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The oxidation of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC), known as oxi-mCs, garners significant interest in plants as potential epigenetic marks. While research in mammals has established a role in cell reprogramming, carcinogenesis, and gene regulation, their functions in plants remain unclear. In rice, 5hmC has been associated with transposable elements (TEs) and heterochromatin. This study utilizes Silene latifolia , a dioecious plant with heteromorphic sex chromosomes and a genome with a large proportion of TEs, which provides a favourable environment for the study of oxi-mCs in individual sexes. Notably, we detected surprisingly high levels of oxi-mCs in S. latifolia comparable with mammals. Nuclei showed enrichment in heterochromatic regions, except for 5hmC whose signal was homogeneously distributed. Intriguingly, the same X chromosome in females displayed overall enrichment of 5hmC and 5fC compared with its counterpart. This fact is shared with 5mC, resembling dosage compensation. Co-localization showed higher correlation between 5mC and 5fC than with 5hmC, indicating no potential relationship between 5hmC and 5fC. Additionally, the promoter of several sex-linked genes and sex-biased TEs clustered in a clear sex-dependent way. Together, these findings unveil a hypothetical role for oxi-mCs in S. latifolia sex chromosome development, warranting further exploration. [ABSTRACT FROM AUTHOR]

Evolution of a non‐recombining sex‐specific region on the Y (or W) chromosome (NRY) is a key step in sex chromosome evolution, but how recombination suppression evolves is not well understood. Studies in many different organisms indicated that NRY evolution often involves several expansion steps. Why such NRY expansions occur remains unclear, although it is though that they are likely driven by sexually antagonistic selection. This paper describes a recent NRY expansion due to shift of the pseudoautosomal boundary on the sex chromosomes of a dioecious plant Silene latifolia. The shift resulted in inclusion of at least 16 pseudoautosomal genes into the NRY. This region is pseudoautosomal in closely related Silene dioica and Silene diclinis, indicating that the NRY expansion occurred in S. latifolia after it speciated from the other species ~120 thousand years ago. As S. latifolia and S. dioica actively hybridise across Europe, interspecific gene flow could blur the PAR boundary in these species. The pseudoautosomal genes have significantly elevated genetic diversity (π ~ 3% at synonymous sites), which is consistent with balancing selection maintaining diversity in this region. The recent shift of the PAR boundary in S. latifolia offers an opportunity to study the process of on‐going NRY expansion. [ABSTRACT FROM AUTHOR]

Dioecious plants possess diverse sex determination systems and unique mechanisms of reproductive organ development; however, little is known about how sex-linked genes shape the expression of regulatory cascades that lead to developmental differences between sexes. In Silene latifolia , a dioecious plant with stable dimorphism in floral traits, early experiments suggested that female-regulator genes act on the factors that determine the boundaries of the flower whorls. To identify these regulators, we sequenced the transcriptome of male flowers with fully developed gynoecia, induced by rapid demethylation in the parental generation. Eight candidates were found to have a positive role in gynoecium promotion, floral organ size, and whorl boundary, and affect the expression of class B MADS-box flower genes. To complement our transcriptome analysis, we closely examined the floral organs in their native state using field emission environmental scanning electron microscopy, and examined the differences between females and androhermaphrodites in their placenta and ovule organization. Our results reveal the regulatory pathways potentially involved in sex-specific flower development in the classical model of dioecy, S. latifolia. These pathways include previously hypothesized and unknown female-regulator genes that act on the factors that determine the flower boundaries, and a negative regulator of anther development, SUPERMAN - like (SlSUP). [ABSTRACT FROM AUTHOR]

