The role of cytokinin signalling in rice root vascular patterning

The vascular anatomy of rice roots is an important factor in drought tolerance, but little is known about the mechanisms governing its patterning. The Arabidopsis thaliana root vascular tissues are patterned by a mutually inhibitory feedback loop between auxin and cytokinin signalling (Mähönen et al. 2006). Cytokinin signalling in the procambium promotes accumulation of auxin in neighbouring cells which consequently differentiate as xylem. In these cells, high auxin levels promote expression of the pseudo-histidine phosphotransfer protein (PHP) AHP6, an inhibitor of cytokinin signalling (Bishopp et al. 2011). Whereas the root vasculature of Arabidopsis consists of a single xylem axis with phloem poles on either side, that of rice roots show a central metaxylem vessel surrounded by multiple xylem poles, between which are phloem. I hypothesised that the basic interaction between auxin and cytokinin in vascular patterning is conserved between Arabidopsis and rice, but is adapted to enable development of these different tissue patterns. Chemical treatments revealed that auxin and cytokinin are central regulators of root vascular patterning in rice, as is the case in Arabidopsis. In an effort to test whether this conservation extended to individual components of the molecular circuitry, I examined the role of the three OsPHPs, homologues of AHP6. These genes are not auxin inducible and are not able to rescue the Arabidopsis AHP6 mutant, suggesting they do not function in rice root vascular patterning. However, screening known inhibitors of cytokinin signalling for in auxin inducibility in the root tip revealed a subset of the type-A RRs (OsRR1, OsRR6 and OsRR7) are auxin inducible, and were able to rescue the Arabidopsis ahp6 mutant, suggesting these genes may have been recruited to function in the hormonal crosstalk regulating root vascular patterning. Phylogenetic analyses revealed a single amino acid substitution in a conserved region of the PHPs which differs between the dicots and the monocots. To directly determine activity of the OsPHPs, and the relevance of these substitutions, in-vitro phosphotransfer assays were performed. Preliminary results suggest these substitutions do not affect protein function. To characterise candidate genes, transcriptional reporters and mutant plants were generated. Reporters show expression of most candidate genes in the root, with some localised to root protoxylem. Mutants were generated using CRISPR and homozygous and heterozygous mutants were identified. Together, results described here give insight into how regulatory networks may be adapted to bring about differing responses

The role of cytokinin signalling in rice root vascular patterning

The vascular anatomy of rice roots is an important factor in drought tolerance, but little is known about the mechanisms governing its patterning. The Arabidopsis thaliana root vascular tissues are patterned by a mutually inhibitory feedback loop between auxin and cytokinin signalling (Mähönen et al. 2006). Cytokinin signalling in the procambium promotes accumulation of auxin in neighbouring cells which consequently differentiate as xylem. In these cells, high auxin levels promote expression of the pseudo-histidine phosphotransfer protein (PHP) AHP6, an inhibitor of cytokinin signalling (Bishopp et al. 2011). Whereas the root vasculature of Arabidopsis consists of a single xylem axis with phloem poles on either side, that of rice roots show a central metaxylem vessel surrounded by multiple xylem poles, between which are phloem. I hypothesised that the basic interaction between auxin and cytokinin in vascular patterning is conserved between Arabidopsis and rice, but is adapted to enable development of these different tissue patterns. Chemical treatments revealed that auxin and cytokinin are central regulators of root vascular patterning in rice, as is the case in Arabidopsis. In an effort to test whether this conservation extended to individual components of the molecular circuitry, I examined the role of the three OsPHPs, homologues of AHP6. These genes are not auxin inducible and are not able to rescue the Arabidopsis AHP6 mutant, suggesting they do not function in rice root vascular patterning. However, screening known inhibitors of cytokinin signalling for in auxin inducibility in the root tip revealed a subset of the type-A RRs (OsRR1, OsRR6 and OsRR7) are auxin inducible, and were able to rescue the Arabidopsis ahp6 mutant, suggesting these genes may have been recruited to function in the hormonal crosstalk regulating root vascular patterning. Phylogenetic analyses revealed a single amino acid substitution in a conserved region of the PHPs which differs between the dicots and the monocots. To directly determine activity of the OsPHPs, and the relevance of these substitutions, in-vitro phosphotransfer assays were performed. Preliminary results suggest these substitutions do not affect protein function. To characterise candidate genes, transcriptional reporters and mutant plants were generated. Reporters show expression of most candidate genes in the root, with some localised to root protoxylem. Mutants were generated using CRISPR and homozygous and heterozygous mutants were identified. Together, results described here give insight into how regulatory networks may be adapted to bring about differing responses

