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逆境反应的关键遗传位点编码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素的调节，在调节植物生长及其对环境变化的反应中起着重要作用。这项拟议的研究计划旨在了解种子对环境变化(水分和后成熟)做出反应的分子机制。 植物激素脱落酸(ABA)调节种子休眠和萌发等多种发育和生理过程。干燥的种子积累高水平的ABA，在种子吸胀(吸水)过程中ABA水平下降，这是种子萌发的关键检查点。种子吸胀过程中ABA水平的下降受CYP707A2基因的调节，该基因编码一种负责ABA分解代谢的P450单加氧酶。CYP707A2的表达受多种环境信号的调控，如硝酸盐、水分、后熟、光和温度等。Nambara实验室以拟南芥为模型系统，研究了这些环境信号如何调控种子中CYP707A2的表达。遗传和表达分析表明，CYP707A2的转录调控是环境信号的枢纽，决定着种子是否萌发。 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，休眠和非休眠的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分的反应的活跃机制。虽然种子吸胀过程中细胞色素P707A2的表达上调，但限制吸水条件下的种子吸胀降低了细胞色素P707A2的表达。后熟是种子干储存期，种子的表现和发芽都会受到影响。我的研究小组之前证明了后成熟增强了CYP707A2的表达，而在CYP707A2中存在缺陷的突变株需要长时间的后成熟才能萌发。然而，这些环境信号如何影响CYP707A2表达的分子机制在很大程度上仍不清楚。 我们将重点研究CYP707A2对水分和后成熟的转录调控。此外，该项目将调查这些环境因素(即水分和后成熟)如何影响种子对硝酸盐的反应。在不断变化的环境中稳定的种子萌发和随后的成苗是植物生物技术的一个重要目标。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一种新的解决方案。

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.