Detection and transcript expression of S-RNase gene associated with self-incompatibility in apricot (Prunus armeniaca L.)

Self-Incompatibility in Apricot: Identifying Pollination Requirements to Optimize Fruit Production

In recent years, an important renewal of apricot cultivars is taking place worldwide, with the introduction of many new releases. Self-incompatible genotypes tolerant to the sharka disease caused by the plum pox virus (PPV), which can severely reduce fruit production and quality, are being used as parents in most breeding programs. As a result, the self-incompatibility trait present in most of those accessions can be transmitted to the offspring, leading to the release of new self-incompatible cultivars. This situation can considerably affect apricot management, since pollination requirements were traditionally not considered in this crop and information is lacking for many cultivars. Thus, the objective of this work was to determine the pollination requirements of a group of new apricot cultivars by molecular identification of the S-alleles through PCR amplification of RNase and SFB regions with different primer combinations. The S-genotype of 66 apricot cultivars is reported, 41 for the first time. Forty-nine cultivars were considered self-compatible and 12 self-incompatible, which were allocated in their corresponding incompatibility groups. Additionally, the available information was reviewed and added to the new results obtained, resulting in a compilation of the pollination requirements of 235 apricot cultivars. This information will allow an efficient selection of parents in apricot breeding programs, the proper design of new orchards, and the identification and solution of production problems associated with a lack of fruit set in established orchards. The diversity at the S-locus observed in the cultivars developed in breeding programs indicates a possible genetic bottleneck due to the use of a reduced number of parents.

LC-MS based metabolic fingerprinting of apricot pistils after self-compatible and self-incompatible pollinations

KEY MESSAGE

LC-MS based metabolomics approach revealed that putative metabolites other than flavonoids may significantly contribute to the sexual compatibility reactions in Prunus armeniaca. Possible mechanisms on related microtubule-stabilizing effects are provided. Identification of metabolites playing crucial roles in sexual incompatibility reactions in apricot (Prunus armeniaca L.) was the aim of the study. Metabolic fingerprints of self-compatible and self-incompatible apricot pistils were created using liquid chromatography coupled to time-of-flight mass spectrometry followed by untargeted compound search. Multivariate statistical analysis revealed 15 significant differential compounds among the total of 4006 and 1005 aligned metabolites in positive and negative ion modes, respectively. Total explained variance of 89.55% in principal component analysis (PCA) indicated high quality of differential expression analysis. The statistical analysis showed significant differences between genotypes and pollination time as well, which demonstrated high performance of the metabolic fingerprinting and revealed the presence of metabolites with significant influence on the self-incompatibility reactions. Finally, polyketide-based macrolides similar to peloruside A and a hydroxy sphingosine derivative are suggested to be significant differential metabolites in the experiment. These results indicate a strategy of pollen tubes to protect microtubules and avoid growth arrest involved in sexual incompatibility reactions of apricot.

Intra-strain biological and epidemiological characterization of plum pox virus

Plum pox virus (PPV) is one of the most important plant viruses causing serious economic losses. Thus far, strain typing based on the definition of 10 monophyletic strains with partially differentiable biological properties has been the sole approach used for epidemiological characterization of PPV. However, elucidating the genetic determinants underlying intra-strain biological variation among populations or isolates remains a relevant but unexamined aspect of the epidemiology of the virus. In this study, based on complete nucleotide sequence information of 210 Japanese and 47 non-Japanese isolates of the PPV-Dideron (D) strain, we identified five positively selected sites in the PPV-D genome. Among them, molecular studies showed that amino acid substitutions at position 2,635 in viral replicase correlate with viral titre and competitiveness at the systemic level, suggesting that amino acid position 2,635 is involved in aphid transmission efficiency and symptom severity. Estimation of ancestral genome sequences indicated that substitutions at amino acid position 2,635 were reversible and peculiar to one of two genetically distinct PPV-D populations in Japan. The reversible amino acid evolution probably contributes to the dissemination of the virus population. This study provides the first genomic insight into the evolutionary epidemiology of PPV based on intra-strain biological variation ascribed to positive selection.

