Two component systems: physiological effect of a third component

Signal transduction systems mediate the response and adaptation of organisms to environmental changes. In prokaryotes, this signal transduction is often done through Two Component Systems (TCS). These TCS are phosphotransfer protein cascades, and in their prototypical form they are composed by a kinase that senses the environmental signals (SK) and by a response regulator (RR) that regulates the cellular response. This basic motif can be modified by the addition of a third protein that interacts either with the SK or the RR in a way that could change the dynamic response of the TCS module. In this work we aim at understanding the effect of such an additional protein (which we call "third component") on the functional properties of a prototypical TCS. To do so we build mathematical models of TCS with alternative designs for their interaction with that third component. These mathematical models are analyzed in order to identify the differences in dynamic behavior inherent to each design, with respect to functionally relevant properties such as sensitivity to changes in either the parameter values or the molecular concentrations, temporal responsiveness, possibility of multiple steady states, or stochastic fluctuations in the system. The differences are then correlated to the physiological requirements that impinge on the functioning of the TCS. This analysis sheds light on both, the dynamic behavior of synthetically designed TCS, and the conditions under which natural selection might favor each of the designs. We find that a third component that modulates SK activity increases the parameter space where a bistable response of the TCS module to signals is possible, if SK is monofunctional, but decreases it when the SK is bifunctional. The presence of a third component that modulates RR activity decreases the parameter space where a bistable response of the TCS module to signals is possible.     

Lability of chlorophylls in solvent

Journal of Applied Phycology - DMSO (dimethyl sulfoxide, (CH3)2SO) is an alternative solvent for the spectroscopic assay of chlorophylls (Chl) but has mainly been used on Chl a and b organisms, but...     

Cytokines as a key component of cancer-related inflammation

Inflammatory conditions in some tissues increase the risk of cancer. Cytokines and chemokines are components of an intensive dialog promoting angiogenesis, metastasis, subversion of adaptive immunity and changing response to hormones and to chemotherapeutic agents. Cytokines involved in cancer-related inflammation represent a target for innovative diagnostic and therapeutic strategies, and a future challenge for scientists and clinicians.     

Evolution as a critical component of plankton dynamics

Microevolution is typically ignored as a factor directly affecting ongoing population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for more than 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific but reproducible plankton dynamics which are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.     

Biological control by Clonostachys rosea as a key component in the integrated management of strawberry gray mold

Gray mold, caused by Botrytis cinerea, is an important strawberry disease. As gray mold control is difficult, there is a need to evaluate integrated methods to successfully manage the disease. The efficiency of integrating Clonostachys rosea sprays, fungicide sprays, and crop debris removal to manage gray mold was evaluated in field experiments conducted in 2006 and 2007. Leaf colonization by C. rosea (LAC), average number of B. cinerea conidiophores (ANC), gray mold incidence in both flowers (Iflower) and fruits (Ifruit), and yield were evaluated weekly. In both years, LAC was higher in the treatments with no fungicide. When compared to the check, ANC, Iflower and Ifruit were most reduced in treatments that included C. rosea sprays. Maximal reductions were achieved with the combination of C. rosea sprays, fungicide sprays and debris removal (96.62%, 86.54% and 65.33% reductions of ANC, Iflower and Ifruit, respectively). Otherwise, maximal yield (103.14% increase as compared to the check) was achieved with the combination of the three treatments. With just C. rosea sprays, ANC, Iflower and Ifruit were reduced by 92.01%, 68.48% and 65.33%, respectively, whereas yield was increased by 75.15%. Considering the individual effects, application of C. rosea was the most efficient treatment. Chemical control was effective only in plots without debris removal. Elimination of crop debris was the least effective method in reducing gray mold incidence in both flowers and fruits. The integrated control approach enhanced the efficacy of the individual methods of gray mold control and provided high strawberry yield. An important component of this integrated approach it the biological control with C. rosea.     

Phenotypic plasticity as a component of evolutionary change

Phenotypic plasticity has often been assumed to buffer the effects of natural selection and thus act as a constraint on evolutionary change. It has become increasingly clear, however, that phenotypic plasticity actually represents a fundamental component of evolutionary change. Where genetic variation for plasticity exists, a population with a different mean plasticity can evolve. Recent attention has been focused on the conditions necessary for the evolution of phenotypic plasticity, i.e. those under which a generalist strategy, as opposed to a range of genetically differentiated specialists, will be favoured. It is also now clear that genotypes that perform best in one environment usually perform less well than other genotypes in a different environment; hence, their greater response is not an adaptation to environmental variation. A response to environmental variation is only adaptive if it represents a mechanism by which relative fitness is maintained in the face of environmental variation. Adaptive plasticity may thus involve both physiological homeostasis and morphological response.     

Tubulin as a molecular component of coated vesicles

Two proteins of 53,000 and 56,000 mol wt have been found to be associated with coated vesicles (CV) purified from bovine brain and chicken liver. These proteins share molecular weights, isoelectric points, and antigenic determinants with alpha- and beta-tubulins purified from bovine brain. Based on SDS PAGE and electron microscopic analysis of controlled pore glass bead exclusion column fractions, both the tubulins and the major CV polypeptide clathrin were found to chromatograph as components of a single kinetic particle. In addition, tubulin and CV antigens assayed by a sensitive enzyme-linked-immunoadsorbent method eluted from the columns with constant stoichiometry. These data provide evidence that tubulin is a molecular component of coated vesicles.     

