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Self-compatibility is a major breeding objective in sweet cherry. The identification and characterization of new sources of self-compatibility will be useful for breeding and research purposes. In this work, self-compatibility of four local Spanish sweet cherry varieties was investigated by crossing experiments and molecular genetic analysis of two self-incompatibility loci. Crossing experiments included self- and cross-pollinations in the laboratory followed by microscopic observation of pollen tube growth and fruit set assay in the field. After crossing experiments, two accessions, 'Son Miró' and 'Talegal Ahín', were self-compatible while the other two were self-incompatible. Inheritance of S-locus and microsatellite EMPaS02 (linked to self-compatibility, Sc) were investigated in self-pollination progeny of both self-compatible genotypes. Results indicate that self-compatibility in 'Talegal Ahín' is similar to self-compatibility described in sweet cherry 'Cristobalina' and may be caused by the same mutation. That is a pollen part mutation not linked to the S-locus but linked to microsatellite EMPaS02 in cherry LG3. In 'Son Miró' self-compatibility seems more complex, affecting pollen and style function, and probably involving more than one mutation not described previously in sweet cherry. Together with 'Cristobalina', the newly described self-compatible varieties 'Son Miró' and 'Talegal Ahín' confirm the existence of unique self-compatible plant material in local germplasm from Spain that should be conserved and characterized for its use in breeding and research. [ABSTRACT FROM AUTHOR]

Highlights: [•] We identified the S-genotype of 13 North Western European pear cultivars. [•] All described cultivars differed by their S-genotypes. [•] Several identified S-alleles were rare alleles. [Copyright &y& Elsevier]

Using 11 consensus primer pairs designed from S-linked F-box genes of apple and Japanese pear, 10 new F-box genes ( MdFBX21 to 30) were isolated from the apple cultivar 'Spartan' ( S S). MdFBX21 to 23 and MdFBX24 to 30 were completely linked to the S- RNase and S- RNase, respectively, and showed pollen-specific expression and S-haplotype-specific polymorphisms. Therefore, these 10 F-box genes are good candidates for the pollen determinant of self-incompatibility in apple. Phylogenetic analysis and comparison of deduced amino acid sequences of MdFBX21 to 30 with those of 25 S-linked F-box genes previously isolated from apple showed that a deduced amino acid identity of greater than 88.0 % can be used as the tentative criterion to classify F-box genes into one type. Using this criterion, 31 of 35 F-box genes of apple were classified into 11 types (SFBB1-11). All types included F-box genes derived from S- and S-haplotypes, and seven types included F-box genes derived from S-, S-, and S-haplotypes. Moreover, comparison of nucleotide sequences of S- RNases and multiple F-box genes among S-, S-, and S-haplotypes suggested that F-box genes within each type showed high nucleotide identity regardless of the identity of the S- RNase. The large number of F-box genes as candidates for the pollen determinant and the high degree of conservation within each type are consistent with the collaborative non-self-recognition model reported for Petunia. These findings support that the collaborative non-self-recognition system also exists in apple. [ABSTRACT FROM AUTHOR]

Most fruit trees in the Rosaceae exhibit self-incompatibility, which is controlled by the pistil S gene, encoding a ribonuclease (S-RNase), and the pollen S gene at the S-locus. The pollen S in Prunus is an F-box protein gene (SLF/SFB) located near the S-RNase, but it has not been identified in Pyrus and Malus. In the Japanese pear, various F-box protein genes (PpSFBB-α–γ) linked to the S-RNase are proposed as the pollen S candidate. Two bacterial artificial chromosome (BAC) contigs around the S-RNase genes of Japanese pear were constructed, and 649 kb around S4-RNase and 378 kb around S2-RNase were sequenced. Six and 10 pollen-specific F-box protein genes (designated as PpSFBB4-u1–u4, 4-d1–d2 and PpSFBB2-u1–u5, 2-d1–d5, respectively) were found, but PpSFBB4-α–γ and PpSFBB2-γ were absent. The PpSFBB4 genes showed 66.2–93.1% amino acid identity with the PpSFBB2 genes, which indicated clustering of related polymorphic F-box protein genes between haplotypes near the S-RNase of the Japanese pear. Phylogenetic analysis classified 36 F-box protein genes of Pyrus and Malus into two major groups (I and II), and also generated gene pairs of PpSFBB genes and PpSFBB/Malus F-box protein genes. Group I consisted of gene pairs with 76.3–94.9% identity, while group II consisted of gene pairs with higher identities (>92%) than group I. This grouping suggests that less polymorphic PpSFBB genes in group II are non-S pollen genes and that the pollen S candidates are included in the group I PpSFBB genes. [ABSTRACT FROM PUBLISHER]

