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The reproductive mechanism of Kernel-apricot involves Gametophytic self-incompatibility (GSI) which is under S-allele control. It encodes a polymorphic pistil ribonuclease (S-RNase), which is multiallelic and ideal markers for S-genotypes characterisation. In this study, six S-RNase primers were used to identify theS-genotypes of 10 Kernel-apricot, including three self-design primers and three universal primers. Ten S-alleles were identified in 10 Kernel-apricot through sequencing and comparing in NCBI. Moreover, some Kernel-apricot S-genotypes were confirmed by experiment of fruit-setting ratio and pollen tube growth. In conclusion, S-genotypes information of Kernel-apricot will be helpful for breeders and growers to plan compatible hybridised combination for ensuring effective pollination and high fruit-setting ratio. [ABSTRACT FROM AUTHOR]

Plant self-incompatibility (SI) is of great significance in reproductive biology and is also the main factor affecting yield in agricultural production. Late-acting self-incompatibility (LSI) is one of the main types of plant SI, but the mechanism of LSI is not systematically analyzed. Tea oil Camellia, a strictly outcrossing plant, is a well-known woody oil cash crop. SI is one of the main reasons for the low yield of tea oil Camellia. In this study, we found that C. drupifera , one of the main species of tea oil Camellia, shows LSI, in which SI occurs in the style, and pollen tube growth in the ovary ceases at 96 h after selfing. The CdS-RNase gene of Camellia drupifera was successfully cloned, and the gene showed a length of 922 bp and encoded 238 amino acids. CdS-RNase had typical S-RNase characteristics. The functional validation results revealed that CdS-RNase was a key female factor for SI in C. drupifera , indicating that S-RNase plays an important role in the plant LSI mechanism. CdS-RNase localized to the cell membrane, was specifically expressed in the style and transferred to the ovary, and inhibited pollen tube growth in the style and ovary. There was an "enhancer factor" for the expression of CdS-RNase in selfing styles. Between 24 h and 48 h after selfing, CdS-RNase expression was significantly upregulated 28.3 times, which was more than 2.5 times higher than the outcross expression level and more than 5 times lower than the cross expression level. A total of 28 CdS-RNase proteins were identified, including 6 CdSm-RNases, and outcrossing among different CdS-RNase genotypes had a significant effect on the fruit setting rate. It may be that mismatches among CdS-RNase genotypes and self-inbreeding are the main reasons for the low yield of C. drupifera. These results provide a basis for the systematic analysis of the LSI mechanism and for solving the SI problem of tea oil Camellia. • The first combined field pollination test comprehensively confirmed CdS-RNase as a determinant of LSI. • Confirm that S-RNase plays an important role in inhibiting the growth of self pollinating pollen tubes in the ovary. • The first analysis proposed that there was an "enhancing factor" that enhanced CdS-RNase expression. • Confirm that outcrossing combinations among different S genotypes had a significant effect on fruit rate. [ABSTRACT FROM AUTHOR]

PREMISE OF THE STUDY: Self-incompatibility (SI) prevents self-fertilization and reduces inbreeding. While SI is common in plants, transitions to self-compatibility (SC) occur frequently. Little is known about the genetic changes and evolutionary steps underlying these shifts. METHODS: In the Solanaceae, SI is gametophytic, with specificity determined by S-RNases in the pistil and S-locus F-box proteins (SLFs) in pollen. We examined the role of two pollen factors, Cullin1 (CUL1) and SLF-23, in SI → SC transitions in wild tomato species from the Arcanum species group ( Solanum arcanum, S. neorickii, and S. chmielewskii). Pollen compatibility was assessed on tester lines that reject pollen lacking functional SLF-23 or CUL1. Complementation tests, gene sequencing, and phylogenetic analyses were used to characterize both functional and nonfunctional alleles. KEY RESULTS: We found evidence for multiple independent SI → SC transitions. In S. arcanum and S. chmielewskii, SC is caused by loss of pistil S-RNase activity, while in S. neorickii SC is associated with expression of a functional SLF-23 that recognizes the S9 type S-RNase expressed in its pistils. Interestingly, we found identical deletion mutations in CUL1 exon 7 of S. chmielewskii as previously seen in S. habrochaites. CONCLUSIONS: Mating system transitions in the Arcanum group have occurred via both pistil loss-of-function and pollen gain-of-function SC mutations. Mutations common to S. chmielewskii and S. habrochaites must have arisen in a common ancestor, possibly to the entire tomato clade, then became fixed in different lineages after loss of pistil-side SI function. [ABSTRACT FROM AUTHOR]

Loquat ( Eriobotrya japonica Lindl) is an evergreen fruit tree and belongs to Maloideae in the Rosaceae, which carries the RNase-dependent gametophytic self-incompatibility system (GSI). Use of appropriate pollinator trees is essential for increasing fruit production. S -allele specific amplification system is an efficient and rapid method to identify S -genotypes. In this research, according to the sequences of S-RNase alleles, 9 specific primer pairs for amplifying S-RNase alleles ( S 2 , S 7 , S 6 , S 8 , S 9 , S 10 , S 11 ,S 12 and S 13 ) were designed, which located in the introns or in the areas with high polymorphism. The specificity of the 9 allele specific primer pairs was evaluated by eight loquat cultivars with known S -genotypes. After being verified their effectiveness, they were used to S- genotype 39 loquat cultivars from Longan and loquat nurseries in Fuzhou national fruit germplasm. The results showed that the 39 loquat cultivars were S- genotyped efficiently by allele specific PCR with the 9 primer pairs, in which 28 cultivars were identified for the first time and they were classified into 18 groups according to the genotype. The results also proved that the 9 S- allele specific primer pairs can efficiently identified S- genotype, which will be very useful for choosing pollinators or crossing parents in loquat production and breeding. [ABSTRACT FROM AUTHOR]

Key message: Candidate genes were identified and the role of phytohormones such as JA-Me and ABA in the synthesis of S-RNase was emphasized in pear self-incompatibility. Abstract: Self-incompatibility (SI) occurs widely in flowering plants as an intraspecific reproductive barrier. This phenomenon promotes variation within species, but for some species such as Pyrus, SI is a nuisance rather than a benefit in agricultural production. Although many studies have been conducted on SI in pears, its mechanism remains unclear. In this study, high-throughput Illumina RNA sequencing (RNA-seq) was used to identify SI-related genes in pear styles. Using transcriptome comparisons, differentially expressed genes of unpollinated (UP), cross-pollinated (CP), and self-pollinated (SP) styles were identified after 48 h. A total of 1796 and 1890 genes were identified in DSC (UP vs. CP) and DSI (UP vs. SP), respectively. KEGG analysis revealed that genes involved in the 'plant hormone signal transduction pathway' and 'plant-pathogen interaction pathway' were significantly enriched in DSI (UP vs. SP) compared to those in DSC (UP vs. CP). The expression level of S-glycoprotein ribonuclease (S-RNase) was dramatically reduced in cross-pollinated (CP) styles. To better understand the relationship between the expression patterns of S-RNase and two major KEGG pathways, the concentrations of phytohormones were measured, and the expression pattern of S-RNase was analysed using qRT-PCR. Our results demonstrate that methyl jasmonate and abscisic acid may enhance the expression level of S-RNase, and pollination can affect the synthesis of methyl jasmonate and abscisic acid in pear styles. Overall, this study is a global transcriptome analysis of SI in pear. A relationship between self-rejection, plant hormones, and pathogen defence was shown in pear. [ABSTRACT FROM AUTHOR]

