Genetic Control of Polar Nuclei Number in Maize Embryo Sacs

0080353与动物不同，减数分裂的单倍体产物不会分化为配子，而是经历几轮细胞分裂，产生产生配子的多细胞配子体。这在拥有大型自由生活配子体的低等植物中很明显，但在被子植物中也是如此，被子植物的配子体尺寸大大缩小。在拟南芥和玉米中，雌配子体的发育始于减数分裂产物中的一个经历三轮自由核分裂，然后细胞化，形成七细胞胚囊。自由核分裂在数量上是不变的，它们的同步性表明它们受到严格的控制，并伴随着刻板印象的核迁移。胚囊由四种细胞类型组成：反足细胞、中央细胞、助细胞和卵细胞。为了进一步了解雌配子体发育的遗传调控，将以玉米为模式系统，详细描述在受精后形成胚乳的中央细胞中具有过剩极核的突变体的特征。玉米胚乳发育对单个极核的增加或减少的敏感性为这些突变体提供了一个敏感的筛选。这些突变体预计会影响两个基本过程中的一个或两个：核定位和分割或对自由核分裂的负调控。已经确定了几个具有过剩极性核的突变体，并开始描述它们的特征。在这些突变体中产生额外极核的机制将通过使用共聚焦激光扫描显微镜研究胚囊个体发育来确定。基因之间的相互作用将通过构建它们之间的双突变来确定。通过对现有突变体集合的遗传筛选和与当前基因组计划的合作，将识别出更多具有额外极核的突变体。对这些基因中最具特征的基因之一--不确定配子体的分子分析正在启动。对这些基因及其相互作用的详细分析将有助于更好地了解胚囊发育，特别是控制核分裂和位置的基本调控。

0080353KermicleIn contrast to animals, the haploid products of meiosis do not differentiate into the gametes but undergo a few rounds of cell division to produce a multicellular gametophyte which produces the gametes. This is obvious in lower plants with large free-living gametophytes but is also the case in angiosperms, the gametophytes of which are highly reduced in size. Female gametophyte development in Arabidopisis and maize, begins when one of the products of meiosis undergoes three rounds of free nuclear division followed by cellularization to give rise to a seven celled embryo sac. The free nuclear divisions are invariant in number, tightly regulated as indicated by their synchrony, and accompanied by stereotypical nuclear migrations. The embryo sac consists of four cell types: the antipodal cells, the central cell, the synergids, and the egg. To further understand genetic regulation of female gametophyte development, mutants with excess polar nuclei in the central cell, which upon fertilization gives rise to the endosperm, are to be characterized in detail using maize as a model system. The sensitivity of maize endosperm development to the addition or subtraction of a single polar nucleus provides a sensitive screen for these mutants. These mutants are expected to affect one or both of two basic processes: nuclear positioning and partitioning or negative regulation of free nuclear divisions. Several mutants with excess polar nuclei have already been identified, and their characterization begun. The mechanism by which extra polar nuclei are produced in these mutants is to be determined by studying embryo sac ontogeny using confocal laser scanning microscopy. Interactions between the genes are to be determined by constructing double mutants between them. More mutants with extra polar nuclei are to be identified through genetic screens of existing mutant collections and collaborations with current genome projects. Molecular analysis of one of the best characterized of these genes, indeterminate gametophytel, is being initiated. A detailed analysis of these genes and their interactions should provide greater understanding of embryo sac development, particularly control of basic regulation of nuclear division and position.