木本植物性别决定基因研究进展

雌雄异株植物是研究性别决定遗传机制及性染色体起源与进化的理想材料,而克隆性别决定基因是解析性别决定遗传机制的关键。木本植物中有丰富的雌雄异株植物,且包括2种相反的性别决定系统：XY型(雌株为同配型的XX,雄株为异配型的XY)和ZW型(雌株为异配型的ZW,雄株为同配型的ZZ)。此外,不同性别植株的经济价值也有所不同。在木...     

植物性别决定的研究进展

通过回顾近年来以多种植物为材料进行的性染色体观察,性别决定基因及调控方式的研究,对植物性别决定的机制进行了初步探讨,从而可以看出不同植物具有不同的性别决定机制：对于有性染色体的植物而言,目前已经从Y染色体上分离和鉴定了许多与雄性发育紧密相关的基因;部分性别决定基因和调控序列已利用构建减法文库,诱导突变体等方法从一些植物中获得。此外,还有研究表明,DNA脱甲基化,以及某些激素(如赤霉素、乙烯、Ace)都对植物的性别决定有重要作用。     

Sex-Biased Temporal Gene Expression in Male and Female Floral Buds of Seabuckthorn (Hippophae rhamnoides)

Seabuckthorn is an economically important dioecious plant in which mechanism of sex determination is unknown. The study was conducted to identify seabuckthorn homologous genes involved in floral development which may have role in sex determination. Forty four putative Genes involved in sex determination (GISD) reported in model plants were shortlisted from literature survey, and twenty nine seabuckthorn homologous sequences were identified from available seabuckthorn genomic resources. Of these, 21 genes were found to differentially express in either male or female flower bud stages. HrCRY2 was significantly expressed in female flower buds only while HrCO had significant expression in male flowers only. Among the three male and female floral development stages (FDS), male stage II had significant expression of most of the GISD. Information on these sex-specific expressed genes will help in elucidating sex determination mechanism in seabuckthorn.     

Sex Determination by Sex Chromosomes in Dioecious Plants

Abstract: Sex chromosomes have been reported in several dioecious plants. The most general system of sex determination with sex chromosomes is the XY system, in which males are the heterogametic sex and females are homogametic. Genetic systems in sex determination are divided into two classes including an X chromosome counting system and an active Y chromosome system. Dioecious plants have unisexual flowers, which have stamens or pistils. The development of unisexual flowers is caused by the suppression of opposite sex primordia. The expression of floral organ identity genes is different between male and female flower primordia. However, these floral organ identity genes show no evidence of sex chromosome linkage. The Y chromosome of Rumex acetosa contains Y chromosome-specific repetitive sequences, whereas the Y chromosome of Silene latifolia has not accumulated chromosome-specific repetitive sequences. The different degree of Y chromosome degeneration may reflect on evolutionary time since the origination of dioecy. The Y chromosome of S. latifolia functions in suppression of female development and initiation and completion of anther development. Analyses of mutants suggested that female suppressor and stamen promoter genes are localized on the Y chromosome. Recently, some sex chromosome-linked genes were isolated from flower buds of S. latifolia.     

Plant sex determination and sex chromosomes

Sex determination systems in plants have evolved many times from hermaphroditic ancestors (including monoecious plants with separate male and female flowers on the same individual), and sex chromosome systems have arisen several times in flowering plant evolution. Consistent with theoretical models for the evolutionary transition from hermaphroditism to monoecy, multiple sex determining genes are involved, including male-sterility and female-sterility factors. The requirement that recombination should be rare between these different loci is probably the chief reason for the genetic degeneration of Y chromosomes. Theories for Y chromosome degeneration are reviewed in the light of recent results from genes on plant sex chromosomes.     

黄瓜性型分化的分子机制

黄瓜(Cucumis sativus)是雌雄异花植物性型分化研究的重要模式植物,近年来虽然其性型分化的分子机制研究取得了一定的成果,但其性型分化的调控机制尚未完全阐明。该文综合花器官发育基因、性别决定基因、内源激素、环境因子、性型分化假说,在分子水平构建了黄瓜性型分化的表达调控网络。同时对激素和性别决定基因协控的黄瓜单性花器官凋亡机制进行了阐述,并就miRNA在黄瓜性型分化调控中的作用进行了探讨。     

Multiple molecular approaches yield no evidence for sex‐determining genes in lake sturgeon (Acipenser fulvescens)