Seedlessness is an excellent economical trait, and self-incompatibility (SI) is one of important factors resulting in seedless fruit in Citrus . However, SI molecular mechanism in Citrus is still unclear. In this study, RNA-Seq technology was used to identify differentially expressed genes related to SI reaction of ‘Wuzishatangju’ ( Citrus reticulata Blanco). A total of 35.67 GB raw RNA-Seq data was generated and was de novo assembled into 50,364 unigenes with an average length of 897 bp and N50 value of 1549. Twenty-three candidate unigenes related to SI were analyzed using qPCR at different tissues and stages after self- and cross-pollination. Seven pollen S genes ( Unigene0050323 , Unigene0001060 , Unigene0004230 , Unigene0004222 , Unigene0012037 , Unigene0048889 and Unigene0004272 ), three pistil S genes ( Unigene0019191 , Unigene0040115 , Unigene0036542 ) and three genes ( Unigene0038751 , Unigene0031435 and Unigene0029897 ) associated with the pathway of ubiquitin-mediated proteolysis were identified. Unigene0031435 , Unigene0038751 and Unigene0029897 are probably involved in SI reaction of ‘Wuzishatangju’ based on expression analyses. The present study provides a new insight into the molecular mechanism of SI in Citrus at the transcriptional level. [ABSTRACT FROM AUTHOR]

Loquat ( Eriobotrya japonica Lindl.), a member of Rosaceae, exhibits gametophytic self −incompatibility (GSI) that is controlled by the multiallelic S- locus. The S -locus encodes polymorphic S-RNase for the pistil-part S determinant. Identifying the S- genotypes of loquat cultivars is important for the selection of pollen donors for fruit production and breeding of loquat cultivars. In this study, we determined 20 loquat cultivar S- genotypes by PCR-based analysis with the consensus and allele-specific primers. In the 20 loquat cultivars, 9 S- haplotypes were identified including 7 S-RNases ( S 2 , S 7 , S 6 , S 8 , S 9 , S 10 , S 11 ) previously reported and two new S-RNase alleles. The partial genomic sequences of the two new S- RNases show high similarity (>95%) with Pyrus S-RNase, inserted by an intron in hypervariable region (RHV) with the length of 151 bp and 806 bp respectively, and encode amino acid sequences having the common structures of S-RNases. The two S-RNase genes were deposited in GenBank with name S 12 -RNase (accession number: KR149297) and S 13 -RNase (accession numbers: KR149298). Twenty loquat cultivars were classified into 12 groups according to S- genotypes. Seventeen cultivars have two different S- haplotypes except ‘Fengyu’, ‘Ninghaibai’ and ‘Bahong’ containing one S- haplotype. This research would contribute to a more efficient breeding program and pollinator selection of loquat. [ABSTRACT FROM AUTHOR]

Self-incompatibility ( SI) is a self/non-self discrimination system found widely in angiosperms and, in many species, is controlled by a single polymorphic S-locus. In the Solanaceae, Rosaceae and Plantaginaceae, the S-locus encodes a single S- RNase and a cluster of S-locus F-box ( SLF) proteins to control the pistil and pollen expression of SI, respectively. Previous studies have shown that their cytosolic interactions determine their recognition specificity, but the physical force between their interactions remains unclear. In this study, we show that the electrostatic potentials of SLF contribute to the pollen S specificity through a physical mechanism of 'like charges repel and unlike charges attract' between SLFs and S- RNases in Petunia hybrida. Strikingly, the alteration of a single C-terminal amino acid of SLF reversed its surface electrostatic potentials and subsequently the pollen S specificity. Collectively, our results reveal that the electrostatic potentials act as a major physical force between cytosolic SLFs and S- RNases, providing a mechanistic insight into the self/non-self discrimination between cytosolic proteins in angiosperms. [ABSTRACT FROM AUTHOR]

Self-incompatibility (SI) prevents inbreeding depression in angiosperms. Camellia sinensis is an important cash crop, but breeding improvements and genetic studies of the plant are hindered by SI. However, the SI mechanism in C. sinensis remains unclear. In this study, a putative S-RNase gene (KU852488) was cloned from C. sinensis . The full-length cDNA of CsS-RNase is 1121 bp, which encodes 238 amino acids. It shares the closest relationship with an S-RNase gene (ADA67883.1), which was cloned from a self-incompatibility Citrus reticulata cultivar ‘Wuzishatangju’. The expression level of CsS-RNase in the styles were 3–259 (‘Fuding Dabaicha’) and 5.6–119 (‘Zhongcha108’) times higher than the other tissues, for example petals, pollen grains, filaments and buds. And its expression rose in self-pollinated styles with 24 h earlier than cross-pollinated styles. The genotypes of CsS-RNase in 10 cultivars and one breeding line of C. sinensis were analyzed. Totally, 11 polymorphic amino acid residues were identified. A single nucleotide polymorphism (SNP) marker of CsS-RNase was developed. Finally, the CsS-RNase was mapped onto a reference genetic linkage map of tea plant. [ABSTRACT FROM AUTHOR]

The family Rosaceae includes a range of important fruit trees, most of which have the S-RNase-based self-incompatibility (SI). Several models have been developed to explain how pollen (SLF) and pistil (S-RNase) components of the S-locus interact. It was discovered in 2010 that additional SLF proteins are involved in pollen specificity, and a Collaborative Non-Self Recognition model has been proposed for SI in Solanaceae; however, the validity of such model remains to be elucidated for other species. The results of this study support the divergent evolution of the S-locus genes from two Rosaceae subfamilies, Prunoideae/Amygdaloideae and Maloideae, The difference identified in the selective pressures between the two lineages provides evidence for positive selection at specific sites in both the S-RNase and the SLF proteins. The evolutionary findings of this study support the role of multiple SLF proteins leading to a Collaborative Non-Self Recognition model for SI in the Maloideae. Furthermore, the identification of the sites responsible for SI specificity determination and the mapping of these sites onto the modelled tertiary structure of ancestor proteins provide useful information for rational functional redesign and protein engineering for the future engineering of new functional alleles providing increased diversity in the SI system in the Maloideae. [ABSTRACT FROM AUTHOR]

Gametophytic self-incompatibility in Japanese pear (Pyrus pyrifolia Nakai) is controlled by the single, multiallelic S-locus. Information about the S-genotypes is important for breeding and the selection of pollen donors for fruit production. Rapid and reliable S-genotype identification system is necessary for efficient breeding of new cultivars in Japanese pear. We designed S allele-specific PCR primer pairs for ten previously reported S-RNase alleles (S¹-S9 and Sk) as simple and reliable method. Specific nucleotide sequences were chosen to design the primers to amplify fragments of only the corresponding S alleles. The developed primer pairs were evaluated by using homozygous S-genotypes (S¹/S¹-S9/S9 and S4sm/S4sm) and 14 major Japanese pear cultivars, and found that S allele-specific primer pairs can identify S-genotypes effectively. The S allele-specific primer pairs developed in this study will be useful for efficient S-genotyping and for marker-assisted selection in Japanese pear breeding programs. [ABSTRACT FROM AUTHOR]

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Seedlessness is a desirable character in lemons and other citrus species. Seedless fruit can be induced in many ways, including through self-incompatibility (SI). SI is widely used as an intraspecific reproductive barrier that prevents self-fertilization in flowering plants. Although there have been many studies on SI, its mechanism remains unclear. The 'Xiangshui' lemon is an important seedless cultivar whose seedlessness has been caused by SI. It is essential to identify genes involved in SI in 'Xiangshui' lemon to clarify its molecular mechanism. In this study, candidate genes associated with SI were identified using high-throughput Illumina RNA sequencing (RNA-seq). A total of 61,224 unigenes were obtained (average, 948 bp; N50 of 1,457 bp), among which 47,260 unigenes were annotated by comparison to six public databases (Nr, Nt, Swiss-Prot, KEGG, COG, and GO). Differentially expressed genes were identified by comparing the transcriptomes of no-, self-, and cross-pollinated stigmas with styles of the 'Xiangshui' lemon. Several differentially expressed genes that might be associated with SI were identified, such as those involved in pollen tube growth, programmed cell death, signal transduction, and transcription. NADPH oxidase genes associated with apoptosis were highly upregulated in the self-pollinated transcriptome. The expression pattern of 12 genes was analyzed by quantitative real-time polymerase chain reaction. A putative S- RNase gene was identified that had not been previously associated with self-pollen rejection in lemon or citrus. This study provided a transcriptome dataset for further studies of SI and seedless lemon breeding. [ABSTRACT FROM AUTHOR]

