TheTIME FOR COFFEEGene Maintains the Amplitude and Timing of Arabidopsis Circadian Clocks[W]

Abstract

Plants synchronize developmental and metabolic processes with the earth's 24-h rotation through the integration of circadian rhythms and responses to light. We characterize the time for coffee ( tic ) mutant that disrupts circadian gating, photoperiodism, and multiple circadian rhythms, with differential effects among rhythms. TIC is distinct in physiological functions and genetic map position from other rhythm mutants and their homologous loci. Detailed rhythm analysis shows that the chlorophyll a/b -binding protein gene expression rhythm requires TIC function in the mid to late subjective night, when human activity may require coffee, in contrast to the function of EARLY-FLOWERING3 ( ELF3 ) in the late day to early night. tic mutants misexpress genes that are thought to be critical for circadian timing, consistent with our functional analysis. Thus, we identify TIC as a regulator of the clock gene circuit. In contrast to tic and elf3 single mutants, tic elf3 double mutants are completely arrhythmic. Even the robust circadian clock of plants cannot function with defects at two different phases.

Plant Circadian Rhythms

“…Light input is negatively regulated by ELF3; loss-of-function alleles of elf3 yield conditional arrhythmicity in continuous light but remain rhythmic in the dark (Hicks et al, 1996(Hicks et al, , 2001McWatters et al, 2000;Covington et al, 2001;Liu et al, 2001). TIME FOR COFFEE (TIC) may have a similar effect on gating light input, although during a distinct phase; the tic elf3 double mutant is fully arrhythmic in light or dark (Hall et al, 2003). The period alteration of ztl mutants shows fluence rate dependence, suggesting a role for ZTL in light input .…”

Abiotic stress and the plant circadian clock

“…These include genes such as ELF3, 43 ELF4, 25 TIME FOR COFFEE, 44,45 SENSITIVITY TO RED LIGHT REDUCED (SRR1), 46 LIGHT INSENSITIVE PERIOD 1 (LIP1), 47,48 and XAP5 CIRCADIAN TIMEKEEPER (XCT ). 49 None of these genes encode a protein with apparent chromophore interactions, required as a canonical domain involved in light perception, which suggests that their protein products act as signaling components in a step downstream of the light signal perception.…”

ELF4Is Required for Oscillatory Properties of the Circadian Clock

“…Plates were stored in the dark for 3 to 4 d at 4°C, placed at 22°C in the darkness for 1 d, and irradiated with light for 6 d, as described (Davis et al, 2001). The light sources were as described in Hall et al (2003). For circadian and real-time PCR experiments, seeds were similarly treated, except that they were plated on 13 Murashige and Skoog medium (4.4 g/L) with 3% Suc and 1% agar before being stratified at 4°C for 48 h. The seeds were then transferred to growth chambers programmed for appropriate light and temperature regimes for 7 d before the start of an experiment.…”

“…Where appropriate, data were normalized. Here, normalization was plotted as the quotient of the absolute data point over the mean of the entire dataset, as a method in identical fashion to Hall et al (2003). This allows the data to be qualitatively compared for each genotype while plotting on the same axes and preserving the waveforms.…”