Molecular locks and keys: the role of small molecules in phytohormone research

Plant adaptation, growth and development rely on the integration of many environmental and endogenous signals that collectively determine the overall plant phenotypic plasticity. Plant signaling molecules, also known as phytohormones, are fundamental to this process. These molecules act at low concentrations and regulate multiple aspects of plant fitness and development via complex signaling networks. By its nature, phytohormone research lies at the interface between chemistry and biology. Classically, the scientific community has always used synthetic phytohormones and analogs to study hormone functions and responses. However, recent advances in synthetic and combinational chemistry, have allowed a new field, plant chemical biology, to emerge and this has provided a powerful tool with which to study phytohormone function. Plant chemical biology is helping to address some of the most enduring questions in phytohormone research such as: Are there still undiscovered plant hormones? How can we identify novel signaling molecules? How can plants activate specific hormone responses in a tissue-specific manner? How can we modulate hormone responses in one developmental context without inducing detrimental effects on other processes? The chemical genomics approaches rely on the identification of small molecules modulating different biological processes and have recently identified active forms of plant hormones and molecules regulating many aspects of hormone synthesis, transport and response. We envision that the field of chemical genomics will continue to provide novel molecules able to elucidate specific aspects of hormone-mediated mechanisms. In addition, compounds blocking specific responses could uncover how complex biological responses are regulated. As we gain information about such compounds we can design small alterations to the chemical structure to further alter specificity, enhance affinity or modulate the activity of these compounds.This work was partially funded by the National Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant RGPIN-2014-06468 to Abel Rosado and funding from the Canada Research Chairs program. John Vaughan-Hirsch is funded through the BBSRC Doctoral Training Programme. Anthony Bishopp is supported by the Royal Society through a University Research Fellowship. Andrea Chini is supported by a “Ramon y Cajal” fellowship (RYC-2010-05680) and this work was partially funded the Ministerio de Economía y Competitividad project BIO2013-44407-R, the AECID AP/040886/11 and the CSIC i-COOP060. This project was supported by NSTIP strategic technologies programs, number (11-BIO-2119-02) in the Kingdom of Saudi Arabia to Andrea Chini.Peer reviewedPeer Reviewe

A core mechanism for specifying root vascular patterning can replicate the anatomical variation seen in diverse plant species

Pattern formation is typically controlled through the interaction between molecular signals within a given tissue. During early embryonic development, roots of the model plant Arabidopsis thatiana have a radially symmetric pattern, but a heterogeneous input of the hormone auxin from the two cotyledons forces the vascular cylinder to develop a diarch pattern with two xylem poles. Molecular analyses and mathematical approaches have uncovered the regulatory circuit that propagates this initial auxin signal into a stable cellular pattern. The diarch pattern seen in Arabidopsis is relatively uncommon among flowering plants, with most species having between three and eight xylem poles. Here, we have used multiscale mathematical modelling to demonstrate that this regulatory module does not require a heterogeneous auxin input to specify the vascular pattern. Instead, the pattern can emerge dynamically, with its final form dependent upon spatial constraints and growth. The predictions of our simulations compare to experimental observations of xylem pole number across a range of species, as well as in transgenic systems in Arabidopsis in which we manipulate the size of the vascular cylinder. By considering the spatial constraints, our model is able to explain much of the diversity seen in different flowering plant species.Peer reviewe

Cyberspace Knowledge Gaps and Boundaries in Sustainability Science: Topics, Regions, Editorial Teams and Journals

The scholarly world of sustainability science is one that is international and interdisciplinary, but is one, on close reading of research contributions, editoral teams, journal citations, and geographic coverage, that has much unevenness. The focus of this paper is on the cyberspace boundaries between and within fields and disciplines studying sustainability; these boundaries separate knowledge gaps or uneven patterns in sustainability scholarship. I use the volume of hyperlinks on Google Search Engine and Google Scholar to illustrate the nature and extent of the boundaries in cyberspace that exist and also the subject and geographic gaps in the home countries of sustainability journal editors and editorial board members of 69 journals, many which have appeared since 2000. The results reveal that knowledge boundaries are part of the current nature of sustainability scholarship and that, while there is global coverage in our knowledge of sustainability, as well as sustainability maps and photographs, we know much less about sustainability in countries of the Global South than the Global North. This unevenness extends to the dominance of North America, Europe, and China as leaders in what we know. English-speaking countries also tend to dominate both journal editors and editorial board members, even though countries in the Global South have representation. The volumes of hyperlinks for the sustainability journals associated with both databases are similar with major interdisciplinary journals having the largest numbers. As the field of international sustainability science continues to evolve, it bears observing whether the cyberspace knowledge or boundary gaps will narrow in what is recognized by most science and policy scientists as one of the most important transdisciplinary fields of study in the Global South and North

Mid-Pleistocene thin-skinned glaciotectonic thrusting of the Aberdeen Ground Formation, Central Graben region, central North Sea

This paper presents the results of a high-resolution 2D seismic survey of mid-Pleistocene glaciogenic sediments in the Central Graben region of the central North Sea. Sediments have undergone major glaciotectonic thrusting and folding associated with the repeated southerly advance of a mid-Pleistocene ice sheet. The total observed length of the thrust-stacked section is approximately 5–6 km, comprising a series of discrete thrust slices, which range in length from  700 m. The basal detachment of the thrust complex occurs at a depth of ca. 220 m below the sea bed within the upper Aberdeen Ground Formation. A thin-skinned glaciotectonic model involving proglacial to ice-marginal glaciotectonic thrusting followed by post-tectonic deposition is proposed. Initial ice advance led to the over-pressurizing of groundwater within a laterally extensive sand sheet in the upper Aberdeen Ground Formation, promoting the formation of a major décollement surface at the base of the developing thrust-stack. Over-pressurization of the groundwater system is thought to have occurred in response to rapid ice advance, suggesting that the development of large-scale thrust complexes may be associated with surge-type behaviour. The proposed model evidences complex dynamics of mid-Pleistocene ice sheets within the central North Sea