S-RNase-based self-incompatibility in Petunia is a self/non-self recognition system that allows the pistil to reject self-pollen to prevent inbreeding and to accept non-self pollen for outcrossing. Cloning of S-RNase in 1986 marked the beginning of nearly three decades of intensive research into the mechanism of this complex system. S-RNase was shown to be the sole female determinant in 1994, and the first male determinant, S-locus F-box protein1 (SLF1), was identified in 2004. It was discovered in 2010 that additional SLF proteins are involved in pollen specificity, and recently two S-haplotypes of Petunia inflata were found to possess 17 SLF genes based on pollen transcriptome analysis, further increasing the complexity of the system. Here, we first summarize the current understanding of how the interplay between SLF proteins and S-RNase in the pollen tube allows cross-compatible pollination, but results in self-incompatible pollination. We then discuss some of the aspects that are not yet elucidated, including uptake of S-RNase into the pollen tube, nature, and assembly of SLF-containing complexes, the biochemical basis for differential interactions between SLF proteins and S-RNase, and fate of non-self S-RNases in the pollen tube. [ABSTRACT FROM AUTHOR]

The flowering plant Solanum chacoense uses an S-RNase-based self-incompatibility system in order to reject pollen that shares the same genes at the S-locus (S-haplotype) with the style (an incompatible reaction). Two different models have been advanced to explain how compatible pollen tubes are protected from the cytotoxic effects of the S-RNase, sequestration of the S-RNase in a vacuolar compartment or degradation of the S-RNase in the cytoplasm. Here, we examine the subcellular distribution of an S11-RNase 18 and 24 h post pollination (hpp) in compatible and incompatible crosses by immunogold labeling and transmission electron microscopy. We find that the S-RNase is present in the cytoplasm of both compatible and incompatible crosses by 18 hpp, but that almost all the cytoplasmic S-RNase is degraded by 24 hpp in compatible crosses. These results provide compelling evidence that S-RNases are degraded in compatible but not in incompatible pollen tubes. [ABSTRACT FROM AUTHOR]

Self-incompatibility ( SI) is a reproductive isolation mechanism in flowering plants. Plants in the Solanaceae, Rosaceae and Plantaginaceae belong to the gametophytic self-incompatibility type. S- RNase, which is encoded by a female-specific gene located at the S locus, degrades RNA in the pollen tube and causes SI. Recent studies have provided evidence that S- RNase is transported non-selectively into the pollen tube, but have not specified how this transportation is accomplished. We show here that the apple ( Malus domestica) MdABCF protein, which belongs to group F of the ABC transporter family, assists in transportation of S- RNase into the pollen tube. MdABCF is located in the pollen tube membrane and interacts with S- RNase. S- RNase was unable to enter the pollen tube when MdABCF was silenced by antisense oligonucleotide transfection. Our results show that MdABCF assists in transportation of either self or non-self S- RNase into the pollen tube. Moreover, MdABCF coordinates with the cytoskeleton to transport S- RNase. Blockage of S- RNase transport disrupts self-incompatibility in this system. [ABSTRACT FROM AUTHOR]

S-RNase is the female determinant of gametophytic self-incompatibility in apple and is usually considered to be the reason for rejection of pollen. In this study, we investigated the role of microtubules (MTs) in internalization of S-RNases by pollen tubes cultured in vitro. The results showed that S-RNase was imported into the pollen tube where it inhibits pollen tube growth, and that S-RNase is co-localized with the Golgi vesicle during the internalization process. Moreover, MT depolymerization is observed following accumulation of S-RNases in the pollen cytosol. On the other hand, S-RNase was prevented from entering the pollen tube when the pollen was treated with the actin filament (AF) inhibitor latrunculin A (LatA), the MT inhibitor oryzalin, or the MT stabilizer taxol at subtoxic concentrations. These hindered the construction of the MT, with pollen tubes capable of growth under these conditions. Pollen tubes showed improved growth in self-pollinated styles that were pre-treated with taxol. This suggests that cytoskeleton antagonists can prevent S-RNase-mediated inhibition of pollen tubes in vivo by blocking S-RNase internalization. These results suggest that an intact and dynamic cytoskeleton is required for the in vitro internalization of S-RNase, as shown by the effects of various cytoskeleton inhibitors. S-RNase internalization takes place via a membrane/cytoskeleton-based Golgi vesicle system, which can also affect self-incompatibility in apple. [ABSTRACT FROM AUTHOR]

The Pyrus species exhibit the so-called S-RNase-based gametophytic self-incompatibility system, which is considered to be the most widespread self-incompatibility system among flowering plants. In this study, 57 Iranian pear ( Pyrus communis L.) domestic cultivars and wild genotypes, plus 21 European pear cultivars used as references, were genotyped adopting a PCR-based genotyping assay using consensus and allele-specific primers. The results revealed traces of significant genetic contribution in the Iranian traditional varieties and genotypes from other Pyrus species; the genetic contribution of Japanese pear clearly emerged with the detection of some Pyrus pyrifolia S-RNase alleles. Moreover, our results highlighted the presence of three new S-RNase alleles (named S, S, and S) that were not previously identified in P. communis, possibly introduced in the germplasm of cultivated pear through gene transfer from other cultivated or wild species. [ABSTRACT FROM AUTHOR]

The stylar determinant of gametophytic self-incompatibility (GSI) in Solanaceae, Rosaceae, and Plantaginaceae is an S-RNase encoded by a multiallelic S-locus. The primary structure of S-RNases shows five conserved (C) and two hypervariable (HV) regions, the latter forming a domain implicated in S-haplotype-specific recognition of the pollen determinant to SI. All S-RNases are glycosylated at a conserved site in the C2 region, although previous studies have shown that N-linked glycans at this position are not required for S-haplotype-specific recognition and pollen rejection. Here the incompatibility phenotype of three constructs derived from an originally monoglycosylated S11-RNase of Solanum chacoense, that were designed to explore the role of the HV domain in determining pollen recognition and the role of the N-linked glycan in the C2 region, is reported. In one series of experiments, a second glycosylation site was introduced in the HVa region to test for inhibition of pollen-specific recognition. This modification does not impede pollen rejection, although analysis shows incomplete glycosylation at the new site in the HVa region. A second construct, designed to permit complete glycosylation at the HVa site by suppression of the conserved site in the C2 region, did increase the degree of site occupancy, but, again, glycosylation was incomplete. Plants expressing this construct rejected S11 pollen and, surprisingly, also rejected S13 pollen, thus displaying an unusual dual specificity phenotype. This construct differs from the first by the absence of the conserved C2 glycosylation site, and thus the dual specificity is observed only in the absence of the C2 glycan. A third construct, completely lacking glycosylation sites, conferred an ability to reject only S11 pollen, disproving the hypothesis that lack of a conserved glycan would confer a universal pollen rejection phenotype to the plant. [ABSTRACT FROM AUTHOR]

As with other self-incompatible Prunus species, cultivars of Japanese apricot ( Prunus mume Sieb. et Zucc.) display the S-RNase-based gametophytic self-incompatibility system. In this study, S-genotypes of ten Japanese apricot cultivars native to China were subjected to polyacrylamide gel electrophoresis (PAGE) analysis using an efficient Prunus S-RNase primer pair, Pru-C2 and PCE-R. In addition, three new S-RNase genes ( S, S and S -RNase) and six new SFB genes ( PmSFB14, PmSFB18, PmSFB22, PmSFB24, PmSFB31 and PmSFB34) were identified and their sequences were characterized and deposited in the GenBank database. [ABSTRACT FROM AUTHOR]

