Self-incompatibility Mechanism Research Articles

LOCATION OF QTLS AFFECTING SELF-INCOMPATIBILITY IN ALMOND

Although self-incompatibility (SI) in Rosaceae has been considered a single-locus qualitative trait, the evidence observed in different Prunus species has indicated the presence of modifier genes located outside the S locus. The almond progeny from the cross 'Vivot' × 'Blanquerna' has shown an unexpected self-incompatible behavior in most of the seedlings, thus requiring further study. Both parents possess the Sf allele, but with different phenotypic expressions. The male parent is self-compatible with the inactive Sf haplotype and the female parent is self-incompatible with the active Sf allele. Thus, the presence of other factors or genes involved in the mechanism of self-incompatibility in almond could explain the unexpected results. The use of microsatellite markers in this progeny has allowed identification of several loci involved in the SI reaction and to locate these modifier genes in the ‘V×B’ map. These results may indicate that almond is a species with a genetic background of pseudo-self-compatibility controlled by modifier genes.

Molecular mechanism of self-incompatibility and CO2 induced self-fertilization in the Brassicaceae

Molecular mechanism of self-incompatibility and CO2 induced self-fertilization in the Brassicaceae

Progress towards elucidating the mechanisms of self-incompatibility in the grasses: further insights from studies in Lolium.

Self-incompatibility (SI) in flowering plants ensures the maintenance of genetic diversity by ensuring outbreeding. Different genetic and mechanistic systems of SI among flowering plants suggest either multiple origins of SI or considerable evolutionary diversification. In the grasses, SI is based on two loci, S and Z, which are both polyallelic: an incompatible reaction occurs only if both S and Z alleles are matched in individual pollen with alleles of the pistil on which they alight. Such incompatibility is referred to as gametophytic SI (GSI). The mechanics of grass GSI is poorly understood relative to the well-characterized S-RNase-based single-locus GSI systems (Solanaceae, Rosaceae, Plantaginaceae), or the Papaver recognition system that triggers a calcium-dependent signalling network culminating in programmed cell death. There is every reason to suggest that the grass SI system represents yet another mechanism of SI. S and Z loci have been mapped using isozymes to linkage groups C1 and C2 of the Triticeae consensus maps in Secale, Phalaris and Lolium. Recently, in Lolium perenne, in order to finely map and identify S and Z, more closely spaced markers have been developed based on cDNA and repeat DNA sequences, in part from genomic regions syntenic between the grasses. Several genes tightly linked to the S and Z loci were identified, but so far no convincing candidate has emerged. From subtracted Lolium immature stigma cDNA libraries derived from S and Z genotyped individuals enriched for SI potential component genes, kinase enzyme domains, a calmodulin-dependent kinase and a peptide with several calcium (Ca(2+)) binding domains were identified. Preliminary findings suggest that Ca(2+) signalling and phosphorylation may be involved in Lolium GSI. This is supported by the inhibition of Lolium SI by Ca(2+) channel blockers lanthanum (La(3+)) and verapamil, and by findings of increased phosphorylation activity during an SI response.

Expression and trans-specific polymorphism of self-incompatibility RNases in coffea (Rubiaceae).

Self-incompatibility (SI) is widespread in the angiosperms, but identifying the biochemical components of SI mechanisms has proven to be difficult in most lineages. Coffea (coffee; Rubiaceae) is a genus of old-world tropical understory trees in which the vast majority of diploid species utilize a mechanism of gametophytic self-incompatibility (GSI). The S-RNase GSI system was one of the first SI mechanisms to be biochemically characterized, and likely represents the ancestral Eudicot condition as evidenced by its functional characterization in both asterid (Solanaceae, Plantaginaceae) and rosid (Rosaceae) lineages. The S-RNase GSI mechanism employs the activity of class III RNase T2 proteins to terminate the growth of “self” pollen tubes. Here, we investigate the mechanism of Coffea GSI and specifically examine the potential for homology to S-RNase GSI by sequencing class III RNase T2 genes in populations of 14 African and Madagascan Coffea species and the closely related self-compatible species Psilanthus ebracteolatus. Phylogenetic analyses of these sequences aligned to a diverse sample of plant RNase T2 genes show that the Coffea genome contains at least three class III RNase T2 genes. Patterns of tissue-specific gene expression identify one of these RNase T2 genes as the putative Coffea S-RNase gene. We show that populations of SI Coffea are remarkably polymorphic for putative S-RNase alleles, and exhibit a persistent pattern of trans-specific polymorphism characteristic of all S-RNase genes previously isolated from GSI Eudicot lineages. We thus conclude that Coffea GSI is most likely homologous to the classic Eudicot S-RNase system, which was retained since the divergence of the Rubiaceae lineage from an ancient SI Eudicot ancestor, nearly 90 million years ago.

