Molecular Genetic Analysis Of Plant Circadian Rhythms

增加对植物对环境输入和内源性时间线索的反应的理解具有农业意义。生物钟整合了时间信息，协调了生物学的许多方面，包括基本代谢和对生物和非生物压力的反应。此外，环境线索和昼夜节律钟有助于光周期开花。内源性时间机制与外部时间的适当协调赋予适应性优势，而昼夜节律功能受损与适应性降低有关。模式植物拟南芥（Arabidopsis thaliana）为研究昼夜节律的分子机制提供了一个强大且易于实验处理的系统。由于植物是密切相关的，从拟南芥研究中获得的认识很可能很容易转移到农艺学上重要的物种。在气候变化和需要开发日益边缘化的栖息地的背景下，更充分地了解时钟机制可能为提高作物生产力提供策略。本项目主要研究拟南芥（Arabidopsis thaliana）家族的5个伪反应调控因子（Pseudo-Response Regulators, PRRs）。突变分析表明，尽管个体发挥着不同的作用，但它们对昼夜节律系统都很重要。事实上，拟南芥中第一个真正意义上的时钟突变体是prr1，也被称为toc1。该突变体是根据叶片运动和基因表达监测的昼夜周期缩短而分离出来的。Toc1突变体在光周期诱导开花方面也表现出缺陷。本项目重点研究PRR9和PRR7。这些基因座的突变赋予了与其他PRR基因座不同的表型——prr9表现为滞后期，prr7表现为长周期，而包括TOC1在内的其他三个家族成员的突变缩短了这一时期。双prr7 prr9突变体在白光下的表型夸张（非常长周期，非常滞后期），这表明prr7和prr9之间存在部分功能冗余。PRR7和PRR9的生物钟缺陷出现在光-暗周期或温度（暖-冷）周期之后。这表明PRR7和PRR9在环境信号的感知或转导中起着核心作用。也有可能这些PRRs可能在中心振荡器中起作用，类似于TOC1 (PRR1)，它被认为是拟南芥时钟的关键组成部分。该项目采用遗传和生化方法来阐明PRR7和PRR9作为输入通路或振荡器本身的组成部分的作用。这些包括过表达，使用双突变和三重突变来评估遗传相互作用，以及筛选增强或抑制prr7或prr9突变表型的第二突变。将测试PRR7和PRR9之间的物理相互作用，并寻求与PRR7和PRR9的其他相互作用。

Increased understanding of plant responses to environmental input and to endogenous temporal cues has agricultural importance. The clock integrates temporal information and coordinates many aspects of biology, including basic metabolism and responses to biotic and abiotic stresses. Additionally, environmental cues and the circadian clock contribute to the photoperiodic flowering. Proper coordination of the endogenous timing mechanism with the external day confers adaptive advantage, and impaired circadian function is associated with reduced fitness. The model plant, Arabidopsis thaliana, offers a powerful and experimentally tractable system in which to investigate the molecular mechanisms of circadian rhythmicity. Because plants are closely related, it is quite likely that understanding derived from Arabidopsis studies will be readily transferred to agronomically important species. In the context of climate change and the need to exploit increasingly marginal habitats, fuller understanding of clock mechanism may offer strategies to improve crop productivity.This project focuses on the Arabidopsis thaliana family of five Pseudo-Response Regulators (PRRs). Mutational analysis indicates that each is important to the circadian system, although individuals play distinct roles. Indeed, the first bona fide clock mutant in Arabidopsis was prr1, known also as toc1. This mutant was isolated on the basis of a shortened circadian period as monitored by leaf movement and by gene expression. toc1 mutants also exhibit defects in photoperiodic induction of flowering. This project focuses on PRR9 and PRR7. Mutation of these loci confers phenotypes distinct from those of the other PRR loci-prr9 exhibits lagging phase and prr7 exhibits long period, whereas mutation of the other three family members, including TOC1, shortens the period. The double prr7 prr9 mutant has an exaggerated phenotype in white light (very long period, very lagging phase), which suggests partial functional redundancy between PRR7 and PRR9. The clock defects of PRR7 and PRR9 are seen following entrainment either to light-dark cycles or to temperature (warm-cool) cycles. This argues for a central role of PRR7 and PRR9 in the perception or transduction of environmental signals. It is also possible that these PRRs may act within the central oscillator, analogously to TOC1 (PRR1), which is accepted as a crucial component of the Arabidopsis clock. This project employs genetic and biochemical approaches to elucidate the roles of PRR7 and PRR9 as components of input pathways or of the oscillator itself. These include overexpression, use of double and triple mutants to assess genetic interaction, and screens for second mutations that enhance or suppress prr7 or prr9 mutant phenotypes. Physical interaction between PRR7 and PRR9 will be tested, and other interactors with PRR7 and PRR9 will be sought.