Key message: We report a rapid and reliable method for S genotyping of Rosaceae fruit trees, which would to be useful for successful planting of cross-compatible cultivars in orchards. Abstract: Japanese plum ( Prunus salicina) and sweet cherry ( Prunus avium), belonging to the family Rosaceae, possess gametophytic self-incompatibility controlled by a single polymorphic locus containing at least two linked genes, S- RNase and SFB ( S-haplotype-specific F-box gene). For successful planting of cross-compatible cultivars of Rosaceae fruit trees in commercial orchards, it is necessary to obtain information on S genotypes of cultivars. Recently, a method of dot-blot analysis utilizing allele-specific oligonucleotides having sequences of SFB-HVa region has been developed for identification of S haplotypes in Japanese plum and sweet cherry. However, dot-blot hybridization requires considerable time and skill for analysis even of a small number of plant samples. Thus, a quick and efficient method for S genotyping was developed in this study. In this method, instead of a nylon membrane used for dot-blot hybridization, streptavidin-coated magnetic beads are used to immobilize PCR products, which are hybridized with allele-specific oligonucleotide probes. Our improved method allowed us to identify 10 S haplotypes ( S- a, S- b, S- c, S- d, S- e, S- f, S- h, S- k, S- 7 and S- 10) of 13 Japanese plum cultivars and 10 S haplotypes ( S- 1, S- 2, S- 3, S- 4, S- 4′, S- 5, S- 6, S- 7, S- 9 and S- 16) of 13 sweet cherry cultivars utilizing SFB or S- RNase gene polymorphism. This method would be suitable for identification of S genotypes of a small number of plant samples. [ABSTRACT FROM AUTHOR]

Many species in the families of Rosaceae, Solanaceae, and Scrophulariaceae exhibit gametophytic self-incompatibility, a phenomenon controlled by two polymorphic genes at the S-locus, style- S ( S-RNase) and pollen- S ( SFB). Sequences of both genes show high levels of diversity, characteristic of genes involved in recognition of self-incompatibility systems in plants. In this study, S -RNase and SFB alleles were cloned from Prunus armeniaca cv. Chuanzhihong (Chinese apricot). Sequence comparisons of deduced amino acid sequences revealed that the P. armeniaca S-haplotype has different SFB alleles, but shares a single S-RNase allele with P. armeniaca S-haplotype. Moreover, P. armeniaca S -RNase haplotype has a single and three different alleles with S -RNase of P. tenella (dwarf almond) and S -RNase of P. mira (smooth pit peach), respectively. The functionalities of SFB and SFB have been evaluated by pollen tube growth and controlled field tests of P. tenella and P. mira. Genetic analysis of the two intercrosses showed that progenies segregated 1:1 into two S-genotype classes, which is consistent with the expected ratio for semi-compatibility. These findings imply that the allelic function of the S-haplotype is identical to that of the S-haplotype in a self-incompatibility reaction. Thus, these two Prunus S-haplotypes are in fact two neutral variants of the same S-haplotype. The evolution of the S-allele is also discussed in terms of both functions and differences between S- and S-haplotypes in Prunus. [ABSTRACT FROM AUTHOR]

Self-incompatibility is an important genetic mechanism that prevents inbreeding and promotes genetic polymorphism and heterosis in flowering plants. Many fruit species in the Rosaceae, including apple, pear, plum, apricot, sweet cherry, Japanese apricot, and almond, exhibit typical gametophytic self-incompatibility (GSI) controlled by an apparently single multi-allelic locus. This locus encodes at least two components from both the pollen and the pistil, and controls recognition of self- and non-self pollen. Recently, the GSI system has been investigated at the molecular and cellular levels in Rosaceae, and findings have provided some important insights as to how these two genes interact within pollen tubes that lead to specific inhibition of germination and/or growth of self-pollen tubes. In this review, molecular features of S-determinants of both pistil and pollen, identification of S-alleles, mechanisms of self-incompatibility break-down, and evolution of S-alleles are presented. Moreover, hypothetical signal transduction models in a self-incompatible system in Rosaceae are proposed based on recent findings that indicate that several signal factors are involved in GSI responses. [ABSTRACT FROM PUBLISHER]

Japanese pear has a genetically controlled self-incompatibility system, but both the pollen-tube growth in a semi in vivo assay and fruit set after self-pollination differ considerably among cultivars. The percentage of styles in which pollen tubes have reached the base ranges from 0 to 36 %, a value determined by culture of styles in vitro, and fruit set ranges from 0.6 to 15.2 %. Based on these data, we have assigned a value for the self-incompatibility weakness to each cultivar. Here, we showed that pollen factors control the degree of self-incompatibility. When the pollen-tube growth of 13 cultivars was compared in a completely compatible 'Hougetsu' ( S S) style, it differed a fair amount among cultivars and showed a significantly positive relation to self-incompatibility weakness ( r = 0.707). The degree of self-incompatibility of pear is, therefore, determined by pollen factor(s) unrelated to the S-locus. Although the fruit set and fruit growth of 'Hougetsu' were not affected by the pollen donor, a positive relationship was also observed between seed number and self-incompatibility weakness ( r = 0.972). However, in a style with no S-RNase production (genotype: S S), the relationship disappeared ( r = 0.341) and pollen-tube growth was promoted by 12-36 % except in one cultivar. These results suggest that S-RNase functions as a cytotoxin on compatible pollen in a cultivar-dependent manner, and that the degree of inhibition is determined by pollen factor(s) unrelated to the S-locus. The pollen factor also functions on S-RNase in incompatible styles, resulting in a different degree of self-incompatibility. [ABSTRACT FROM AUTHOR]

The molecular bases of the gametophytic self-incompatibility (GSI) system of species of the subtribe Pyrinae (Rosaceae), such as apple and pear, have been widely studied in the last two decades. The characterization of S-locus genes and of the mechanisms underlying pollen acceptance or rejection have been topics of major interest. Besides the single pistil-side S determinant, the S-RNase, multiple related S-locus F-box genes seem to be involved in the determination of pollen S specificity. Here, we collect and review the state of the art of GSI in the Pyrinae. We emphasize recent genomic data that have contributed to unveiling the S-locus structure of the Pyrinae, and discuss their consistency with the models of self-recognition that have been proposed for Prunus and the Solanaceae. Experimental data suggest that the mechanism controlling pollen–pistil recognition specificity of the Pyrinae might fit well with the collaborative ‘non-self’ recognition system proposed for Petunia (Solanaceae), whereas it presents relevant differences with the mechanism exhibited by the species of the closely related genus Prunus, which uses a single evolutionarily divergent F-box gene as the pollen S determinant. The possible involvement of multiple pollen S genes in the GSI system of Pyrinae, still awaiting experimental confirmation, opens up new perspectives to our understanding of the evolution of S haplotypes, and of the evolution of S-RNase-based GSI within the Rosaceae family. Whereas S-locus genes encode the players determining self-recognition, pollen rejection in the Pyrinae seems to involve a complex cascade of downstream cellular events with significant similarities to programmed cell death. [ABSTRACT FROM AUTHOR]

