Genetic mapping of AFLP/AMF-derived DNA markers in the vicinity of the self-incompatibility locus in<Emphasis Type="Italic"> Ipomoea trifida</Emphasis>

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

Isolation of S-alleles from a wild population of Brassica campestris L. at Balcesme,Turkey and their characterization by S-glycoproteins

Summary S-alleles of self-incompatibility were isolated from a wild population of Brassica campestris growing at Balcesme, Turkey. Out of 88 plants observed, 73 were self-incompatible and 4 were self-compatible. In certain families, selfed progenies from a self-incompatible plant segregated into fewer than three incompatibility classes, which is consistent with a one-locus sporophytic genetic control of self-incompatibility. Out of 25 combinations of S-alleles tested, dominance interactions were observed in 6 of them on the pollen side and on 5 of them on the stigma side. The 35 S-homozygotes thus isolated consisted of 18 independent S-alleles. The number of S-alleles in this population was estimated to be more than 30. The S-locus glycoproteins (SLGs) corresponding to the respective S-alleles were identified by iso-electric focusing (IEF)-gel immunoblotting with a polyclonal antiserum against SLG⁸. SLGs in a stigma were generally composed of several bands, one major and a few minor ones, whose molecular weight was similar to each other, and the major and minor bands were heritable in correlation with each other. SDS-PAGE analysis of SLGs differentiated a few juxtaposed bands between 50 and 60 kDa, and the variations in these bands were considered to be due to differences in the number of polysaccharide residues. General features of the variation of S-genes and their SLGs between the populations in Balcesme, Turkey and Oguni, Japan, were comparatively similar to one another, despite the different surroundings and history of these populations.     

PCR detection of transcripts homologous to the self-incompatibility gene in anthers ofBrassica

The polymerase chain reaction (PCR) is particularly well suited for the detection of rare sequences. Taking advantage of the recent isolation of sequences associated with stigma self-incompatibility inBrassica oleracea, we used PCR amplifications with primers synthesized to the S6 cDNA sequence, to demonstrate the presence of mRNA homologous to stigmaS-locus gene (SLG) in anthers during early microsporogenesis. In addition, otherS-locus-related (SLR) sequences were shown to be transcribed in sexual as well as in vegetative tissues (roots, leaves), suggesting that the SLG family might be involved not only in pollen-stigma recognition, but more generally in various forms of plant cell signalling processes. This information corroborates the recent discovery of a cDNA-deduced protein kinase from maize roots, whose extracellular receptor displays high homology withBrassica S-locus-specific glycoproteins.Communicated by H.F. Linskens     

Self-incompatibility in Petunia inflata: isolation and characterization of cDNAs encoding three S-allele-associated proteins

Summary We have identified three alleles of the S-locus controlling self-incompatibility and their associated pistil proteins in Petunia inflata, a species that displays monofactorial gametophytic self-incompatibility. These S-allele-associated proteins (S-proteins) are pistil specific, and their levels are developmentally regulated. The amino-terminal sequences determined for the three S-proteins are highly conserved and show considerable homology to those of S-proteins from Petunia hybrida, Nicotiana alata and Lycopersicon peruvianum, three other species of the Solanaceae that also exhibit gametophytic self-incompatibility. cDNA clones encoding the three S-proteins were isolated and sequenced. Comparison of their deduced amino acid sequences reveals an average homology of 75.6%, with conserved and variable residue interspersed throughout the protein. Of the 137 conserved residues, 53 are also conserved in the N. alata S-proteins studies so far; of the 64 variable residues, 29 were identified as hypervariable based on calculation of the Similarity Index. There is only one hypervariable region of significant length, and it consists of eight consecutive hypervariable residues. This region correspond approximately to the hypervariable region HV2 identified in N. alata S-proteins. Of the two classes of N. alata S-proteins previously identified, one class exhibits greater homology to the three P. inflata S-proteins reported here than to the other class of N. alata S-proteins.     

