Genes Involved in the Regulation of Seed Germination

种子萌发是植物生命周期中的一个关键阶段，在生态学和农业学上都是如此，并且对内源激素和环境因素都很敏感。 种子整合生理和环境信息，以确定是否发芽或保持休眠。 两种重要的发芽生理调节剂是通常促进发芽的赤霉素（GA）和发芽抑制剂脱落酸（阿坝）。 发芽行为的一个关键环境决定因素是水的可用性，因为胚根的出现需要吸水和细胞扩张。 番茄中的单基因突变阻断GA或阿坝的合成，导致对休眠、发芽率和对水分供应减少的敏感性的对比效应。 这些突变体已被用于与激素的应用相结合，以证明通过改变水势阈值，允许胚根出现的萌发的调节发生。 建立了一个能描述种子萌发对植物生长调节剂GA和阿坝以及种子水势响应的定量数学模型。 这是一个关键的特点是认识到，个别种子不同的阈值响应GA，阿坝和水势。 番茄种子萌发的敏感阈值是由薄胚乳层对胚根穿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弱化，允许胚根出现。 成功完成发芽可能需要多种因素，它们的综合影响设定了给定种子的敏感性阈值。 这个项目的目标是确定从静止或休眠到萌发的转变是否与基因表达的特定变化有关。 利用差异显示反转录PCR技术研究了GA和阿坝对突变体番茄内囊帽中mRNA表达的影响。 吸收的野生型种子也将在可见发芽之前使用单个种子测定分选成休眠和非休眠类别。 两类胚乳帽中表达的mRNA将类似地显示。 在所有比较中始终与休眠或萌发相关的信息将通过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GA、阿坝和水势的调节。 将使用组织打印在单个种子中研究在一系列激素和环境条件下选定基因的表达，以确定它们是否在种群内的种子中受到调节，以保持阈值模型的预测。 这种方法将区分基因参与调控胚根出现与那些与萌发后的事件，如储备动员。 这些基因及其启动子的功能的表征将提供深入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.