Fenologia reprodutiva, biologia floral e polinização de Allamanda blanchetii, uma Apocynaceae endêmica da Caatinga

(Fenologia reprodutiva, biologia floral e polinizacao de Allamanda blanchetii, uma Apocynaceae endemica da Caatinga). A fenologia reprodutiva, a biologia floral, o mecanismo de polinizacao e o sistema reprodutivo de Allamanda blanchetii A.DC. foram analisados em populacoes naturais na Fazenda Almas, Paraiba, Brasil. Allamanda blanchetii e uma especie arbustiva, endemica da Caatinga, com floracao de fevereiro a julho e pico nos meses de marco e abril. A frutificacao acompanhou a floracao e estendeu-se ate o mes de setembro. As flores sao tubulares e de coloracao rosa, cuja forte hercogamia evita a autopolinizacao. O polen e depositado na parte superior da cabeca do estilete (regiao nao receptiva), ainda na fase de botao em pre antese (anteras deiscentes), caracterizando a apresentacao secundaria de polen. As flores produzem uma media de 36,6 µL de nectar, o qual e o unico recurso para os visitantes florais. Allamanda blanchetii e auto-incompativel e os resultados sugerem mecanismo de incompatibilidade de acao tardia. Seus atributos florais estao relacionados com as sindromes de melitofilia e psicofilia e, de fato, os polinizadores registrados foram a abelha Eulaema nigrita Lepeletier como principal polinizador e quatro especies de borboletas que atuam como polinizadores secundarios. A ocorrencia de forte hercogamia, apresentacao secundaria de polen e mecanismo de auto-incompatibilidade indicam o elevado grau de especializacao dos sistemas de polinizacao e reproducao de A. blanchetii.

Petunia. Evolutionary, developmental and physiological genetics

Petunia. Evolutionary, developmental and physiological genetics

Reproductive biology of Setaria magna Griseb. (Poaceae: Panicoideae: Paniceae)

The genus Setaria is economically important because many species are cultivated for grains or forage. Setaria magna is an American species, native to North America and introduced in South America. The morphological aspect of this species is similar to S. italica (foxtail millet), suggesting its potential value as a crop. The purpose of this work was to understand the breeding system (self-pollination vs. open pollination) of S. magna; additionally, the floral development was described. The results of the breeding system analysis indicated that S. magna is mainly autogamous and does not appear to have a self-incompatibility mechanism. The floral development observed was similar to that described for other Paniceae; in most of the spikelets only the upper anthecium developed fruit, but a small number of spikelets presented bisexual lower florets. These spikelets produced two caryopses per spikelet. Thus, S. magna can produced two types of dispersal units; a few whitish naked caryopses from the lower anthecium that fall without their lemma and palea at maturity; and a high number of brown caryopses protected by the lemma and palea from the upper anthecium. The presence of a normal embryo sac in the upper anthecium suggests that S. magna would present normal sexual reproduction, although we can not reject the formation of apomitic seeds in the lower anthecium.

The amino terminal F-box domain of Petunia inflata S-locus F-box protein is involved in the S-RNase-based self-incompatibility mechanism

