Watching the hands of the Arabidopsis biological clock

Oligonucleotide and cDNA microarrays have been used to analyse the mRNA levels of 8,000 genes in Arabidopsis thaliana throughout the day/night cycle. Genes involved in signal transduction and in various metabolic pathways were found to be coordinately regulated by circadian rhythms and/or by light

Recent advances in computational modeling as a conduit to understand the plant circadian clock

The circadian clock is necessary for plants to anticipate environmental changes. This leads to a coordination of plant development and growth and thus to increased fitness. Many clock components were identified by genetic and biochemical approaches, and studies on these components revealed a core oscillator with multiple feedback loops. A suite of computation analyses is uncovering the outputs of this oscillating network. Mathematical analysis is contributing to our understanding of the network under clock control, moving toward an explanation of how the clock integrates and coordinates various developmental programs with daily environmental cues. From there, these systems approaches will look to establish further nodes within the clock network

Effect of rotational disruption on the size-frequency distribution of the Main Belt asteroid population

The size distribution of small asteroids in the Main Belt is assumed to be determined by an equilibrium between the creation of new bodies out of the impact debris of larger asteroids and the destruction of small asteroids by collisions with smaller projectiles. However, for a diameter less than 6 km we find that YORP-induced rotational disruption significantly contributes to the erosion even exceeding the effects of collisional fragmentation. Including this additional grinding mechanism in a collision evolution model for the asteroid belt, we generate size-frequency distributions from either an accretional (Weidenschilling, 2011) or an "Asteroids were born big" (Morbidelli, 2009) initial size-frequency distribution that are consistent with observations reported in Gladman et al. (2009). Rotational disruption is a new mechanism that must be included in all future collisional evolution models of asteroids.Comment: 5 pages, 3 figures, accepted in MNRAS letter

Light-sensing phytochromes feel the heat

Plant phytochrome activity is governed not just by light, but also by prevailing temperature</jats:p

Environmental memory from a circadian oscillator:the Arabidopsis thaliana clock differentially integrates perception of photic vs. thermal entrainment

The constraint of a rotating earth has led to the evolution of a circadian clock that drives anticipation of future environmental changes. During this daily rotation, the circadian clock of Arabidopsis thaliana (Arabidopsis) intersects with the diurnal environment to orchestrate virtually all transcriptional processes of the plant cell, presumably by detecting, interpreting, and anticipating the environmental alternations of light and temperature. To comparatively assess differential inputs toward phenotypic and physiological responses on a circadian parameter, we surveyed clock periodicity in a recombinant inbred population modified to allow for robust periodicity measurements after entrainment to respective photic vs. thermal cues, termed zeitgebers. Lines previously thermally entrained generally displayed reduced period length compared to those previously photically entrained. This differential zeitgeber response was also detected in a set of diverse Arabidopsis accessions. Thus, the zeitgebers of the preceding environment direct future behavior of the circadian oscillator. Allelic variation at quantitative trait loci generated significant differences in zeitgeber responses in the segregating population. These were important for periodicity variation dependent on the nature of the subsequent entrainment source. Collectively, our results provide a genetic paradigm for the basis of environmental memory of a preceding environment, which leads to the integrated coordination of circadian periodicity

FLOWERING LOCUS C -dependent and -independent regulation of the circadian clock by the autonomous and vernalization pathways

Background The circadian system drives pervasive biological rhythms in plants. Circadian clocks integrate endogenous timing information with environmental signals, in order to match rhythmic outputs to the local day/night cycle. Multiple signaling pathways affect the circadian system, in ways that are likely to be adaptively significant. Our previous studies of natural genetic variation in Arabidopsis thaliana accessions implicated FLOWERING LOCUS C (FLC) as a circadian-clock regulator. The MADS-box transcription factor FLC is best known as a regulator of flowering time. Its activity is regulated by many regulatory genes in the "autonomous" and vernalization-dependent flowering pathways. We tested whether these same pathways affect the circadian system. Results Genes in the autonomous flowering pathway, including FLC, were found to regulate circadian period in Arabidopsis. The mechanisms involved are similar, but not identical, to the control of flowering time. By mutant analyses, we demonstrate a graded effect of FLC expression upon circadian period. Related MADS-box genes had less effect on clock function. We also reveal an unexpected vernalization-dependent alteration of periodicity. Conclusion This study has aided in the understanding of FLC's role in the clock, as it reveals that the network affecting circadian timing is partially overlapping with the floral-regulatory network. We also show a link between vernalization and circadian period. This finding may be of ecological relevance for developmental programing in other plant species