Mechanisms of suppression of pistil primordia in male flowers and of stamen primordia in female flowers differ in diclinous plants. In this study, we investigated how cell death and cell cycle arrest are related to flower organ formation in Silene latifolia. Using in situ hybridization and a TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling) assay, we detected both cell cycle arrest and cell death in suppressed stamens of female flowers and suppressed pistils of male flowers in S. latifolia. In female flowers infected with Microbotryum lychnidis-dioicae, developmental suppression of stamens is released, and cell cycle arrest and cell death do not occur. Smut spores are formed in S. latifolia anthers infected with M. lychnidis-dioicae, followed by cell death in the endothelium, middle layer, tapetal cells and pollen mother cells. Cell death is difficult to detect using a fluorescein isothiocyanate-labeled TUNEL assay due to strong autofluorescence in the anther. We therefore combined a TUNEL assay in an infrared region with transmission electron microscopy to detect cell death in anthers. We show that following infection by M. lychnidis-dioicae, a TUNEL signal was not detected in the endothelium, middle layer or pollen mother cells, and cell death with outflow of cell contents, including the nucleoplast, was observed in tapetal cells. [ABSTRACT FROM AUTHOR]

Dimorphic mating-type chromosomes in fungi are excellent models for understanding the genomic consequences of recombination suppression. Their suppressed recombination and reduced effective population size are expected to limit the efficacy of natural selection, leading to genomic degeneration. Our aim was to identify the sequences of the matingtype chromosomes (a1 and a2) of the anther-smut fungi and to investigate degeneration in their nonrecombining regions. We used the haploid a1 Microbotryum lychnidis-dioicae reference genome sequence. The a1 and a2 mating-type chromosomes were both isolated electrophoretically and sequenced. Integration with restriction-digest optical maps identified regions of recombination and nonrecombination in the mating-type chromosomes. Genome sequence data were also obtained for 12 other Microbotryum species. We found strong evidence of degeneration across the genus in the nonrecombining regions of the mating-type chromosomes, with significantly higher rates of nonsynonymous substitution (dN/dS) than in nonmating-type chromosomes or in recombining regions of the mating-type chromosomes. The nonrecombining regions of the mating-type chromosomes also showed high transposable element content, weak gene expression, and gene losses. The levels of degeneration did not differ between the a1 and a2 mating-type chromosomes, consistent with the lack of homogametic/heterogametic asymmetry between them, and contrasting with X/Y or Z/W sex chromosomes. [ABSTRACT FROM AUTHOR]

Neo-sex chromosomes, which form through the major restructuring of ancestral sex chromosome systems, have evolved in various taxa. Such restructuring often consists of the fusion of an autosome to an existing sex chromosome, resulting in novel sex chromosome formations (e.g. X1X2Y or XY1Y2.). Comparative studies are often made between restructured sex chromosome systems of closely related species, and here we evaluate the consequences of variable sex chromosome systems to hybrids. If neo-sex chromosomes are improperly inherited across species, this could lead to aberrant development and reproductive isolation. In this study, we examine the fate of neo-sex chromosomes in hybrids of the flowering plants Silene diclinis and Silene latifolia. Silene diclinis has a neo-sex chromosome system ( XY1Y2) that is thought to have evolved from an ancestral XY system that is still present in S. latifolia. These species do not hybridize naturally, and improper sex chromosome inheritance could contribute to reproductive isolation. We investigated whether this major restructuring of sex chromosomes prevents their proper inheritance in a variety of hybrid crosses, including some F2- and later-generation hybrids, with sex chromosome-linked, species-specific, polymorphic markers and chromosome squashes. We discovered that despite the differences in sex chromosomes that exist between these two species, proper segregation had occurred in hybrids that made it to flowering, including later-generation hybrids, indicating that neo-sex chromosome formation alone does not result in complete reproductive isolation between these two species. Additionally, hybrids with aberrant sex expression (e.g. neuter, hermaphrodite) also inherited the restructured sex chromosomes properly, highlighting that issues with sexual development in hybrids can be caused by intrinsic genetic incompatibility rather than improper sex chromosome inheritance. [ABSTRACT FROM AUTHOR]

Dioecy (i.e. having separate sexes) is a rather rare breeding system in flowering plants. Such rareness may result from a high probability of extinction in dioecious species because of less efficient dispersal and the costs of sexual selection, which are expected to harm dioecious species' survival on the long term. These handicaps should decrease the effective population size ( [ABSTRACT FROM AUTHOR]

