Epigenetic control of sexual phenotype in a dioecious plant,Melandrium album

Melandrium album (syn.Silene latifolia) is a model dioecious species in which theY chromosome, present only in heterogametic males, plays both a male-determining and a strict female-suppressing role. We showed that treatment with 5-azacytidine (5-azaC) induces a sex change to androhermaphroditism (andromonoecy) in about 21% of male plants, while no apparent phenotypic effect was observed in females. All of these bisexual androhermaphrodites (with the standard male 24,AA +XY karyotype) were mosaics possessing both male and hermaphrodite flowers and, moreover, the hermaphrodite flowers displayed various degrees of gynoecium development and seed setting. Southern hybridization analysis with a repetitive DNA probe showed that the 5-azacytidine-treated plants were significantly hypomethylated in CG doublets, but only to a minor degree in CNG triplets. The bisexual trait was transmitted to two successive generations, but only when androhermaphrodite plants were used as pollen donors. The sex reversal was inherited with incomplete penetrance and varying expressivity. Based on the uniparental inheritance pattern of androhermaphroditism we conclude that it originated either by 5-azaC induced inhibition ofY-linked female-suppressing genes or by a heritable activation of autosomal female-determining/promoting genes which can be reversed, on passage through female meiosis, by a genomic imprinting mechanism. The data presented indicate that female sex suppression inM. album XY males is dependent on methylation of specific DNA sequences and can be heritably modified by hypomethylating drugs.     

The Development of Male and Female Regenerants by In Vitro Androgenesis in Dioecious Plant Melandrium album

We examined induced androgenesis in vitro in the dioecious plantMelandrium album and aimed to produce complete plants from culturedimmature microspores. Flow cytometric analysis of nuclear DNAcontent was used to screen ploidy levels in regenerated plantsand to estimate the nuclear genome size in plants differingin sex. Haploid and spontaneous dihaploid (polyhaploid) femalesdominated among androgenic regenerants. Androgenic males occurredsporadically. They were exclusively dihaploid and geneticallysupermales (AAYY). The progenies obtained as a result of thecrosses between supermales and standard females contained onlymales. This is the first report on complete androgenesis inM. album from the microspores carrying the Y chromosome.Copyright1994, 1999 Academic Press Melandrium album (Miller) Garcke, pollen androgenesis, sex, female, male, supermale, flow-cytometry, nuclear genome size     

Epigenetic control of sexual phenotype in a dioecious plant,Melandrium album

Melandrium album (syn.Silene latifolia) is a model dioecious species in which theY chromosome, present only in heterogametic males, plays both a male-determining and a strict female-suppressing role. We showed that treatment with 5-azacytidine (5-azaC) induces a sex change to androhermaphroditism (andromonoecy) in about 21% of male plants, while no apparent phenotypic effect was observed in females. All of these bisexual androhermaphrodites (with the standard male 24,AA +XY karyotype) were mosaics possessing both male and hermaphrodite flowers and, moreover, the hermaphrodite flowers displayed various degrees of gynoecium development and seed setting. Southern hybridization analysis with a repetitive DNA probe showed that the 5-azacytidine-treated plants were significantly hypomethylated in CG doublets, but only to a minor degree in CNG triplets. The bisexual trait was transmitted to two successive generations, but only when androhermaphrodite plants were used as pollen donors. The sex reversal was inherited with incomplete penetrance and varying expressivity. Based on the uniparental inheritance pattern of androhermaphroditism we conclude that it originated either by 5-azaC induced inhibition ofY-linked female-suppressing genes or by a heritable activation of autosomal female-determining/promoting genes which can be reversed, on passage through female meiosis, by a genomic imprinting mechanism. The data presented indicate that female sex suppression inM. album XY males is dependent on methylation of specific DNA sequences and can be heritably modified by hypomethylating drugs.     

Gynodioecy inSaxifraga granulata L. (Saxifragaceae)

The occurrence of gynodioecy in two populations in northern England of the normally hermaphroditeSaxifraga granulata is reported. Female plants have aborted stamens, and smaller petals than hermaphrodites. At Staindrop, County Durham, an estimated 23% of the flowering stems were female; at Macclesfield, Cheshire, 4% were female. The inheritance of male sterility is not simple, and probably involves at least one cytoplasmic and two nuclear genes. The secondary sexual characteristics, hermaphrodite-predominant sex ratios, and complex inheritance of male sterility, are typical of gynodioecious populations.     

