花粉发育的转录组研究进展

在受精过程中花粉通过其极性生长的花粉管将精细胞运送到胚囊启动双受精, 除了在有性生殖过程中的重要作用外,花粉及其极性生长的花粉管也是研究植物生长发育的重要模式材料。随着模式植物拟南芥和水稻基因组测序的完成, 在基因组水平上揭示花粉发育以及花粉管极性生长的分子基础已成为可能。经过最近几年的研究已初步明确了花粉转录组特征。本文主要讨论了拟南芥花粉转录组学的研究进展, 以期帮助读者对花粉发育的研究有全面了解。     

花粉萌发转录基因组研究

为了解花粉萌发的详细细节,中国科学家利用拟南芥基因组芯片,首次发现从脱水成熟花粉粒,到含水花粉粒,再到拟南芥的花粉管的转录组变化。在花粉萌发和花粉管生长过程中,与细胞存活、转录、信号传导和细胞转运有关的表达基因发生了很大变化,尤其是那些正调控的基因。此外,类钙调蛋白、阳离子交换因子、以及热激蛋白家族在花粉萌发和花粉管生长过程中变化较大,     

极性生长的细胞中胞嘧啶甲基化的动态变化及其对GABA信号的响应

DNA胞嘧啶(C)的甲基化(5m C)在植物发育过程中具有重要的调节作用,多种环境因子如逆境胁迫、植物内/外源性因子等均会触发DNA甲基化的变化。为探讨γ-氨基丁酸(GABA)对植物发育的可能调节机制,本研究以极性生长的烟草花粉管和拟南芥根为材料,分析5m C的含量及其对GABA信号的响应。结果表明,1.0 mmol/L GABA能显著促进烟草花粉管和拟南芥根的极性生长;同时,GABA处理使烟草花粉管和拟南芥根的基因组中5m C含量显著降低、5-羟基胞嘧啶(5hm C)含量显著增加。5hm C是5m C去甲基化途径中的一个重要中间产物,本研究证实了GABA可以作为一种重要的外源信号调节DNA甲基化的动态变化。     

蕨类植物孢子与种子植物花粉萌发的比较

蕨类植物孢子与种子植物花粉在有性生殖过程中都具有重要的作用。花粉作为种子植物的雄配子体, 通过萌发后极性生长的花粉管将精细胞送到胚囊完成受精作用。蕨类植物孢子作为配子体的原始细胞, 通过不对称的有丝分裂产生一大一小两个细胞, 小细胞萌发出极性生长的假根, 大细胞继续分裂发育为原叶体(配子体)。成熟的花粉和蕨类植物孢子都是代谢高度静止的细胞, 两者的萌发过程不仅都受到各种不同环境因子的影响, 而且在信号转导、极性建立和能量代谢等方面可能有着相似的调控机制。本文综述了蕨类植物孢子和种子植物花粉萌发过程的差异和保守性特征。     

蕨类植物孢子与种子植物花粉萌发的比较

蕨类植物孢子与种子植物花粉在有性生殖过程中都具有重要的作用。花粉作为种子植物的雄配子体,通过萌发后极性生长的花粉管将精细胞送到胚囊完成受精作用。蕨类植物孢子作为配子体的原始细胞,通过不对称的有丝分裂产生一大一小两个细胞,小细胞萌发出极性生长的假根,大细胞继续分裂发育为原叶体（配子体）。成熟的花粉和蕨类植物孢子都是代谢高度静止的细胞,两者的萌发过程不仅都受到各种不同环境因子的影响,而且在信号转导、极性建立和能量代谢等方面可能有着相似的调控机制。本文综述了蕨类植物孢子和种子植物花粉萌发过程的差异和保守性特征。     

《Molecular Plant》文章中文摘要

拟南芥配子体发育相关的减数分裂和有丝分裂细胞周期突变体（综述）;基于S-核酸酶的自交不亲合的生化模型（综述）;GEX3,在拟南芥雄配子体和卯细胞中表达,对于珠孔花粉管定向生长非常重要同时在胚胎早期发育中起作用;绒毡层降解阻滞对水稻花粉发育过程中的脂肪代谢和基因调控很关键;拟南芥双受精涉及阻断卯细胞的多精受精而非中央细胞……     