The evolution of sexual dimorphism will depend on how sexual, fecundity and viability selection act within each sex, with the different forms of selection potentially operating in opposing directions. We examined selection in the dioecious plant Silene latifolia using planted arrays of selection lines that differed in flower size (small vs. large). In this species, a flower size/number trade-off exists within each sex, and males produce smaller and more numerous flowers than females. Moreover, floral traits are genetically correlated with leaf physiology. Sexual selection favoring males in the small-flower line occurred via greater overlap in the timing of flower output between males from this line and females. Fecundity selection favored males with high flower production, as siring success was proportionate to pollen production. Viability selection opposed sexual selection, favoring males from the large-flower line. In females, fecundity and viability selection operated in the same direction, favoring those from the large-flower line via greater seed production and survival. These results concur with the pattern of floral sexual dimorphism. Together with previous results they suggest that the outcome of the different forms of selection will be environmentally dependent, and therefore help to explain variation among populations in sexually dimorphic traits. [ABSTRACT FROM AUTHOR]

Patterns of codon usage bias (CUB) convey useful information about the selection on synonymous codons induced by gene expression and contribute to an understanding of substitution patterns observed at synonymous sites. They can also be informative about the distinctive evolutionary properties of sex chromosomes such as genetic degeneration of the Y chromosome, dosage compensation, and hemizygosity of the X chromosome in males, which can affect the selection on codon usage. Here, we study CUB in Silene latifolia, a species of interest for studying the early stages of sex chromosome evolution. We have obtained a large expressed sequence tag data set containing more than 1,608 sequence fragments by 454 sequencing. Using three different methods, we conservatively define 21 preferred codons. Interestingly, the preferred codons in S. latifolia are almost identical to those in Arabidopsis thaliana, despite their long divergence time (we estimate average nonsynonymous site divergence to be 0.216, and synonymous sites are saturated). The agreement suggests that the nature of selection on codon usage has not changed significantly during the long evolutionary time separating the two species. As in many other organisms, the frequency of preferred codons is negatively correlated with protein length. For the 43 genes with both exon and intron sequences, we find a positive correlation between gene expression levels and GC content at third codon positions, but a strong negative correlation between expression and intron GC content, suggesting that the CUB we detect in S. latifolia is more likely to be due to natural selection than to mutational bias. Using polymorphism data, we detect evidence of ongoing natural selection on CUB, but we find little support for effects of biased gene conversion. An analysis of ten sex-linked genes reveals that the X chromosome has experienced significantly more unpreferred to preferred than preferred to unpreferred substitutions, suggesting that it may be evolving higher CUB. In contrast, numbers of substitutions between preferred and unpreferred codons are similar in both directions in the Y-linked genes, contrary to the expectation of genetic degeneration. [ABSTRACT FROM PUBLISHER]

Background and Aims: Silene dioica and S. latifolia experience only limited introgression despite overlapping flowering phenologies, geographical distributions, and some pollinator sharing. Conspecific pollen precedence and other reproductive barriers operating between pollination and seed germination may limit hybridization. This study investigates whether barriers at this stage contribute to reproductive isolation between these species and, if so, which mechanisms are responsible. [ABSTRACT FROM PUBLISHER]

Carpel suppression is a trigger for sexual dimorphism in the dioecious plant Silene latifolia. To clarify what kind of genes are involved in carpel suppression in this species, we generated a bisexual mutant, R025, by C-ion beam irradiation. R025 produces bisexual flowers with a mature gynoecium and mature stamens. Genetic analysis of R025 attributed the bisexual trait to mutations on the Y chromosome. Scanning electron microscopy (SEM) analysis of early floral development revealed that the carpel size of R025 was different from that of wild-type males in spite of the male background in R025. We also identified an S. latifolia CLAVATA1-like gene (SlCLV1) as a candidate of the CLAVATA–WUSCHEL (CLV–WUS) pathway. Two separate pathways, the CLV–WUS pathway and the CUP-SHAPED COTYLEDON (CUC)–SHOOT MERISTEMLESS (STM) pathway, contribute to carpel development in the Arabidopsis floral meristem. SlSTM1 and SlSTM2 (orthologs of STM) and SlCUC (an ortholog of CUC1 and CUC2) have already been identified in S. latifolia. We therefore examined the expression patterns of SlCLV1, SlSTM (SlSTM1 and SlSTM2) and SlCUC in young flowers of R025 and wild-type males and females. The expression patterns of the three genes in the two pathways differ between the wild-type male and the bisexual mutant, and the differences in expression patterns of the three genes occur at the same stage. These results suggest that in addition to SlSTM1, SlSTM2 and SlCUC, SlCLV1 is also involved in carpel suppression in S. latifolia. They also suggest that a gynoecium-suppressing factor (GSF), which is lost in the R025 Y chromosome, acts on an upstream gene that is common to the two pathways, triggering sexual dimorphism in S. latifolia. [ABSTRACT FROM PUBLISHER]