Pollination Type Recognition from a Distance by the Ovary Is Revealed Through a Global Transcriptomic Analysis

Sexual reproduction in flowering plants involves intimate contact and continuous interactions between the growing pollen tube and the female reproductive structures. These interactions can trigger responses in distal regions of the flower well ahead of fertilization. While pollination-induced petal senescence has been studied extensively, less is known about how pollination is perceived at a distance in the ovary, and how specific this response is to various pollen genotypes. To address this question, we performed a global transcriptomic analysis in the ovary of a wild potato species, Solanum chacoense, at various time points following compatible, incompatible, and heterospecific pollinations. In all cases, pollen tube penetration in the stigma was initially perceived as a wounding aggression. Then, as the pollen tubes grew in the style, a growing number of genes became specific to each pollen genotype. Functional classification analyses revealed sharp differences in the response to compatible and heterospecific pollinations. For instance, the former induced reactive oxygen species (ROS)-related genes while the latter affected genes associated to ethylene signaling. In contrast, incompatible pollination remained more akin to a wound response. Our analysis reveals that every pollination type produces a specific molecular signature generating diversified and specific responses at a distance in the ovary in preparation for fertilization.

Identification of Self-Incompatibility Alleles by Specific PCR Analysis and S-RNase Sequencing in Apricot

Self-incompatibility (SI) is one of the most efficient mechanisms to promote out-crossing in plants. However, SI could be a problem for fruit production. An example is apricot (Prunus armeniaca), in which, as in other species of the Rosaceae, SI is determined by an S-RNase-based-Gametophytic Self-Incompatibility (GSI) system. Incompatibility relationships between cultivars can be established by an S-allele genotyping PCR strategy. Until recently, most of the traditional European apricot cultivars were self-compatible but several breeding programs have introduced an increasing number of new cultivars whose pollination requirements are unknown. To fill this gap, we have identified the S-allele of 44 apricot genotypes, of which 43 are reported here for the first time. The identification of S_c in 15 genotypes suggests that those cultivars are self-compatible. In five genotypes, self-(in)compatibility was established by the observation of pollen tube growth in self-pollinated flowers, since PCR analysis could not allowed distinguishing between the S_c and S₈ alleles. Self-incompatible genotypes were assigned to their corresponding self-incompatibility groups. The knowledge of incompatibility relationships between apricot cultivars can be a highly valuable tool for the development of future breeding programs by selecting the appropriate parents and for efficient orchard design by planting self-compatible and inter-compatible cultivars.

Comprehensive screening of antimicrobials to control phytoplasma diseases using an in vitro plant-phytoplasma co-culture system

Phytoplasmas are plant-pathogenic bacteria that infect many important crops and cause serious economic losses worldwide. However, owing to an inability to culture phytoplasmas, screening of antimicrobials on media is difficult. The only antimicrobials being used to control phytoplasmas are tetracycline-class antibiotics. In this study, we developed an accurate and efficient screening method to evaluate the effects of antimicrobials using an in vitro plant-phytoplasma co-culture system. We tested 40 antimicrobials, in addition to tetracycline, and four of these (doxycycline, chloramphenicol, thiamphenicol and rifampicin) decreased the accumulation of 'Candidatus (Ca.) Phytoplasma asteris'. The phytoplasma was eliminated from infected plants by the application of both tetracycline and rifampicin. We also compared nucleotide sequences of rRNAs and amino acid sequences of proteins targeted by antimicrobials between phytoplasmas and other bacteria. Since antimicrobial target sequences were conserved among various phytoplasma species, the antimicrobials that decreased accumulation of 'Ca. P. asteris' may also have been effective against other phytoplasma species. These approaches will provide new strategies for phytoplasma disease management.