Physical linkage of the SLG and SRK genes at the self-incompatibility locus of Brassica oleracea

Summary In Brassica oleracea, the pollen-stigma interaction of self-incompatibility is controlled by a single genetically defined locus designated S. Molecular studies have identified two genes that are tightly linked to the classically defined S locus: The S-Locus Glycoprotein (SLG) gene and the S-Receptor Kinase (SRK) gene. In previous RFLP linkage analyses with probes specific for SLG and SRK, we were unable to identify any recombination events between SLG, SRK, and self-incompatibility phenotype. In this paper, we use pulsed-field gel electrophoresis (PFGE) in conjunction with DNA blot analysis to characterize the S-locus region from two highly divergent self-incompatibility genotypes, S ₂ and S ₆. We establish the physical linkage of SLG and SRK in each genotype, and demonstrate that the two genes are separated by a maximum distance of 220 kb in the S ₆ genotype and 350 kb in the S ₂ genotype. Furthermore, a comparison of the data from the two genotypes reveals that a high level of polymorphism exists across the entire S-locus region.     

Members of the<Emphasis Type="Italic"> S</Emphasis>-receptor kinase multigene family in<Emphasis Type="Italic"> Senecio squalidus</Emphasis> L. (Asteraceae), a species with sporophytic self-incompatibility

While the molecular basis of sporophytic self-incompatibility (SSI) has been investigated extensively in the Brassicaceae, almost nothing is known about the molecular regulation of SSI in other families, such as the Asteraceae. In species of Brassica and in Arabidopsis lyrata, a stigma-specific serine-threonine receptor kinase (SRK) and its cognate ligand, a pollen coating-borne cysteine-rich protein (SCR/SP11), determine the female and male sides of the SSI response, respectively. Here we have used RT-PCR with degenerate primers to conserved regions of SRK to amplify three SRK-like gene fragments expressed in stigmas of Senecio squalidus (Asteraceae). The Senecio S-receptor-like kinase (SSRLK) sequences share ~43% amino acid sequence identity with Brassica SRK₃ but higher amino acid sequence identity (~50%) with two Solanum bulbocastanum receptor-like kinase genes of unknown function. Despite expression in stigmas, all three SSRLKs were expressed at varying levels in floral and vegetative tissues. No allelic polymorphism was detected for the three SSRLKs in two S homozygous lines of S. squalidus or three other lines of S. squalidus carrying different S alleles. A full-length cDNA clone was obtained for SSRLK1 and its predicted amino acid sequence revealed significant structural differences to Brassica SRKs, most notably a major N-terminal truncation of 169 amino acids and the presence of just 8 conserved cysteine residues within the putative receptor domain instead of 12. Together, the sequence characteristics and expression characteristics of SSRLKs suggest that they are unlikely to be directly involved in the SSI response of S. squalidus. These findings are discussed in terms of the evolution of the SRK multigene family and the molecular basis of SSI in S. squalidus and the Asteraceae.     

Pollinator visitation in populations of tristylous Eichhornia paniculata in northeastern Brazil

Summary The frequencies of floral morphs in populations of tristylous Eichhornia paniculata often deviate from the theoretical expectation of equality. This variation is associated with the breakdown of tristyly and the evolution of self-fertilization. Differences in morph frequencies could result from selection pressures due to variable levels of insect visitation to populations and contrasting foraging behavior among the floral morphs. We estimated pollinator densities in 16 populations and quantified visitation sequences to morphs in five populations of E. paniculata in northeastern Brazil. Foraging behavior among floral morphs was measured as the frequency of visits to morphs relative to their frequency in the population (preference) and number of flights between inflorescences of the same versus different morphs (constancy). Pollinator density (number/m²/minute) was not correlated with population size, plant density or morph diversity. Pollinator densities varied most among populations of less than 200 plants. Whether pollinators discriminated among the morphs, depended on whether they primarily collected nectar or pollen. In four populations, nectar-feeding bees (Ancyloscelis and Florilegus spp.) and butterflies showed no consistent preference or constancy among the morphs. In contrast, pollen-collecting bees (Trigona sp.) visited a lower proportion of longstyled inflorescences than expected and tended to visit more mid-and short-styled inflorescences in succession, once they were encountered. Pollinator constancy for morphs did not result from differences in inflorescence production or spatial patchiness among the morphs. Although non-random pollinator visitation to morphs in heterostylous populations could potentially affect mating and hence morph frequencies, the observed visitation patterns in this study do not provide evidence that pollinators play a major role in influencing floral morph frequencies.     