Pistils of flowering plants possessing self-incompatibility (SI) can distinguish between self and non-self pollen, and only allow non-self pollen to effect fertilization. For Petunia inflata, the S-RNase gene encodes pistil specificity and multiple S-locus F-box (SLF) genes encode pollen specificity. Each SLF produced in pollen interacts with a subset of non-self S-RNases to mediate their ubiquitination and degradation by the 26S proteasome. S-locus F-box has been proposed to function as a component of the conventional SCF (SKP1-CULLIN-F-box protein) complex, based on the finding that two SKP1-like proteins, AhSSK1 (Antirrhinum hispanicum SLF-interacting SKP1-like1) and PhSSK1 (Petunia hybrida SSK1), interact with the F-box domain of some allelic variants of SLF. However, we previously showed that PiSLF (P. inflata SLF) did not interact with any SKP1 of P. inflata or Arabidopsis thaliana, but instead interacted with a RING-finger protein, PiSBP1 (P. inflata S-RNase-Binding Protein1), which may also play the role of SKP1. Thus, the biochemical nature of the SLF-containing complex is as yet unclear. To examine whether the F-box domain of PiSLF is required for SI function, we expressed a truncated PiSLF(2) (S(2) allelic variant) without this domain in S(2)S(3) plants and showed that, unlike the full-length PiSLF(2), it did not cause breakdown of SI in S(3) pollen. We identified PiSSK1 (P. inflata SSK1) and found that it did not interact with PiSLF(1), PiSLF(2) or PiSLF(3). The finding that the truncated PiSLF(2) did not cause breakdown of SI in S(3) transgenic pollen suggests that the F-box domain of PiSLF(2) is required for mediating degradation of S(3)-RNase, a non-self S-RNase, in S(3) pollen, and thus is required for SI function. The finding that PiSSK1 did not interact with three allelic variants of PiSLF is consistent with our previous finding that PiSLF might not be in a conventional SCF complex.

Self-Fertilization of a Schlumbergera truncata Cultivar: Breakdown of Self-incompatibility

Plants of the genus Schlumbergera are popular houseplants cultivated throughout the world. While most species in the genus, including the cultivars of Schlumbergera truncata, have been found to be self-incompatible, one cultivar, S. truncata ‘Thor Olga’, is shown here to produce fruit containing viable seeds through self pollination. Three of seven flowers (~43%) set fruit, including two fruits from which viable seeds were collected. A total of 35 seeds from these two fruits were sown, of which nine germinated (~26% viability). The phylloclade shape for all nine progeny plants appeared similar to the S. × buckleyi type for the first year, with gently scalloped rounded edges and no teeth. After the first year, the phylloclade shape began to differentiate, with some remaining similar to the S. × buckleyi shape and others developing the typical S. truncata shape. One of the progeny resulting from the self fertilization was brought to flower, and, in addition to differing in flower color from the parent plant, the progeny plant is very dissimilar to its parent in its branching architecture and its arching pendulous habit, as well as in the size and shape of the phylloclades. The breakdown in self-incompatibility is thought to be associated with delayed pollination, since fresh mature pollen was placed on over-mature stigmas. This appears to be the first time successful self-fertilization of Schlumbergera truncata has been reported in the literature. It is reasonable to predict that other Schlumbergera cultivars/hybrids may likewise exhibit some degree of self-compatibility. The fact that the self-incompatibility mechanisms can be broken down, may lead to the development of a new range of cultivars with unique traits.

Estimation of Self-incompatibility Genotypes of Citrus Cultivars with Got-3 Allozyme Markers

Self-incompatibility (SI) in Citrus is known in cultivars and plants of pummelo, pummelo relative, and mandarin; however, the detailed mechanism of self-incompatibility and the allelic diversity of the SI gene (S) are not known because of the presence of barriers such as nucellar embryony, male sterility, and a long juvenile phase. Thus, there is little information on S genotypes of Citrus cultivars at present. In this study, the S genotypes of Citrus cultivars were estimated with the aid of allozymes produced by a glutamate oxaloacetate transaminase isozyme gene (Got-3), which appeared to link to the S gene. Of twenty-two F1 progenies from eleven crosses and their reciprocal crosses with eight monoembryonic SI cultivars, including ‘Banpeiyu’ pummelo, three F1 progenies from three crosses and three from reciprocal crosses showed segregation distortion for the Got-3 gene, suggesting the presence of the same S alleles in the cultivars used for the reciprocal crosses. Defining the ‘Banpeiyu’ genotype as S1S2, the genotype was estimated as S1S3 for ‘Tosa Buntan’, S4S5 for ‘Hassaku’, S6S7 for ‘Yuge-hyokan’, and S1S6 for ‘Shishiyuzu’. Further allozyme analyses for segregation distortion in progenies from eight crosses with eight monoembryonic SI cultivars suggested the possibility that ‘Hyuganatsu’ has S1 allele, while those from 15 crosses between the eight monoembryonic SI cultivars and five polyembryonic self-compatible cultivars suggested the possibility that ‘Rough lemon’ has S1 allele. The estimated genotypes, consisting of two of the nine alleles (S1 to S8 and Sf) in these Citrus cultivars, may be useful for further estimation and determination of S genotypes in Citrus cultivars and plants.