Heterostyly is a plant breeding system occurring in approximately 28 plant families and it has often been used as a model system in plant genetics and evolution. Although heterostyly has been studied for over a century beginning with Charles Darwin, the genes determining floral architecture and incompatibility are still unknown. To identify the genes residing at the S-locus of distylous Turnera subulata, we used a positional cloning strategy and assembled three BAC contigs across the S-locus region. In total, 31 overlapping BAC clones were assembled into contigs 1, 2 and SL. We developed and mapped numerous co-dominant markers from the ends of BAC clones across the S-locus region and assayed X-ray deletion mutants to delimit the region of the contig containing the S-locus. Deletion mapping revealed that a single BAC clone (L22s) within contig-SL contains the s haplotype, while two additional BAC clones (I1 and K15) may contain parts of the dominant S haplotype. Furthermore, we exploited the contigs assembled and investigated the rates of recombination at the S-locus as well as in two regions on either side of the S-locus. We found that recombination rates (estimated in kb/cM) are 2-5 times lower at the S-locus relative to flanking regions, although they are not statistically significant. The present study represents a landmark in the molecular characterization of the S-locus of a heterostylous species. We are now on the verge of identifying the genes that have remained elusive since Darwin's comprehensive study of heterostylous systems more than 125 years ago. [ABSTRACT FROM AUTHOR]

The effect of selection on patterns of genetic structure within and between populations may be studied by contrasting observed patterns at the genes targeted by selection with those of unlinked neutral marker loci. Local directional selection on target genes will produce stronger population genetic structure than at neutral loci, whereas the reverse is expected for balancing selection. However, theoretical predictions on the intensity of this signal under precise models of balancing selection are still lacking. Using negative frequency-dependent selection acting on self-incompatibility systems in plants as a model of balancing selection, we investigated the effect of such selection on patterns of spatial genetic structure within a continuous population. Using numerical simulations, we tested the effect of the type of self-incompatibility system, the number of alleles at the self-incompatibility locus and the dominance interactions among them, the extent of gene dispersal, and the immigration rate on spatial genetic structure at the selected locus and at unlinked neutral loci. We confirm that frequency-dependent selection is expected to reduce the extent of spatial genetic structure as compared to neutral loci, particularly in situations with low number of alleles at the self-incompatibility locus, high frequency of codominant interactions among alleles, restricted gene dispersal and restricted immigration from outside populations. Hence the signature of selection on spatial genetic structure is expected to vary across species and populations, and we show that empirical data from the literature as well as data reported here on three natural populations of the herb Arabidopsis halleri confirm these theoretical results. [ABSTRACT FROM AUTHOR]

Abstract: Since self-compatibility has become the primary objective of most almond breeding programmes, search for new self-compatibility sources has acquired a great importance in almond research. The local Spanish cultivar ‘Vivot’, identified as showing the genotype S 23 S f , thus presumably self-compatible, was found to be unexpectedly self-incompatible in spite of the presence of the S f allele, as also observed in other almond cultivars. However, not only the coding sequences of both the S f -RNase and the SFB f of ‘Vivot’ and ‘Blanquerna’, a confirmed self-compatible cultivar, were identical, but also the 5′ regulatory sequence of the S f -RNase of both. Thus, the reason for the different expression of the S f is independent of the complete genetic identity found in the whole chromosome region bordering the S-locus in the almond cultivars sharing the S f allele. [Copyright &y& Elsevier]

We review and analyze the available literature on the frequency and distribution of self-incompatibility (SI) among angiosperms and find that SI is reported in more than 100 families and occurs in an estimated 39% of species. SI frequently has been lost but rarely has been gained during angiosperm diversification, and there is no evidence that any particular system of SI, once lost, has been regained. Irreversible loss of SI systems is thought to occur because transitions to self-compatibility (SC) are accompanied by collapse of variation at the S-locus and by accumulation of loss-of-function mutations at multiple loci involved in the incompatibility response. The asymmetry in transitions implies either that SI is declining in frequency or that it provides a macroevolutionary advantage. We present a model in which the loss of SI is irreversible and species can be SI, SC but outcrossing, or predominantly selfing. Increased diversification rates of SI relative to SC taxa are required to maintain SI at equilibrium, while transition rates between states, together with state-specific diversification rates, govern the frequency distribution of breeding-system states. We review empirical studies about the causes and consequences of the loss of SI, paying particular attention to the model systems Arabidopsis and Solanum sect. Lycopersicon. In both groups, losses of SI have been recent and were accompanied by loss of most or all of the functional variation at the S-locus. Multiple loss-of-function mutations are commonly found. Some evidence indicates that mutations causing SC strongly increase the selfing rate and that SC species have lower genetic diversity than their SI relatives, perhaps causing an increase in the extinction rate. [ABSTRACT FROM AUTHOR]

