颈卵器植物MADS-box基因的研究进展

作者通过对颈卵器植物MADS_box基因最新研究结果的概述 ,介绍了MADS_box基因与颈卵器植物生殖器官决定、发育和进化的关系以及被子植物花器官发育的ABCD模型在三类颈卵器植物中的表现形式和进化关系。这些结果表明MADS_box基因的结构、功能和表达模式的变化是植物生殖器官决定、发育和进化的主要原因。     

颈卵器植物颈细胞结构与功能的研究进展

颈卵器是苔藓、蕨类、裸子植物的雌性生殖器官,由卵细胞、腹沟细胞和颈细胞(颈沟细胞)构成。其中,颈细胞是这类植物雄配子进入颈卵器并完成受精作用的唯一通道,在颈卵器的发育和受精过程中发挥着重要作用。该文就近年来国内外有关对颈细胞的发生和发育、结构特点和功能等进行较为系统全面的分析和总结,并对未来的研究方向进行展望。     

颈卵器与植物演化

真核植物普遍存在着有性生殖的繁殖方式。苔藓植物与蕨类植物的雌性生殖器官均以颈卵器的形式出现 ,在裸子植物中 ,也有颈卵器退化的痕迹。因此 ,这 3类植物又合称为颈卵器植物。颈卵器是高等植物的重要雌性繁殖结构。如图 :颈卵器的外形呈烧瓶状 ,分为下部的腹部和上部的颈部 ,腹部膨大 ,内有卵细胞和腹沟细胞各 1 ;颈部狭窄 ,仅单层细胞构成 ,内有一列颈沟细胞。由于卵的成熟 ,促使颈沟细胞与腹沟细胞的破裂。精子游到颈卵器的附近 ,通过破裂的颈沟细胞与腹沟细胞而与卵结合。精子与卵结合后形成合子 ,合子分裂而形成胚 ,胚在颈卵器内发育…     

阔鳞瘤蕨颈卵器形成与卵发生的初步研究

运用光学显微镜与透射电镜对阔鳞瘤蕨（Phymatosorus hainanensis(Noot.) S.G.Lu）颈卵器形成和卵发生进行了研究。阔鳞瘤蕨颈卵器产生于雌配子体生长点下方分枝毛状体内侧。切片观察表明颈卵器起源于配子体表面的原始细胞,该细胞经两次不等分裂形成3个细胞,上下两个细胞分别发育为颈卵器的颈部与底部壁细胞,中间的细胞为初生细胞,含有较丰富的细胞器。初生细胞进行两次不等分裂产生颈沟细胞、腹沟细胞与卵细胞。成熟颈卵器内颈沟细胞和腹沟细胞退化,卵细胞上表面产生受精孔。本研究阐述了阔鳞瘤蕨颈卵器形成和卵发生的细胞学过程,对阐明蕨类植物雌性生殖器官的发育特征有一定的科学意义。     

核心薄囊蕨类颈卵器多细胞起源的形态学观察

核心薄囊蕨类是真蕨纲中的主要类群,其颈卵器壁细胞的起源问题尚未见报道。该研究以华北鳞毛蕨为例,在人工培养条件下,用石蜡切片法综合观察了颈卵器的发育过程,分析颈沟细胞、腹沟细胞、卵细胞等的发生与分化,并结合桫椤科等十多个类群性器官的研究成果,探讨核心薄囊蕨类颈卵器的起源。结果表明:(1)颈卵器由配子体1个原始细胞和多个营养细胞共同发育而成。(2)原始细胞经两次不均等分裂由外向内依次形成颈壁细胞、中央细胞、基细胞。(3)中央细胞分裂形成1个卵细胞、1个腹沟细胞和颈沟细胞。(4)基细胞分化为颈卵器腹壁最下方的1~4个壁细胞。(5)颈卵器腹部周围的壁细胞由卵细胞周围的多个营养细胞直接转化而来。该研究首次提出了核心薄囊蕨类颈卵器为多细胞起源,并为探讨颈卵器植物的有性生殖演化规律提供了形态学依据。     

亮毛蕨的配子体发育特征及其系统学意义

采用原生境土培养方法对亮毛蕨(Acystopteris japonica)进行培养,并对其配子体发育过程进行了观察。结果表明:亮毛蕨植物的孢子二面体型,极面观为椭圆形,赤道面观肾形,单裂缝,无周壁,外壁具棒状纹饰,孢子萌发为书带蕨型(Vittaria-type),原叶体发育为铁线蕨型(Adiantum-type)。丝状体4～7个细胞,片状体小楔状,仅3～5个细胞宽,成熟原叶体心形,裸露,初生假根具叶绿体,颈卵器较短;配子体发育较迅速,假根具分枝和膨大,精子器囊由3个壁细胞构成,颈卵器略弯曲。本研究首次观察到亮毛蕨的颈卵器壁细胞内含有球形颗粒,但其功能不详。亮毛蕨的配子体发育过程兼有原始和进化的特点。在适宜的光照和温度下,土壤培养亮毛蕨原叶体的成苗率达95%以上,移栽成活率达89%以上。     