High-resolution mapping of the <Emphasis Type="Italic">S</Emphasis>-locus in <Emphasis Type="Italic">Turnera</Emphasis> leads to the discovery of three genes tightly associated with the <Emphasis Type="Italic">S</Emphasis>-alleles

While the breeding system known as distyly has been used as a model system in genetics, and evolutionary biology for over a century, the genes determining this system remain unknown. To positionally clone genes determining distyly, a high-resolution map of the S-locus region of Turnera has been constructed using segregation data from 2,013 backcross progeny. We discovered three putative genes tightly linked with the S-locus. An N-acetyltransferase (TkNACE) flanks the S-locus at 0.35 cM while a sulfotransferase (TkST1) and a non-LTR retroelement (TsRETRO) show complete linkage to the S-locus. An assay of population samples of six species revealed that TsRETRO, initially discovered in diploid Turnera subulata, is also associated with the S-allele in tetraploid T. subulata and diploid Turnera scabra. The sulfotransferase gene shows some level of differential expression in long versus short styles, indicating it might be involved in some aspect of distyly. The complete linkage of TkST1 and TsRETRO to the S-locus suggests that both genes may reside within, or in the immediate vicinity of the S-locus. Chromosome walking has been initiated using one of the genes discovered in the present study to identify the genes determining distyly. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Comparison of S-alleles and S-glycoproteins between two wild populations of Brassica campestris in Turkey and Japan

Summary The number of identical S-alleles between two wild populations of B. campestris, one in Turkey, the other in Japan, that have been independent of one another for a long time was investigated. Diallel pollination tests between 38 S-allele homozygotes, i.e., 16 S-allele homozygotes from Turkey and 22 from Japan, revealed that these were 29 different S-alleles only 4 common ones. These S-alleles were differentiated by the iso-electric focusing (IEF) analysis of S-locus glycoproteins (SLGs) stained with an antiserum against SLG⁸. All identical S-alleles had the major SLG band at the same pI value without exception, even though they were collected from different populations. However, the number of minor bands of SLGs varied between the two populations; the S-alleles in Balcesme had generally fewer minor bands than those in Oguni. The 29 independent S-alleles were numbered from S ²¹ to S ⁴⁹ according to the pI value of the major SLG band. The major bands whose pI values were 7.5–8.5 were most common. Blot-hybridization patterns of genomic DNA hybridized with SLG ⁸ cDNA were not always the same among the strains of identical S-alleles obtained from different populations. Because about 20% of the S-alleles were shared between the two populations, it can be inferred that more than hundreds of S-alleles have been accumulated by mutation in B. campestris throughout the world.     

Analysis of the Tissue-SpecificS RNase gene promoter associated with self-incompatibility in tomato (Lycopersicon peruvianum L.)

To understand the expression pattern of theS RNase gene in the floral tissues associated with self-incompatibility (SI), promoter region of S₁₁ RNase gene was serially deleted and fused GUS. Five chimeric constructs containing a deleted promoter region of the S₁₁ RNase gene were constructed, and introduced intoNicotiana tabacum using Agrobacterium-mediated transformation. Northern blot analysis revealed that the GUS gene was expressed in the style, anther, and developing pollen of all stages in each transgenic tobacco plant The developing pollen expressed the same amount of GUS mRNA in all stages in transgenic tobacco plants. In addition, histochemical analysis showed GUS gene expression in vascular bundle, endothecium, stomium, and tapetum cells during pollen development in transgenic plants. From these results, it is speculated that SI ofLycopersicon peruvianum may occur through the interaction ofS RNase expressed in both style and pollen tissues.     

Sequence and expression of endogenous S-locus glycoprotein genes in self-compatible Brassica napus

Brassica napus is an amphidiploid plant which is self-compatible even though it is derived from hybridisation of the self-incompatible species B. oleracea and B. campestris. Experiments were undertaken to establish if S-locus glycoprotein (SLG) genes exist in B. napus and whether these are expressed as in self-incompatible Brassica species. Two different stigma-specific cDNA sequences homologous to SLG genes were obtained from the B. napus cultivar Westar. One of these sequences, SLG _WS1, displayed highest homology to class I SLG alleles, whereas the other, SLG _WS2, showed greatest homology to class II SLG genes. Both were expressed at high levels in Westar stigmas following a developmental pattern typical of SLG genes in the self-incompatible diploids. We infer that they represent the endogenous SLG genes at the two homoeologous S-loci. The occurrence of normally expressed SLG genes and its relevance to the self-compatible phenotype of B. napus is discussed.     

