Molecular Genetic Analysis of Plant Circadian Rhythms

在没有环境时间提示的情况下，节律性生物现象每隔大约24小时重复一次，称为昼夜节律，其时间由内源性生物钟调节。昼夜节律在任何给定的生物体和不同的分类群中都是广泛存在的。遗传和分子生物学研究，主要是在模式生物的一个子集中，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理解也很先进，但植物在识别中央昼夜节律振荡器的组成部分方面落后。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，特别是因为环境线索和昼夜节律钟都有助于光周期决定开花。此外，对生物和非生物压力的反应存在时间差异，这可能与提高农业生产力的努力特别相关。受生物钟功能影响的拟南芥突变体，被称为昼夜节律时序缺陷（ctd）和相位失调（oop），已经被分离出来，利用对二氧化硫暴露的抗性/敏感性的昼夜节律，这是由气孔孔径和气体交换的昼夜节律引起的。例如，oop1和oop2分别代表光感受器光敏色素B和CRYPTOCHROME 1的新等位基因。确定phyBoop1和cry10op2影响昼夜节律的分子机制将有助于深入了解昼夜节律的这一完整但鲜为人知的方面。phyBoop1和cry10op2以半显性方式影响蓝光和红光信号传导，这表明突变蛋白对红光和蓝光信号传导途径中常见的组分进行了调节，这些组分为生物钟提供光输入。鉴定与phyBoop1和cry10op2相互作用的蛋白是阐明这一途径的重要目标。第二个目标是克隆和长周期突变ctd2的遗传和分子特征。虽然目前尚未确定CTD2基因编码中央时钟振荡器的组成部分，但CTD2突变体的表征和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一个组成部分，作为向时钟提供环境信息的输入途径的一个组成部分，以及作为从时钟向明显节律现象传递时间信息的输出途径的一个组成部分。

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.