The Phagocyte, Metchnikoff, and the Foundation of Immunology

ABSTRACTSince the ability of some cells to engulf particulate material was observed before Metchnikoff, he did not "discover" phagocytosis, as is sometimes mentioned in textbooks. Rather, he assigned to particle internalization the role of defending the host against noxious stimuli, which represented a new function relative to the previously recognized task of intracellular digestion. With this proposal, Metchnikoff built the conceptual framework within which immunity could finally be seen as an active host function triggered by noxious stimuli. In this sense, Metchnikoff can be rightly regarded as the father of all immunological sciences and not only of innate immunity or myeloid cell biology. Moreover, the recognition properties of his phagocyte fit surprisingly well with recent discoveries and modern models of immune sensing. For example, rather than assigning to immune recognition exclusively the function of eliminating nonself components (as others did after him), Metchnikoff viewed phagocytes as homeostatic agents capable of monitoring the internal environment and promoting tissue remodeling, thereby continuously defining the identity of the organism. No doubt, Metchnikoff's life and creativity can provide, still today, a rich source of inspiration

The citation advantage of open-access articles

This article published was published in the journal, Journal of the American Society for Information Science [© 2008 ASIS&T] and the definitive version is available at: http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1532-2890Four subjects, ecology, applied mathematics, sociology and economics, were selected to assess whether there is a citation advantage between journal articles that have an open access (OA) version on the Internet compared to those articles that are exclusively toll access (TA). Citations were counted using the Web of Science and the OA status of articles was determined by searching OAIster, OpenDOAR, Google and Google Scholar. Of a sample of 4633 articles examined, 2280 (49%) were OA and had a mean citation count of 9.04, whereas the mean for TA articles was 5.76. There appears to be a clear citation advantage for those articles that are OA as opposed to those that are TA. This advantage, however, varies between disciplines, with sociology having the highest citation advantage but the lowest number of OA articles from the sample taken and ecology having the highest individual citation count for OA articles but the smallest citation advantage. Tests of correlation or association between OA status and a number of variables were generally found to be weak or inconsistent. The cause of this citation advantage has not been determined

Macaque models of human infectious disease.

Macaques have served as models for more than 70 human infectious diseases of diverse etiologies, including a multitude of agents-bacteria, viruses, fungi, parasites, prions. The remarkable diversity of human infectious diseases that have been modeled in the macaque includes global, childhood, and tropical diseases as well as newly emergent, sexually transmitted, oncogenic, degenerative neurologic, potential bioterrorism, and miscellaneous other diseases. Historically, macaques played a major role in establishing the etiology of yellow fever, polio, and prion diseases. With rare exceptions (Chagas disease, bartonellosis), all of the infectious diseases in this review are of Old World origin. Perhaps most surprising is the large number of tropical (16), newly emergent (7), and bioterrorism diseases (9) that have been modeled in macaques. Many of these human diseases (e.g., AIDS, hepatitis E, bartonellosis) are a consequence of zoonotic infection. However, infectious agents of certain diseases, including measles and tuberculosis, can sometimes go both ways, and thus several human pathogens are threats to nonhuman primates including macaques. Through experimental studies in macaques, researchers have gained insight into pathogenic mechanisms and novel treatment and vaccine approaches for many human infectious diseases, most notably acquired immunodeficiency syndrome (AIDS), which is caused by infection with human immunodeficiency virus (HIV). Other infectious agents for which macaques have been a uniquely valuable resource for biomedical research, and particularly vaccinology, include influenza virus, paramyxoviruses, flaviviruses, arenaviruses, hepatitis E virus, papillomavirus, smallpox virus, Mycobacteria, Bacillus anthracis, Helicobacter pylori, Yersinia pestis, and Plasmodium species. This review summarizes the extensive past and present research on macaque models of human infectious disease

North, east, south, west: mapping vascular tissues onto the Arabidopsis root

The Arabidopsis root has provided an excellent model for understanding patterning processes and cell fate specification. Vascular patterning represents an especially interesting process, as new positional information must be generated to transform an approximately radially symmetric root pole into a bisymmetric structure with a single xylem axis. This process requires both growth of the embryonic tissue alongside the subsequent patterning. Recently researchers have identified a series of transcription factors that modulate cell divisions to control vascular tissues growth. Spatial regulation in the signalling of two hormones, auxin and cytokinin, combine with other transcription factors to pattern the xylem axis. We are now witnessing the discovery of increasingly complex interactions between these hormones that can be interpreted through the use of mathematical models