Optimizing Production in the New Generation of Apricot Cultivars: Self-incompatibility, S-RNase Allele Identification, and Incompatibility Group Assignment

Apricot (Prunus armeniaca L.) is a species of the Rosaceae that was originated in Central Asia, from where it entered Europe through Armenia. The release of an increasing number of new cultivars from different breeding programs is resulting in an important renewal of plant material worldwide. Although most traditional apricot cultivars in Europe are self-compatible, the use of self-incompatible cultivars as parental genotypes for breeding purposes is leading to the introduction of a number of new cultivars that behave as self-incompatible. As a consequence, there is an increasing need to interplant those new cultivars with cross-compatible cultivars to ensure fruit set in commercial orchards. However, the pollination requirements of many of these new cultivars are unknown. In this work, we analyze the pollination requirements of a group of 92 apricot cultivars, including traditional and newly-released cultivars from different breeding programs and countries. Self-compatibility was established by the observation of pollen tube behavior in self-pollinated flowers under the microscope. Incompatibility relationships between cultivars were established by the identification of S-alleles by PCR analysis. The self-(in)compatibility of 68 cultivars and the S-RNase genotype of 74 cultivars are reported herein for the first time. Approximately half of the cultivars (47) behaved as self-compatible and the other 45 as self-incompatible. Identification of S-alleles in self-incompatible cultivars allowed allocating them in 11 incompatibility groups, six of them reported here for the first time. The determination of pollination requirements and the incompatibility relationships between cultivars is highly valuable for the appropriate selection of apricot cultivars in commercial orchards and of parental genotypes in breeding programs. The approach described can be transferred to other woody perennial crops with similar problems.

Characterization of the 'Xiangshui' lemon transcriptome by de novo assembly to discover genes associated with self-incompatibility

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.

Molecular characterization and expression analysis of S1 self-incompatibility locus-linked pollen 3.15 gene in Citrus reticulata

Gametophytic self-incompatibility (GSI) is controlled by a highly polymorphic locus called the S-locus, which is an important factor that can result in seedless fruit in Citrus. The S1 self-incompatibility locus-linked pollen 3.15 gene (S1-3.15 ) belongs to a type of S locus gene. The role of S1-3.15 in the SI reaction of Citrus has not yet been reported. In this study, full-length sequences of cDNA and DNA encoding the S1-3.15 gene, referred to as CrS1-3.15 , were isolated from 'Wuzishatangju' (Self-incompatibility, SI) and 'Shatangju' (Self-compatibility, SC). The predicted amino acid sequences of CrS1-3.15 between 'Wuzishatangju' and 'Shatangju' differ by only three amino acids. Compared to 'Wuzishatangju', three bases were substituted in the genomic DNA of CrS1-3.15 from 'Shatangju'. Southern blot results showed that one copy of CrS1-3.15 existed in the genomic DNA of both 'Wuzishatangju' and 'Shatangju'. The expression level of the CrS1-3.15 gene in the ovaries of 'Shatangju' was approximately 60-fold higher than that in the ovaries of 'Wuzishatangju'. When 'Wuzishatangju' was cross-pollinated, the expression of CrS1-3.15 was upregulated in the ovaries at 3 d, and the highest expression levels were detected in the ovaries at 6 d after cross-pollination of 'Wuzishatangju' × 'Shatangju'. To obtain the CrS1-3.15 protein, the full-length cDNA of CrS1-3.15 genes from 'Wuzishatangju' and 'Shatangju' was successfully expressed in Pichia pastoris. Pollen germination frequency of 'Wuzishatangju' was inhibited significantly with increasing CrS1-3.15 protein concentrations from SI 'Wuzishatangju'.

An S-locus independent pollen factor confers self-compatibility in 'Katy' apricot

Loss of pollen-S function in Prunus self-compatible cultivars has been mostly associated with deletions or insertions in the S-haplotype-specific F-box (SFB) genes. However, self-compatible pollen-part mutants defective for non-S-locus factors have also been found, for instance, in the apricot (Prunus armeniaca) cv. ‘Canino’. In the present study, we report the genetic and molecular analysis of another self-compatible apricot cv. termed ‘Katy’. S-genotype of ‘Katy’ was determined as S₁S₂ and S-RNase PCR-typing of selfing and outcrossing populations from ‘Katy’ showed that pollen gametes bearing either the S₁- or the S₂-haplotype were able to overcome self-incompatibility (SI) barriers. Sequence analyses showed no SNP or indel affecting the SFB₁ and SFB₂ alleles from ‘Katy’ and, moreover, no evidence of pollen-S duplication was found. As a whole, the obtained results are compatible with the hypothesis that the loss-of-function of a S-locus unlinked factor gametophytically expressed in pollen (M’-locus) leads to SI breakdown in ‘Katy’. A mapping strategy based on segregation distortion loci mapped the M’-locus within an interval of 9.4 cM at the distal end of chr.3 corresponding to ∼1.29 Mb in the peach (Prunus persica) genome. Interestingly, pollen-part mutations (PPMs) causing self-compatibility (SC) in the apricot cvs. ‘Canino’ and ‘Katy’ are located within an overlapping region of ∼273 Kb in chr.3. No evidence is yet available to discern if they affect the same gene or not, but molecular markers seem to indicate that both cultivars are genetically unrelated suggesting that every PPM may have arisen independently. Further research will be necessary to reveal the precise nature of ‘Katy’ PPM, but fine-mapping already enables SC marker-assisted selection and paves the way for future positional cloning of the underlying gene.