芥菜型油菜与白菜正反杂交的胚胎学研究

利用荧光技术对芥菜型油菜（Brassica juncea）与白菜（B．pekinesis）种间正反杂交后花粉萌发和花粉管生长过程进行了观察。结果显示：芥菜型油菜与白菜正交授粉后,花粉在柱头上能正常萌发,多数花粉管沿花柱到达胚珠完成受精,且受精方式有珠孔受精、合点受精和中部受精,少量花粉管生长不正常,出现花粉管顶端膨大扭曲,花粉管分支等异常现象;反交授粉后,花粉在柱头上萌发时柱头乳突细胞产生强烈胼胝质反应,影响花粉管生长,只有少量花粉管通过花柱到达胚珠完成受精。用石蜡切片技术观察了正反杂交后杂种的胚胎发育,正交杂种胚胎发育较早,胚和胚乳生长较正常,杂种胚一般均能发育至成熟;反交杂种胚发育至心型期便不能继续发育,胚乳也停滞在游离核阶段并最终败育。综合分析表明,芥菜型油菜与白菜正反杂交都存在一定程度的受精不亲和性。     

芥菜型油菜与白菜正反杂交的胚胎学研究

利用荧光技术对芥菜型油菜(Brassica juncea)与白菜(B. pekinesis)种间正反杂交后花粉萌发和花粉管生长过程进行了观察。结果显示: 芥菜型油菜与白菜正交授粉后, 花粉在柱头上能正常萌发, 多数花粉管沿花柱到达胚珠完成受精, 且受精方式有珠孔受精、合点受精和中部受精, 少量花粉管生长不正常, 出现花粉管顶端膨大扭曲, 花粉管分支等异常现象; 反交授粉后, 花粉在柱头上萌发时柱头乳突细胞产生强烈胼胝质反应, 影响花粉管生长, 只有少量花粉管通过花柱到达胚珠完成受精。用石蜡切片技术观察了正反杂交后杂种的胚胎发育, 正交杂种胚胎发育较早, 胚和胚乳生长较正常, 杂种胚一般均能发育至成熟; 反交杂种胚发育至心型期便不能继续发育, 胚乳也停滞在游离核阶段并最终败育。综合分析 表明, 芥菜型油菜与白菜正反杂交都存在一定程度的受精不亲和性。     

花粉蛋白质组学研究进展

花粉是高度退化的生物体(雄配子体), 在植物有性生殖过程中具有重要作用。解析花粉发育、花粉-柱头识别、萌发和花粉管生长等细胞学过程的分子机制是当前研究的热点问题之一。近年来, 应用高通量的蛋白质组学技术平台, 对水稻、拟南芥和裸子植物花粉的蛋白质组学研究揭示了花粉中表达蛋白质的功能类群特征。花粉中参与细胞壁代谢、蛋白质代谢、细胞骨架动态和信号转导的蛋白质被高度代表, 并且近1/4蛋白质有多个同工型。本文综述了花粉蛋白质组学的研究进展。     

微丝骨架的构成及其对花粉管极性生长的调控作用

微丝骨架是细胞骨架的重要组成部分,它由肌动蛋白和肌动蛋白结合蛋白组成,广泛存在于真核细胞中。近年来,大量研究表明植物花粉及花粉管中存在丰富的微丝骨架。目前,在微丝骨架作为信号转导途径的靶标参与对花粉管极性生长的调控、微丝骨架在花粉和花粉管中的分布及其在花粉管生长过程中与其他信号分子之间的相互作用等方面取得了一系列突破性进展。     

