Female gamete specification in flowering plants

第1部分：非技术性种子在人类和牲畜的饮食中提供了相当大一部分蛋白质和卡路里。种子的形成需要称为配子的特殊细胞，这些细胞在花中发育。从机制上理解植物是如何产生配子的，可以提高种子作物的种子质量和数量。该项目将阐明发生在花器官内的配子形成过程中潜在的基因和遗传网络。该项目还将为本科生、研究生和博士后研究人员提供植物遗传学和发育方面的培训。兰斯顿大学是一所以本科生为主、历史上以黑人为主的大学，它的一项外展计划将刺激少数族裔本科生参与植物生物学研究。技术：开花植物产生两种类型的雌配子，卵细胞和中央细胞，这两种配子都是在单倍体胚囊中指定的，该胚囊在胚珠减数分裂后发育。卵细胞是单倍体，由胚囊远端的单个核指定，而中央细胞是同源二倍体，由两个核指定，分别来自胚囊的每一极。通过花粉对雌配子进行双重受精，产生一个种子，该种子含有从卵细胞产生的二倍体胚胎，以及从中央细胞产生的三倍体营养组织--胚乳。两个具有非常不同特征的雌配子被指定的分子机制在很大程度上还没有确定。先前的研究表明，CKI1基因编码细胞分裂素信号通路的组氨酸激酶激活物，在模式植物拟南芥的雌配子指定中起着关键作用。CKI1表达缺失会导致中央细胞转化为卵细胞，导致种子发育受阻。CKI1的异位表达导致卵细胞转化为中央细胞，产生具有双胚乳的种子，而没有胚胎。结合对发育中胚囊中CKI1蛋白定位的观察，建立了一种通过CKI1在胚囊近端区域的差异表达和定位来控制雌配子指定的模型。这个项目将确定和表征在雌配子体中作用于CKI1上游和下游的因子。激活或限制CKI1表达的转录因子将通过筛选CKI1的上游调控因子来识别。候选调控基因将通过基因分析来确定其功能特征。将通过使用突变反应调节器测试候选基因的表达来寻找作用于CKI1下游的转录因子，以促进中央细胞的命运。该项目将提供对空间调控网络的见解，该网络指定发育中的雌配子体的细胞身份，以及开花植物中形成雌配子的潜在机制。

Part 1: Non-technicalSeeds provide a significant fraction of the protein and calories in the diets of humans and livestock. Formation of seeds requires specialized cells called gametes that develop within a flower. A mechanistic understanding of how gametes are produced by plants can lead to an improvement of seed quality and quantity in seed crops. This project will elucidate the genes and genetic networks underlying the process of gamete formation occurring within the flower organs. The project will also provide training in plant genetics and development for undergraduate students, graduate students, and postdoctoral researchers. An outreach program with Langston University, a primarily undergraduate and historically black university, will stimulate involvement by minority undergraduate students in plant biology research. Part 2: TechnicalFlowering plants produce two types of female gametes, the egg cell and the central cell, that are both specified within a haploid embryo sac which develops following meiosis in an ovule. The egg cell is haploid, specified from a single nucleus at the distal pole of the embryo sac, whereas the central cell is homodiploid, specified by two nuclei, one from each pole of the embryo sac. Double fertilization of the female gametes by pollen results in a seed containing a diploid embryo arising from the egg cell, and a triploid nourishing tissue, the endosperm, arising from the central cell. The molecular mechanisms by which two female gametes with very distinct characteristics are specified have been largely uncharacterized. Previous research has revealed that the CKI1 gene, encoding a histidine kinase activator of the cytokinin signaling pathway, plays a key role in female gamete specification in the model plant Arabidopsis. Loss of CKI1 expression results in conversion of the central cell to an egg cell leading to arrested seed development. Ectopic expression of CKI1 results in conversion of the egg cell to a central cell, producing seeds with dual endosperms and no embryos. These findings, together with observations of CKI1 protein localization in the developing embryo sac, lead to a model by which female gamete specification is controlled by differential expression and localization of CKI1 to the proximal domain of the embryo sac. This project will identify and characterize factors acting upstream and downstream of CKI1 in the female gametophyte. Transcription factors that activate or restrict CKI1 expression will be identified by screens for upstream regulators of CKI1. Candidate regulatory genes will be functionally characterized by genetic analysis. Transcription factors that act downstream of CKI1 to promote central cell fate will be sought by testing expression of candidate genes using mutant response regulators. The project will provide insights into the spatial regulatory networks that specify cell identities in the developing female gametophyte, and the mechanisms underlying the formation of female gametes in flowering plants.