Norihito Nakamichi

An interlocking transcriptional-translational feedback loop of clock-associated genes is thought to be the central oscillator of the circadian clock in plants. TIMING OF CAB EXPRESSION1 (also called PSEUDO-RESPONSE REGULATOR1 [PRR1]) and two MYB transcription factors, CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY), play pivotal roles in the loop. Genetic studies have suggested that PRR9, PRR7, and PRR5 also act within or close to the loop; however, their molecular function

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

Arabidopsis PSEUDO RESPONSE REGULATOR (PRR) genes are components of the circadian clock mechanism. In order to understand the scope of genome-wide transcriptional regulation by PRR genes, a comparison survey of gene expression in wild-type Arabidopsis and a prr9-11 prr7-10 prr5-10 triple mutant (d975) using mRNA collected during late daytime was conducted using an Affymetrix ATH-1 GeneChip. The expression of 'night genes' increased and the expression of 'day genes' decreased toward the end of th

The circadian clock is an endogenous time-keeping mechanism that enables organisms to adapt to external daily cycles. The clock coordinates biological activities with these cycles, mainly through genome-wide gene expression. However, the exact mechanism underlying regulation of circadian gene expression is poorly understood. Here we demonstrated that an Arabidopsis PSEUDO-RESPONSE REGULATOR 5 (PRR5), which acts in the clock genetic circuit, directly regulates expression timing of key transcripti

Photoperiodism allows organisms to measure daylength, or external photoperiod, and to anticipate coming seasons. Daylength measurement requires the integration of light signal and temporal information by the circadian clock. In the long-day plant Arabidopsis thaliana, CONSTANS (CO) plays a crucial role in integrating the circadian rhythm and environmental light signals into the photoperiodic flowering pathway. Nevertheless, the molecular mechanism by which the circadian clock modulates the cycli

In Arabidopsis thaliana, a number of clock-associated protein factors have been identified. Among them, TOC1 (TIMING OF CAB EXPRESSION 1) is believed to be a component of the central oscillator. TOC1 is a member of a small family of proteins, designated as ARABIDOPSIS PSEUDO-RESPONSE REGULATOR, including PRR1/TOC1, PRR3, PRR5, PRR7 and PRR9. It has not been certain whether or not other PRR family members are also implicated in clock function per se. To clarify this problem, here we constructed a

A wide range of biological processes exhibit circadian rhythm, enabling plants to adapt to the environmental day-night cycle. This rhythm is generated by the so-called 'circadian clock'. Although a number of genetic approaches have identified >25 clock-associated genes involved in the Arabidopsis clock mechanism, the molecular functions of a large part of these genes are not known. Recent comprehensive studies have revealed the molecular functions of several key clock-associated proteins. This p

Flowering plants produce a meristem at the shoot tip where specialized tissue generates shoot apical meristems at the appropriate time to differentiate into reproductive structures, pollinate and efficiently generate seeds. The complex set of molecular and phenological events culminating in development of a flowering meristem is referred to as 'flowering time'. Flowering time affects plant productivity because plants dedicate energy to produce flowers and seeds rather than vegetative tissue once

Plant circadian clocks control the timing of a variety of genetic, metabolic and physiological processes. Recent studies revealed a possible molecular mechanism for circadian clock regulation. Arabidopsis thaliana (Arabidopsis) PSEUDO-RESPONSE REGULATOR (PRR) genes, including TIMING OF CAB EXPRESSION 1 (TOC1), encode clock-associated transcriptional repressors that act redundantly. Disruption of multiple PRR genes results in drastic phenotypes, including increased biomass and abiotic stress tole

Recent intensive studies have begun to shed light on the molecular mechanisms underlying the plant circadian clock in Arabidopsis thaliana. During the course of these previous studies, the most powerful technique, elegantly adopted, was a real-time bioluminescence monitoring system of circadian rhythms in intact plants carrying a luciferase (LUC) fusion transgene. We previously demonstrated that Arabidopsis cultured cells also retain an ability to generate circadian rhythms, at least partly. To

The complete genome sequence of Arabidopsis thaliana revealed that this higher plant has a tremendous number of protein kinases. We recently isolated a novel type of protein kinase, named AtWNK1, which shows an in vitro ability to phosphorylate the APRR3 member of the APRR1/TOC1 quintet that has been implicated in a mechanism underlying circadian rhythms in Arabidopsis. We here address two issues, one general and one specific, as to this novel protein kinase. We first asked the general question

The circadian clock is the biological timekeeping system that governs the approximately 24-h rhythms of genetic, metabolic, physiological and behavioral processes in most organisms. This oscillation allows organisms to anticipate and adapt to day-night changes in the environment. Molecular studies have indicated that a transcription-translation feedback loop (TTFL), consisting of transcriptional repressors and activators, is essential for clock function in <i>Arabidopsis thaliana</i> (Arabidopsi

A small family of genes, named Arabidopsis Pseudo Response Regulator (APRR), are intriguing with special reference to circadian rhythms in plants, based on the fact that one of the members (APRR1) is identical to TOC1 (Timing of CAB Expression 1) that is believed to encode a clock component. In Arabidopsis plants, each transcript of the APRR1/TOC1 quintet genes starts accumulating after dawn rhythmically and one after another at intervals in the order of APRR9 --> APRR7 --> APRR5 --> APRR3 --> A

During and after the domestication of crops from ancestral wild plants, humans selected cultivars that could change their flowering time in response to seasonal daylength. Continuous selection of this trait eventually allowed the introduction of crops into higher or lower latitudes and different climates from the original regions where domestication initiated. In the past two decades, numerous studies have found the causal genes or alleles that change flowering time and have assisted in adapting

Plants flower under appropriate day-length conditions by integrating temporal information provided by the circadian clock with light and dark information from the environment. A sub-group of plant specific circadian clock-associated <i>PSEUDO-RESPONSE REGULATOR</i> (<i>PRR</i>) genes (PRR7/PRR3 sub-group) controls flowering time both in long-day and short-day plants; however, flowering control by the other two PRR gene sub-groups has been reported only in <i>Arabidopsis thaliana</i> (Arabidopsis