The sex chromosomes of the plant species Silene latifolia (white campion) are very young (only 5–10 My old), and all 11 X-linked genes so far described have Y-linked homologues. Theory predicts that X chromosomes should accumulate a nonrandom set of genes. However, little is known about the importance of gene movements between the X and the autosomes in plants, or in any very young sex chromosome system. Here, we isolate from cDNA a new gene, Slcyt, on the S. latifolia X, which encodes a cytochrome B protein. We genetically mapped SlCyt and found that it is located ∼1 cM from the pseudoautosomal region. Genes in this region of the X chromosome have low divergence values from their homologous Y-linked genes, indicating that the X only recently stopped recombining with the Y. Genetic mapping in Silene vulgaris suggests that Slcyt originally belonged to a different linkage group from that of the other S. latifolia X-linked genes. Silene latifolia has no Y-linked homologue of Slcyt, and also no autosomal paralogues seem to exist. Slcyt moved from an autosome to the X very recently, as the Cyt gene is also X linked in Silene dioica, the sister species to S. latifolia, but is probably autosomal in Silene diclinis, implying that a translocation to the X probably occurred after the split between S. diclinis and S. latifolia/S. dioica. Diversity at Slcyt is extremely low (πsyn = 0.16%), and we find an excess of high frequency–derived variants and a negative Tajima's D, suggesting that the translocation was driven by selection. [ABSTRACT FROM PUBLISHER]

Reproductive barriers are important determinants of gene flow between divergent populations or species. We studied pollen competition as a post-mating reproductive barrier between Silene dioica and S. latifolia. Gene flow between these species is extensive, but early-generation hybrids are rare. In an experiment with conspecific, heterospecific and 50 : 50 mixed pollinations in the two species, pollination treatments did not significantly affect seed set and seed weight. However, molecular determination of siring success after mixed pollinations showed that fewer than expected hybrids were produced in S. latifolia (18% hybrids) but not in S. dioica (51% hybrids). This constitutes an asymmetric post-mating reproductive barrier and likely contributes to the rarity of early-generation hybrids. Our study shows that pollen competition can be an effective barrier to hybridization between closely related species that likely acts in concert with other reproductive barriers. [ABSTRACT FROM AUTHOR]

Mechanisms preventing interspecific pollination are important in closely related plant species, in particular when post-zygotic barriers are weak or absent. We investigated the role of floral odour in reproductive isolation between the two closely related species Silene latifolia and S. dioica. First, we tested whether floral odour composition and emission differed between the species. We found significant odour differences, but contrary to expectations, both species showed a rhythmic emission of the same compounds between day and night. Second, in a field experiment, odour of the two species was made more similar by applying phenylacetaldehyde to flowers. This manipulation led to higher pollen-analogue transfer between species, revealing that floral odour differences are important for maintaining reproductive isolation. We conclude that differences in single key compounds can reduce pollen transfer across species boundaries by pollinators and demonstrate that odour differences are an important component of premating floral isolation between closely related plant species. [ABSTRACT FROM AUTHOR]