ABORTED GAMETOPHYTE 1 is required for gametogenesis in Arabidopsis

In flowering plants, the male and female gametogenesis is a crucial step of sexual reproduction. Although many genes have been identi fied as being involved in the gametogenesis process, the genetic mechanisms underlying gametogenesis remains poorly understood. We reported here characterization of the gene, ABORTED GAMETOPHYTE 1(AOG1) that is newly identi fied as essential for gametogenesis in Arabidopsis thaliana. AOG1 is expressed predominantly in reproductive tissues including the developing pollen grains and ovules. The AOG1 protein shares no signi ficant amino acid sequence similarity with other documented proteins and is located mainly in nuclei of the cells. Mutation in AOG1 caused degeneration of pollen at the uninucleate microspore stage and severe defect in embryo sacs, leading to a signi ficant reduction in male and female fertility.Furthermore, the molecular analyses showed that the aog1 mutant signi ficantly affected the expression of several genes, which are required for gametogenesis. Our results suggest that AOG1 plays important roles in gameto genesis at the stage prior to pollen mitosis I(PMI)in Arabidopsis, possibly through collaboration with other genes.     

Cytological analysis and genetic control of rice anther development

Microsporogenesis and male gametogenesis are essential for the alternating life cycle of flowering plants between diploid sporophyte and haploid gametophyte generations.Rice (Oryza sativa) is the world's major staple food,and manipulation of pollen fertility is particularly important for the demands to increase rice grain yield.Towards a better understanding of the mechanisms controlling rice male reproductive development,we describe here the cytological changes of anther development through 14 stages,including cell division,differentiation and degeneration of somatic tissues consisting of four concentric cell layers surrounding and supporting reproductive cells as they form mature pollen grains through meiosis and mitosis.Furthermore,we compare the morphological difference of anthers and pollen grains in both monocot rice and eudicot Arabidopsis thaliana.Additionally,we describe the key genes identified to date critical for rice anther development and pollen formation.     

The Arabidopsis MALE STERILITY 2 protein shares similarity with reductases in elongation/condensation complexes

The Arabidopsis thaliana MALE STERILITY 2 ( MS2 ) gene product is involved in male gametogenesis. The first abnormalities in pollen development of ms2 mutants are seen at the stage in microsporogenesis when microspores are released from tetrads. Expression of the MS2 gene is observed in tapetum of wild-type flowers at, and shortly after, the release of microspores from tetrads. The MS2 promoter controls GUS expression at a comparable stage in the tapetum of transgenic tobacco containing an MS2 promoter–GUS fusion. The occasional pollen grains produced by mutant ms2 plants have very thin pollen walls. They are also sensitive to acetolysis treatment, which is a test for the presence of an exine layer. The MS2 gene product shows sequence similarity to a jojoba protein that converts wax fatty acids to fatty alcohols. A possible function of the MS2 protein as a fatty acyl reductase in the formation of pollen wall substances is discussed.     

AtSAP130/AtSF3b-3 function is required for reproduction in Arabidopsis thaliana

Flowering plants produce multicellular gametophytes through an elaborate regulation of gametogenesis. During female and male gametogenesis in Arabidopsis thaliana, sporogenous cells differentiate and undergo meiosis to produce megaspores and microspores, which in turn go through mitosis to develop into multicellular gametophytes. Here we report that the Arabidopsis spliceosomal protein, SPLICEOSOME-ASSOCIATED PROTEIN 130 (AtSAP130), is required for proper reproduction. AtSAP130 is encoded by two genes, AtSAP130a and AtSAP130b. Plants with reduced expression of the AtSAP130 genes, induced by RNA interference, showed a defect in fertilization. Besides functional impairment observed in the female reproductive organs, analysis focusing on pollen development revealed defects in the transition from the microspore to the bicellular stage. Our results suggest that AtSAP130a and AtSAP130b play an indispensable role in specific spatiotemporal events in reproduction.     

