Ovule Development in Higher Plants

9505813费希尔胚珠是植物繁殖的基本单位，它产生雌配子体，调节受精过程，并支持胚胎的发育。这一提议的长期目标是通过分析在费舍尔博士的实验室克隆的两个拟南芥基因BELL1(BEL1)和胚珠MUTATION2(OVM2)来了解控制胚珠早期发育的遗传电路。BEL1基因产物在胚珠鉴定中起着重要作用。BEL1突变胚珠通常转化为类心皮结构，分离和测序表明BEL1基因编码同源结构域转录因子。据认为，BEL1基因通过负调控花同源异型基因AGAMOUS(AG)的表达，防止心皮发育程序凌驾于胚珠发育之上。OVM2基因产物在不同的阈值水平上分别控制胚珠和雌配子体的发育。在没有活性的OVM2蛋白的情况下，胚珠和雌配子体的发育都会受到显著的抑制，而低水平的OVM2蛋白会导致没有功能的胚珠特别是缺乏雌配子体。OVM2基因的分离和测序表明，它与花同源异型基因APETALA2(AP2)有关。因此，BEL1和OVM2基因是胚珠和雌配子体发育的重要调节基因，突变导致器官的同源异型转换和缺失。为了了解它们的作用机制、控制胚珠早期发育的关键步骤以及胚珠和花发育程序之间的关系，将进行以下实验：1)确定BEL1和OVM2活性的时空定位；2)确定胚珠和花调控基因之间的遗传关系；3)对BEL1和OVM2功能进行分子分析；4)进行遗传筛选，以寻找控制大配子发生的新基因。***

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. ***