Primula species provide possibly the best known examples of heteromorphic flower development and this breeding system has attracted considerable attention, including that of Charles Darwin. However, despite considerable recent advances in molecular genetics, nothing is known about the molecular basis of floral heteromorphy. The first molecular marker for the Primula S-locus is reported here. This DNA sequence was identified by random amplification of polymorphic DNA (RAPD)-PCR, further defined as a sequence characterized amplified region (SCAR) marker, and subsequently shown to correspond to a restriction fragment length polymorphism (RFLP) that is linked to the thrum allele of the Primula S-locus. The sequence of 8.8 kb of genomic DNA encompassing this thrum-specific RFLP is presented. Analysis of this DNA reveals a highly repetitive sequence structure similar to that found at the S-locus in other species; it also contains sequences similar to elements of a Gypsy-like retrotransposon. The identification of a specific DNA sequence associated with the thrum allele of the Primula S-locus provides the first molecular probe with which to investigate the molecular basis of heteromorphic flower development in Primula. [ABSTRACT FROM PUBLISHER]

Sporophytic self-incompatibility of diploid Ipomoea trifida is controlled by a single multiallelic locus, the S-locus. To make a fine linkage map around the S-locus, AFLP (amplified restriction fragment length polymorphism) and AMF (AFLP-based mRNA fingerprinting) analyses were performed using bulked genomic DNA and mRNA, respectively, from several plants of each S-haplotype in a segregating population. Putative S-haplotype-specific fragments were obtained and subjected to RFLP analysis of genomic DNA to confirm genetic linkage to the S-locus. Eight DNA markers co-segregating with the S-haplotype were identified and mapped in close proximity to the S-locus. One of them, AAM-68, was the most tightly linked to the S-locus, because no recombinants were detected in the 873 plants of the segregating population analyzed. The S-locus region was defined to be within 1.25 cM in the linkage map. These markers are useful for positional cloning of the S-locus genes in Ipomoea. [ABSTRACT FROM AUTHOR]

Escape of transgenes from genetically modified oilseed rape, Brassica napus, into wild radish, Raphanus raphanistrum, depends on sexual compatibility. The variation in prezygotic barriers of two different cultivars for interspecific hybridization with a population of wild radish was investigated by hand crossing and fluorescence microscopy of pistils. Significant differences were observed between oilseed rape cultivars in their ability to accept wild radish pollen germinating onto their stigma and the rate of fertilization of ovules. Some differences among the pollen donor plants were also detected. These results suggest that the rate of interspecific hybridization in the field would depend upon the oilseed rape cultivar and the genotype composition of the local wild populations. The implication of S-related genes, as revealed through identification by pistil tissue prints of class I and II S-types of SLG (S-Locus Glycoprotein) and SLR1 (S-Locus Related), and immuno-IEF, was not significant. [ABSTRACT FROM AUTHOR]

In Brassica, self-incompatibility genes SLG (for S-locus glycoprotein) and SRK (for S-receptor kinase) are located in the S-locus complex region with several other S-linked genes. The S locus is a highly polymorphic region: polymorphism has been observed not only in sequences of SLG and SRK but also in the location of the S-locus genes. In order to compare the physical location of the S-locus genes in various S haplotypes, we used six class-I S haplotypes of B. rapa and seven class-I S haplotypes of B. oleracea in this study. DNA gel blot analysis using pulsed-field gel electrophoresis (PFGE) showed that the physical distances between SLG and SRK in B. rapa are significantly shorter than those in B. oleracea and that the sizes of MluI and BssHII fragments harboring SLG and SRK are less variable within B. rapa than within B. oleracea. We concluded that several large genomic fragments might have been inserted into the S-locus region of B. oleracea after allelic differentiation of S-locus genes. [ABSTRACT FROM AUTHOR]