Background and Aims The integrity of actin filaments (F-actin) is essential for pollen-tube growth. In S-RNase-based self-incompatibility (SI), incompatible pollen tubes are inhibited in the style. Consequently, research efforts have focused on the alterations of pollen F-actin cytoskeleton during the SI response. However, so far, these studies were carried out in in vitro-grown pollen tubes. This study aimed to assess the timing of in vivo changes of pollen F-actin cytoskeleton taking place after compatible and incompatible pollinations in Nicotiana alata. To our knowledge, this is the first report of the in vivo F-actin alterations occurring during pollen rejection in the S-RNase-based SI system. Methods The F-actin cytoskeleton and the vacuolar endomembrane system were fluorescently labelled in compatibly and incompatibly pollinated pistils at different times after pollination. The alterations induced by the SI reaction in pollen tubes were visualized by confocal laser scanning microscopy. Key Results Early after pollination, about 70 % of both compatible and incompatible pollen tubes showed an organized pattern of F-actin cables along the main axis of the cell. While in compatible pollinations this percentage was unchanged until pollen tubes reached the ovary, pollen tubes of incompatible pollinations underwent gradual and progressive F-actin disorganization. Colocalization of the F-actin cytoskeleton and the vacuolar endomembrane system, where S-RNases are compartmentalized, revealed that by day 6 after incompatible pollination, when the pollen-tube growth was already arrested, about 80 % of pollen tubes showed disrupted F-actin but a similar percentage had intact vacuolar compartments. Conclusions The results indicate that during the SI response in Nicotiana, disruption of the F-actin cytoskeleton precedes vacuolar membrane breakdown. Thus, incompatible pollen tubes undergo a sequential disorganization process of major subcellular structures. Results also suggest that the large pool of S-RNases released from vacuoles acts late in pollen rejection, after significant subcellular changes in incompatible pollen tubes. [ABSTRACT FROM AUTHOR]

The gametophytic self-incompatibility system in Rosaceae is controlled by a single highly polymorphic gene complex, termed the S locus, which is comprised of tightly linked stylar-expressed gene, S-RNase, with a pollen-expressed gene. In this study, seven novel S haplotype-specific F-box protein genes, PmSFB to PmSFB in Prunus mume, have been identified and characterised. Similarities amongst the deduced amino acid sequences of these SFBs ranged from 73.2% to 90.9%. Comparisons of two trans-specific pairs of haplotypes, PmS with PspS and PmS/ ParS with PspS, indicated high degrees of polypeptide sequence identity. The deduced amino acid sequences of PmSFB and PspSFB showed similarity scores of 99.1%. In addition, the deduced amino acid sequences of the corresponding S-RNases, PmS-RNase and PspS-RNase exhibited a high similarity score of 99.0%. The similarity scores of the sequences physically positioned between S-RNase and SFB in the PmS haplotype and PspS were 94.6%. The deduced amino acid sequence of PmSFB showed high similarity scores with those of PspSFB and ParSFB at 99.3% and 97.9%, respectively. At the deduced amino acid level, the similarity scores of the PmS-RNase with the PspS-RNase or the ParS-RNase were 99.0% or 99.1%, respectively. Moreover, the similarity score of the sequence separating S-RNase and SFB in PmS was 96.1% compared with that of the PspS haplotype and 99.0% compared with that of the ParS haplotype. Our results suggest that the S haplotypes in P. mume, P. armeniaca and P. spinosa may have a common ancestor. [ABSTRACT FROM AUTHOR]

Pyrus displays gametophytic self-incompatibility controlled by a single highly polymorphic gene complex termed S locus, which comprises a stylar-expressed gene ( S-RNase) tighlty linked with a pollen expressed gene, that determines the specificity of the self-incompatibility locus. Deduced amino acid sequence of 'Meigetsu' S-RNase in Pyrus pyrifolia and 'Kuerlexiangli' S-RNase in P. sinkiangensis showed 100% identity. S-RNase in Malus spectabilis was also found to be similar to S-RNase in P. pyrifolia with 96.9% identity in the deduced amino acid sequence. The intron, which is generally highly polymorphic between alleles, was also remarkably well conserved within these allele pairs. The intron of PpS-RNase showed 95.3 and 91.9% identity with PsS-RNase and MsS-RNase, respectively. Pollen tube growth in styles, pollen tube length in artificial media containing different S-RNases and segregation of S haplotypes in F plants revealed commonality of the recognition specificity between PpS-RNase and PsS-RNase and between PpS-RNase and MsS-RNase. Results suggested that PpS-RNase, PsS-RNase and MsS-RNase have maintained the same recognition specificity after the divergence of the two species and that amino acid substitutions found between PpS-RNase and MsS-RNase do not alter the recognition specificity. [ABSTRACT FROM AUTHOR]

Apricot (Prunus armeniaca L.) cultivars show a gametophytic self-incompatibility (GSI) system, like other fruit species of Rosaceae family. Thus, it is necessary to determine their S-genotypes in order for stable fruit set in commercial cultivation. S-genotypes of apricots were determined by PCR and test crosses. Three sets of consensus primers designed from Prunus S-RNases were used to amplify fragments containing the first and second S-RNase intron, respectively. Through the results obtained from the 3 PCRs, we could identify SI genotypes of 33apricot cultivars. Several cultivars such as 'Heiwa', 'Yamagata No.3' and 'Shinsuoomi' had the self-compatible (Sc) allele. Self-pollination tests revealed that cultivars with Sc allele were self-compatible. Cross-pollination tests confirmed that there was cross-incompatibility between the cultivars with the same S-genotypes. These results might be very useful for growers for effective pollination and for breeders using these in cross breeding programs. [ABSTRACT FROM AUTHOR]

Loquat ( Eriobotrya japonica Lindl.; Pyrinae, Rosaceae) is an evergreen fruit tree which is acquiring increasing importance as an alternative crop in warm-temperate and subtropical regions. Recent pollination studies suggest that crop intensification has resulted in a reduction of fruit productivity in different locations. Loquat exhibits gametophytic self-incompatibility (GSI) and, consequently, fruit set strongly depends on cross-pollination between intercompatible cultivars. S-genotyping and incompatibility group assignment is therefore essential for adequate loquat orchard design. This study reports the molecular characterization of the S- RNase allele composition of 31 loquat cultivars grown in Spain. PCR with primers developed from loquat S- RNase sequences was used in combination with high-performance capillary polyacrilamide electrophoresis for the fine-evaluation of length polymorphisms at the S- RNase gene. This approach allowed to uncover a new S- RNase allele ( S), whose sequence is reported and to characterize the first six S- RNase-based incompatibility groups (I-VI) in loquat, resulting from the combination of five S-alleles ( S- S). The large number of cultivars that could be assigned to only six groups suggests a narrow genetic base for this crop in Spain and stresses the need for careful determination of the S-genotype of cultivars in an attempt to overcome production problems associated with inadequate pollination. [ABSTRACT FROM AUTHOR]

Background S-RNase-based self-incompatibility (SI) occurs in the Solanaceae, Rosaceae and Plantaginaceae. In all three families, compatibility is controlled by a polymorphic S-locus encoding at least two genes. S-RNases determine the specificity of pollen rejection in the pistil, and S-locus F-box proteins fulfill this function in pollen. S-RNases are thought to function as S-specific cytotoxins as well as recognition proteins. Thus, incompatibility results from the cytotoxic activity of S-RNase, while compatible pollen tubes evade S-RNase cytotoxicity. Scope The S-specificity determinants are known, but many questions remain. In this review, the genetics of SI are introduced and the characteristics of S-RNases and pollen F-box proteins are briefly described. A variety of modifier genes also required for SI are also reviewed. Mutations affecting compatibility in pollen are especially important for defining models of compatibility and incompatibility. In Solanaceae, pollen-side mutations causing breakdown in SI have been attributed to the heteroallelic pollen effect, but a mutation in Solanum chacoense may be an exception. This has been interpreted to mean that pollen incompatibility is the default condition unless the S-locus F-box protein confers resistance to S-RNase. In Prunus, however, S-locus F-box protein gene mutations clearly cause compatibility. Conclusions Two alternative mechanisms have been proposed to explain compatibility and incompatibility: compatibility is explained either as a result of either degradation of non-self S-RNase or by its compartmentalization so that it does not have access to the pollen tube cytoplasm. These models are not necessarily mutually exclusive, but each makes different predictions about whether pollen compatibility or incompatibility is the default. As more factors required for SI are identified and characterized, it will be possible to determine the role each process plays in S-RNase-based SI. [ABSTRACT FROM PUBLISHER]

