Nakamichi Norihito, Kita Masanori, Ito Shogo, Yamashino Takafumi, Mizuno Takeshi
Laboratory of Molecular Microbiology, School of Agriculture, Nagoya University, Chikusa-ku, Nagoya, 464-8601 Japan.
Plant Cell Physiol. 2005 May;46(5):686-98. doi: 10.1093/pcp/pci086. Epub 2005 Mar 13.
In Arabidopsis thaliana, a number of clock-associated protein components have been identified. Among them, CCA1 (CIRCADIAN CLOCK-ASSOCIATED 1)/LHY (LATE ELONGATED HYPOCOTYL) and TOC1 (TIMING OF CAB EXPRESSION 1) are believed to be the essential components of the central oscillator. CCA1 and LHY are homologous and partially redundant Myb-related DNA-binding proteins, whereas TOC1 is a member of a small family of proteins, designated as PSEUDO-RESPONSE REGULATOR. It is also believed that these two different types of clock components form an autoregulatory positive/negative feedback loop at the levels of transcription/translation that generates intrinsic rhythms. Nonetheless, it was not yet certain whether or not other PRR family members (PRR9, PRR7, PRR5 and PRR3) are implicated in clock function per se. Employing a set of prr9, prr7 and prr5 mutant alleles, here we established all possible single, double and triple prr mutants. They were examined extensively by comparing them with each other with regard to their phenotypes of circadian rhythms, photoperiodicity-dependent control of flowering time and photomorphogenic responses to red light during de-etiolation. Notably, the prr9 prr7 prr5 triple lesions in plants resulted in severe phenotypes: (i) arrhythmia in the continuous light conditions, and an anomalous phasing of diurnal oscillation of certain circadian-controlled genes even in the entrained light/dark cycle conditions; (ii) late flowering that was no longer sensitive to the photoperiodicity; and (iii) hyposensitivity (or blind) to red light in the photomorphogenic responses. The phenotypes of the single and double mutants were also characterized extensively, showing that they exhibited circadian-associated phenotypes characteristic for each. These results are discussed from the viewpoint that PRR9/PRR7/PRR5 together act as period-controlling factors, and they play overlapping and distinctive roles close to (or within) the central oscillator in which the relative, PRR1/TOC1, plays an essential role.
在拟南芥中，已鉴定出许多与生物钟相关的蛋白质成分。其中，CCA1（生物钟相关1）/LHY（晚伸长下胚轴）和TOC1（CAB表达时间1）被认为是中央振荡器的关键成分。CCA1和LHY是同源且部分冗余的Myb相关DNA结合蛋白，而TOC1是一个小蛋白家族的成员，被称为伪响应调节因子。人们还认为，这两种不同类型的生物钟成分在转录/翻译水平上形成了一个自调节的正/负反馈环，从而产生内在节律。然而，其他PRR家族成员（PRR9、PRR7、PRR5和PRR3）是否本身就参与生物钟功能尚不确定。利用一组prr9、prr7和prr5突变等位基因，我们在此构建了所有可能的单、双和三prr突变体。通过将它们相互比较，对其昼夜节律表型、光周期依赖性开花时间控制以及脱黄化过程中对红光的光形态建成反应进行了广泛研究。值得注意的是，植物中的prr9 prr7 prr5三重损伤导致了严重的表型：（i）在连续光照条件下心律不齐，即使在同步的光/暗周期条件下，某些生物钟控制基因的昼夜振荡也出现异常相位；（ii）开花延迟，不再对光周期敏感；（iii）在光形态建成反应中对红光的敏感性降低（或无反应）。对单突变体和双突变体的表型也进行了广泛表征，表明它们各自表现出与生物钟相关的特征表型。从PRR9/PRR7/PRR5共同作为周期控制因子的角度对这些结果进行了讨论，它们在靠近（或在）中央振荡器的位置发挥重叠且独特的作用，其中相对的PRR1/TOC1起着至关重要的作用。
