-expressed SFB alleles were not identical, harbouring 12 amino-acid replacements between those of P. tenella SFB(8) and P. avium SFB(1). Implications of this finding for hypotheses about the evolution of new S-specificities are discussed.
authors.affiliation: Institute of Molecular Genetics and Genetic Engineering, Vojvode Stepe 444a, PO Box 23, 11 000 Belgrade, Serbia. nada.surbanovski@emr.ac.uk
authors.forename: Nada
authors.initials: N
authors.lastname: Surbanovski
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Tobutt
authors.forename: Miroslav
authors.initials: M
authors.lastname: Konstantinović
authors.forename: Vesna
authors.initials: V
authors.lastname: Maksimović
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Sargent
authors.forename: Vladimir
authors.initials: V
authors.lastname: Stevanović
authors.forename: Radovan I
authors.initials: RI
authors.lastname: Bosković
mesh_terms: D000483:Alleles; D000595:Amino Acid Sequence; D001483:Base Sequence; D003001:Cloning, Molecular; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D027861:Prunus / Q000235:genetics / Q000276:immunology* / Q000502:physiology; D012098:Reproduction; D012260:Ribonucleases / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity
chemical_list: D012260:Ribonucleases