High-Frequency Resonant SEPIC Converter With Wide Input and Output Voltage Ranges

This paper presents a resonant single-ended-primary-inductor-converter (SEPIC) converter and control method suitable for high frequency (HF) and very high frequency (VHF) dc-dc power conversion. The proposed design provides high efficiency over a wide input and output voltage range, up-and-down voltage conversion, small size, and excellent transient performance. In addition, a resonant gate drive scheme is presented that provides rapid startup and low-loss at HF and VHF frequencies. The converter regulates the output using an ON-OFF control scheme modulating at a fixed frequency (170 kHz). This control method enables fast transient response and efficient light-load operation while providing controlled spectral characteristics of the input and output waveforms. A hysteretic override technique is also introduced which enables the converter to reject load disturbances with a bandwidth much greater than the modulation frequency, limiting output voltage disturbances to within a fixed value. An experimental prototype has been built and evaluated. The prototype converter, built with two commercial vertical MOSFETs, operates at a fixed switching frequency of 20 MHz, with an input voltage range of 3.6-7.2 V, an output voltage range of 3-9 V, and an output power rating of up to 3 W. The converter achieves higher than 80% efficiency across the entire input voltage range at nominal output voltage and maintains good efficiency across the whole operating range

A systematic survey in Arabidopsis thaliana of transcription factors that modulate circadian parameters

<p>Abstract</p> <p>Background</p> <p>Plant circadian systems regulate various biological processes in harmony with daily environmental changes. In <it>Arabidopsis thaliana</it>, the underlying clock mechanism is comprised of multiple integrated transcriptional feedbacks, which collectively lead to global patterns of rhythmic gene expression. The transcriptional networks are essential within the clock itself and in its output pathway.</p> <p>Results</p> <p>Here, to expand understanding of transcriptional networks within and associated to the clock, we performed both an <it>in silico </it>analysis of transcript rhythmicity of transcription factor genes, and a pilot assessment of functional phenomics on the <it>MYB</it>, <it>bHLH</it>, and <it>bZIP </it>families. In our <it>in silico </it>analysis, we defined which members of these families express a circadian waveform of transcript abundance. Up to 20% of these families were over-represented as clock-controlled genes. To detect members that contribute to proper oscillator function, we systematically measured rhythmic growth <it>via </it>an imaging system in hundreds of misexpression lines targeting members of the transcription-factor families. Three transcription factors were found that conferred aberrant circadian rhythms when misexpressed: <it>MYB3R2</it>, <it>bHLH69</it>, and <it>bHLH92</it>.</p> <p>Conclusion</p> <p>Transcript abundance of many transcription factors in Arabidopsis oscillates in a circadian manner. Further, a developed pipeline assessed phenotypic contribution of a panel of transcriptional regulators in the circadian system.</p

AKIN10 Activity as a Cellular Link Between Metabolism and Circadian-Clock Entrainment in Arabidopsis thaliana

AKIN10, the catalytic subunit of the Snf1 (sucrose non-fermenting 1)-related kinase 1 (SnRK1) complex, acts as an energy sensor in plants. We showed that AKIN10-induced expression affects the pace of the circadian clock and particularly the phase of expression of GIGANTEA (GI). The AKIN10 effect on period length required TIME FOR COFFEE (TIC), a circadian-clock component with developmental and metabolic roles. Here we expand on the possible interactions between AKIN10, whose activity is involved in transcriptional reprogramming, and clock elements GI and TIC. We hypothesize how they could participate in clock entrainment through a metabolic signal derived from carbon pools and starch metabolism. Additionally, we consider further the role of cellular energy status to the clock through the formation of a hypothetical protein complex. We also demonstrate the role of AKIN10, but not its sequence-related kinase AKIN11, on clock periodicity. Altogether we present a model of action of these elements in metabolic-related clock entrainment