Self-incompatibility in the Solanaceae is mediated by S- RNase alleles expressed in the style, which confer specificity for pollen recognition. Nicotiana alata has been successfully used as an experimental model to elucidate cellular and molecular aspects of S-RNase-based self-incompatibility in Solanaceae. However, S- RNase alleles of this species have not been surveyed from natural populations and consequently the S-haplotype diversity is poorly known. Here the molecular and functional characterization of seven S- RNase candidate sequences, identified from a natural population of N. alata, are reported. Six of these candidates, S 5, S 27, S 70, S 75, S 107, and S 210, showed plant-specific amplification in the natural population and style-specific expression, which increased gradually during bud maturation, consistent with the reported S- RNase expression. In contrast, the S 63 ribonuclease was present in all plants examined and was ubiquitously expressed in different organs and bud developmental stages. Genetic segregation analysis demonstrated that S 27, S 70, S 75, S 107, and S 210 alleles were fully functional novel S- RNases, while S 5 and S 63 resulted to be non- S- RNases, although with a clearly distinct pattern of expression. These results reveal the importance of performing functional analysis in studies of S-RNase allelic diversity. Comparative phylogenetic analysis of six species of Solanaceae showed that N. alata S- RNases were included in eight transgeneric S-lineages. Phylogenetic pattern obtained from the inclusion of the novel S- RNase alleles confirms that N. alata represents a broad sample of the allelic variation at the S-locus of the Solanaceae. [ABSTRACT FROM AUTHOR]

Mate choice is an essential process during sexual plant reproduction, in which self-incompatibility (SI) is widely adopted as an intraspecific reproductive barrier to inhibit self-fertilization by many flowering plants. Genetic studies show that a single polymorphic S-locus, encoding at least two components from both the pollen and pistil sides, controls the discrimination of self and non-self pollen. In the Solanaceae, Plantaginaceae, and Rosaceae, an S-RNase-based SI mechanism is involved in such a discrimination process. Recent studies have provided some important clues to how a decision is made to accept cross pollen or specifically to reject self pollen. In this review, the molecular features of the pistil and pollen S-specificity factors are briefly summarized and then our current knowledge of the molecular control of cross-pollen compatibility (CPC) and self-pollen incompatibility (SPI) responses, respectively, is presented. The possible biochemical mechanisms of the specificity determinant between the pistil and pollen S factors are discussed and a hypothetical S-RNase endosome sorting model is proposed to illustrate the distinct destinies of pollen tubes following compatible and incompatible pollination. [ABSTRACT FROM PUBLISHER]

The endomembrane system offers many potential points where plant mating can be effectively controlled. This results from two basic features of angiosperm reproduction: the requirement for pollen tubes to pass through sporophytic tissues to gain access to ovules and the physiology of pollen tube growth that provides it with the capacity to do so. Rapid pollen tube growth requires extravagant exocytosis and endocytosis activity as cell wall material is deposited and membrane is recovered from the actively growing tip. Moreover, recent results show that pollen tubes take up a great deal of material from the pistil extracellular matrix. Regarding the stigma and style as organs specialized for mate selection focuses attention on their complementary roles in secreting material to support the growth of compatible pollen tubes and discourage the growth of undesirable pollen. Since these processes also involve regulated activities of the endomembrane system, the potential for regulating mating by controlling endomembrane events exists in both pollen and pistil. [ABSTRACT FROM PUBLISHER]

Abstract: Most Prunus fruit tree species exhibit a homomorphic gametophytic self-incompatibility (GSI) system, in which specificity of self/nonself-recognition is controlled by products encoded within the S locus. In the pollination event, a self-incompatibility (SI) reaction is triggered when the same “S allele” specificity is expressed in both the pollen and pistil. During the last two decades, much progress has been made in our understanding of the molecular basis of the gametophytic self-incompatibility system in Prunus. Identification of the pistil S and pollen S determinants led to the development of PCR-based S genotyping and marker-assisted selection for self-compatible (SC) individuals. Molecular and genetic analyses of Prunus SC S haplotypes and polyploid sour cherry (Prunus cerasus) reveal the possible existence of a distinct SI/SC recognition mechanism in the S-RNase-based GSI system of Prunus. This review summarizes the current molecular knowledge of the S-RNase-based GSI system in Prunus with reference to data collected for S-RNase-based GSI in other plants and its potential usefulness in SC breeding. [Copyright &y& Elsevier]

Abstract: In the last 5 years 18 S-RNase alleles have been cloned from European pear (Pyrus communis L.). The annotation of the S-RNase alleles that have been cloned from European pear (Pyrus communis L.) was not consistent, and they were named both by letters and by numbers. In addition crosses between European and Japanese pear (Pyrus pyrifolia Nakai) for breeding purposes created the need to distinguish clearly between the origins of the various S-RNases. In an attempt to end this confusion, a joint decision of the research groups that had cloned the European pear S-RNase alleles and had S-genotyped many of the cultivars, undertook to renumber the European pear S-RNase alleles. The new numeration starts from 101 where the first digit unequivocally identifies the S-RNase alleles as belonging to the European pear gene pool. Accordingly, the new S-genotype designations of 133 European pear cultivars are presented. In addition, a description of the 18th pear S-RNase allele, S109, is reported. [Copyright &y& Elsevier]

Almond is a highly heterozygous species with a high number of S-alleles controlling its gametophytic self-incompatibility system (GSI). In this work, we have analysed 14 Spanish local almond cultivars for S-RNase allele diversity. Five new S-RNase alleles were identified by cloning and sequencing, S 31 (804 bp) in ‘Pou de Felanitx’ and ‘Totsol’, S 32 (855 bp) in ‘Taiatona’, S 33 (1165 bp) in ‘Pou d’Establiments’ and ‘Muel’, S 34 (1663 bp) in ‘Pané-Barquets’ and S 35 (1658 bp) in ‘Planeta de les Garrigues’. Additionally, seven already known almond alleles could be recognized in the local cultivars studied. The high number of new alleles identified reveals the wide diversity of almond germplasm still existing and requiring characterization, and points to the possibility of new findings by a wider study focusing on other provenances. The almond S-RNases have been compared to those of other Prunus species, showing a high identity and confirming that the S-RNase gene in this genus presents a probable common ancestor. [ABSTRACT FROM AUTHOR]

Tetraploid sour cherry (Prunus cerasus L.) exhibits gametophytic self-incompatibility (GSI) whereby the specificity of self-pollen rejection is controlled by alleles of the stylar and pollen specificity genes, S-RNase and SFB (S haplotype-specific F-box protein gene), respectively. As sour cherry selections can be either self-compatible (SC) or self-incompatible (SI), polyploidy per se does not result in SC. Instead the genotype-dependent loss of SI in sour cherry is due to the accumulation of non-functional S-haplotypes. The presence of two or more non-functional S-haplotypes within sour cherry 2x pollen renders that pollen SC. Two new S-haplotypes from sour cherry, S33 and S34, that are presumed to be contributed by the P. fruticosa species parent, the complete S-RNase and SFB sequences of a third S-haplotype, S35, plus the presence of two previously identified sweet cherry S-haplotypes, S14 and S16 are described here. Genetic segregation data demonstrated that the S16-, S33-, S34-, and S35-haplotypes present in sour cherry are fully functional. This result is consistent with our previous finding that ‘hetero-allelic’ pollen is incompatible in sour cherry. Phylogenetic analyses of the SFB and S-RNase sequences from available Prunus species reveal that the relationships among S-haplotypes show no correspondence to known organismal relationships at any taxonomic level within Prunus, indicating that polymorphisms at the S-locus have been maintained throughout the evolution of the genus. Furthermore, the phylogenetic relationships among SFB sequences are generally incongruent with those among S-RNase sequences for the same S-haplotypes. Hypotheses compatible with these results are discussed. [ABSTRACT FROM PUBLISHER]