Many species exhibit sexual dimorphism in a variety of characters, and the underlying genetic architecture of dimorphism potentially involves sex-specific differences in the additive-genetic variance--covariance matrix (G) of dimorphic traits. We investigated the quantitative-genetic structure of dimorphic traits in the dioecious plant Silene latifolia by estimating G (including within-sex matrices, Gm, Gf, and the between-sex variance--covariance matrix, B), and the phenotypic variance--covariance matrix (P) for seven traits. Flower number was the most sexually dimorphic trait, and was significantly genetically correlated with all traits within each sex. Negative genetic correlations between flower size and number suggested a genetic trade-off in investment, but positive environmental correlations between the same traits resulted in no physical evidence for a trade-off in the phenotype. Between-sex genetic covariances for homologous traits were always greater than 0 but smaller than 1, showing that some, but not all, of the variation in traits is caused by genes or alleles with sex-limited expression. Using common principal-components analysis (CPCA), a maximum-likelihood (ML) estimation approach, and element-by-element comparison to compare matrices, we found that Gm and Gf differed significantly in eigenstructure because of dissimilarity in covariances involving leaf traits, suggesting the presence of variation in sex-limited genes with pleiotropic effects and/or linkage between sex-limited loci. The sex-specific structure of G is expected to cause differences in the correlated responses to selection within each sex, promoting the further evolution and maintenance of dimorphism. [ABSTRACT FROM AUTHOR]

Microbotryum violaceum is a fungus that causes the sterilizing anther smut disease in Caryophyllaceae. Its diploid teliospores normally produce equal proportions of haploid sporidia of its two mating types. However natural populations contain high frequencies of individuals producing sporidia of only one mating type (‘biased strains’). This mating type-ratio bias is caused by deleterious alleles at haploid phase (‘haplo-lethals’) linked to the mating type locus that can be transmitted only by intra-tetrad selfing. We used experimental inoculations to test some of the hypotheses proposed to explain the maintenance of haplo-lethals. We found a disadvantage of biased strains in infection ability and high intra-tetrad mating rates. Biased strains had no higher competitive ability nor shorter latency and their higher spore production per flower appeared insufficient to compensate their disadvantages. These findings were only consistent with the hypothesis that haplo-lethals are maintained under a metapopulation structure because of high intra-tetrad selfing rates, founder effects and selection at the population level. [ABSTRACT FROM AUTHOR]

Silene latifolia is a dioecious plant in which sex is determined by X and Y chromosomes. Expression of the B-function gene SLM2, an ortholog of PISTILLATA (PI) in Arabidopsis, was examined by in situ hybridization. SLM2 was not expressed in suppressed stamens of female flowers, but was expressed in developing stamens of smut-infected female flowers. These results indicate that the control of SLM2 is independent of the presence of the Y chromosome. Smut-infected females provide a useful system for clarifying the relationship between the B-function gene and the sex determination factor. [ABSTRACT FROM AUTHOR]

The action of natural selection is expected to reduce the effective population size of a nonrecombining chromosome, and this is thought to be the chief factor leading to genetic degeneration of Y-chromosomes, which cease recombining during their evolution from ordinary chromosomes. Low effective population size of Y chromosomes can be tested by studying DNA sequence diversity of Y-linked genes. In the dioecious plant,Silene latifolia, which has sex chromosomes, one comparison (SlX1vs.SlY1) indeed finds lower Y diversity compared with the homologous X-linked gene, and one Y-linked gene with no X-linked homologue has lower species-wide diversity than a homologous autosomal copy (SlAp3Y vs.SlAp3A). To test whether this is a general pattern for Y-linked genes, we studied two further recently described X and Y homologous gene pairs in samples from several populations ofS. latifoliaandS. dioica. Diversity is reduced for both Y-linked genes, compared with their X-linked homologues. Our new data are analysed to show that the low Y effective size cannot be explained by different levels of gene flow for the X vs. the Y chromosomes, either between populations or between these closely related species. Thus, all four Y-linked genes that have now been studied in these plants (the two studied here, and two previously studied genes, have low diversity). This supports other evidence for an ongoing degeneration process in these species. [ABSTRACT FROM AUTHOR]