Late-acting self-incompatibility in Acca sellowiana (Myrtaceae)

Acca sellowiana (Berg) Burret is a predominantly allogamous species with hermaphrodite flowers that has barriers to self-fertilisation such as dichogamy by protogyny and self-incompatibility. This study aimed to identify when self-incompatibility occurs in A. sellowiana flowers submitted to self-pollinations. Pollinations were made using nine known self-incompatible accessions in several treatments including manual cross-pollination, manual self-pollination, no pollination and natural pollination. Flowers were pollinated and pistils collected at times ranging from 1 to 30 days after pollination (DAP). In both cross- and self-pollinations the fertilisation occurred from 18 DAP and the zygote was visualised at 24 and 26 DAP, respectively. The abscission of the self-pollinated flowers increased from 26 DAP onwards, when significant differences (P < 0.05) were found for the percentage of abscission among self-pollinated and cross-pollinated flowers. At 30 DAP, 72% of self-pollinated flowers were abscised. The size of ovules and ovaries of self-pollinated flowers showed no significant difference from those of non-pollinated flowers throughout 30 DAP, while those from cross-pollinated flowers were significantly larger (P < 0.05) than the other treatments from 22 and 24 DAP, respectively. After 40 DAP, there was no fruit development in self-pollination and non-pollination treatments. Our study brings greater clarity to the mechanism of self-incompatibility in A. sellowiana, indicating late-acting self-incompatibility occurring through the rejection/abscission of self-pollinated flowers precisely after syngamy and zygote formation.

S-RNase disrupts tip-localized reactive oxygen species and induces nuclear DNA degradation in incompatible pollen tubes of Pyrus pyrifolia

Pear (Pyrus pyrifolia L.) has an S-RNase-based gametophytic self-incompatibility (SI) mechanism, and S-RNase has also been implicated in the rejection of self-pollen and genetically identical pollen. However, RNA degradation might be only the beginning of the SI response, not the end. Recent in vitro studies suggest that S-RNase triggers mitochondrial alteration and DNA degradation in the incompatible pollen tube of Pyrus pyrifolia, and it seems that a relationship exists between self S-RNase, actin depolymerization and DNA degradation. To further uncover the SI response in pear, the relationship between self S-RNase and tip-localized reactive oxygen species (ROS) was evaluated. Our results show that S-RNase specifically disrupted tip-localized ROS of incompatible pollen tubes via arrest of ROS formation in mitochondria and cell walls. The mitochondrial ROS disruption was related to mitochondrial alteration, whereas cell wall ROS disruption was related to a decrease in NADPH. Tip-localized ROS disruption not only decreased the Ca(2+) current and depolymerized the actin cytoskeleton, but it also induced nuclear DNA degradation. These results indicate that tip-localized ROS disruption occurs in Pyrus pyrifolia SI. Importantly, we demonstrated nuclear DNA degradation in the incompatible pollen tube after pollination in vivo. This result validates our in vitro system in vivo.

Self-incompatibility

There are several different types of self-incompatibility in different flowering plant species, and there has recently been progress in understanding their molecular genetics by using combined molecular and evolutionary approaches. Questions include the mechanism of self-incompatibility (both the nature of the proteins encoded by the genes and whether incompatibility systems all have separate genes for the pollen and pistil recognition proteins, which is the focus of this mini-review) and whether these systems involve chromosome regions with suppressed recombination and, if so, the size of these regions.

Cloning and mapping multiple S-locus F-box genes in European pear (Pyrus communis L.)