Molecular cloning and expression of squalene synthase and 2,3-oxidosqualene cyclase genes in persimmon (Diospyros kaki L.) fruits

Oleanolic acid (OA) and ursolic acid (UA) are the main triterpene acids in persimmon fruit, and squalene synthase and 2,3-oxidosqualene cyclases are important enzymes in pentacyclic triterpene biosynthesis. In order to study their relationship, DkSQS and DkOSC were cloned from persimmon fruits in the present study. The full-length cDNA of DkSQS was 1647 bp, containing an open reading frame (ORF) of 1245 bp that encoded a peptide of 415 amino acids (AA). The 3'-end of DkOSC cDNA fragment contained 522 bp, including a partial ORF of 298 bp, a full poly A tail that encoded 98 AA. Two cultivars of persimmon, i.e. cv. Nishimurawase and cv. Niuxinshi, were used to study the content of OA and UA and the related gene expression. Results showed that OA and UA contents changed in both cultivars during fruit development, the difference in cv. Nishimurawase was greater than that in cv. Niuxinshi. The expression of DkSQS and DkOSC had no obvious correlation with the biosynthesis of OA and UA in the flesh. There may be two main reasons. Firstly, different enzymes involved in the biosynthesis of triterpenes and mutual adjustment were existed in different gene expressions. Secondly, it was not clear that the DkOSC cloned in this research belonged to which subfamily. Therefore, the real relationship between triterpenes and DkSQS and DkOSC in persimmon fruits is still to be revealed.

Cloning and expression analysis of S-RNase homologous gene in Citrus reticulata Blanco cv. Wuzishatangju

S-RNase-based self-incompatibility is the most widespread form of genetically controlled mate selection in plants and that S-RNase controls pollination specificity in the pistils. 'Wuzishatangju' (Citrus reticulata Blanco), a nature bud mutant from a self-compatible (SC) cultivar 'Shatangju', displays gametophytic self-incompatibility (GSI). In this study, full-length sequences of cDNA and DNA of the S-RNase homologous gene were obtained from 'Wuzishatangju' and 'Shatangju'. There was no difference in ORF sequences of the S-RNase cDNA between 'Wuzishatangju' and 'Shatangju'. However, 13, 9 and 6 consecutive bases were missing in 'Wuzishatangju' cDNA 5' UTR, 3' UTR and genomic DNA, respectively. Tissue-specific expression of the S-RNase gene was detected using semi-quantitative RT-PCR and quantitative real-time PCR. The expression level of the S-RNase gene in styles of 'Wuzishatangju' was approximately 10- and 5-fold higher than that in leaves and pollen, respectively. When 'Wuzishatangju' was self-pollinated, the expression of S-RNase in pistils peaked at 3 days, which was approximately 10-fold higher than that at 4h and 7 days, while in cross-pollination of 'Wuzishatangju' x 'Shatangju' the expression was very weak at 3 days. Results from a Southern blot showed that two copies of the S-RNase gene existed in genomic DNA of both 'Wuzishatangju' and 'Shatangju'.