Common DNA‐based sexing assays have been widely used for the conservation and management of mammals and birds. However, many fishes do not have genetic sex determination and in those that do, the plasticity of the genes involved means that species‐specific assays are normally required. Such DNA‐sexing markers would be especially valuable in lake sturgeon (Acipenser fulvescens) because of their sexual monomorphism, delayed sexual maturity, and conservation status. We tried to identify genetic differences between male and female lake sturgeon using several different molecular genetic methods, including randomly amplified polymorphic DNA, representational difference analyses, subtractive hybridization, and a candidate gene approach. Ultimately, a number of genes were identified but none was sex‐specific. Although the ultimate mechanism of sex determination is yet unknown, it is possible that sex determination is environmental in lake sturgeon, especially since recent studies have also failed to identify sex determination genes in other sturgeon species.     

Sex determination in the monoecious species cucumber is confined to specific floral whorls

In unisexual flowers, sex is determined by the selective repression of growth or the abortion of either male or female reproductive organs. The mechanism by which this process is controlled in plants is still poorly understood. Because it is known that the identity of reproductive organs in plants is controlled by homeotic genes belonging to the MADS box gene family, we analyzed floral homeotic mutants from cucumber, a species that bears both male and female flowers on the same individual. To study the characteristics of sex determination in more detail, we produced mutants similar to class A and C homeotic mutants from well-characterized hermaphrodite species such as Arabidopsis by ectopically expressing and suppressing the cucumber gene CUCUMBER MADS1 (CUM1). The cucumber mutant green petals (gp) corresponds to the previously characterized B mutants from several species and appeared to be caused by a deletion of 15 amino acid residues in the coding region of the class B MADS box gene CUM26. These homeotic mutants reveal two important concepts that govern sex determination in cucumber. First, the arrest of either male or female organ development is dependent on their positions in the flower and is not associated with their sexual identity. Second, the data presented here strongly suggest that the class C homeotic function is required for the position-dependent arrest of reproductive organs.     

Isolation of a partial sequence of a putative nucleotide sugar epimerase, which may involve in stamen development in cucumber (Cucumis sativus L.)

Sex determination is the most widely studied subject in cucumber. The sex of cucumber plants can be monoecious, hermaphrodite, gynoecious, androecious, or andromonoecious. Besides environmental factors, three major genes, F/f, M/m, and A/a mainly govern the sex types in cucumber. Regardless of their sex all floral buds are bisexual at the early bud stage. A stage specific arrest of either stamen or carpel leads to unisexual flower development. The possible downstream product of the interaction of the sex determining genes that may directly allow the growth or selectively arrest stamen or pistil is not yet identified. Therefore, in the current study, we performed suppression subtractive hybridization using floral buds from nearly isogenic gynoecious and hermaphrodite cucumber plants and identified for the first time a cDNA homologous to nucleotide sugar epimerase. The expression level of the isolated putative nucleotide sugar epimerase is weak in female floral buds but strong in bisexual and male flowers. The weak level of the putative nucleotide sugar epimerase may be an indication for its improper functioning, which may influence stamen development in cucumber plants.     

Polygenic sex determination in vertebrates – is there any such thing?

Genetic sex determination (SD) in most vertebrates is controlled by a single master sex gene, which ensures a 1:1 sex ratio. However, more complex systems abound, and several have been ascribed to polygenic SD (PSD), in which many genes at different loci interact to produce the sexual phenotype. Here we examine claims for PSD in vertebrates, finding that most constitute transient states during sex chromosome turnover, or aberrant systems in species hybrids. To avoid confusion about terminology, we propose a consistent nomenclature for genetic SD systems.     

WT1在哺乳动物性别发育过程中的调控作用

哺乳动物的性别发育大致可分为性别决定和性别分化两步,是一个由WT1/Wt1、SRY/Sry和MIS/Mis等多基因参与的级联过程,但目前对于这些基因之间的相互作用尚不清楚。在性别发育过程中持续表达的WT1/Wt1与多种伴有性别发育异常的疾病相关,其重要性表现为对多个性别发育关键基因在转录水平和转录后水平的调控。简要概述了WT1/Wt1的复杂性及其对多基因的调控作用,以期为阐明性别发育机制和基因间的相互关系提供参考。     

The evolution of female sexuality and mate selection in humans

Understanding female sexuality and mate choice is central to evolutionary scenarios of human social systems. Studies of female sexuality conducted by sex researchers in the United States since 1938 indicate that human females in general are concerned with their sexual well-being and are capable of sexual response parallel to that of males. Across cultures in general and in western societies in particular, females engage in extramarital affairs regularly, regardless of punishment by males or social disapproval. Families are usually concerned with marriage arrangements only insofar as those arrangements are economically or politically advantageous, but females most often have a voice in arranged marriages. Extended families also concentrate on a couple’s future reproduction rather than on sexual exclusivity. Although marriage for females is often compromised by male or family reproductive interests (which may not in fact differ from female interests), females appear to exercise their sexuality with more freedom than has previously been suggested. Notions of human females as pawns in the male reproductive game, or as traders of sex for male services, should be dispelled.     