SLOW WALKER1, essential for gametogenesis in Arabidopsis, encodes a WD40 protein involved in 18S ribosomal RNA biogenesis

The progression of mitotic division cycles and synchronous development between and within the male and female reproductive organs are essential for plant sexual reproduction. Little is known about the genetic control of the progression of mitotic cycles of the haploid genome during gametogenesis in higher plants. Here, we report the phenotypic and molecular characterization of an Arabidopsis thaliana mutant, slow walker1 (swa1), in which the progression of the mitotic division cycles of the female gametophyte was disrupted. Confocal microscopy revealed that megagametophyte development was asynchronous in swa1, causing embryo sacs to arrest at two-, four-, or eight-nucleate stages within the same pistil. A delayed pollination experiment showed that a small fraction of the swa1 embryo sacs were able to develop into functional female gametophytes. The swa1 mutation also showed a slight reduction in penetrance through the male gametophyte, although the pollen grains were morphologically normal. Molecular analysis indicates that SWA1 encodes a protein with six WD40 repeats that is localized in the nucleolus in interphase cells. The SWA1 gene is expressed in cells undergoing active cell divisions, including functional megaspores and the female gametophytic cells. RNA interference results indicated that knockout of SWA1 inhibited root growth significantly and led to the accumulation of unprocessed 18S pre-rRNA. These data suggest that SWA1 most likely plays a role in rRNA biogenesis that is essential for the progression of the mitotic division cycles during gametogenesis in plants.     

The ubiquitin-specific protease subfamily UBP3/UBP4 is essential for pollen development and transmission in Arabidopsis

Deubiquitinating enzymes are essential to the ubiquitin (Ub)/26S proteasome system where they release Ub monomers from the primary translation products of poly-Ub and Ub extension genes, recycle Ubs from polyubiquitinated proteins, and reverse the effects of ubiquitination by releasing bound Ubs from individual targets. The Ub-specific proteases (UBPs) are one large family of deubiquitinating enzymes that bear signature cysteine and histidine motifs. Here, we genetically characterize a UBP subfamily in Arabidopsis (Arabidopsis thaliana) encoded by paralogous UBP3 and UBP4 genes. Whereas homozygous ubp3 and ubp4 single mutants do not display obvious phenotypic abnormalities, double-homozygous mutant individuals could not be created due to a defect in pollen development and/or transmission. This pollen defect was rescued with a transgene encoding wild-type UBP3 or UBP4, but not with a transgene encoding an active-site mutant of UBP3, indicating that deubiquitination activity of UBP3/UBP4 is required. Nuclear DNA staining revealed that ubp3 ubp4 pollen often fail to undergo mitosis II, which generates the two sperm cells needed for double fertilization. Substantial changes in vacuolar morphology were also evident in mutant grains at the time of pollen dehiscence, suggesting defects in vacuole and endomembrane organization. Even though some ubp3 ubp4 pollen could germinate in vitro, they failed to fertilize wild-type ovules even in the absence of competing wild-type pollen. These studies provide additional evidence that the Ub/26S proteasome system is important for male gametogenesis in plants and suggest that deubiquitination of one or more targets by UBP3/UBP4 is critical for the development of functional pollen.     

The Arabidopsis dynamin-related protein2 family is essential for gametophyte development

Clathrin-mediated membrane trafficking is critical for multiple stages of plant growth and development. One key component of clathrin-mediated trafficking in animals is dynamin, a polymerizing GTPase that plays both regulatory and mechanical roles. Other eukaryotes use various dynamin-related proteins (DRP) in clathrin-mediated trafficking. Plants are unique in the apparent involvement of both a family of classical dynamins (DRP2) and a family of dynamin-related proteins (DRP1) in clathrin-mediated membrane trafficking. Our analysis of drp2 insertional mutants demonstrates that, similar to the DRP1 family, the DRP2 family is essential for Arabidopsis thaliana development. Gametophytes lacking both DRP2A and DRP2B were inviable, arresting prior to the first mitotic division in both male and female gametogenesis. Mutant pollen displayed a variety of defects, including branched or irregular cell plates, altered Golgi morphology and ectopic callose deposition. Ectopic callose deposition was also visible in the pollen-lethal drp1c-1 mutant and appears to be a specific feature of pollen-defective mutants with impaired membrane trafficking. However, drp2ab pollen arrested at earlier stages in development than drp1c-1 pollen and did not accumulate excess plasma membrane or display other gross defects in plasma membrane morphology. Therefore, the DRP2 family, but not DRP1C, is necessary for cell cycle progression during early gametophyte development. This suggests a possible role for DRP2-dependent clathrin-mediated trafficking in the transduction of developmental signals in the gametophyte.