Self-incompatible Plants Research Articles

The impact of self-incompatibility systems on the prevention of biparental inbreeding.

Inbreeding in hermaphroditic plants can occur through two different mechanisms: biparental inbreeding, when a plant mates with a related individual, or self-fertilization, when a plant mates with itself. To avoid inbreeding, many hermaphroditic plants have evolved self-incompatibility (SI) systems which prevent or limit self-fertilization. One particular SI system—homomorphic SI—can also reduce biparental inbreeding. Homomorphic SI is found in many angiosperm species, and it is often assumed that the additional benefit of reduced biparental inbreeding may be a factor in the success of this SI system. To test this assumption, we developed a spatially-explicit, individual-based simulation of plant populations that displayed three different types of homomorphic SI. We measured the total level of inbreeding avoidance by comparing each population to a self-compatible population (NSI), and we measured biparental inbreeding avoidance by comparing to a population of self-incompatible plants that were free to mate with any other individual (PSI). Because biparental inbreeding is more common when offspring dispersal is limited, we examined the levels of biparental inbreeding over a range of dispersal distances. We also tested whether the introduction of inbreeding depression affected the level of biparental inbreeding avoidance. We found that there was a statistically significant decrease in autozygosity in each of the homomorphic SI populations compared to the PSI population and, as expected, this was more pronounced when seed and pollen dispersal was limited. However, levels of homozygosity and inbreeding depression were not reduced. At low dispersal, homomorphic SI populations also suffered reduced female fecundity and had smaller census population sizes. Overall, our simulations showed that the homomorphic SI systems had little impact on the amount of biparental inbreeding in the population especially when compared to the overall reduction in inbreeding compared to the NSI population. With further study, this observation may have important consequences for research into the origin and evolution of homomorphic self-incompatibility systems.

Relatively weak inbreeding depression in selfing but also in outcrossing populations of North American Arabidopsis lyrata.

Hermaphroditic plants can potentially self-fertilize, but most possess adaptations that promote outcrossing. However, evolutionary transitions to higher selfing rates are frequent. Selfing comes with a transmission advantage over outcrossing, but self-progeny may suffer from inbreeding depression, which forms the main barrier to the evolution of higher selfing rates. Here, we assessed inbreeding depression in the North American herb Arabidopsis lyrata, which is normally self-incompatible, with a low frequency of self-compatible plants. However, a few populations have become fixed for self-compatibility and have high selfing rates. Under greenhouse conditions, we estimated mean inbreeding depression per seed (based on cumulative vegetative performance calculated as the product of germination, survival and aboveground biomass) to be 0.34 for six outcrossing populations, and 0.26 for five selfing populations. Exposing plants to drought and inducing defences with jasmonic acid did not magnify these estimates. For outcrossing populations, however, inbreeding depression per seed may underestimate true levels of inbreeding depression, because self-incompatible plants showed strong reductions in seed set after (enforced) selfing. Inbreeding-depression estimates incorporating seed set averaged 0.63 for outcrossing populations (compared to 0.30 for selfing populations). However, this is likely an overestimate because exposing plants to 5% CO2 to circumvent self-incompatibility to produce selfed seed might leave residual effects of self-incompatibility that contribute to reduced seed set. Nevertheless, our estimates of inbreeding depression were clearly lower than previous estimates based on the same performance traits in outcrossing European populations of A.lyrata, which may help explain why selfing could evolve in North American A.lyrata.

Chlorosis of Ogura-CMS Brassica rapa is due to down-regulation of genes for chloroplast proteins

