Female gamete specification in flowering plants

第1部分：非技术种子在人类和牲畜的饮食中提供了很大一部分蛋白质和卡路里。种子的形成需要一种叫做配子的特殊细胞，这种细胞在花中发育。对植物产生配子的机理的理解可以提高种子作物的种子质量和数量。本项目将阐明在花器官中配子形成过程的基因和遗传网络。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。与兰斯顿大学（Langston University）合作的一个拓展项目将鼓励少数族裔本科生参与植物生物学研究。兰斯顿大学是一所以本科生为主的历史悠久的黑人大学。开花植物产生两种类型的雌性配子，卵细胞和中心细胞，它们都被指定在一个单倍体胚囊中，在胚珠减数分裂后发育。卵细胞是单倍体，在胚囊的远端有一个核，而中央细胞是同二倍体，有两个核，在胚囊的两端各有一个核。雌性配子通过花粉的双重受精产生的种子包含由卵细胞产生的二倍体胚胎和由中央细胞产生的三倍体滋养组织——胚乳。两个具有非常明显特征的雌性配子被指定的分子机制在很大程度上尚未被描述。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因子，在模式植物拟南芥的雌性配子规范中起关键作用。CKI1表达缺失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心细胞，产生双胚乳而无胚胎的种子。这些发现，再加上对发育中的胚囊中CKI1蛋白定位的观察，导致了一个模型，通过该模型，雌性配子的规格是由CKI1在胚囊近端区域的差异表达和定位控制的。本项目将确定和表征在雌性配子体中作用于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的上游调节因子来确定。候选调控基因将通过遗传分析进行功能表征。通过使用突变反应调节因子测试候选基因的表达，将寻找在CKI1下游作用以促进中枢细胞命运的转录因子。该项目将深入研究发育中的雌性配子体细胞身份的空间调控网络，以及开花植物中雌性配子体形成的机制。

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.