• Background and Aims The overall goal of this paper is to construct an overview of the genetic basis for flower size evolution in Silene latifolia. It aims to examine the relationship between the molecular bases for flower size and the underlying assumption of quantitative genetics theory that quantitative variation is ultimately due to the impact of a number of structural genes.• Scope Previous work is reviewed on the quantitative genetics and potential for response to selection on flower size, and the relationship between flower size and nuclear DNA content in S. latifolia. These earlier findings provide a framework within which to consider more recent analyses of a joint quantitative trait loci (QTL) analysis of flower size and DNA content in this species.• Key Results Flower size is a character that fits the classical quantitative genetics model of inheritance very nicely. However, an earlier finding that flower size is correlated with nuclear DNA content suggested that quantitative aspects of genome composition rather than allelic substitution at structural loci might play a major role in the evolution of flower size. The present results reported here show that QTL for flower size are correlated with QTL for DNA content, further corroborating an earlier result and providing additional support for the conclusion that localized variations in DNA content underlie evolutionary changes in flower size.• Conclusions The search image for QTL should be broadened to include overall aspects of genome regulation. As we prepare to enter the much-heralded post-genomic era, we also need to revisit our overall models of the relationship between genotype and phenotype to encompass aspects of genome structure and composition beyond structural genes. [ABSTRACT FROM AUTHOR]

Sexual dimorphism is one of the most widespread and recognizable patterns of phenotypic variation in the biotic world. Sexual dimorphism in floral display is striking in the dioecious plant Silene latifolia, with males making many, small flowers compared to females. We investigated this dimorphism via artificial selection on two populations to determine whether genetic variation exists within populations for flower size and the extent of the between-sex correlation, whether a flower size and number trade-off exists within each sex, and whether pollen and ovule production vary with flower size. We selected for decreased flower size (calyx width) in females and increased flower size in males and measured the response to selection in size and correlated responses in flower dry mass, flower number, and pollen or ovule number per flower. Four bouts of selection in each of two selection programs were performed, for a total of three selection lines to decrease size, three to increase it, and two control lines. Flower size always significantly responded to selection and we always found a significant correlated response in the sex not under selection. Selection decreased but did not eliminate the sexual dimorphism in flower dry mass and number. A negative relationship between flower size and number within each sex was revealed. Whereas ovule number showed a significant correlated response to selection on flower size, pollen number did not. Our results indicate that although substantial additive genetic variation for flower size exists, the high between-sex genetic correlation would likely constrain flower size from becoming more sexually dimorphic. Furthermore, floral display within each sex is constrained by a flower size and number trade-off. Given this trade-off and lack of variation in pollen production with flower size, we suggest that sexual dimorphism evolved via sexual selection to increase flower number in males but not females. [ABSTRACT FROM AUTHOR]

Dioecy in the model dioecious plant Silene latifolia is determined genetically by its heteromorphic sex chromosomes. A bacterial arti.cial chromosome (BAC) clone, #19B12, was isolated by screening a BAC library from S. latifolia using polymerase chain reaction (PCR) with a set of sequence tagged site (STS) primers, ScD05, which are specific to the Y chromosome. A portion of #19B12 was subcloned to construct plasmid #25-1, with an insert of 7.8 kb. This 7.8-kb fragment encodes ScD05 homolog and an antherspecific gene, CCLS96.1. Northern blot analysis of CCLS96.1 indicated a faint band of 1.8 kb in male and female flower buds. 5′ and 3′ rapid amplification of cDNA ends (RACE) indicated that transcripts of CCLS96.1 are very varied in size. Moreover, semi-quantitative reverse transcription-PCR (RT-PCR) showed that CCLS96.1 was also expressed in both male and female leaves. RACE produced at least ten species of transcripts, with 79–97% similarity among them. However, no significant ORFs could be predicted from their nucleotide sequences, since each has numerous stop codons throughout all three reading frames. Genomic Southern hybridization showed that the S. latifolia genome contains numerous CCLS96.1 homologs. These results suggest that the transcripts of CCLS96.1 play some role as multiple non-coding RNAs in S. latifolia. [ABSTRACT FROM PUBLISHER]