Corema album: unbiased dioecy in a competitive environment

• Corema album is a dioecious coastal shrub. Dioecious plants growing in these resource‐limited habitats may present spatial segregation of the sexes (SSS) or demographic biases because of the different reproductive effort between sexes. In these environments facilitation is a more common interaction between plants than competition. To assess factors determining the distribution of C. album male and female plants, we investigated the influence of habitat type (sand dunes and coastal woodlands), assessed the occurrence of SSS or demographic biases and also a possible role of these shrubs as nurse plants.
• We selected three C. album populations with the two habitat types. All C. album individuals were sexed, mapped and measured in three plots (20 m × 20 m) per population/habitat type. Presence and abundance of all plant species were recorded under five female and five male C. album plants as well as in equivalent open ground area in each of 15 plots.
• According to Ripley's K function result, C. album did not display SSS. Generalised linear mixed models (GLMM) show that differences in plant size were not related to plant sex. Plant inventory correspondence analysis showed that species composition and abundance were influenced by habitat type, population and the presence of a C. album individual, but not by its sex. GLMM indicated a detrimental effect of C. album on the co‐occurring plants.
• Our results show that sexual dimorphism has allowed C. album to adapt to the environment avoiding SSS or significant demographic bias, suggesting a positive outlook for its conservation.

     

In vitro induced androgenesis inMelandrium album

Haploid and dihaploid female and rare dihaploid male plants were produced inMelandrium album throughin vitro induced androgenesis. In the seed progeny obtained from cross-hybridization between dihaploid androgenic males (supermales) and standard females only male plants were observed. The microspores containing Y chromosome gave rise to supermales.     

Differenze Morfologiche ed Anatomiche in Individui Maschili E Femminili di Ginkyo Biloba L.

Abstract

Anatomical and histological differences between ♀ and ♂ plants of GINKYO BILOBA L. — Morphological characters in several ♀ and ♂ specimens of Ginkyo have been checked, with the aim to put in evidence those which are sex-linked. Anatomical data from a previous research have been utilized. (Maugini 1965).

The main results are here summarized.

In the climate of Florence the female plants unfold their buds in the first ten days of April, the male ones in the middle of March, so that the males break their dormancy about one month before the females.

From the buds opening, brachyblasts are formed both in males and females, and catkins and ovules appear. At the beginning of May, the ovules have considerably grown, and catkins are faded. In the meanwhile the leaves have completely grown up in both sexes. Between the end of September and the beginning of October, the seeds become gold-yellow and begin to be shed off. Dissemination may go on for a long while, and still be active when all the leaves are fallen.

Buds are formed during summer, they are very little and sharp in the female, round and bigger in the male.

In both sexes leaves turn yellow and begin to fall between the end of October and the beginning of November. Females are generally considered more precocious than males in shedding leaves, but this behaviour did not result constant in the plants under observations so that the « leaf-fall time » cannot be considered a sex-linked character.

In shoots and stems of males and females, proceeds downwards tracheid deposition and differentiation, the highest activity being in the brachyblasts, where cambium works continuosly, and the lowest in the stem, where late wood formation can be found only in the male plants. Unevenness of cambial activity along the plant axis is particularly evident in the female, where late wood formation in the stem is rare.

The rhythm of cambial activity along shoots and stems of males and females have been compared with that of the buds, with the following results: both in the female and male plants the young leaves start expanding about two months before cambium activity starts in the stem. The male plant is more precocious than the female, probably the slower vegetation rhythm of the female being related to the seed ripening process.     

