Molecular Genetic Analysis of Plant Circadian Rhythms

在没有环境时间提示的情况下，大约每隔24小时重复一次的节律生物现象被称为昼夜节律，其时间由内源生物钟调节。昼夜节律在任何特定的生物体和不同的类群中都是普遍存在的。遗传和分子生物学研究，主要是在模式生物体的子集中，已经开始确定昼夜节律系统的组成部分。尽管植物提供了许多节律输出的例子，我们对昼夜节律输入途径的光感受器的了解也很深入，但植物在识别中央昼夜节律振荡器的组成部分方面一直落后。增加对植物对环境输入和内源时间线索的反应的理解具有重要的农业意义，特别是因为环境线索和生物钟都有助于光周期决定开花。此外，对生物和非生物胁迫的反应存在时间上的差异，这可能被证明与提高农业生产力的努力特别相关。利用由气孔和气体交换的昼夜节律引起的对SO2暴露的抗性/敏感性的昼夜节律，已分离到影响生物钟功能的突变体，称为昼夜节律缺陷(CTD)和异相(OOP)。例如，oop1和oop2分别代表光感受器光敏色素B和隐花色素1的新等位基因。PhyBoop1和Cry1oop2影响昼夜节律的分子机制的确定将有助于深入了解昼夜节律这一完整但鲜为人知的方面。PhyBoop1和Cry1oop2以半显性方式影响蓝光和红光信号，这表明突变蛋白滴定红光和蓝光信号通路的共同成分，为时钟提供光输入。鉴定与PhyBoop1和Cry1oop2相互作用的蛋白质是阐明这一途径的一个重要目标。第二个目标是克隆长周期突变体ctd2，并对其进行遗传和分子表征。虽然目前尚未确定CTD2基因编码中枢时钟振荡器的一个组成部分，但CTD2突变体的鉴定和CTD2基因的分离将有助于阐明时钟功能的机制。CTD2基因及其产物的潜在功能包括作为中央振荡器的组成部分，作为向时钟提供环境信息的输入通路的组成部分，以及将时钟的时间信息传递到公开的节律现象的输出通路的组成部分。

Rhythmic biological phenomena which recur at approximately 24 hour intervals in the absence of environmental time cues are termed circadian rhythms, and their timing is regulated by an endogenous biological clock. Circadian rhythms are widespread both within any given organism and among diverse taxa. Genetic and molecular biological studies, primarily in a subset of model organisms, have begun to identify the components of circadian systems. Although plants have provided many examples of rhythmic outputs and our understanding of photoreceptors of circadian input pathways is well-advanced, plants have lagged in the identification of components of the central circadian oscillator. Increased understanding of plant responses to environmental input and to endogenous temporal cues has agricultural importance, in particular because both environmental cues and the circadian clock contribute to the photoperiodic decision to flower. In addition, there is temporal variation in the response to biotic and abiotic stresses, which may prove particularly relevant to attempts to increase agricultural productivity. Arabidopsis mutants affected in clock function, termed circadian timing defective (ctd) and out of phase (oop), have been isolated using the circadian rhythm in resistance/sensitivity to SO2 exposure that results from circadian rhythms in stomatal aperture and gas exchange. For example, oop1 and oop2 represent novel alleles of the photoreceptors PHYTOCHROME B and CRYPTOCHROME 1, respectively. The determination of the molecular mechanisms by which phyBoop1 and cry1oop2 affect circadian phase will afford insight into this integral but poorly understood aspect of circadian rhythmicity. phyBoop1 and cry1oop2 affect both blue and red light signaling in a semi-dominant manner, suggesting that the mutant proteins titrate components common to red and blue light signaling pathways that provide photic input to the clock. The identification of proteins interacting with phyBoop1 and cry1oop2 represents an important goal in the elucidation of this pathway. A second goal is the cloning and the genetic and molecular characterization of a long period mutant, ctd2. Although it has not yet been established that the CTD2 gene encodes a component of a central clock oscillator, the characterization of the ctd2 mutant and the isolation of the CTD2 gene will contribute to the elucidation of the mechanisms of clock function. Potential functions for the CTD2 gene and its product include roles as a component of the central oscillator, as a component of input pathways that provide environmental information to the clock, as well as a component of output pathways that transmit temporal information from the clock to the overtly rhythmic phenomena.