Cytoplasmic male sterility (CMS) is a maternally inherited trait leading to loss of the ability to produce fertile pollen and is extensively used in hybrid crop breeding. Ogura- CMS was originally generated by insertion of orf138 upstream of atp8 in the radish mitochondrial genome and transferred to Brassica crops for hybrid breeding. Gene expression changes by dysfunctional mitochondria in Ogura-CMS result in pollen developmental defects, but little is known about gene expression patterns in vegetative tissue. To examine the interaction between nuclear and organellar regulation of gene expression, microarray and subsequent gene expression experiments were conducted with leaves of F1 hybrid Chinese cabbage derived from self-incompatible (SI) or Ogura-CMS parents (Brassica rapa ssp. pekinensis). Out of 24,000 genes deposited on a KBGP24K microarray, 66 genes were up-regulated and 26 genes were down-regulated by over 2.5 fold in the CMS leaves. Up-regulated genes included stress-response genes and mitochondrial protein genes, while genes for ascorbic acid biosynthesis and thylakoid proteins were down-regulated. Most of the major component genes for light reactions of photosynthesis were highly expressed in leaves of both SI and CMS plants, but most of the cor-responding proteins were found to be greatly reduced in leaves of CMS plants, indicating posttranscriptional regulation. Reduction in thylakoid proteins and chlorophylls led to reduction in photosynthetic efficiency and chlorosis of Ogura- CMS at low temperatures. This research provides a foundation for studying chloroplast function regulated by mitochondrial signal and for using organelle genome introgression in molecular breeding.

Identification, genealogical structure and population genetics of S-alleles in Malus sieversii, the wild ancestor of domesticated apple.

The self-incompatibility (SI) gene that is specifically expressed in pistils encodes the SI-associated ribonuclease (S-RNase), functioning as the female-specificity determinant of a gametophytic SI system. Despite extensive surveys in Malus domestica, the S-alleles have not been fully investigated for Malus sieversii, the primary wild ancestor of the domesticated apple. Here we screened the M. sieversii S-alleles via PCR amplification and sequencing, and identified 14 distinct alleles in this species. By contrast, nearly 40 are present in its close wild relative, Malus sylvestris. We further sequenced 8 nuclear genes to provide a neutral reference, and investigated the evolution of S-alleles via genealogical and population genetic analyses. Both shared ancestral polymorphism and an excess of non-synonymous substitution were detected in the S-RNases of the tribe Maleae in Rosaceae, indicating the action of long-term balancing selection. Approximate Bayesian Computations based on the reference neutral loci revealed a severe bottleneck in four of the six studied M. sieversii populations, suggesting that the low number of S-alleles found in this species is mainly the result of diversity loss due to a drastic population contraction. Such a bottleneck may lead to ambiguous footprints of ongoing balancing selection detected at the S-locus. This study not only elucidates the constituents and number of S-alleles in M. sieversii but also illustrates the potential utility of S-allele number shifts in demographic inference for self-incompatible plant species.

Mutant selection in the self-incompatible plant radish (Raphanus sativus L. var. sativus) using two-step TILLING.

Radish (Raphanus sativus L. var. sativus), a widely cultivated root vegetable crop, possesses a large sink organ (the root), implying that photosynthetic activity in radish can be enhanced by altering both the source and sink capacity of the plant. However, since radish is a self-incompatible plant, improved mutation-breeding strategies are needed for this crop. TILLING (Targeting Induced Local Lesions IN Genomes) is a powerful method used for reverse genetics. In this study, we developed a new TILLING strategy involving a two-step mutant selection process for mutagenized radish plants: the first selection is performed to identify a BC1M1 line, that is, progenies of M1 plants crossed with wild-type, and the second step is performed to identify BC1M1 individuals with mutations. We focused on Rubisco as a target, since Rubisco is the most abundant plant protein and a key photosynthetic enzyme. We found that the radish genome contains six RBCS genes and one pseudogene encoding small Rubisco subunits. We screened 955 EMS-induced BC1M1 lines using our newly developed TILLING strategy and obtained six mutant lines for the six RsRBCS genes, encoding proteins with four different types of amino acid substitutions. Finally, we selected a homozygous mutant and subjected it to physiological measurements.

Genetic variation in the invasive weed Mikania micrantha (Asteraceae) suggests highways as corridors for its dispersal in southern China.

