Genes Involved in the Regulation of Seed Germination

种子萌发是植物生态和农业生命周期的关键阶段，对内源激素和环境因素都很敏感。种子综合了生理和环境信息来决定是发芽还是休眠。两个重要的发芽生理调节剂是赤霉素（GA）和脱落酸（ABA），前者通常促进发芽，后者是发芽抑制剂。发芽行为的关键环境决定因素是水分的可用性，因为胚根的萌发需要水分的吸收和细胞的扩张。阻断GA或ABA合成的单基因突变对番茄的休眠、发芽率和对水分利用率降低的敏感性产生了截然不同的影响。这些突变体已与激素应用结合使用，以证明通过改变水势阈值来调节发芽，从而允许胚根出现。建立了种子萌发对植物生长调节剂GA和ABA及种子水势响应的定量数学模型。其中一个关键特征是认识到单个种子对GA、ABA和水势的阈值反应不同。番茄种子萌发的敏感阈值是由胚乳薄层对胚根渗透的机械阻力决定的。当刺激萌发时，这些胚乳帽细胞的壁被降解和削弱，使胚根萌发。成功完成发芽可能需要多种因素，它们的综合影响为给定种子设定了敏感性阈值。该项目的目的是确定从静止或休眠到发芽的转变是否与基因表达的特定变化有关。GA和ABA对突变体番茄胚乳m帽mRNA群体的影响将通过差异显示反转录PCR技术可视化。吸收的野生型种子也将被分为休眠和非休眠类别之前，使用单一种子试验可见发芽。这两种类型的胚乳帽中表达的mrna将被类似地显示出来。在所有比较中，与休眠或发芽一致的信息将通过RNA印迹和原位杂交进行评估，以确定它们的丰度、时间和组织位置是否如预期的那样受到GA、ABA和水势的调节。选择的基因在一系列激素和环境条件下的表达将在单个种子中进行研究，使用组织打印来确定它们是否在种群内的种子中受到调节，以符合阈值模型的预测。这种方法将区分参与调控胚根出现的基因与那些与发芽后事件（如储备动员）相关的基因。这些基因及其启动子的功能特征将有助于了解植物如何整合多种内部和环境信号来控制一个关键的发育过程。

Seed germination is a critical phase in the plant life cycle, both ecologically and agriculturally, and is sensitive to both endogenous hormones and environmental factors. Seeds integrate physiological and environmental information to determine whether to germinate or remain dormant. Two important physiological regulators of germination are gibberellin (GA), which generally promotes germination, and abscisic acid (ABA), an inhibitor of germination. A key environmental determination of germination behavior is the availability of water, since radicle emergence requires water uptake and cell expansion. Single-gene mutations in tomato which block synthesis of either GA or ABA result in contrasting effects on dormancy, germination rates, and sensitivity to reduced water availability. These mutants have been used in combination with hormonal application to demonstrate that the regulation of germination occurs via alterations in the water potential threshold, allowing radicle emergence. A quantitative mathematical model has been developed that can describe the responses of seed germination to the plant growth regulators GA and ABA and to the seed water potential. A key feature of this is the recognition that individual seeds vary in their threshold responses to GA, ABA, and water potential. The sensitivity thresholds for tomato seed germination are determined by the mechanical resistance of a thin endosperm layer to penetration by the radicle. When stimulated to germinate, the walls of these endosperm cap cells are degraded and weakened, allowing radicle emergence. Multiple factors are likely to be required for successful completion of germination, with their combined influence setting the sensitivity threshold for a given seed. The goal of this project is to determine whether the transition from quiescence or dormancy to germination is associated with specific changes in gene expression. The effects of GA and ABA on mRNA populations in mutant tomato endosper m caps will be visualized by a differential display reverse transcription PCR technique. Imbibed wild type seeds will also be sorted into dormant and nondormant categories prior to visible germination using a single seed assay. The mRNAs expressed in the endosperm caps of the two categories will be similarly displayed. Messages that are consistently associated with either dormancy or germination in all comparisons will be evaluated by RNA blot and in situ hybridization to determine whether their abundance, timing and tissue location are regulated by GA, ABA, and water potential as expected. Expression of selected genes under a range of hormonal and environmental conditions will be investigated in single seeds using tissue printing to determine whether they are regulated among seeds within a population in keeping with the predictions of the threshold models. This approach will distinguish genes involved in the regulation of radicle emergence from those that are associated with post-germinative events such as reserve mobilization. Characterization of the function of these genes and their promoters will provide insight into how plants integrate multiple internal and environmental signals to control a critical developmental process.