Diel time-courses of leaf growth in monocot and dicot species: endogenous rhythms and temperature effects

Diel (24 h) leaf growth patterns were differently affected by temperature variations and the circadian clock in several plant species. In the monocotyledon Zea mays, leaf elongation rate closely followed changes in temperature. In the dicotyledons Nicotiana tabacum, Ricinus communis, and Flaveria bidentis, the effect of temperature regimes was less obvious and leaf growth exhibited a clear circadian oscillation.These differences were related neither to primary metabolism nor to altered carbohydrate availability for growth. The effect of endogenous rhythms on leaf growth was analysed under continuous light in Arabidopsis thaliana, Ricinus communis, Zea mays, and Oryza sativa. No rythmic growth was observed under continuous light in the two monocotyledons, while growth rhythmicity persisted in the two dicotyledons. Based on model simulations it is concluded that diel leaf growth patterns in mono- and dicotyledons result from the additive effects of both circadian-clock-controlled processes and responses to environmental changes such as temperature and evaporative demand. Apparently very distinct diel leaf growth behaviour of monocotyledons and dicotyledons can thus be explained by the different degrees to which diel temperature variations affect leaf growth in the two groups of species which, in turn, depends on the extent of the leaf growth control by internal clocks

Assessing uncertainty in housing stock infiltration rates and associated heat loss: English and UK case studies

Strategies to reduce domestic heating loads by minimizing the infiltration of cold air through adventitious openings located in the thermal envelopes of houses are highlighted by the building codes of many countries. Consequent reductions of energy demand and CO2e emission are often unquantified by empirical evidence. Instead, a mean heating season infiltration rate is commonly inferred from an air leakage rate using a simple ratio scaled to account for the physical and environmental properties of a dwelling. The scaling does not take account of the permeability of party walls in conjoined dwellings and so cannot differentiate between the infiltration of unconditioned ambient air that requires heating, and conditioned air from adjacent dwellings that does not. A stochastic method is presented that applies a theoretical model of adventitious infiltration to predict distributions of mean infiltration rates and the associated total heat loss in any stock of dwellings during heating hours. The method is applied to the English and UK housing stocks and provides probability distribution functions of stock infiltration rates and total heat loss during the heating season for two extremes of party wall permeability. The distributions predict that up to 79% of the current English stock could require additional purpose-provided ventilation to limit negative health consequences. National models predict that fewer dwellings are under-ventilated. The distributions are also used to predict that infiltration is responsible for 3–5% of total UK energy demand, 11–15% of UK housing stock energy demand, and 10–14% of UK housing stock carbon emissions

A Morning-Specific Phytohormone Gene Expression Program underlying Rhythmic Plant Growth

Most organisms use daily light/dark cycles as timing cues to control many essential physiological processes. In plants, growth rates of the embryonic stem (hypocotyl) are maximal at different times of day, depending on external photoperiod and the internal circadian clock. However, the interactions between light signaling, the circadian clock, and growth-promoting hormone pathways in growth control remain poorly understood. At the molecular level, such growth rhythms could be attributed to several different layers of time-specific control such as phasing of transcription, signaling, or protein abundance. To determine the transcriptional component associated with the rhythmic control of growth, we applied temporal analysis of the Arabidopsis thaliana seedling transcriptome under multiple growth conditions and mutant backgrounds using DNA microarrays. We show that a group of plant hormone-associated genes are coexpressed at the time of day when hypocotyl growth rate is maximal. This expression correlates with overrepresentation of a cis-acting element (CACATG) in phytohormone gene promoters, which is sufficient to confer the predicted diurnal and circadian expression patterns in vivo. Using circadian clock and light signaling mutants, we show that both internal coincidence of phytohormone signaling capacity and external coincidence with darkness are required to coordinate wild-type growth. From these data, we argue that the circadian clock indirectly controls growth by permissive gating of light-mediated phytohormone transcript levels to the proper time of day. This temporal integration of hormone pathways allows plants to fine tune phytohormone responses for seasonal and shade-appropriate growth regulation

Molecular Mechanisms Underlying the Arabidopsis Circadian Clock

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 progress has provided mechanistic insights into how key clock-associated proteins are integrated, and may help in understanding the essence of the clock's molecular mechanisms