Patterns of growth,reproduction, defense,and herbivory in the dioecious shrub Baccharis halimifolia (Compositae)

Summary Patterns of growth, reproduction, defense (leaf resin) and herbivory were compared between the sexes of the dioecious shrub Baccharis halimifolia (Compositae). Male plants possessed longer shoots and more tender leaves, grew faster, and flowered and senesced earlier than female plants. Levels of leaf nitrogen, water content, and acetone-soluble resin (shown to deter feeding by polyphagous insect herbivores) did not differ between male and female plants. When offered a choice between leaves from male and female plants, adults of two leaf beetles (Chrysomelidae), the monophagous Trirhabda bacharidis and the polyphagous Paria thoracica, both preferred to feed on male leaves. Similarly, the daily fecundity of older females of T. bacharidis was higher when they were fed leaves from male compared to female plants. However, adult survivorship and total fecundity of T. baccharidis did not differ between male and female leaf treatments. We attribute the feeding preference for and slight increase in fecundity on male plants to the tenderness of male leaves. Larvae of the fly Tephritis subpura (Tephritidae) fed exclusively in the sterile receptacle of male flower heads (85% infested), but the phenology was such that pollen production was not adversely affected. Larvae of two other flies Dasineura sp. and Contarinia sp. (Cecidomyiidae) occupied >95% of only female flower heads where they fed among and on the developing seeds. We conclude that foliage-feeding herbivores are unlikely candidates to explain the female-biased sex ratio (59% female) of B. halimifolia plants in the field, and that their preference for male plants is a result of plant characteristics (e.g. rapid growth) that have been selected by some other factor. However, our data on selective floral herbivory in B. halimifolia are in accord with the argument that dioecy reduces the inadvertent loss of flower parts of one sex when herbivores feed on flower parts of the opposite sex.     

Identification of two markers linked to the sex locus in dioecious <Emphasis Type="Italic">Asparagus officinalis</Emphasis> plants

One hundred decamer primers of random-amplified polymorphic DNA were tested on dioecious Asparagus officinalis plants to identify sex-linked molecular markers. One primer (S368) produced two markers (S368-928 and S368-1178) in female plants. These two DNA markers were identified in 30 male and female plants, respectively, and a S368-928 marker was proved to be linked to the female sex locus. The female-linked S368-928 marker was sequenced and specific primers were synthesized to generate a 928 bp marker of sequence characterized amplified regions (SCAR) in female plants, SCAR₉₂₈. SCAR₉₂₈ could be used to correctly screen homozygous mm female plants of A. officinalis. However, results of Southern blot analysis suggest that the hybridization pattern of S368-928 was presented in both sex plants. This text was submitted by the authors in English.     

Nutrient deficiency promotes male-biased apparent sex ratios at the ramet level in the dioecious plant <Emphasis Type="Italic">Myrica gale</Emphasis> var. <Emphasis Type="Italic">tomentosa</Emphasis> in oligotrophic environments in bogs

In populations of dioecious plants, the differences in the cost of reproduction between male and female plants can promote a male-biased sex ratio. In this study, we examine the macronutrient levels in tissues of the dioecious wetland shrub Myrica gale to identify the cost of reproduction for male and female plants and to examine the effect of nutrients on the apparent sex ratio at the ramet level. We examined plants across 12 populations of M. gale inhabiting bogs and fens in Japan. For each population, we used line transects to estimate the apparent sex ratio and measured the concentrations of nitrogen (N), phosphorus (P), and potassium (K) in the leaves sampled from male and female plants and in the fruits from female plants. For five of the populations, we calculated the flowering frequency, mortality, and the recruitment rate (as the rate of clonal propagation). We found that the proportion of females was positively affected, and the male bias of sex ratios reduced, by increases in P concentration in leaves sampled from female plants. Neither mortality nor recruitment was affected by sex or by the nutrient concentration (P, K). The flowering frequency was not affected by sex or by K concentration, but decreased with decreases in the P concentration measured in leaves. This study confirmed that reproduction in M. gale is P-limited. We found no distinct differences in the flowering frequency, mortality, or recruitment rate between the male and female plants.     

The genetic control of isovitexin-glycosylation in the petals of Melandrium album

Summary The glycosylation of flavones in the petals of Melandrium album is shown to be controlled by the genes G, X and A. In the presence of the recessive alleles of these genes, only the aglycone isovitexin (6-C-glucosylapigenin) is found in the petals. The gene G controls the transfer of glucose, the gene X the transfer of xylose to the 7-hydroxyl group of isovitexin. The gene G is epistatic over X. In the presence of the gene A arabinose is coupled to the carbon-carbon bound glucose of isovitexin. In the presence of both G and A, or both X and A the corresponding di-glycosides are formed.The petals of the plants in which all genes for the flavone glycosylation are present in the homozygous recessive form are of a particular phenotype.     