Roads as corridors of seed or fruit spatial dispersal have major impacts on the establishment and spread of invasive species, but their precise role in population genetic variation remains poorly understood. The South American weed Mikania micrantha has spread rapidly across southern China since its introduction to the Shenzhen area in 1984. This study investigated how its genetic diversity is distributed along highways, and whether highways have acted as corridors for the rapid expansion of M. micrantha METHODS: Twenty-seven roadside populations were sampled along four highways in southern China, and 787 samples were examined using 12 microsatellite markers. Variation in genetic diversity among populations was quantified and patterns of genetic differentiation were analysed. A high level of genetic diversity was found at both the species and the population levels in this self-incompatible plant (expected heterozygosity = 0·497 and 0·477, respectively; allelic richness = 2·580 and 2·521, respectively). The Wright F-statistic value among populations (0·044, P < 0·01) and the analysis of molecular variance (91% of genetic variation residing within populations, 9% among populations within highways and 0% among the four highways) showed a relatively low level of genetic differentiation among populations, while the principal coordinate and cluster analyses also indicated a lack of clear geographical genetic structure among populations. The calculated Nm value of 5·5 signifies strong gene flow. The pattern of genetic variation is consistent with facilitated dispersal along highways. The genetic admixtures among the roadside populations imply the occurrence of multiple population introductions during colonization. The long-distance dispersal of seeds associated with vehicular transportation on highways may have played important roles in shaping the genetic variation. This finding highlights the importance of highways as corridors for the spread of M. micrantha in southern China.

Clonal structure and high genetic diversity at peripheral populations of Sorbus torminalis (L.) Crantz.

Abstract: Knowing the level of genetic diversity and structure in marginal plant populations is essential for managing their genetic resources. This is particularly important for rare scattered tree species, such as Sorbus torminalis (L.) Crantz. We investigated the genetic diversity and its spatial distribution in peripheral populations of S. torminalis. As the species is known to reproduce vegetatively, we also evaluated clonal structure within populations. Using 13 nuclear microsatellite loci designed in two multiplexes, we genotyped 172 individuals revealing the existence of 100 distinct genotypes. Number of ramets per genotype was variable across populations with an average of 1.72. Examples of somaclonal variation at particular loci were detected. Measures of genetic diversity of the total sample were relatively high (mean allelic richness AR = 10.293; expected heterozygosity He = 0.756), as compared to other S. torminalis populations. We noticed a slightly negative inbreeding coefficient (FIS = -0.029) indicating a small excess of heterozygotes, which is typical for self-incompatible plants. Genetic differentiation among populations was low (FST = 0.048), but Bayesian clustering methods revealed the existence of three distinct genetic clusters only in part related to population structure. Significant spatial genetic structure within populations was also detected (Sp = 0.0125) indicating fine-scale pattern of isolation by distance. Our study demonstrated that peripheral populations of S. torminalis may exhibit relatively high levels of genetic diversity despite the existence of vegetative propagation. Nevertheless, if the studied or similar populations are expected to be utilized as seed sources for ex-situ or in-situ conservation purposes, the existence of clonal structure and spatial genetic structure must be taken into account in order to avoid excessive sampling of the same or closely related genets.

Vegetative and generative maintenance of self-incompatibility in six accessions of German chamomile

Self-incompatible (SI) plants are able to form ideal mother lines for hybrid crossing in hermaphroditic plants, assuring fertilization from the desired father line. To find out suitable ways to maintain SI was the aim of this study. Among 220 plants of German chamomile (Matricaria recutita (L.) Rauschert) within six accessions SI-genotypes were selected. SI was determined as staying seedless in three flower heads per plant. Initial SI-plants formed the basic paternal generation (P1) of i) maintaining the same genotypes over six months and repeating seed set analysis (P2) and of ii) conducting crossings in three versions (SI × SI, SI × NSI (not SI evaluated plants) and NSI × SI), thereby producing the F1 population. F1 exhibited 78% SI and P2 62% SI, indicating a higher environmental than genetic influence on SI. But heritability, calculated from the results of SI × SI crossings, showed high values (h(2) = 0.71). Within generative propagation, the influence of generation/crossing version was highly significant (p = 0.001) and the cultivar 'Degumille' explored the highest value of SI (86%) after SI × NSI crossings. Therefore, the intra-cultivar combination of 'Degumille' SI mother plants crossed with NSI father plants can be recommended as the most promising version to maintain SI in chamomile.