Cloning of phytoene desaturase and expression analysis of carotenogenic genes in persimmon (Diospyros kaki L.) fruits

Persimmon is a commercially important fruit crop, and the fruit is rich in different kinds of bioactive compounds, among which carotenoids contribute significantly to its color and nutritional value. In this study, the cDNA of phytoene desaturase gene (PDS) was isolated by rapid amplification of cDNA ends (RACE) technique. Sequence analysis indicated that the full-length cDNA of PDS was 2064 bp, encoding 586 amino acids and containing one open reading frame (ORF) of 1761 bp. Homology analysis showed that DkPDS, which had been submitted in GenBank with accession number GU112527, shared high similarities of 80-86% with PDS cloned from other plants. Prediction of deduced proteins showed that there was no signal peptide and transmembrane topological structure in DkPDS. It was a hydrophilic and stable protein, and located in chloroplast. To examine the specific expression patterns of carotenogenic genes we had cloned from persimmon, including phytoene synthase (DkPSY), DkPDS, ζ-carotene desaturase (DkZDS), lycopene β-cyclase (DkLCYB) and β-carotene hydroxylase (DkBCH), real-time quantitative PCR (Q-PCR) was performed in flesh at five different developmental stages. The results revealed that the expression levels of DkPSY, DkPDS and DkZDS gradually increased. Nevertheless, the expression level of DkLCYB was very low and maintained relatively stable. The expression level of DkBCH was also at a low level from stage 1 to 4, and then reached the maximum at stage 5. In addition, the expression level of DkZDS was higher than that of other genes. Carotenoid detection demonstrated that both β-cryptoxanthin and total carotenoids increased with fruit development, and zeaxanthin had little change, but with a sudden increase in final stage.

Self-compatibility of 'Katy' apricot (Prunus armeniaca L.) is associated with pollen-part mutations

Apricot (Prunus armeniaca L.) cultivars originated in China display a typical S-RNase-based gametophytic self-incompatibility (GSI). 'Katy', a natural self-compatible cultivar belonging to the European ecotype group, was used as a useful material for breeding new cultivars with high frequency of self-compatibility by hybridizing with Chinese native cultivars. In this work, the pollen-S genes (S-haplotype-specific F-box gene, or SFB gene) of 'Katy' were first identified as SFB₁ and SFB (8), and the S-genotype was determined as S₁ S₈. Genetic analysis of 'Katy' progenies under controlled pollination revealed that the stylar S₁-RNase and S₈-RNase have a normal function in rejecting wild-type pollen with the same S-haplotype, while the pollen grains carrying either the SFB₁ or the SFB₈ gene are both able to overcome the incompatibility barrier. However, the observed segregation ratios of the S-genotype did not fit the expected ratios under the assumption that the pollen-part mutations are linked to the S-locus. Moreover, alterations in the SFB₁ and SFB₈ genes and pollen-S duplications were not detected. These results indicated that the breakdown of SI in 'Katy' occurred in pollen, and other factors not linked to the S-locus, which caused a loss of pollen S-activity. These findings support a hypothesis that modifying factors other than the S-locus are required for GSI in apricot.

CgSL2, an S-like RNase gene in 'Zigui shatian' pummelo (Citrus grandis Osbeck), is involved in ovary senescence

'Zigui shatian' pummelo (Citrus grandis Osbeck) is one nature mutant from 'Shatian' pummelo, which showed self-compatibility, because self-pollen tubes were not arrested in the style, moreover abnormal post-zygotic development in ovary caused seed abortion in the cultivar. Herein we constructed a cDNA library from flowers of 'Zigui shatian' pummelo and identified one RNase gene fragment. The full length of cDNA sequence of this gene, with an open reading frame of 834 bp, was isolated by 5'-RACE method. The gene, named as CgSL2, contained five conserved regions and two histidine residues essential for RNase activity. Phylogenetic analysis indicated that CgSL2 was mostly similar to AhSL28, an S-like RNase from Antirrhinum. Southern hybridization verified CgSL2 existed in the genome as multiple copies. qRT-PCR and RT-PCR analysis showed that the expression of CgSL2 was not tissue-specific. The expression of CgSL2 was down-regulated during senescence of stem, petal, style and stamen, whereas up-regulated during ovary senescence. Further in situ hybridization of CgSL2 in the ovary during the balloon stage to anthesis stage also showed that it dramatically increased in mature flower, consistent with qRT-PCR and RT-PCR results. These findings suggested that CgSL2 might play an important role during ovary senescence.

