Ovule Development in Higher Plants

胚珠是植物生殖的基本单位，产生雌性配子体，调节受精过程，支持胚胎的发育。这项提议的长期目标是通过分析Fischer博士实验室克隆的两个拟南芥基因BELL1 （BEL1）和ovule MUTATION2 （OVM2）来了解控制胚珠早期发育的遗传回路。BEL1基因产物在胚珠身份的规范中起作用。bel1突变体的胚珠经常转化为心皮样结构，对bel1基因的分离和测序表明，它编码一种同源结构域转录因子。据认为，BEL1基因通过负向调控花同源基因AGAMOUS（AG）的表达来阻止心皮发育程序超越胚珠发育。OVM2基因产物在不同的阈值水平下分别控制胚珠和雌性配子体的发育。没有活性的OVM2蛋白，胚珠和雌性配子体的发育都会受到显著抑制，而低水平的OVM2蛋白会导致缺乏雌性配子体的无功能胚珠。OVM2基因的分离和测序表明，该基因与花同源基因aptala2 （AP2）有关。因此，BEL1和OVM2基因是调控胚珠和雌性配子体发育的重要基因，其突变可导致同种异体转化和器官缺失。为了了解它们的作用机制，控制早期胚珠发育的关键步骤，以及胚珠与花发育程序之间的关系，将进行实验：1)确定BEL1和OVM2活性的时空定位，2)确定胚珠与花调控基因的遗传关系，3)对BEL1和OVM2功能进行分子分析，4)进行遗传筛选，发现控制巨体发育的新基因。* * *

9505813 Fischer The ovule is a fundamental unit of plant reproduction that generates the female gametophyte, mediates fertilization processes, and support the development of the embryo. The long term goal of this proposal is to understand the genetic circuits that control the early development of the ovule by analyzing two Arabidopsis genes, BELL1 (BEL1) and OVULE MUTATION2 (OVM2), that were cloned in Dr. Fischer's laboratory. The BEL1 gene product plays a role in the specification of ovule identity. bel1 mutant ovules are often transformed into carpel like structures, isolation and sequencing of the BEL1 gene indicates that it encodes a homeodomain transcription factor. It is thought that the BEL1 gene prevents the carpel developmental program from over-riding ovule development by negatively regulating expression of the floral homeotic gene, AGAMOUS(AG). The OVM2 gene product is needed at distinct threshold levels to control ovule and female gametophyte development, respectively. With no active OVM2 protein, both ovule and female gametophyte development are dramatically suppressed, whereas a low level of OVM2 protein results in nonfunctional ovules that specifically lack a female gametophyte. Isolation and sequencing of the OVM2 gene indicates that it is related to the floral homeotic gene APETALA2 (AP2). Thus, BEL1 and OVM2 genes are important regulators of ovule and female gametophyte development, with mutations resultilg in homeotic conversions and deletions of organs. To understand their mechanism of action, the critical steps that control early ovule development, and the relationship between ovule and floral developmental programs, experiments will be carried out to: 1) Determine the temporal and spatial localization of BEL1 and OVM2 activity, 2) Determine the genetic relationships between ovule and floral regulatory genes, 3) Carry out a molecular analysis of BEL1 and OVM2 function, and 4) Carry out a genetic screen to identify new genes that control megagametogenesis. ***