谭清苏铁性别连锁的RAPD和SCAR分子标记

利用RAPD(Random amplified polymorphic DNA)分子标记技术,寻找谭清苏铁（Cycas tanqingii）中与性别相关的分子标记,筛选了160个10bp的随机引物,产生了2500多个RAPD条带。只有引物S0465 (CCCCGGTAAC)产生了一条大约500bp的雌性特异RAPD标记,该分子标记出现在所有的供试雌性植株中,而所有的供试雄性植株都不具有该标记。对该特异片段进行了克隆和序列测定,并根据序列分析结果将RAPD标记转化为重复性和特异性更好的特异特征序列扩增区域（SCAR）分子标记,并命名为STQC-S465-483。分子标记的建立可用于谭清苏铁幼苗性别的早期鉴定,为谭清苏铁就地保护和迁地保护提供技术支持。     

On the genetic control of the regeneration response in the dioecious Melandrium album

Summary Melandrium album (2n = 24), a dioecious species with heteromorphic sex chromosomes (XY, male; XX, female), has a strong genetic commitment for sex determination. So far the in vitro regeneration response in this species has appeared to be restricted to female plants. We report here a procedure for achieving active regeneration from explants and mesophyll protoplasts of selected female plants. Shoots were frequently induced in hormone-free media and in the presence of cytokinins or low concentrations (<0.5 mg/l) of auxins. The in vitro conditions employed did not affect the sex expression of the regenerated plants. Crosses between selected female plants with high regeneration capacity and nonregenerating males indicated that the regeneration response is genetically controlled and can be transmitted sexually into male and female progenies.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - 2iP (2-isopentenyl)-adenine - IAA indole acetic acid - IBA indole butyric acid - NAA naphthalene acetic acid - BAP 6-benzylaminopurine     

Composition of epiphytic bacterial communities differs on petals and leaves

The epiphytic bacterial communities colonising roots and leaves have been described for many plant species. In contrast, microbiologists have rarely considered flowers of naturally growing plants. We identified bacteria isolated from the surface of petals and leaves of two plant species, Saponaria officinalis (Caryophyllaceae) and Lotus corniculatus (Fabaceae). The bacterial diversity was much lower on petals than on leaves of the same plants. Moreover, the bacterial communities differed strongly in composition: while Pseudomonadaceae and Microbacteriaceae were the most abundant families on leaves, Enterobacteriaceae dominated the floral communities. We hypothesise that antibacterial floral volatiles trigger the low diversity on petals, which is supported by agar diffusion assays using substances emitted by flowers and leaves of S. officinalis. These results suggest that bacteria should be included in the interpretation of floral traits, and possible effects of bacteria on pollination are proposed and discussed.     

Isolation affects reproductive success in low-density but not high-density populations of two wind-pollinated <Emphasis Type="Italic">Thalictrum</Emphasis> species

Since pollen usually travels limited distances in wind-pollinated plant species, plants growing at low density may become pollen limited. We examined how local pollen availability and population density affect reproductive success in two wind-pollinated, dioecious species, Thalictrum fendleri and Thalictrum dioicum. Distance to the nearest flowering male, the number of flowering males within 2 m, and flower number on those males served as measures of local pollen availability. Increased distance from pollen donors reduced seed set in the lowest-density population of each species, but seed set in high-density populations was not correlated with local pollen availability. For plants in high- and low-density populations at similar distances from pollen donors, this distance only affected seed set in low-density populations. To ensure that differences in resource availability were not causing spurious correlations between seed set and plant density, we constructed low-density artificial arrays in populations of T. dioicum. In these, seed set decreased rapidly with increases in distance from pollen donors. Despite these effects, the density of males in a population was not correlated with average seed set in T. dioicum, and hand pollination in the T. dioicum populations also failed to increase seed set over natural levels. These results suggest that pollen receipt only limits seed set on isolated plants within low- density populations of T. dioicum and T. fendleri.     