Maytenus obtusifolia Mart. (Celastraceae): a tropical woody species in a transitional evolutionary stage of the gynodioecy–dioecy pathway

‘Gynodioecy–dioecy’ is one of the pathways by which dioecy can arise from hermaphroditism. Studies on sex determination and development of gynodioecious systems have focused on temperate and/or annual species. Little is known about the evolutionary dynamics of gynodioecy and dioecy in perennial tropical species, where these systems have more frequently evolved. Maytenus obtusifolia is an abundant species in restingas in southeastern Brazil. The sexual system of M. obtusifolia was investigated by studying the floral structure and reproductive biology. We considered the sexual system as an intermediate step in the pathway gynodioecy-dioecy. The characterization of the hermaphrodite morph was complex, because of a gradient of variation in floral morphology and reproductive characteristics (sizes of the style and stigmatic surface, pollen viability, embryo sacs containing hypertrophied synergids, and fruit set). This variation leads to different proportions of functional male and female flowers among hermaphrodite plants and is responsible for the different levels of reproductive success. Female reproductive success and pollen viability were negatively correlated with the hermaphrodite morph (r = ?0.67). The higher fruiting intensity and fruit/flower ratio of females (41 %) compared to hermaphrodites (2 %) and the fact that female plants produce more and better-quality seeds support the female compensation. We suggest that female sterility may be linked to the set of changes in the carpels. The differences in the quality and quantity of pollen grains of hermaphrodite plants, and the similar individual rates of pollen viability observed for three consecutive flowering events, may indicate a relationship with nuclear cytoplasmic sex determination.     

Regulation of flower organogenesis: Phytohormone control of mRNA populations during sexual differentiation inMercurialis annua L.

Some general data on the genetic control and the possibilities of regulation of developmental paths inDrosophila are furnished. The insights to be gained from this insect will surely have implications that extend far beyond the fruit-fly. For example, in plants, developmental programs for floral organs, implying specific proteins are known. Developmental mutants in which mutate alleles control developmental programs for flowering were also selected in several species (Zea, Pisum, Sorghum, Cucumis, Mercurialis). Chemicals, especially phytohormones interfering with these programs are discussed. The case of sexual differentiation ofMercurialis is discussed in more detail. In this species, sex organs are controlled by sex determination genes and by auxins (male) and cytokinins (female). Flowers of each sex can be characterized by specific mRNA populations. They were evidenced by translationin vitro in a cell-free system of the various kinds of mRNAs [poly(A), non poly(A), polysomes]. The feminisation of genetic males by cytokinins induces the mRNA population of female type. Evidence concerning the implications of cytokinins in protein synthesis before translation level is presented. This is also probably true for auxins, although direct evidence is lacking.     

Gender plasticity in Sagittaria sagittifolia (Alismataceae), a monoecious aquatic species

 Aquatic plants are well known for their high degree of phenotypic plasticity in vegetative structures, particularly leaves. Less well understood is the extent to which their sexuality can be modified by environmental conditions. Here we investigate gender plasticity in the European clonal monoecious aquatic Sagittaria sagittifolia (Alismataceae) to determine how floral sex ratios may vary with plant size and inflorescence order. We sampled two populations from aquatic habitats in East Anglia, U.K. and measured a range of plant attributes including ramet size and the number of female and male flowers per inflorescence. The two populations exhibited similar patterns of phenotypic gender, despite contrasting patterns of total allocation to female and male flower number. Plants produced male-biased floral sex ratios but female flower number increased from the first to the second inflorescence whereas male flower number decreased. Size-dependent gender modification occurred in both populations, but the patterns of allocation to female flower production differed between the two populations. Our results are consistent with the view that monoecy is a sexual strategy that enables plants to adjust female and male allocation in response to changing environmental conditions. Received September 16, 2002; accepted October 23, 2002 Published online: March 20, 2003