Sexual reproduction efficiency and genetic diversity of endangered Betula humilis Schrk. populations from edge and sub-central parts of its range

Outcrossed mating systems play a very important role in the persistence of endangered, self-incompatible plants such as shrub birch, Betula humilis Schrk. The goal of this study was to estimate, for the first time, the effectiveness of sexual reproduction in threatened edge and sub-central populations of shrub birch. The amplified fragment length polymorphism (AFLP) method revealed that all of the individuals at each locality had different genotypes. The matrix incompatibility count (MIC) suggested that the effectiveness of recombination was similar among all the populations of shrub birch under study. However, taking into account the greater germination ability of seeds in sub-central populations, we conclude that sexual reproduction in those populations can be more efficient. The germination capacity of seeds depends on their mass, which was significantly lower in dry or more shaded sites compared to wet or more exposed sites. Non-significant results of multiple regression models suggest that chemical parameters of the habitat (pH, EC, NH4+, PO43−) had no influence on the reproductive output of B. humilis. The discrepancy between the still quite substantial genetic diversity and the poor sexual reproduction in shrub birch populations can be explained by the production of a few phosphorus-rich seeds, insufficient time for a decrease in genetic variation in the disappearing part of the range or hybridization with close congeners.

Vegetative and generative maintenance of self-incompatibility in six accessions of German chamomile.

Self-incompatible (SI) plants are able to form ideal mother lines for hybrid crossing in hermaphroditic plants, assuring fertilization from the desired father line. To find out suitable ways to maintain SI was the aim of this study. Among 220 plants of German chamomile (Matricaria recutita (L.) Rauschert) within six accessions SI-genotypes were selected. SI was determined as staying seedless in three flower heads per plant. Initial SI-plants formed the basic paternal generation (P1) of i) maintaining the same genotypes over six months and repeating seed set analysis (P2) and of ii) conducting crossings in three versions (SI × SI, SI × NSI (not SI evaluated plants) and NSI × SI), thereby producing the F1 population. F1 exhibited 78% SI and P2 62% SI, indicating a higher environmental than genetic influence on SI. But heritability, calculated from the results of SI × SI crossings, showed high values (h2 = 0.71). Within generative propagation, the influence of generation/crossing version was highly significant (p = 0.001) and the cultivar ‘Degumille’ explored the highest value of SI (86%) after SI × NSI crossings. Therefore, the intra-cultivar combination of ‘Degumille’ SI mother plants crossed with NSI father plants can be recommended as the most promising version to maintain SI in chamomile.

Population size affects genetic diversity and fine-scale spatial genetic structure in the clonal distylous herb Menyanthes trifoliata

tSmall populations often show a low degree of genetic diversity. In distylous clonal plants, genetic diversitymay also be influenced by other factors, such as floral morph aggregation, clonality and spatial geneticstructure. Nevertheless, the relationships between population size, genetic diversity and spatial geneticstructure are poorly understood. We tested for the effects of population size on genetic diversity andfine-scale spatial genetic structure (FSGS) in the clonal, distylous aquatic herb Menyanthes trifoliata. Toinvestigate genetic diversity and structure, we used microsatellite markers and genotyped a total of 510ramets from nine populations in southern Belgium. The populations showed a relatively high degreeof genetic diversity (HEc= 0.80; A[12] = 4.45), even if both expected heterozygosity and allelic richnesssignificantly decreased with decreasing population size (genet numbers). Populations were significantlygenetically differentiated (FST= 0.14), indicating reduced gene flow among populations. Morph ratio forgenets did not deviate from 1:1. The phalanx type of clonal growth dominated in the studied populations.Ramet FSGS (which was strongly affected by clonality) was significant in all populations. Sp statisticsignificantly decreased with increasing population size, indicating higher FSGS in smaller populations.Consequently, small populations may suffer from a higher rate of geitonogamous pollination (betweenramets of the same genet). Since M. trifoliata is a strongly self-incompatible herb, no inbred seeds canbe produced from self- (and geitonogamous) pollination. In this case, reproductive success of small andmore spatially structured populations of M. trifoliata may be reduced due to clogging of stigmas withincompatible pollen. We conclude that understanding genetic diversity and fine-scale clonal structure iscrucial for conservation of self-incompatible plant species with extensive clonal propagation.