European pear, as well as its close relatives Japanese pear and apple, exhibits S-RNase-based gameto- phytic self-incompatibility. The male determinant of this self-incompatibility mechanism is a pollen-expressed pro- tein containing an F-box domain; in the genera Petunia (Solanaceae), Antirrhinum (Plantaginaceae), and Prunus (Rosaceae), a single F-box gene determines the pollen S. In apple and Japanese pear, however, multiple S-locus F-box genes were recently identified as candidates for the pollen S, and they were named S-locus F-Box Brothers. These genes were considered good candidates for the pollen S determinant since they exhibit S-haplotype-specific poly- morphisms, pollen-specific expression, and linkage to the S-RNase. In the present study, S-locus F-Box Brothers homologs have been cloned from two of the most agronomically important European pear varieties, "Abbe Fetel" (S104-2/S105) and "Max Red Bartlett" (S101/S102), and they have been mapped on a genetic linkage map developed on their progeny. Our results suggest that the number of F- box genes linked to the S-locus of the European pear is higher than expected according with previous reports for apple and Japanese pear, since up to five genes were found to be linked to a single S-haplotype. Moreover, two of these genes exhibited an incomplete linkage to the S-RNase, allowing the identification of low-frequency recombinant haplotypes, generated by a crossing-over event between the two genes. These F-box genes are most likely placed in close proximity of the S-locus but do not belong to it, and they can thus be excluded from being responsible for the determination of pollen S function.

Sistema reprodutivo e polinização de Senna multijuga (Fabaceae) em Mata Atlântica Montana

Resumo O conhecimento da biologia reprodutiva e polinização de árvores neotropicais vêm aumentando nas últimas décadas. No entanto, ainda é incipiente para a Mata Atlântica e muitas questões persistem, por exemplo, sobre a prevalência de autoincompatibilidade. A biologia floral, o sistema reprodutivo e os visitantes florais de Senna multijuga foram estudados, com o objetivo de verificar a ocorrência de autoincompatibilidade e determinar seus polinizadores. A espécie apresenta características florais típicas do gênero, como flores assimétricas, enantiostilia, heteranteria e deiscência poricida. A antese é diurna e a viabilidade do pólen não diferiu entre os morfos de anteras. Os polinizadores foram abelhas dos gêneros Bombus, Epicharis, Centris e Xylocopa e abelhas menores atuaram como pilhadores de pólen. A reprodução sexual em S. multijuga depende da transferência de pólen pelos polinizadores, pois não foram formados frutos por apomixia ou autopolinização. Este último resultado pode ser devido à depressão por endogamia ou a um mecanismo de autoincompatibilidade de ação tardia, uma vez que houve aborto uniforme de pistilos e penetração de tubos polínicos nos óvulos após autopolinização. Diferença na fecundidade após polinização manual e em condições naturais indica que a limitação polínica afeta o sucesso reprodutivo feminino, assim como a disponibilidade de recursos.

Population genetics of self-incompatibility and developing self-compatible genotypes in niger (Guizotia abyssinica)

Niger (Guizotia abyssinica (L. f.) Cass. (Asteraceae) is a strictly self-incompatible crop species with a sporophytic self-incompatibility mechanism. This characteristic presents a number of difficulties in plant improvement programs. The objective of this study was to determine the number and distribution of S-alleles in Ethiopian niger populations and to identify and develop self-compatible genotypes with various associated advantages. Several aspects of self-incompatibility in niger were compared in self- and cross-pollination experiments in which seed-set was considered to be a measure of compatibility. Our results indicate the presence of a minimum of ten self-incompatibility alleles and one self-compatibility allele at the S-locus in niger. Most of these alleles behave differently in the pollen and pistil. About two-thirds of the allelic interactions in both the pollen and pistil were dominant/recessive, and one-third were codominant. The reciprocal cross-pollinations (RCPs) resulted in progeny with similar levels of compatibility within and among populations because of a wide distribution of S-alleles in the populations and, consequently, low population differentiation at the S-locus. An analysis of molecular variance (AMOVA) revealed that only 2% of the total genetic variation at the S-locus differentiates the populations. In conclusion, self-compatible genotypes from the Ethiopian niger gene pool have been identified and developed for the first time.

Flowering and seeding patterns in primary, secondary and silvopastoral managed Nothofagus antarctica forests in South Patagonia

The success of the reproductive process in trees depends on abiotic and biotic factors that determine the final outcome of natural regeneration. Silviculture alters biotic and abiotic factors and results in secondary forest structures. To effectively manage these forests, it is necessary to understand the bottlenecks in reproductive stages using a whole-cycle approach study. The aim of this study was to analyse flowering and seeding patterns in primary, secondary and silvopastoral managed Nothofagus antarctica forests, including investigating the pre-dispersion foraging of insects and birds, as well as abscised biomass production. A high percentage of female flowers produced fruits (95–96%) in which the main loss factor before seeding was the abscission of immature fruits (11–14%). Seeding was greater in secondary forests (11.4 million ha−1), but managed stands presented a higher percentage of flowers resulting in seeds (82%). However, secondary forests had a better seed quality (17% viable seeds), where the main loss factor was empty seeds in all treatments (39–50%). Biotic factors (foraging by insects and birds) were higher in disturbed than primary forests. Nothofagus antarctica produce large quantities of seeds, but abscised immature fruits and empty seeds due to self-incompatibility mechanisms appeared as the major loss factors.

