Elucidating regulatory mechanisms for the expression of an Arabidopsis abscisic acid 8'-hydroxylase gene in response to environmental signals

植物激素是一种低丰度的信号分子，对植物生长发育的多种过程具有重要影响。功能基因组学研究表明，经典育种选择的产量和胁迫反应的关键遗传位点编码了一系列激素代谢和信号基因。植物激素的代谢受多种环境因子的调控，在调节植物生长及其对环境变化的响应中起着重要作用。该研究计划旨在了解种子如何对环境变化做出反应的分子机制：水分和成熟后。植物激素脱落酸（ABA）调节许多发育和生理过程，包括种子休眠和发芽。干种子大量积累ABA，在吸胀过程中ABA水平下降，这是种子萌发的关键关卡。种子吸胀过程中ABA水平的下降受CYP707A2基因调控，该基因编码的P450单加氧酶负责ABA的分解代谢。CYP707A2的表达受硝酸盐、水分、后熟、光照、温度等多种环境信号的调控。Nambara实验室以拟南芥为模型系统，研究了种子中CYP707A2的表达如何受到这些环境信号的调节。遗传和表达分析表明，CYP707A2的转录调控是环境信号传导的枢纽，并决定种子是否发芽。种子吸胀是种子萌发过程的第一步。我的研究小组已经证明，在种子吸胀的早期阶段，休眠和非休眠种子都需要从头转录，并且表现出相似的转录组特征，这表明种子吸胀涉及对水的积极响应机制。在种子吸胀过程中，CYP707A2的表达上调，而在限制水分吸收条件下，种子吸胀使CYP707A2的表达降低。后熟期是一段干燥的种子贮藏期，在此期间种子的性能和萌发受到影响。我课题组之前的研究表明，催熟后增强了CYP707A2的表达，CYP707A2缺陷突变体需要延长催熟后的萌发时间。然而，这些环境信号如何影响CYP707A2表达的分子机制仍不清楚。我们将重点研究CYP707A2对水分和成熟后的转录调控。此外，该计划将研究这些环境因素（即水分和成熟后）如何影响种子对硝酸盐的响应性。在变化的环境下稳定的种子萌发和随后的幼苗建立是植物生物技术的关键目标。我们的研究将有助于为稳定和可持续的农业实践选择优良作物品种提供新的解决方案。

Plant hormones are low abundant signal molecules, which significantly impact a variety of processes in plant growth and development. Functional genomics research has revealed that key genetic loci selected by classical breeding for yield and stress responses encode a series of hormone metabolism and signaling genes. The metabolism of plant hormones is regulated by a number of environmental factors and play an important role in tuning plant growth and its response to changing environment. The proposed research program aims to understand the molecular mechanism of how seeds respond to environmental changes: water and after-ripening. The phytohormone abscisic acid (ABA) regulates numerous developmental and physiological processes including seed dormancy and germination. Dry seeds accumulate ABA at a high level, and the ABA levels decrease during seed imbibition (water uptake), which is a critical checkpoint for seed germination. The decrease in seed ABA levels during seed imbibition is regulated by CYP707A2, a gene encoding a P450 monooxygenase responsible for ABA catabolism. The expression of CYP707A2 is regulated by multiple environmental signals, such as nitrate, water, after-ripening, light and temperature. The Nambara lab has studied how the expression of CYP707A2 in seeds is regulated by these environmental signals using Arabidopsis as a model system. Genetic and expression analyses have suggested that transcriptional regulation of CYP707A2 is a hub of environmental signaling and determines whether seeds germinate or not. Seed imbibition is the first step in the seed germination processes. My research group has demonstrated that, during the early stage of seed imbibition, both dormant and non-dormant seeds require de novo transcription and exhibit similar transcriptiome profiles, suggesting that seed imbibition involves active mechanisms in response to water. While the expression of CYP707A2 is up-regulated during seed imbibition, seed imbibition under restricted water uptake reduces the expression of CYP707A2. After-ripening is a period of dry seed storage where seed performance and germination are affected. My research group previously demonstrated that after-ripening enhances the expression of CYP707A2, and mutants defective in CYP707A2 require a prolonged period of after-ripening for germination. However, the molecular mechanisms underlying how these environmental signals affect the expression of CYP707A2 remains largely unclear. We will focus on transcriptional regulation of CYP707A2 in response to water and after-ripening. Moreover, this program will investigate how these environmental factors (i.e. water and after-ripening) affect seed responsiveness to nitrate. Stable seed germination and subsequent seedling establishment under changing environments is a key target for plant biotechnology. Our research will help to gain a novel solution to select elite crop varieties for stable and sustainable agricultural practices.