Effects of Polyamines on Self-incompatibility-like Responses in Pollen Tubes of Citrus Cultivars, Banpeiyu and Hyuganatsu

Citrus is a genus with gametophytic self-incompatibility, which prevents fertilization by self-pollination. Polyamines (PAs), as a class of active small molecules, widely participate in various cellular activities. To investigate the effects of the changes in PA contents [putrescine, spermidine (SPD), and spermine] on pollen tube growth in self-incompatible (SI) plants, we cultured pollen of Citrus maxima ‘Banpeiyu’ and C. tamurana ‘Hyuganatsu’ in a Citrus mature pollen culture system and detected the PA content changes in pollen by high-performance liquid chromatography (HPLC) analysis during germination and after treatment with crude protein extracts of compatible or incompatible styles. We profiled the PA content changes during the germination course in pollen of ‘Banpeiyu’ and ‘Hyuganatsu’ by HPLC, and identified increases of free and perchloric-acid-insoluble SPD contents in pollen tubes in the incompatible treatment. Exogenous SPD treatment obviously increased the SPD contents in the pollen tube, inhibited pollen tube elongation, and resulted in some abnormal morphological alterations, such as tip inflation, tube content leakage and tip twist, which were observed in both ‘Banpeiyu’ and ‘Hyuganatsu’ pollen tubes exposed to incompatible treatment. This finding implied that SPD might participate in the SI response in Citrus.

Feedingbehaviour of the dawn bat (&lt;i&gt;Eonycteris spelaea&lt;/i&gt;) promotes cross pollination of economically important plants in Southeast Asia

Eonycteris spelaea is recognized as the principal pollinator of most chiropterophilous plants in SE Asia. The present study describes its feeding behaviour and clarifies its role in cross pollinating these highly self-incompatible plants. Ten individuals of E. spelaea were radio-tracked during the flowering period of durian (Durio zibethinus) and petai (Parkia speciosa) in an agricultural mosaic in southern Thailand. Eonycteris spelaea makes a mean of seven visits per hour to these trees and 80-86% of each feeding bout involves visits to multiple conspecific trees. During each visit, 93% of D. zibethinus stigmas and 50% of P. speciosa stigmas were loaded with conspecific pollen. Eonycteris spelaea was the most common bat visitor to the trees. High visitation frequency and conspecific pollen deposition by E. spelaea to D. zibethinus and P. speciosa indicates that this nectarivorous bat is an effective pollinator. Mixed planting of chiropterophilous trees in fruit orchards is recommended to ensure regular visits of E. spelaea. Protecting natural roost caves of E. spelaea is also essential in order to maintain the vital ecosystem service provided by these bats.

Detection of self-incompatible oilseed rape plants (Brassica napus L.) based on molecular markers for identification of the class I S haplotype.

The selection of desirable genotypes with recessive characteristics, such as self-incompatible plants, is often difficult or even impossible and represents a crucial barrier in accelerating the breeding process. Molecular approaches and selection based on molecular markers can allow breeders to overcome this limitation. The use of self-incompatibility is an alternative in hybrid breeding of oilseed rape. Unfortunately, stable self-incompatibility is recessive and phenotype-based selection is very difficult and time-consuming. The development of reliable molecular markers for detecting desirable plants with functional self-incompatible genes is of great importance for breeders and allows selection at early stages of plant growth. Because most of these reliable molecular markers are based on discrimination of class I S-locus genes that are present in self-compatible plants, there is a need to use an internal control in order to detect possible PCR inhibition that gives false results during genotyping. In this study, 269 double haploid F2 oilseed rape plants obtained by microspore embryogenesis were used to verify the applicability of an improved PCR assay based on the detection of the class I SLG gene along with an internal control. Comparative analysis of the PCR genotyping results vs. S phenotype analysis confirmed the applicability of this molecular approach in hybrid breeding programs. This approach allows accurate detection of self-incompatible plants via a different amplification profile.