The S-genotypes of 16 apricot ( Prunus armeniaca L.) cultivars native to China were determined by the S-allele PCR approach and the results were confirmed by cross-pollination tests among these cultivars. Primer combination EM-PC2consFD + EM-PC3consR, based on the conserved regions C2 and C3 of Rosaceous S-RNase genes, was the most useful primer combination for identifying Chinese apricot S-alleles. Twelve S-RNase alleles were identified using this primer combination, and they were defined as follows: S 9 was 657 bp, S 10 was 266 bp, S 11 was 464 bp, S 12 was 360 bp, S 13 was 401 bp, S 14 was 492 bp, S 15 was 469 bp, S 16 was 481 bp, S 17 was 487 bp, S 18 was 1337 bp, S 19 was 546 bp and S 20 was 1934 bp. S 11– S 20 were new S-RNase genes deposited in GenBank under accession numbers DQ868316, DQ870628-DQ870634, EF133689 and EF160078, respectively. Our findings contribute to a more efficient breeding program of Chinese apricot and further studies on the S-RNase genes. [ABSTRACT FROM AUTHOR]

The Latvian and the Swedish sweet cherry ( Prunus avium L.) genetic resources collections comprise valuable material for breeding. The collections represent local Latvian and Scandinavian genetic resources: semi-wild samples, landraces, and cultivars developed in local breeding programmes, as well as diverse germplasm from the northern temperate zone. The objective of this investigation was to determine which S 1 –S 6 alleles are most important in the sweet cherry genetic resources collections and to compare the identified allelic and genotypic frequencies in material of different origin. Accessions in the two collections were screened for the presence of the self-incompatibility ( S) S 1 to S 6 alleles, using PCR based typing. Significant differences ( P < 0.05) between screened collections were found in frequencies of S 4 and S 5 alleles. Analysis of allele combinations identified the high occurrence of selections with the S-genotype S 3 S 6 in both collections. Compared to the S-allele frequencies published for over 250 sweet cherry cultivars from Western and Southern Europe, the Latvian and Swedish germplasm appeared to have a high frequency of the S 6 allele in both collections, and a relatively high frequency of the S 5 allele in Latvian germplasm. This study represents the first comprehensive S-allele screening for the sweet cherry genetic resources collections in Latvia and Sweden. Both sweet cherry collections contain high proportion of accessions adapted to north central European growing conditions, not typical for the majority of the documented sweet cherry genetic resources, which explains differences in certain S-allele occurrence. [ABSTRACT FROM AUTHOR]

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 ( Ka/ Ks) 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 SFB8 and P. avium SFB1. Implications of this finding for hypotheses about the evolution of new S-specificities are discussed. [ABSTRACT FROM AUTHOR]

We characterized allelic diversity at the locus controlling self-incompatibility (SI) for a population of Lycium parishii (Solanaceae) from Organ Pipe National Monument, Arizona. Twenty-four partial sequences of S-RNase alleles were recovered from 25 individuals. Estimates of allelic diversity range from 23 to 27 alleles and, consistent with expectations for SI, individuals are heterozygous. We compare S-RNase diversity, patterns of molecular evolution, and the genealogical structure of alleles from L. parishii to a previously studied population of its congener L. andersonii. Gametophytic SI is well characterized for Solanaceae and although balancing selection is hypothesized to be responsible for high levels of allelic divergence, the pattern of selection varies depending on the portion of the gene considered. Site-specific models investigating patterns of selection for L. parishii and L. andersonii indicate that positive selection occurs in those regions of the S-RNase gene hypothesized as important to the recognition response, whereas positive selection was not detected for any position within regions previously characterized as conserved. A 10-species genealogy including S-RNases from a pair of congeners from each of five genera in Solanaceae reveals extensive transgeneric evolution of L. parishii S-RNases. Further, within Lycium, the Dn/Ds ratios for pairs of closely related alleles for intraspecific versus interspecific comparisons were not significantly different, suggesting that the S-RNase diversity recovered in these two species was present prior to the speciation event separating them. Despite this, two S-RNases from L. parishii are identical to two previously reported alleles for L. andersonii, suggesting gene flow between these species.Heredity (2006) 96, 434–444. doi:10.1038/sj.hdy.6800818; published online 19 April 2006 [ABSTRACT FROM AUTHOR]

S-RNase participates in at least three mechanisms of pollen rejection. It functions in S-specific pollen rejection (self-incompatibility) and in at least two distinct interspecific mechanisms of pollen rejection in Nicotiana. S-specific pollen rejection and rejection of pollen from Nicotiana plumbaginifolia also require additional stylar proteins. Transmitting-tract-specific (TTS) protein, 120 kDa glycoprotein (120K) and pistil extensin-like protein III (PELP III) are stylar glycoproteins that bind S-RNase in vitro and are also known to interact with pollen. Here we tested whether these glycoproteins have a direct role in pollen rejection. 120K shows the most polymorphism in size between Nicotiana species. Larger 120K-like proteins are often correlated with S-specific pollen rejection. Sequencing results suggest that the polymorphism primarily reflects differences in glycosylation, although indels also occur in the predicted polypeptides. Using RNA interference (RNAi), we suppressed expression of 120K to determine if it is required for S-specific pollen rejection. Transgenic SC N. plumbaginifolia × SI Nicotiana alata ( S105 S105 or SC10 SC10) hybrids with no detectable 120K were unable to perform S-specific pollen rejection. Thus, 120K has a direct role in S-specific pollen rejection. However, suppression of 120K had no effect on rejection of N. plumbaginifolia pollen. In contrast, suppression of HT-B, a factor previously implicated in S-specific pollen rejection, disrupts rejection of N. plumbaginifolia pollen. Thus, S-specific pollen rejection and rejection of N. plumbaginifolia pollen are mechanistically distinct, because they require different non-S-RNase factors. [ABSTRACT FROM AUTHOR]

A cDNA of 417 bp encoding an S-RNase gene, named PA S3, was isolated from apricot, Prunus aremeniaca. Nine S-alleles, S1–S9, were recognized by S-allele-specific PCR and confirmed by Southern blot analysis using PA S3 as probe. The S-genotypes of the six cultivars were determined and the results of self- and cross-pollination tests among the six cultivars were consistent with the predicted S-haplotypes by PCR analysis. [ABSTRACT FROM AUTHOR]

Strong frequency-dependent selection as found in the self-incompatibility loci of flowering plants maintains allelic lineages for extremely long time scales, such that allelic genealogies can shed insight into long-term demographic patterns of species. Effective mutation rate, as well as demographic change such as population bottlenecks, can influence genealogical structure. In addition, loss of functionality at the self-incompatibility locus is likely to affect radiation rates. Partial sequences for 21 S-RNase alleles of the mid-elevation tropical species Witheringia solanacea were obtained in order to compare their substitution rates and genealogy with those of Witheringia maculata and two species in the closely related genus Physalis. Sequences for W. solanacea fell into the three clades within the Solanaceae already identified for the genus. Terminal branch lengths for W. solanacea, scaled to the total depth of its phylogeny, were intermediate between the unusually short terminal branches of W. maculata and those of the two Physalis species. In contrast to the Physalis species, where interspecific dN/dS for closely related alleles exceeded 1.0 to the same degree as did intraspecific dN/dS, in Witheringia only intraspecific comparisons showed an excess of nonsynonymous substitutions, suggesting postspeciation radiation of alleles. Alleles associated with lowered S-RNase production and self-compatibility showed extremely short terminal branches. In summary, it appears that rapid recent diversification of alleles characterizes the Witheringia lineages. In some cases, this rapid diversification can be attributed to relaxed constraints due to breakdown of self-incompatibility.Heredity (2005) 94, 547-555. doi:10.1038/sj.hdy.6800657 Published online 16 March 2005 [ABSTRACT FROM AUTHOR]