Genetics of diapause in the comma butterfly Polygonia c‐album

The processes of local adaptation and ecological speciation can be better understood by studying the genetic background of life‐history decisions. The sex chromosomes host genes for many population differences in the Lepidoptera and therefore the inheritance of diapause determination in the butterfly Polygonia c‐album may be hypothesized to be sex‐linked. In the present study, Polygonia c‐album (L.) from Spain and Sweden and hybrid offspring are raised under an LD 17 : 7 h photocycle that induces most pure Swedish individuals to develop into the diapausing dark morph and most pure Spanish individuals into the light and directly‐developing morph. If inheritance of the daylength threshold for diapause is X‐linked, as is known to be the case for host‐plant preferences, females should follow the developmental path of their male parents' populations. However, female hybrids instead have a diapause propensity intermediate to that of their parental stocks and, consequentially, diapause determination is not X‐linked. However, male hybrids eclose as the diapausing morph to a higher extent than females and, moreover, this pattern is more pronounced in the Spanish female × Swedish male cross than in the reciprocal cross. Hence, it is concluded that the genetic determination of the critical daylength for diapause is mainly autosomal but with some influence of sex‐linked genes and/or parental effects, possibly as an effect of the importance of protandry for males. Such sex effects could provide a starting point for the evolution of population differences inherited on the sex chromosomes.     

Gymnosperm Orthologues of Class B Floral Homeotic Genes and Their Impact on Understanding Flower Origin

Class B floral homeotic genes play a key role in specifying the identity of male reproductive organs (stamens) and petals during the development of flowers. Recently, close relatives (orthologues) of these genes have been found in diverse gymnosperms, the sister group of the flowering plants (angiosperms). The fact that such genes have not been found so far, despite considerable efforts, in mosses, ferns or algae, has been taken as evidence to suggest that B genes originated 300–400 million years ago in a lineage that led to extant seed plants. Gymnosperms do not develop petals, and their male reproductive organs deviate considerably from angiosperm stamens. So what is the function of gymnosperm B genes? Recent experiments revealed that B genes from diverse extant gymnosperms are exclusively expressed in male reproductive organs (microsporophylls). At least for some of these genes it has been shown that they can partially substitute for the Arabidopsis B genes AP3 and PI in ectopic expression experiments, or even partially substitute these genes in different class B floral organ identity gene mutants. This functional complementation, however, is restricted to male organ development. These findings strongly suggest that gymnosperm and angiosperm B genes have highly related interaction partners and equivalent functions in the male organs of their different host species. It seems likely that in extant gymnosperms B genes have a function in specifying male reproductive organs. This function was probably established already in the most recent common ancestor of extant gymnosperms and angiosperms (seed plants) 300 million years ago and thus represents the ancestral function of seed plant B genes, from which other functions (e.g., in specifying petal identity) might have been derived. This suggests that the B gene function is part of an ancestral sex determination system in which B gene expression specifies male reproductive organ development, while the absence of B gene expression leads to the formation of female reproductive organs. Such a simple switch mechanism suggests that B genes might have played a central role during the origin of flowers. In the out-of-male and out-of-female hypotheses changes in B gene expression led to the origin of hermaphroditic flower precursors out of male or female gymnosperm reproductive cones, respectively. We compare these hypotheses with other recent molecular hypotheses on the origin of flowers, in which C/D and FLORICAULA/LEAFY-like genes is given a more prominent role, and we suggest how these hypotheses might be tested in the future.     

Complex sex determination in the stinging nettle Urtica dioica

The dioecious species Urtica dioica harbours wide variation in sex ratio of seeds. We conducted a series of crosses to analyse the genetic basis of sex determination in this species. Dutch populations of U. dioica contain low proportions of monoecious individuals beside male and female plants. Self-pollination of monoecious plants always yielded female, male and monoecious plants, generally in a ratio of one female to three male/monoecious individuals. This motivated us to write down a simple model in which gender is determined by one major sex-determination locus with four alleles. In the model males and monoecious plants have distinct genotypes but are both heterozygous at the sex-determination locus. We first made crosses among progeny obtained after self-pollination of monoecious plants. These crosses showed that the monoecious trait generally showed Mendelian inheritance and was passed on to the next generation via both pollen and seeds. Further crosses between monoecious plants and plants from dioecious system indicated that alleles from the dioecious system are often dominant. However, many exceptions to our genetic model are observed which suggest that dominance is incomplete and/or that more genes are involved in sex determination. We discuss to what extent sex determination genes explain the strongly biased seed sex ratios and argue that additional genes, for instance genes for female choice, must also be involved.