Elucidating molecular mechanisms by which seeds respond to environmental factors

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，经典育种所选择的影响产量和逆境反应的关键遗传位点包括一系列激素代谢和信号基因。植物激素代谢受多种环境因素的调节，在调节植物生长以适应环境变化方面起着重要作用。当前植物生物学和生物技术面临的挑战是了解植物如何感知环境因素并改变植物激素代谢。Nambara研究小组研究植物如何控制植物激素水平的细胞浓度，重点是脱落酸(ABA)的新陈代谢。我们使用拟南芥种子萌发作为一个模型系统，因为种子有复杂的机制来感知环境条件。成熟、干燥的种子含有在适当环境中恢复植物生命周期所需的所有成分。种子感知水分、营养物质、温度、后熟和光线，以确定是否存在合适的萌发环境，这些外部信号的变化会改变植物激素代谢和信号，这决定了种子是萌发还是休眠。这项研究旨在阐明种子感知环境信号和调节植物激素代谢的分子机制，重点是硝酸盐如何调节ABA分解代谢和种子萌发。硝酸盐是土壤中存在的一种主要氮源，作为营养物质和信号影响植物的生长发育。作为一种营养，硝酸盐被同化成铵，然后被结合成氨基酸。作为一个信号，低硝酸盐浓度会导致全基因组基因表达的快速重新编程，即使在硝酸盐同化缺陷的突变体中也是如此。硝酸盐能促进许多植物的种子萌发。在硝酸盐同化缺陷突变体中，可以观察到硝酸盐对种子萌发的影响。这表明它起到了刺激发芽的信号作用。我的研究小组之前报告说，硝酸盐可以激活ABA的分解代谢，减少ABA，一种萌发的抑制因子。尽管最近鉴定了硝酸盐感知和信号转导的必要基因，但硝酸盐调节ABA分解代谢的分子机制仍然很大程度上是未知的。这笔赠款的总体目标是研究硝酸盐调节ABA代谢和种子萌发的分子和细胞机制。我的研究小组最近发现了在拟南芥种子萌发过程中调节这些过程的新因素。我们将阐明这些调控因子在种子硝酸盐信号中的分子功能。在硝酸盐有限的条件下稳定作物产量是植物生物技术的一个关键目标，因为可持续的农业实践必须限制昂贵的和可能造成污染的硝酸盐投入。我们的基础研究将有助于获得一种新的解决方案，以提高作物产量，减少作物损失。

Plant hormones are low abundant signal molecules, which significantly influence a variety of processes in plant growth and development. Functional genomics research in cereals has revealed that key genetic loci for yield production and stress responses selected by the classical breeding include a series of hormone metabolism and signaling genes. The plant hormone metabolism is regulated by a number of environmental factors and plays an important role in tuning plant growth in response to changing environment. Current challenge in plant biology and biotechnology is to understand how plants sense the environmental factors and alter the plant hormone metabolism. The Nambara research group studies how plants control cellular concentrations of the plant hormone levels with a focus on abscisic acid (ABA) metabolism. We use Arabidopsis seed germination as a model system, because seeds have sophisticated mechanisms to sense environmental conditions. Mature, dry seeds contain all the components required to resume the plant’s life cycle in an appropriate environment. The seeds sense water, nutrients, temperature, after-ripening, and light to determine if the appropriate germination environment exists, and a change in these external cues alters plant hormone metabolism and signaling, which determine whether seeds germinate or remain dormant. The proposed research aims to elucidate the molecular mechanisms by which seeds sense environmental signals and regulate plant hormone metabolism, with a focus on how nitrate regulates ABA catabolism and seed germination. Nitrate is a major nitrogen source existing in soil and influences plant growth and development as a nutrient and as a signal. As a nutrient, nitrate is assimilated to ammonium and then incorporated into amino acids. As a signal, low nitrate concentration causes rapid reprogramming of genome-wide gene expression, even in mutants defective in nitrate assimilation. Nitrate promotes seed germination in many plant species. The effect of nitrate on germination can be observed in mutants defective in nitrate assimilation. This indicates that it acts as a signal to stimulate germination. My research group previously reported that nitrate activates ABA catabolism and reduces ABA, an inhibitor of germination. Despite recent identification of essential genes for nitrate sensing and signal transduction, the molecular mechanisms by which nitrate regulates ABA catabolism remain largely unknown. The overall goal of this grant is to investigate the molecular and cellular mechanisms involved in nitrate regulation of ABA metabolism and seed germination. My research group has recently identified the novel factor regulating these processes during Arabidopsis seed germination. We will elucidate the molecular function of the regulators in nitrate signaling in seeds. Stable crop yield under nitrate limited condition is a key target for plant biotechnology, because sustainable agricultural practices must limit expensive and potentially polluting nitrate inputs. Our basic research will help to gain a novel solution to increase crop yield and decrease crop losses.