Duplication of the <Emphasis Type="Italic">S</Emphasis>-locus F-box gene is associated with breakdown of pollen function in an <Emphasis Type="Italic">S</Emphasis>-haplotype identified in a natural population of self-incompatible <Emphasis Type="Italic">Petunia axillaris</Emphasis>

We previously identified both self-incompatible and self-compatible plants in a natural population of self-incompatible Petunia axillaris subsp. axillaris, and found that all the self-compatible plants studied carried either S_C1- or S_C2-haplotype. Genetic crosses showed that S_C2 was identical to S₁₇ identified from another natural population of P. axillaris, except that its pollen function was defective, and that the pollen-part mutation in S_C2 was tightly linked to the S-locus. Recent identification of the S-locus F-box gene (SLF) as the gene that controls pollen specificity in S-RNase-based self-incompatibility has prompted us to examine the molecular basis of this pollen-part mutation. We cloned and sequenced the S₁₇-allele of SLF of P.axillaris, named PaSLF₁₇, and found that S_C2 S_C2 plants contained extra restriction fragments that hybridized to PaSLF₁₇ in addition to all of those observed in S₁₇ S₁₇ plants. Moreover, these additional fragments co-segregated with S_C2. We used the S_C2-specific restriction fragments as templates to clone an allele of PaSLF by PCR. To determine the identity of this allele, named PaSLF_x, primers based on its sequence were used to amplify PaSLFalleles from genomic DNA of 40 S-homozygotes of P. axillaris, S₁ S₁ through S₄₀ S₄₀. Sequence comparison revealed that PaSLF_x was completely identical with PaSLF₁₉ obtained from S₁₉ S₁₉. We conclude that the S-locus of S_C2 contained both S₁₇-allele and the duplicated S₁₉-allele of PaSLF. S_C2 is the first naturally occurring pollen-part mutation of a solanaceous species that was shown to be associated with duplication of the pollen S. This finding lends support to the proposal, based on studies of irradiation-generated pollen-part mutants of solanaceous species, that duplication, but not deletion, of the pollen S, causes breakdown of pollen function.     

Structure and expression of AtS1, an Arabidopsis thaliana gene homologous to the S-locus related genes of Brassica

Summary Genetic and molecular analysis of the self-incompatibility locus (S-locus) of the crucifer Brassica has led to the characterization of a multigene family involved in pollen-stigma interactions. While the crucifer Arabidopsis thaliana does not have a self-incompatibility system, S-related sequences were detected in this species by cross-hybridization with Brassica DNA probes. In this paper, we show that an A. thaliana S-related sequence, designated AtS1, is expressed specifically in flower buds. Sequence analysis suggests that AtS1 encodes a secreted glycoprotein that is most similar to the Brassica S-locus related protein SLR1. As has been proposed for SLR1, this gene may be involved in determining some fundamental aspect of pollen-stigma interactions during pollination. The molecular and genetic advantages of the Arabidopsis system will provide many avenues for testing this hypothesis.     

异质生境对二型花柱植物雪地报春花性状分化的影响

该研究以生长在新疆北部的二型花柱植物雪地报春(Primula nivalis)为研究材料,对7个低海拔(1 657~2 013m)森林居群和7个高海拔(2 400~2 700m)草原居群的花型比例进行调查,对花部特征进行检测,并对长、短花柱植株在不同海拔居群的花性状分化进行了比较研究,以揭示该类群植物的演化与环境的关系。结果表明:(1)在高海拔草原居群中长花柱植株比例高于短花柱植株。(2)比较草原和森林生态系统中的雪地报春居群,长花柱花形态特征间存在显著差异,但短花柱花形态特征间的差异不显著。(3)高海拔草原居群中长花柱花的花冠筒长度、雄蕊长度、雌雄蕊距离、雌雄异位程度以及雌雄蕊空间位置是导致花性状分化的主要因素。(4)在草原居群中,长花柱花的雄蕊、雌雄异位程度及花冠口至雄蕊距离的变化减少了长短花柱花间的互补式对应性。研究认为,在异质生境中长花柱花性状的变化是导致该物种长短花柱花性状分化的主要因素。     

Genetic features of a pollen-part mutation suggest an inhibitory role for the <Emphasis Type="Italic">Antirrhinum</Emphasis> pollen self-incompatibility determinant