Sporophytic self-incompatibility in Senecio squalidus (Asteraceae): S allele dominance interactions and modifiers of cross-compatibility and selfing rates.

Understanding genetic mechanisms of self-incompatibility (SI) and how they evolve is central to understanding the mating behaviour of most outbreeding angiosperms. Sporophytic SI (SSI) is controlled by a single multi-allelic locus, S, which is expressed in the diploid (sporophyte) plant to determine the SI phenotype of its haploid (gametophyte) pollen. This allows complex patterns of independent S allele dominance interactions in male (pollen) and female (pistil) reproductive tissues. Senecio squalidus is a useful model for studying the genetic regulation and evolution of SSI because of its population history as an alien invasive species in the UK. S. squalidus maintains a small number of S alleles (7-11) with a high frequency of dominance interactions. Some S. squalidus individuals also show partial selfing and/or greater levels of cross-compatibility than expected under SSI. We previously speculated that these might be adaptations to invasiveness. Here we describe a detailed characterization of the regulation of SSI in S. squalidus. Controlled crosses were used to determine the S allele dominance hierarchy of six S alleles and effects of modifiers on cross-compatibility and partial selfing. Complex dominance interactions among S alleles were found with at least three levels of dominance and tissue-specific codominance. Evidence for S gene modifiers that increase selfing and/or cross-compatibility was also found. These empirical findings are discussed in the context of theoretical predictions for maintenance of S allele dominance interactions, and the role of modifier loci in the evolution of SI.

Expression and inheritance of sporophytic self‐incompatibility in synthetic allohexaploid Senecio cambrensis (Asteraceae)

Allopolyploid speciation is common in plants and is frequently associated with shifts from outcrossing, for example self-incompatibility, to inbreeding (i.e. selfing). Senecio cambrensis is a recently evolved allohexaploid species that formed following hybridization between diploid self-incompatible S. squalidus and tetraploid self-compatible S. vulgaris. Studies of reproduction in wild populations of S. cambrensis have concluded that it is self-compatible. Here, we investigated self-compatibility in synthetic lines of S. cambrensis generated via hybridization and colchicine-induced polyploidization and wild S. cambrensis using controlled crossing experiments. Synthetic F(1)S. cambrensis individuals were all self-compatible but, in F(2) and later generations, self-incompatible individuals were identified at frequencies of 6.7-9.2%. Self-incompatibility was also detected in wild sampled individuals at a frequency of 12.2%. The mechanism and genetics of self-incompatibility were tested in synthetic S. cambrensis and found to be similar to those of its paternal parent S. squalidus (i.e. sporophytic). These results show, for the first time, that functional sporophytic self-incompatibility can be inherited and expressed in allopolyploids as early as the second (F(2)) generation. Wild S. cambrensis should therefore be considered as possessing a mixed mating system with the potential for evolution towards either inbreeding or outcrossing.

Self-incompatibility alleles in Polish wild pear (Pyrus pyraster (L.) Burgsd.): a preliminary analysis

Wild pear (Pyrus pyraster, syn. P. communis var. pyraster) is thought to be one of the species that gave rise to all other members of the genus Pyrus, although intraspecific hybridizations with cultivated varieties could cause the disappearance of original species characteristics. S-RNase alleles from 7 different wild pear individuals, collected from various regions of Poland, were cloned on the basis of the PCR method and nucleotide sequence analyses. The hypervariable (HV) region is responsible for allele-specific S-RNase activity in the self-incompatibility mechanism. The high level of polymorphism of its sequences may constitute a source of valuable phylogenetic information. From all individuals, 14 sequences were obtained successfully, and 9 of them were novel alleles. Phylogenetic analysis of these alleles was based on the amino acid sequence interpretation of coding regions and intron nucleotide sequences. The research conducted on a limited pool of available P. pyraster alleles gives only an initial insight into possible S-RNase allele polymorphisms in wild populations. At this stage, the results do not confirm a strong influence of cultivated pear species on the wild pear.