Nectar Robbing Positively Influences the Reproductive Success of Tecomella undulata (Bignoniaceae)

The net consequence of nectar robbing on reproductive success of plants is usually negative and the positive effect is rarely produced. We evaluated the influence of nectar robbing on the behaviour of pollinators and the reproductive success of Tecomella undulata (Bignoniaceae) in a natural population. Experimental pollinations showed that the trees were strictly self-incompatible. The three types of floral colour morphs of the tree viz. red, orange and yellow, lacked compatibility barriers. The pollinators (Pycnonotus cafer and Pycnonotus leucotis) and the robber (Nectarinia asiatica) showed equal preference for all the morphs, as they visited each morph with nearly equal frequency and flower-handling time. The sunbirds caused up to 60% nectar robbing, mostly (99%) by piercing through the corolla tube. Although nectar is replenished at regular intervals, insufficient amount of nectar compelled the pollinators to visit additional trees in bloom. Data of manual nectar robbing from the entire tree showed that the pollinators covered lower number of flowers per tree (5 flowers/tree) and more trees per bout (7 trees/bout) than the unrobbed ones (19 flowers/tree and 2 trees bout). The robbed trees set a significantly greater amount of fruits than the unrobbed trees. However, the number of seeds in a fruit did not differ significantly. The study shows that plant-pollinator-robber interaction may benefit the self-incompatible plant species under conditions that increases the visits of pollinators among the compatible conspecifics in a population.

Analysis of S-locus and expression of S-alleles of self-compatible rapid-cycling Brassica oleracea 'TO1000DH3'.

Brassica oleracea is a strictly self-incompatible (SI) plant, but rapid-cycling B. oleracea 'TO1000DH3' is self-compatible (SC). Self-incompatibility in Brassicaceae is controlled by multiple alleles of the S-locus. Three S-locus genes, S-locus glycoprotein (SLG), S-locus receptor kinase (SRK) and S-locus protein 11 or S-locus cysteine-rich (SP11/SCR), have been reported to date, all of which are classified into class I and II. In this study, we investigated the molecular mechanism behind alterations of SI to SC in rapid-cycling B. olerace 'TO1000DH3'. Class I SRK were identified by genomic DNA PCR and PCR-RFLP analysis using SRK specific markers and found to be homozygous. Cloning and sequencing of class I SRK revealed a normal kinase domain without any S-domain/transmembrane domain. Moreover, S-locus sequencing analysis revealed only an SLG sequence, but no SP11/SCR. Expression analysis showed no SRK expression in the stigma, although other genes involved in the SI recognition reaction (SLG, MLPK, ARC1, THL) were found to have normal expression in the stigma. Taken together, the above results suggest that structural aberrations such as deletion of the SI recognition genes may be responsible for the breakdown of SI in rapid-cycling B. oleracea 'TO1000DH3'.

Ecological implications of reduced pollen deposition in alpine plants: a case study using a dominant cushion plant species.

The reproductive assurance hypothesis states that self-incompatible female plants must produce twice the number of seeds relative to their self-compatible hermaphroditic counterparts to persist in gynodioecious populations. This is a viable life-history strategy, provided that pollination rates are sufficiently high. However, reduced pollination rates in alpine plants are likely due to climate induced plant-pollinator mismatches and general declines in pollinators. Using a gynodioecious population of the dominant plant Silene acaulis (Caryophyllaceae), we tested the reproductive assurance hypothesis and also the stress gradient hypothesis with a series of pollinator exclusion trials and extensive measurements of subsequent reproductive output (gender ratio, plant size, percent fruit-set, fruit weight, seeds per fruit, total seeds, seed weight, and seed germination). The reproductive assurance hypothesis was supported with female plants being more sensitive to and less likely to be viable under reductions in pollination rates. These findings are the first to show that the stress gradient hypothesis is also supported under a gradient of pollen supply instead of environmental limitations. Beneficiary abundance was negatively correlated to percent fruit-set under current pollen supply, but became positive under reduced pollen supply suggesting that there are important plant-plant-pollinator interactions related to reproduction in these alpine plant species.