Abstract The degree of sexual dimorphism in a trait may be determined directly by disruptive selection, as well as by correlations with other traits under selection. We grew seeds from nine populations of the dioecious plant Silene latifolia in a common-garden experiment to determine whether phenotypic variation and correlations existed for floral, leaf and resource allocation traits, and whether this variation had a genetic component. We also determined the traits which were sexually dimorphic, the degree of dimorphism, and whether it varied among populations. Seven traits exhibited among-population variation and sexual dimorphism. Variation in the degree of dimorphism occurred only for two traits, suggesting that dimorphism may be evolving more slowly than trait means. Males had more, smaller flowers, shorter leaves, and allocated less of their total biomass to stems and more to leaves than females. Flower production was the most sexually dimorphic trait and was correlated with all measured traits. Most traits exhibited significant correlations between the sexes. The pattern of correlations and the degree of sexual dimorphism among traits lead us to suggest that intrasexual selection for an exaggerated floral display in males has indirectly led to sexual dimorphism in a host of other traits. [ABSTRACT FROM AUTHOR]

Abstract In spatially structured populations, host–parasite coevolutionary potential depends on the distribution of genetic variation within and among populations. Inoculation experiments using the plant, Silene latifolia , and its fungal pathogen, Microbotryum violaceum , revealed little overall differentiation in infectivity/resistance, latency or spore production among host or pathogen populations. Within populations, fungal strains had similar means, but varied in performance across plant populations. Variation in resistance among seed families indicates the potential for parasite-mediated selection, whereas there was little evidence for local pathogen genotype × plant genotype interactions assumed by most theoretical coevolution models. Lower spore production on sympatric than allopatric hosts confirmed local fungal maladaptation already observed for infectivity. Correlations between infectivity and latency or spore production suggest a common mechanism for variation in these traits. Our results suggest low variation available to this pathogen for tracking its coevolving host. This may be caused by random drift, breeding system or migration characteristic of metapopulation dynamics. [ABSTRACT FROM AUTHOR]

Fluorescent differential display (FDD) has been used to screen for cDNAs that are differentially up-regulated in male flowers of the dioecious plant Silene latifolia in which an X/Y chromosome system of sex determination operates. To adapt FDD to the cloning of large numbers of differential cDNAs, a novel method of confirming the differential expression of these has been devised. FDD gels were Southern electro-blotted and probed with mixtures of individual cDNA clones derived from different FDD product ligation reactions. These Southern blots were then stripped and re-probed with further mixtures of individual cloned FDD products to identify the maximum number of recombinant clones carrying the true differential amplification products. Of 135 differential bands identified by FDD, 56 differential amplification products were confirmed; these represent 23 unique differentially expressed genes as determined by virtual Northern analysis and two genes expressed at or below the level of detection by virtual Northern analysis. These two low expressed genes show bands of hybridization on genomic Southern blots that are specific to male plants, indicating that they are derived from, or closely related to, Y chromosome genes. [ABSTRACT FROM PUBLISHER]

DNA methylation represents one of the key processes that play an important role in the transcriptional control of gene expression. The role of cytosine methylation in plant development has been demonstrated by at least three different kinds of evidence: parent‐specific expression of some genes in developing seeds, control of flowering time and floral morphogenesis, and correlation with silencing of intrusive DNA sequences (mobile genetic elements and transgenes). In this work global changes in DNA methylation during seed germination and shoot apical meristem development in Silene latifolia have been studied using an indirect immunohistochemical approach. The data presented show that a rapid decrease in global DNA methylation during seed germination occurs first in endosperm tissue and subsequently in the hypocotyl. Using 5‐bromo‐2′‐deoxyuridine pulses, it has been demonstrated that these demethylation events occurred before cell division had begun. In the early post‐germination period, a decrease in DNA methylation was detected in cotyledons, also before cell division was observed. Taken together, these results indicate that DNA demethylation takes place in a non‐replicative way, probably by an active mechanism. The central zone of the shoot apical meristem remains highly methylated during the whole period of vegetative growth and in this region, only a low cell division activity was found. However, upon the transition of the shoot apical meristem to the floral bud, the meristem both decreased its high methylation status and its cells started to divide. These data indicate that the central zone of the shoot apical meristem can represent a relatively quiescent ‘germ‐line’ which is activated upon flowering to form spores and gametes. [ABSTRACT FROM PUBLISHER]