Self-incompatibility (SI), an important barrier to inbreeding in flowering plants, is controlled in many species by a single polymorphic S-locus. In the Solanaceae, two tightly linked S-locus genes, S-RNase and SLF (S-locus F-box)/SFB (S-haplotype-specific F-box), control SI expression in pistil and pollen, respectively. The pollen S-determinant appears to function to inhibit all but self S-RNase in the Solanaceae, but its genetic function in the closely-related Plantaginaceae remains equivocal. We have employed transposon mutagenesis in a member of the Plantaginaceae (Antirrhinum) to generate a pollen-part SI-breakdown mutant Pma1 (Pollen-part mutation in Antirrhinum1). Molecular genetic analyses showed that an extra telocentric chromosome containing AhSLF-S ₁ is present in its self-compatible but not in its SI progeny. Furthermore, analysis of the effects of selection revealed positive selection acting on both SLFs and SFBs, but with a stronger purifying selection on SLFs. Taken together, our results suggest an inhibitor role of the pollen S in the Plantaginaceae (as represented by Antirrhinum), similar to that found in the Solanaceae. The implication of these findings is discussed in the context of S-locus evolution in flowering plants. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users. Yongbiao Xue, Yijing Zhang, and Qiuying Yang contributed equally to this work.     

Analysis of the S-locus structure in Prunus armeniaca L. Identification of S-haplotype specific S-RNase and F-box genes

The gametophytic self-incompatibility (GSI) system in Rosaceae has been proposed to be controlled by two genes located in the S-locusan S-RNase and a recently described pollen expressed S-haplotype specific F-box gene (SFB). However, in apricot (Prunus armeniaca L.) these genes had not been identified yet. We have sequenced 21kb in total of the S-locus region in 3 different apricot S-haplotypes. These fragments contain genes homologous to the S-RNase and F-box genes found in other Prunusspecies, preserving their basic gene structure features and defined amino acid domains. The physical distance between the F-boxand the S-RNase genes was determined exactly in the S ₂-haplotype (2.9kb) and inferred approximately in the S ₁-haplotype (< 49kb) confirming that these genes are linked. Sequence analysis of the 5 flanking regions indicates the presence of a conserved region upstream of the putative TATA box in the S-RNase gene. The three identified S-RNase alleles (S ₁, S ₂ and S ₄) had a high allelic sequence diversity (75.3 amino acid identity), and the apricot F-box allelic variants (SFB₁, SFB₂ and SFB₄) were also highly haplotype-specific (79.4 amino acid identity). Organ specific-expression was also studied, revealing that S ₁- and S ₂-RNases are expressed in style tissues, but not in pollen or leaves. In contrast, SFB ₁ and SFB ₂ are only expressed in pollen, but not in styles or leaves. Taken together, these results support these genes as candidates for the pistil and pollen S-determinants of GSI in apricot.     

Reproductive biology of Alpinia blepharocalyx (Zingiberaceae): another example of flexistyly

The floral biology and breeding system of Alpinia blepharocalyx were studied in Yunnan province, southwest China. Our results indicate that populations of A. blepharocalyx have two floral morphs, which differ in flowering behaviour: the cataflexistylous morph in which the stigma is held erect above the dehiscent anther when anthesis begins in the morning and becomes curved under the anther at afternoon, and the anaflexistylous morph in which the receptive stigma is curved under the indehiscent anther first and moves into a reflexed superior position above the anther as it begins to shed pollen in the afternoon; the flowering period of both floral morphs is 12 hours; the stylar movements in the two floral morphs are synchronous, and they have similar traits to those found in other Alpinia species previously reported. Also, on average, cataflexistylous flowers are larger than anaflexistylous flowers, especially the labellum and corolla tube length; moreover, the P/O ratio of the two floral morphs is significantly different: the cataflexistylous morph has more pollen grains and fewer ovules than the anaflexistylous morph; the evolutionary significance of this comparison is discussed. Cataflexistylous flowers were observed to produce a lower concentration of nectar than that of anaflexistylous flowers before 11:00 a.m., but they then have higher nectar concentration; cataflexistylous flowers always have more nectar than anaflexistylous flowers. Flowers of A. blepharocalyx were visited by fewer insects at a lower frequency, including honey bees (Apis cerana cerana) and two species of carpenter bees (Xylocopa spp.). No significant differences were found in the fruit set among the hand-pollination treatments regardless of selfing (geitonogamy and autogamy) or crossing (intermorph and intramorph); but all hand-pollination treatments exhibited much higher fruit set than the controls; meanwhile, no fruit set occurred in the unpollinated bagged plants. Pollen tube growth was examined using fluorescence microscopy following self, intramorph, and intermorph hand pollinations at different times of the day; the pollen tubes of both floral morphs have the same growth rate and the capability to reach the ovary. Both the results of pollen tube growth and fruit sets under different pollination conditions show that A. blepharocalyx is self-compatible and dependent upon insects for pollination. The distinctive flexistyly mechanism of A. blepharocalyx is likely a floral mechanism that promotes effective intermorph pollen transfer.     