The driver mutational landscape of ovarian squamous cell carcinomas arising in mature cystic teratoma

Purpose. We sought to identify the genomic abnormalities in squamous cell carcinomas (SCC) arising in ovarian mature cystic teratoma (MCT), a rare gynaecological malignancy of poor prognosis. Experimental design. We performed copy number, mutational state and zygosity analysis of 151 genes in SCC arising in MCT (n=25) using next-generation sequencing. The presence of high/intermediate risk HPV genotypes was assessed by quantitative PCR. Genomic events were correlated with clinical features and outcome Results. MCT had a low mutation burden with a mean of only 1 mutation per case. Zygosity analyses of MCT indicated four separate patterns, suggesting that MCT can arise from errors at various stages of oogenesis. A total of 244 abnormalities were identified in 79 genes in MCT-associated SCC, and the overall mutational burden was high (mean 10.2 mutations per megabase). No SCC was positive for HPV. The most frequently altered genes in SCC were TP53 (20/25 cases, 80%), PIK3CA (13/25 cases, 52%) and CDKN2A (11/25 cases, 44%). Mutation in TP53 was associated with improved overall survival. In 8/20 cases with TP53 mutations, two or more variants were identified, which were bi-allelic. Conclusions. Ovarian SCC arising in MCT has a high mutational burden with TP53 mutation the most common abnormality. The presence TP53 mutation is a good prognostic factor. SCC arising in MCT share similar mutation profiles to other SCC. Given their rarity, they should be included in basket studies that recruit patients with SCC of other organs

PIF Genes Mediate the Effect of Sucrose on Seedling Growth Dynamics

As photoautotrophs, plants can use both the form and amount of fixed carbon as a measure of the light environment. In this study, we used a variety of approaches to elucidate the role of exogenous sucrose in modifying seedling growth dynamics. In addition to its known effects on germination, high-resolution temporal analysis revealed that sucrose could extend the number of days plants exhibited rapid hypocotyl elongation, leading to dramatic increases in ultimate seedling height. In addition, sucrose changed the timing of daily growth maxima, demonstrating that diel growth dynamics are more plastic than previously suspected. Sucrose-dependent growth promotion required function of multiple phytochrome-interacting factors (PIFs), and overexpression of PIF5 led to growth dynamics similar to plants exposed to sucrose. Consistent with this result, sucrose was found to increase levels of PIF5 protein. PIFs have well-established roles as integrators of response to light levels, time of day and phytohormone signaling. Our findings strongly suggest that carbon availability can modify the known photomorphogenetic signaling network

The Functional Interplay between Protein Kinase CK2 and CCA1 Transcriptional Activity Is Essential for Clock Temperature Compensation in Arabidopsis

Circadian rhythms are daily biological oscillations driven by an endogenous mechanism known as circadian clock. The protein kinase CK2 is one of the few clock components that is evolutionary conserved among different taxonomic groups. CK2 regulates the stability and nuclear localization of essential clock proteins in mammals, fungi, and insects. Two CK2 regulatory subunits, CKB3 and CKB4, have been also linked with the Arabidopsis thaliana circadian system. However, the biological relevance and the precise mechanisms of CK2 function within the plant clockwork are not known. By using ChIP and Double–ChIP experiments together with in vivo luminescence assays at different temperatures, we were able to identify a temperature-dependent function for CK2 modulating circadian period length. Our study uncovers a previously unpredicted mechanism for CK2 antagonizing the key clock regulator CIRCADIAN CLOCK-ASSOCIATED 1 (CCA1). CK2 activity does not alter protein accumulation or subcellular localization but interferes with CCA1 binding affinity to the promoters of the oscillator genes. High temperatures enhance the CCA1 binding activity, which is precisely counterbalanced by the CK2 opposing function. Altering this balance by over-expression, mutation, or pharmacological inhibition affects the temperature compensation profile, providing a mechanism by which plants regulate circadian period at changing temperatures. Therefore, our study establishes a new model demonstrating that two opposing and temperature-dependent activities (CCA1-CK2) are essential for clock temperature compensation in Arabidopsis