Sistemas reproductivos de las plantas en tres hábitats de la planicie costera de Paraguaná, Venezuela

Breeding systems were evaluated for 51 plant species according to life form, pollination system, vegetation type, and phenology, in the coastal plain of Paraguaná Peninsula, Venezuela. Sexual systems were no associated to life form, pollination system, vegetation type, and phenology. The frequency distribution of sexual system was 82.3% hermaphroditism, 15.6% monoecy, and 1.9% dioecy. All sexual systems had a peak during the lowest rainfall. Genetic system distribution was 64.8% self-compatibility (including partially self-compatibility) and 35.2% self-incompatibility. Among self-compatible species, 45.1% were autogamous (19.6% not autogamous). The genetic systems were associated significantly to: (1) plant life form: self-compatible species tend to be herbaceous and self-incompatible plants tend to be woody species; (2) vegetation type: self-compatible species were predominant in the three vegetation types, but in the mangrove the frequency of self-compatible and self-incompatibles was similar; and (3) pollination system: most of the self-compatible species were polyphilous. Mating systems: xenogamous and autogamous species were associated only with plant life forms. Xenogamous plants were mostly woody species and autogamous plants were mostly herbaceous species. The high incidence of hermaphroditism, self-compatibility, and autogamy are related to herbaceous life form, polyphilous pollination system, and climatic conditions, together the insularity of the Paraguaná peninsula.

The founding of Mauritian endemic coffee trees by a synchronous long-distance dispersal event.

The stochastic process of long-distance dispersal is the exclusive means by which plants colonize oceanic islands. Baker's rule posits that self-incompatible plant lineages are unlikely to successfully colonize oceanic islands because they must achieve a coordinated long-distance dispersal of sufficiently numerous individuals to establish an outcrossing founder population. Here, we show for the first time that Mauritian Coffea species are self-incompatible and thus represent an exception to Baker's rule. The genus Coffea (Rubiaceae) is composed of approximately 124 species with a paleotropical distribution. Phylogenetic evidence strongly supports a single colonization of the oceanic island of Mauritius from either Madagascar or Africa. We employ Bayesian divergence time analyses to show that the colonization of Mauritius was not a recent event. We genotype S-RNase alleles from Mauritian endemic Coffea, and using S-allele gene genealogies, we show that the Mauritian allelic diversity is confined to just seven deeply divergent Coffea S-RNase allelic lineages. Based on these data, we developed an individual-based model and performed a simulation study to estimate the most likely number of founding individuals involved in the colonization of Mauritius. Our simulations show that to explain the observed S-RNase allelic diversity, the founding population was likely composed of fewer than 31 seeds that were likely synchronously dispersed from an ancestral mainland species.

Characterization of self-incompatibility genes in the intergeneric hybrid xBrassicoraphanus

Brassica rapa and Raphanus sativus are strictly self-incompatible (SI) plants; however, xBrassicoraphanus (baemoochae) is an intergeneric hybrid synthesized following hybridization of B. rapa and R. sativus that is self-compatible (SC). Self-incompatibility in Brassicaceae is controlled by multiple alleles of the S-locus. Two S-locus genes, SRK (S-locus receptor kinase) and SP11/SCR (S-locus protein 11 or S-locus cysteine-rich), have been reported to date, both of which are classified into class I and II. In this study, we investigate if there is an alteration in the structure or the expression in SRK or SP11 genes behind the alteration of SI to SC in baemoochae. Class I and II SRK were identified by PCR of the genomic DNA of baemoochae using SRK-specific universal primers. Cloning and sequencing of both classes of SRK was conducted and compared with SRK genes of parental species. Comparison analysis showed no genomic alterations and both of them showed expression in the stigma. Similarly, SP11 genes also showed no genomic alterations and normally are expressed in the anther. Other SI-related genes (MLPK, ARC1, THL) also showed normal expression in the stigma and anther. Taken together, these results revealed that no structural/gene expression change in these genes was responsible for the breakdown of SI in baemoochae. Rather, the transformation from SI parents to SC descendants could be responding to epigenetic mechanisms.