Compatible pollinations in Solanum chacoense decrease both S-RNase and S-RNase mRNA

Gametophytic self-incompatibility (GSI) allows plants to block fertilization by haploid pollen whose S-allele constitution matches one of the two S-alleles in the diploid styles. GSI in Solanum chacoense requires a stylar S-RNase, first secreted from cells of the transmitting tract then imported into incompatible (self) pollen tubes. However, the molecular mechanisms allowing compatible pollen to evade S-RNase attack are less clear, as compatible pollen tubes also import S-RNase. Using styles of the same age and size in order to lower the degree of inter-style variability in S-RNase levels, we observe reduction of up to 30% of the total non-self stylar S-RNase in vivo during compatible crosses, whereas no degradation of self S-RNases is detected. This marked difference in stylar S-RNase levels dovetails with measurements of pollen-specific Lat52 mRNA, which decreases four-fold in incompatible compared to compatible crosses. Unexpectedly, we also find evidence for a reciprocal signaling mechanism from compatible pollen to the cells of the transmitting tract that results in a roughly three-fold decrease in S-RNase transcript levels. These findings reveal a previously unsuspected feedback loop that may help reinforce the compatible reaction.

Primary molecular features of self-incompatible and self-compatible F(1) seedling from apricot (Prunus armeniaca L.) Katy x Xinshiji

Expression of the S-RNase genes in the self-compatible (SC) apricot (Prunus armeniaca L.) cultivar Katy, the self-incompatible (SI) cultivar Xinshiji and their F(1) seedling was examined in this study. Three S-genotypes, S(9)Sc (Sc, self-compatibility S-gene absent from the style), S(8)S(9), and S(8)S(10), were obtained. Seedlings with S-RNase that migrated as a single band in gel electrophoresis were SC, despite high transcript abundance, and those with S-RNase that migrated as two bands were SI with high transcript abundance or SC with low transcript expression. S(8)-RNase was induced in SI cultivars only 24 h after self-pollination, indicating post-transcriptional regulation of S(8)-RNase in SI apricots. A Proteomic study showed that 35 protein spots were synthesized differently between SC and SI pistils. Fifteen of the 35 protein spots were identified; nine proteins, including receptor protein kinase-like protein, reversibly glycosylated polypeptide-2, and isoflavone reductase-like protein, were detected only in the SC pistils; while nine proteins, including actin 7, a putative serine/threonine kinase, and S-RNase, were detected only in the SI pistils. A mitochondrial NAD-dependent malate dehydrogenase and a probable elongation factor G were up-regulated, while heat shock cognate 70 was down-regulated in the SC pistils compared to those in the SI pistils. The results suggest that the proteins responsible for self-compatibility and self-incompatibility may be different.

Origin and dissemination of the pollen-part mutated SC haplotype which confers self-compatibility in apricot (Prunus armeniaca)

In China, its centre of origin, apricot (Prunus armeniaca) is self-incompatible. However, most European cultivars are self-compatible. In most cases, self-compatibility is a result of a loss-of-function mutation within the pollen gene (SFB) in the SC haplotype. Controlled pollinations performed in this work revealed that the cross 'Ceglédi óriás' (S8S9)x'Ceglédi arany' (SCS9) set well, as expected, but the reciprocal cross did not. Apricot S8, S9 and SC haplotypes were analysed using a multilevel approach including fruit set evaluation, pollen tube growth analysis, RNase activity assays, polymerase chain reaction (PCR) analysis and DNA sequencing of the S-RNase and SFB alleles. SFB8 was revealed to be the first known progenitor allele of a naturally occurring self-compatibility allele in Prunus, and consequently SC=The first intron of SC-RNase is a phase one intron, indicating its more recent evolutionary origin compared with the second intron. Sequence analysis of different cultivars revealed that more single nucleotide polymorphisms accumulated in SC-RNase than in SFBC. New methods were designed to allow high-throughput analysis of S genotypes of apricot cultivars and selections. S-RNase sequence data from various sources helped to elucidate the putative origin and dissemination of self-compatibility in apricot conferred by the SC haplotype.