In the Rosaceae family, which includes Prunus, gametophytic self-incompatibility (GSI) is controlled by a single multiallelic locus (S-locus), and the S-locus product expressed in the pistils is a glycoprotein with ribonuclease activity (S-RNase). Two populations of flowering cherry (Prunus lannesiana var. speciosa), located on Hachijo Island in Japan’s Izu Islands, were sampled, and S-allele diversity was surveyed based on the sequence polymorphism of S-RNase. A total of seven S-alleles were cloned and sequenced. The S-RNases of flowering cherry showed high homology to those of Prunus cultivars (P. avium and P. dulcis). In the phylogenetic tree, the S-RNases of flowering cherry and other Prunus cultivars formed a distinct group, but they did not form species-specific subgroups. The nucleotide substitution pattern in S-RNases of flowering cherry showed no excess of nonsynonymous substitutions relative to synonymous substitutions. However, the S-RNases of flowering cherry had a higher Ka/Ks ratio than those of other Prunus cultivars, and a subtle heterogeneity in the nucleotide substitution rates was observed among the Prunus species. The S-genotype of each individual was determined by Southern blotting of restriction enzyme-digested genomic DNA, using cDNA for S-RNase as a probe. A total of 22 S-alleles were identified. All individuals examined were heterozygous, as expected under GSI. The allele frequencies were, contrary to the expectation under GSI, significantly unequal. The two populations studied showed a high degree of overlap, with 18 shared alleles. However, the allele frequencies differed considerably between the two populations.Heredity (2004) 92, 249-256, advance online publication, 7 January 2004; doi:10.1038/sj.hdy.6800403 [ABSTRACT FROM AUTHOR]

Fruit set after self-pollination varied from 0.6 to 15.2% and the growth rate of self pollen-tubes in the style also varied from 0 to 39% among the Japanese pear cultivars (Pyrus serotina Rehd.); the former data were calculated using the results reported by several workers at different locations during several years, and the latter were our experimental results using a stylar culture technique in vitro. Cultivar differences in fruit set matched well with differences in the tube growth (r=0.852**, n=12) (**; significant at 1% level by t-test). Concentration of the sum of two S-RNases in the style was cultivar-dependent, and it showed a negative relation to fruit set (r=−0.764*, n=7) (*; significant at 5% level) or pollen-tube growth (r=−0.888**, n=18). The correlation coefficients between the pollen-tube growth and S1-, S2-, S3-, S4-, or S5-RNase concentration were; −0.714 (n=5), −0.242 (n=6), −0.560 (n=4), −0.701* (n=9), or −0.948 (n=4), respectively. Cultivar differences in the expression of self-incompatibility may, thus, be present in the Japanese pear and regulated, at least in part, by the concentration of S-RNase differentially produced in the style of each cultivar. [Copyright &y& Elsevier]

Self-compatible cultivars of Japanese apricot (Prunus mume Shieb. et Zucc.), a tree species that normally shows S-RNase-based self-incompatiblity, have a horticultural advantage over self-incompatible cultivars. Inheritance of self-compatibility and a common Sf-RNase allele that is observed in self-compatible cultivars was investigated using progenies from controlled crosses. Total DNAs were isolated from the parents and progenies of seven crosses that included at least one self-compatible cultivar as a parent. These DNAs were PCR-amplified with the Pru-C2 and PCE-R primer pair to determine S-haplotypes of the parents and progenies. A novel S-haplotype, S8, was found. In all crosses examined, the Sf-RNase gene was inherited from either the seed or pollen parent as a pistil S-allele in a non-functional S-haplotype. Self-compatibility of about 20 trees each from reciprocal crosses of 'Benisashi (S7Sf)' and 'Shinpeidayu (S3Sf)', and 26 selections from 16 different crosses was tested by pollination and pollen-tube growth studies. Cosegregation of the Sf-RNase allele and self-compatibility was confirmed with all but selection 1K0-26 (S3S7). Selection 1K0-26 (S3S7) that originated from 'Benisashi (S7Sf)' × 'Koshinoume (S3Sf)' appeared to be self-compatible even without the Sf-RNase allele. The possible role of pollen-S, a presumably existing pollen component of gametophytic self-incompatibility, is discussed. [ABSTRACT FROM AUTHOR]

Summary To elucidate the molecular basis of loss of self-incompatibility in Lycopersicon , S-RNases and HT-proteins were analysed in seven self-compatible (SC) and three self-incompatible (SI) taxa. No or low stylar RNase activity was a common feature in most SC taxa examined, in contrast to the uniformly high levels of activity found in all SI species. The S-RNase gene is most likely deleted in the four red-fruited SC taxa (L. esculentum, L. esculentum var. cerasiforme, L. pimpinellifolium and L. cheesmanii ) because S-RNase genes could not be amplified from genomic DNA. S-RNase genes could, however, be amplified from the genomes of the three green-fruited SC taxa examined. L. chmielewskii and L. hirsutum f. glabratum show a decreased accumulation of transcripts, possibly reflecting changes in the 5′ flanking regions of the S-RNase genes. The remaining green-fruited SC species, L. parviflorum , has a functional S-RNase gene in its genome that is expressed at high levels in the style, suggesting a genetic factor responsible for the low S-RNase activity. Together these results argue for several independent mutations in the S-RNase gene over the course of Lycopersicon diversification, and that loss of S-RNase function is unlikely to the primary cause of the loss of self-incompatibility. We also examined the HT-B genes that play a role in self-incompatibility. HT-B transcripts were markedly reduced in the styles of all the SC taxa examined. A scenario is described where a mutation causing reduced transcription of HT-B in an ancestral SI species was central to the loss of self-incompatibility in Lycopersicon . [ABSTRACT FROM AUTHOR]

The evolution of breeding systems in plants is often viewed as a balance between the adverse consequences of selfing (inbreeding depression and the loss of opportunities to sire seeds on conspecifics) and the benefits of selfing (a genetic transmission advantage and reproductive assurance when cross pollen limits seed production). In this paper we examine the genetic and environmental causes of variation in the expression of self-incompatibility (SI) in Campanula rapunculoides and explore the consequences of this variation on the breeding system. Campanula rapunculoides has an S-RNase based SI system similar to that described in the Solanaceae. However, our studies of plants from two natural populations have revealed that the flowers of most individuals are self-incompatible when they first open but become more self fertile as the flowers age. Moreover, when both cross and self pollen are deposited onto the stigmas of older flowers, the cross pollen tubes grow faster and sire a disproportionate number of the seeds. In short, self-fertilization occurs only after most opportunities for outcrossing have occurred. We also found that there is significant heritable genetic variation in the population for the strength of SI in young and old flowers and for the amount of breakdown in SI indicating that natural selection could operate on the strength of SI and its breakdown. In a multigenerational study, we used controlled crosses to create families of plants with a range of inbreeding coefficients (0, 0·25, 0·5 and 0·75). We found that fitness declined significantly over the range of inbreeding coefficients and that the decline in fitness was less for families derived from weak SI phenotypes. Consequently, it is only advantageous for C. rapunculoides to produce selfed seed when seed production is limited by the availability of cross pollen. Because of plasticity in the SI system, C. rapunculoides has a breeding system that combines the best of both worlds. [ABSTRACT FROM AUTHOR]