极危孑遗物种东方水韭雌配子体及胚胎的解剖学观察

以人工培养的国家一级保护植物东方水韭(Isoetes orientalis)为材料,采用切片技术对雌配子体和胚胎的发育进程进行解剖学观察研究,探讨其有性生殖过程及濒危机制。结果表明:(1)东方水韭大孢子3~5d萌发,成熟雌配子体呈球形,无假根,三裂缝处发育出多个颈卵器,成熟颈卵器只有颈壁细胞与颈沟细胞,无腹沟细胞。(2)多数雌配子体只发育出一个胚胎,偶见多胚共存现象;胚胎发育时期,第一叶原基相比第二、三叶原基发育迅速。(3)颈卵器部分组织常出现分化紊乱,导致雌配子体败育。该研究结果支持"根叶理论",并讨论了腹沟细胞的退化以及双胚共存机制,认为东方水韭雌配子体常停留在游离核阶段、颈卵器形态或位置不规则、卵细胞排列紊乱等可能是其败育的原因。     

水蕨颈卵器的形成与发育

主要运用电子透射显微镜技术对水蕨(Ceratopteris thalictroides(L.)Brongn)颈卵器形成与发育进行了研究。结果表明:水蕨颈卵器是由原叶体分生组织内颈卵器原始细胞形成的。该原始细胞经2次分裂形成3层细胞,上下两层发育成颈卵器颈部与底部的壁细胞,中层为初生细胞。初生细胞是颈卵器内雌配子发生的第一个细胞,该细胞经2次不等分裂形成1个卵细胞,1个腹沟细胞、1个双核的颈沟细胞。本研究首次阐明了水蕨颈卵器内细胞的发育顺序和特征。     

水蕨颈卵器的形成与发育

主要运用电子透射显微镜技术对水蕨（Ceratopteris thalictroides（L．）Brongn）颈卵器形成与发育进行了研究。结果表明：水蕨颈卵器是由原叶体分生组织内颈卵器原始细胞形成的。该原始细胞经2次分裂形成3层细胞,上下两层发育成颈卵器颈部与底部的壁细胞,中层为初生细胞。初生细胞是颈卵器内雌配子发生的第一个细胞,该细胞经2次不等分裂形成1个卵细胞,1个腹沟细胞、1个双核的颈沟细胞。本研究首次阐明了水蕨颈卵器内细胞的发育顺序和特征。     

银杏雌性生殖器官发育过程的显微观察

对银杏(Ginkgo biloba)雌性生殖器官的发育过程进行了连续显微观察。结果表明: 功能大孢子经过大约1个月的分裂形成约5 000个游离核后开始细胞化。授粉后约45天近珠孔端两侧各产生1个颈卵器母细胞。授粉后约50天, 颈卵器母细胞 平周分裂形成初生颈细胞和中央细胞。授粉后约55天, 初生颈细胞垂周分裂形成2个扁平状次生颈细胞, 之后次生颈细胞体积逐渐增大并突入颈卵器腔。授粉后约130天, 2个次生颈细胞斜向分裂形成4个颈细胞, 中央细胞不均等分裂形成腹沟细胞和卵细胞。套细胞起源于颈卵器母细胞的周围细胞, 授粉后70天至受精作用发生前, 套细胞内不断积累营养物质, 且套细胞与中央细胞间的细胞壁以及套细胞之间角隅处的细胞壁均出现明显增厚现象。在受精及胚胎早期发育过程中, 套细胞内营养物质逐渐消失, 细胞逐渐解体。授粉后55天, 2个颈卵器之间的一些细胞向上突起形成帐篷柱, 之后帐篷柱体积逐渐增加, 并突入颈卵器腔。自授粉后120天至受精前帐篷柱细胞内开始积累大量营养物质, 随后这些营养物质在受精过程中被逐渐消耗。到了原胚游离核后期, 帐篷柱的顶端细胞发生变形并解体。     

Genome-wide analysis reveals widespread roles for RcREM genes in floral organ development in Rosa chinensis

Members of the REM (Reproductive Meristem) gene family are expressed primarily in reproductive meristems and floral organs. However, their evolution and their functional profiles in flower development remain poorly understood. Here, we performed genome-wide identification and evolutionary analysis of the REM gene family in Rosaceae. This family has been greatly expanded in rose (Rosa chinensis) compared to other species, primarily through tandem duplication. Expression analysis revealed that most RcREM genes are specifically expressed in reproductive organs and that their specific expression patterns are dramatically altered in rose plants with mutations affecting floral organs. Protein-protein interaction analysis indicated that RcREM14 interact with RcAP1 (one of the homology of A class genes in ABCDE model), highlighting the roles of RcREM genes in floral organ identity. Finally, co-expression network analysis indicated that RcREM genes are co-expressed with a high proportion of key genes that regulate flowering time, floral organ development, and cell proliferation and expansion in R. chinensis.     