Identification of <Emphasis Type="Italic">S</Emphasis>-haplotype-specific F-box gene in Japanese plum (<Emphasis Type="Italic">Prunus salicina</Emphasis> Lindl.)

Self-incompatibility has been studied extensively at the molecular level in Solanaceae, Rosaceae and Scrophulariaceae, all of which exhibit gametophytic self-incompatibility controlled by a single polymorphic locus containing at least two linked genes, i.e., the S-RNase gene and the pollen-expressed SFB/SLF (S-haplotype-specific F-box/S-locus F-box) gene. However, the SFB gene in Japanese plum (Prunus salicina Lindl.) has not yet been identified. We determined eight novel sequences homologous to the SFB genes of other Prunus species and named these sequences PsSFB. The gene structure of the SFB genes and the characteristic domains in deduced amino acid sequences were conserved. Three sequences from 410 to 2,800 bp of the intergenic region between the PsSFB sequences and the S-RNase alleles were obtained. The eight identified PsSFB sequences showed S-haplotype-specific polymorphism, with 74–83% amino acid identity. These alleles were exclusively expressed in the pollen. These results suggest that the PsSFB alleles are the pollen S-determinants of GSI in Japanese plum. Nucleotide sequence data reported are available in the NCBI database under the accession numbers DQ849084–DQ849090 and DQ849118.     

Sequence variability and gene structure at the self-incompatibility locus of Solanum tuberosum

Summary Allelic complexity is a key feature of self-incompatibility (S) loci in gametophytic plants. We describe in this report the allelic diversity and gene structure of the S locus in Solanum tuberosum revealed by the isolation and characterization of genomic and cDNA clones encoding S-associated major pistil proteins from three alleles (S ₁, S _r1, S ₂). Genomic clones encoding the S₁ and S₂ proteins provide evidence for a simple gene structure: Two exons are separated by a small intron of 113 (S ₁) and 117 by (S ₂). Protein sequences deduced from cDNA clones encoding S₁ and S_r1 proteins show 95% homology. 15 of the 25 residues that differ between these S ₁and S _r1alleles are clustered in a short hypervariable protein segment (amino acid positions 44–68), which corresponds in the genomic clones to DNA sequences flanking the single intron. In contrast, these alleles are only 66% homologous to the S ₂allele, with the residues that differ between the alleles being scattered throughout the sequence. DNA crosshybridization experiments identify a minimum of three classes of potato S alleles: one class contains the alleles S ₁, S _r1and S ₃, the second class S ₂and an allele of the cultivar Roxy, and the third class contains at present only S ₄. It is proposed that these classes reflect the origin of the S alleles from a few ancestral S sequence types.     

Protein expression of a self-compatible allele from Lycopersicon peruvianum: introgression and behavior in a self-incompatible background

Lycopersicon peruvianum (wild tomato) is a gametophytic self-incompatible (SI) species. One natural population has been shown to harbor a self-compatible (SC) allele. A stylar protein associated with the self-compatibility allele has been elucidated using SDS-PAGE. The temporal and spatial expression of this protein is presented and compared with protein expression of two SI alleles. Hybrids containing the SC and SI alleles were used in a backcrossing program to introgress the SC allele into SI backgrounds in six independent lines. Controlled pollinations and SDS-PAGE were used to identify and select classes of progeny. After four backcross generations (approximately 97% recovery of the SI backgrounds) the SC allele still confers self-fertility in lines that contain this allele, providing evidence that the mutation to SC occurred at the S-locus and that the associated protein is likely responsible.