Nitric oxide as a key component in hormone-regulated processes

Nitric oxide (NO) is a small gaseous molecule, with a free radical nature that allows it to participate in a wide spectrum of biologically important reactions. NO is an endogenous product in plants, where different biosynthetic pathways have been proposed. First known in animals as a signaling molecule in cardiovascular and nervous systems, it has turned up to be an essential component for a wide variety of hormone-regulated processes in plants. Adaptation of plants to a changing environment involves a panoply of processes, which include the control of CO₂ fixation and water loss through stomatal closure, rearrangements of root architecture as well as growth restriction. The regulation of these processes requires the concerted action of several phytohormones, as well as the participation of the ubiquitous molecule NO. This review analyzes the role of NO in relation to the signaling pathways involved in stomatal movement, plant growth and senescence, in the frame of its interaction with abscisic acid, auxins, gibberellins, and ethylene.     

Behavior as a key component of integrative biology in a human-altered world

A major grand challenge in biology is to understand the interactions between an organism and its environment. Behavior resides in the central core of this association as it affects and is affected by development, physiology, ecological dynamics, environmental choice, and evolution. We present this central role of behavior in a diagram illustrating the multifaceted program emphasizing the necessity for understanding this nexus and to fully appreciate the organism in its environment given the ongoing changes affected by contemporary human induced, rapid environmental change (HIREC). We call for the consideration of educational and research focuses to concentrate on the interdisciplinary role that behavior plays in the integration of biological processes.     

Evolutionary Lability of Context-Dependent Codon Bias in Bacteria

In bacteria, synonymous codon usage can be considerably affected by base composition at neighboring sites. Such context-dependent biases may be caused by either selection against specific nucleotide motifs or context-dependent mutation biases. Here we consider the evolutionary conservation of context-dependent codon bias across 11 completely sequenced bacterial genomes. In particular, we focus on two contextual biases previously identified in Escherichia coli; the avoidance of out-of-frame stop codons and AGG motifs. By identifying homologues of E. coli genes, we also investigate the effect of gene expression level in Haemophilus influenzae and Mycoplasma genitalium. We find that while context-dependent codon biases are widespread in bacteria, few are conserved across all species considered. Avoidance of out-of-frame stop codons does not apply to all stop codons or amino acids in E. coli, does not hold for different species, does not increase with gene expression level, and is not relaxed in Mycoplasma spp., in which the canonical stop codon, TGA, is recognized as tryptophan. Avoidance of AGG motifs shows some evolutionary conservation and increases with gene expression level in E. coli, suggestive of the action of selection, but the cause of the bias differs between species. These results demonstrate that strong context-dependent forces, both selective and mutational, operate on synonymous codon usage but that these differ considerably between genomes. Received: 6 May 1999 / Accepted: 29 October 1999     

Evolutionary Lability of Integration in Cambrian Ptychoparioid Trilobites

Phenotypic integration can influence evolutionary rate and direction by channeling variation into few dimensions. The extent to which that channeling serves as a constraint over macroevolutionary timescales is determined in part by the evolutionary lability of phenotypic integration. Evolutionary change in patterns of pleiotropy, potentially reducing that constraint, is thought to be more readily achieved when pleiotropy is structured by variation arising in parallel along different developmental pathways rather than by variation arising from direct interactions within and between those pathways. Herein we test two predictions that follow from that hypothesis: (1) that clades undergoing dramatic diversification are characterized by integration that is weakly influenced by direct interactions; and (2) that the structure of integration arising from direct interactions is more conservative than that arising from parallel variation. We examine integration of the cranidium of two Cambrian ptychoparioid trilobites, Crassifimbra walcotti and Eokochaspis nodosa, comparing them to each other and to a previously studied species, C.? metalaspis. Shape variation is decomposed into components representing variation among individuals and variation due to direct interactions. In all three species, variation among individuals was only weakly influenced by direct interactions, suggesting that integration was unlikely to have been a long-term constraint on the Cambrian diversification of ptychoparioids. Phenotypic integration of E. nodosa is no more similar than expected by chance to either Crassifimbra species, but the component due to direct interactions is more similar than expected by chance to that of C.? metalaspis. Conversely, the two Crassifimbra species are generally similar (although not identical) in phenotypic integration, but markedly differ in their structure of direct interactions. Integration arising from direct interactions was therefore not immune to restructuring over even short evolutionary timescales, and was not always more conservative than that arising from parallel variation.     

Genetic control of a membrane component and zein deposition in maize endosperm

Summary An association is reported between an albuminlike protein (b-70) and the semidominant locus fluory-2 (fl2) which reduces the level of zein polypeptides in the maize endosperm. The protein b-70 is present at low level in wild-type endosperms and derppressed in fl2 endosperms. A correlation between the doses of the fl2 allele and the b-70 level has been found. Moreover a concomitant loss of the regulatory role of fl2 on zein level and on b-70 overproduction is evident when fl2 is genetically associated with o2 and o7, two recessive alleles of other zein regulatory loci. Protein b-70 is located on the membrane of the protein body where zein polypeptides accumulate. The existence of a functional relationship between this protein and the zein-secretory system is suggested or, as an alternative, that b-70 is a type of storage protein different from zeins, repressed in normal endosperms and derepressed by the fl2 allele.Abbreviations DAP days after pollination - ER endoplasmic reticulum - RER rough endoplasmic reticulum - DTT dithiothreitol - EDTA ethylene-diamintetra-acetate - NADH nicotinamide-adenine dinucleotide, reduced - PMSF phenylmethylsulfonyl-fluoride - SDS sodium dodecylsulfate - PAGE polyacrylamide gel electrophoresis - PBS phosphate buffered saline (0.15 M NaCl, 0.01 M Na phosphate, pH 6.8)