A novel MADS-box gene subfamily with a sister-group relationship to class B floral homeotic genes

Class B floral homeotic genes specify the identity of petals and stamens during the development of angiosperm flowers. Recently, putative orthologs of these genes have been identified in different gymnosperms. Together, these genes constitute a clade, termed B genes. Here we report that diverse seed plants also contain members of a hitherto unknown sister clade of the B genes, termed B(sister) (B(s)) genes. We have isolated members of the B(s) clade from the gymnosperm Gnetum gnemon, the monocotyledonous angiosperm Zea mays and the eudicots Arabidopsis thaliana and Antirrhinum majus. In addition, MADS-box genes from the basal angiosperm Asarum europaeum and the eudicot Petunia hybrida were identified as B(s) genes. Comprehensive expression studies revealed that B(s) genes are mainly transcribed in female reproductive organs (ovules and carpel walls). This is in clear contrast to the B genes, which are predominantly expressed in male reproductive organs (and in angiosperm petals). Our data suggest that the B(s) genes played an important role during the evolution of the reproductive structures in seed plants. The establishment of distinct B and B(s) gene lineages after duplication of an ancestral gene may have accompanied the evolution of male microsporophylls and female megasporophylls 400-300 million years ago. During flower evolution, expression of B(s) genes diversified, but the focus of expression remained in female reproductive organs. Our findings imply that a clade of highly conserved close relatives of class B floral homeotic genes has been completely overlooked until recently and awaits further evaluation of its developmental and evolutionary importance. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00438-001-0615-8.     

木本植物开花调节基因的分离克隆及其童期控制

高等植物在萌发后需要经历一定时间的营养生长 ,即童期 ,才能进入生殖发育阶段。控制植物生殖转变调节童期的基因主要有花序分生组织特异基因、花分生组织特异基因、花器官分生组织特异基因。对近几年木本植物开花调节基因的分离克隆及其童期控制研究进行综述 ,对了解木本植物开花基因的作用功能 ,以及缩短童期和植物进化研究将有所裨益。     

A short history of MADS-box genes in plants

Evolutionary developmental genetics (evodevotics) is a novel scientific endeavor which assumes that changes in developmental control genes are a major aspect of evolutionary changes in morphology. Understanding the phylogeny of developmental control genes may thus help us to understand the evolution of plant and animal form. The principles of evodevotics are exemplified by outlining the role of MADS-box genes in the evolution of plant reproductive structures. In extant eudicotyledonous flowering plants, MADS-box genes act as homeotic selector genes determining floral organ identity and as floral meristem identity genes. By reviewing current knowledge about MADS-box genes in ferns, gymnosperms and different types of angiosperms, we demonstrate that the phylogeny of MADS-box genes was strongly correlated with the origin and evolution of plant reproductive structures such as ovules and flowers. It seems likely, therefore, that changes in MADS-box gene structure, expression and function have been a major cause for innovations in reproductive development during land plant evolution, such as seed, flower and fruit formation.     

Molecular evolution of the petal and stamen identity genes, APETALA3 and PISTILLATA, after petal loss in the Piperales

Organ loss is an evolutionary phenomenon commonly observed in all kinds of multicellular organisms. Across the angiosperms, petals have been lost several times over the course of their diversification. We examined the evolution of petal and stamen identity genes in the Piperales, a basal lineage of angiosperms that includes the perianthless (with no petals or sepals) families Piperaceae and Saururaceae as well as the Aristolochiaceae, which exhibit a well-developed perianth. Here, we provide evidence for relaxation of selection on the putative petal and stamen identity genes, homologs of APETALA3 and PISTILLATA, following the loss of petals in the Piperales. Our results are particularly interesting as the B-class genes are not only responsible for the production of petals but are also central to stamen identity, the male reproductive organs that show no modification in these plants. Relaxed purifying selection after the loss of only one of these organs suggests that there has been dissociation of the functional roles of these genes in the Piperales.     

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.     

植物离体器官发生控制机理研究进展

植物离体器官发生不仅是获得大量无性繁殖植物和进行基因转化的重要途径, 而且亦是研究植物发育问题的主要实验系统之一。迄今为止, 包括营养器官和生殖器官在内的几乎所有的器官都可以在离体条件下得到再生, 为深入研究植物离体器官发生的分子机理奠定了基础。本文着重介绍了营养器官发生过程基因表达的调节及重要功能基因的作用, 并对器官特征决定基因在生殖器官发生过程中的作用进行了分析, 提出了揭示离体器官发生分子机理的主要途径。     

植物离体器官发生控制机理研究进展

植物离体器官发生不仅是获得大量无性繁殖植物和进行基因转化的重要途径,而且亦是研究植物发育问题的主要实验系统之一。迄今为止,包括营养器官和生殖器官在内的几乎所有的器官都可以在离体条件下得到再生,为深入研究植物离体器官发生的分子机理奠定了基础。本文着重介绍了营养器官发生过程基因表达的调节及重要功能基因的作用,并对器官特征决定基因在生殖器官发生过程中的作用进行了分析,提出了揭示离体器官发生分子机理的主要途径。