Factors regulating cortex cell file proliferation under low phosphorus stress in Arabidopsis thaliana roots

Radial patterning of root hair bearing cells (trichoblasts) in Arabidopsis thaliana (arabidopsis) follows the type 3 root hair patterning mechanism whereby the radial positioning of trichoblasts is coordinated according to the position of underlying cortex cells (Pemberton et al. 2001). Epidermal cells which are positioned over the cleft between two underlying cortex cell files adopt trichoblast identity. Low phosphate stress in arabidopsis roots has been show to result in an increase in the number of cortex cell files from 8 to 12-16, which in turn results in an increase in the number of trichoblast position cells (Zhang et al. 2003, Cederholm and Benfey, 2015). However, little is known about what mechanisms control this proliferation in cortex tissue. Zhang et al. (2003) demonstrate that eir1 (an allele of pinformed2, pin2) mutants are deficient in this response to low P. This finding suggests that PIN2 (an efflux facilitator of directional auxin transport) is required to orchestrate proliferation of cortex cell files under low P. This implies that directional auxin transport and, ultimately, auxin response are required to enable proliferative divisions in cortex tissues under low P. First of all, a deeper anatomical understanding of the cortex cell file number response to low P was developed. That showed that the divisions which lead to the increase in cortex cell file number occur in the first cortex cell next to the quiescent centre. It was also found that the anatomical changes only significantly affect the number of cortex cell and trichoblast cell files, suggesting that it is a cortex specific response to increase radial root hair density. It was further discovered that the root is sensitive to up to 400μM P and responds with increased cortex cell file number within 24 hours. I also showed that this response is independent of iron concentration. It was next hypothesised that the role of directional auxin transport implied that other PIN and AUX/LAX genes may be required as well as activating AUXIN RESPONSE FACTORs (ARFs). These experiments revealed that no other PINs or ARFs play a crucial role in this response. However it was found that PIN2:GFP protein changes its subcellular localisation in response to low P, suggesting that changes in auxin flux direction is required. Based on this, it was hypothesised that PIN2 complementation in the cortex in pin2 would rescue the phenotype. This was indeed the case, but also for PIN2 under the AUX1 promoter, suggesting an additional role for PIN2 in the epidermis and root cap during the low P response. Mathematical modelling suggested that auxin flux out of the cortex, mediated by PIN2, would be required for the response. However, results testing this in vivo with the DII:VENUS auxin reporter were inconclusive. It was suspected that ground tissues patterning regulators, BIRD genes, may also play a role in tissue patterning under low P. jkd (jackdaw) and mgp (magpie) mutants did not show any strong phenotype on low P, but expression analysis using reporter lines and reverse transcription qPCR did suggest changes in regulation. It was then hypothesised that BIRD genes and PIN2 may interact, by crossing pin2 and jkd I found that the two interact to a small degree but it is not evident that they interact directly within the same pathway. It was concluded that this response to low P was controlled by a number of regulatory networks which definitely involves PIN2 mediated auxin transport with a contribution from BIRD genes

The ‘Nordstrom Tower’: a landmark daylight injury study

This paper describes a landmark daylight injury study whereby measures predicted using climate-based daylight modelling formed part of the legal agreement for the development of a skyscraper building in New York. Now known as the Nordstrom Tower, when completed in 2018 it will become the world’s tallest residential building. The evaluation was carried out in two stages: original design proposal in 2005, and the final design in 2013. The background/context for the study, and the daylight injury evaluations carried out at both stages are described. The potential implications of this unique study for planning guidelines are discussed

Stock Assessment of Queensland East Coast black jewfish (Protonibea diacanthus), Australia, with data to December 2021

Black jewfish (Protonibea diacanthus) are caught on the east coast of Queensland by commercial, recreational, charter and Indigenous fishers. The fishery is focused around Central Queensland, and has recently experienced a large shift in commercial effort and gear types. The species was historically considered a byproduct species within the inshore net fishery, but has now become a targeted line caught species. In Australia, black jewfish are found from Exmouth Gulf in Western Australia, north and east across Northern Australia, to the east coast of Queensland. Research suggests that stocks cover hundreds of kilometres. This is the first stock assessment of the Queensland East Coast stock. The stock assessment was conducted on calendar years and included input data through to December 2021. Eight model scenarios were run, covering different combinations of recreational dead catch and population steepness (productivity parameter). Base case (preferred) scenario results suggested that biomass declined gradually from the 1940s to the 1980s and has increased slightly since then. The spawning stock level at the beginning of 2022 for base-case scenarios was estimated to be between 56% and 99% with a median estimate of 79%. The estimates from other scenarios ranged from 80% to 92%. Despite high uncertainty around the exact level of biomass, the model outputs indicate that the biomass is probably at or above the target reference point of 60% unfished biomass

Auxin fluxes through plasmodesmata modify root-tip auxin distribution

© 2020. Published by The Company of Biologists Ltd. Auxin is a key signal regulating plant growth and development. It is well established that auxin dynamics depend on the spatial distribution of efflux and influx carriers on the cell membranes. In this study, we employ a systems approach to characterise an alternative symplastic pathway for auxin mobilisation via plasmodesmata, which function as intercellular pores linking the cytoplasm of adjacent cells. To investigate the role of plasmodesmata in auxin patterning, we developed a multicellular model of the Arabidopsis root tip. We tested the model predictions using the DII-VENUS auxin response reporter, comparing the predicted and observed DII-VENUS distributions using genetic and chemical perturbations designed to affect both carrier-mediated and plasmodesmatal auxin fluxes. The model revealed that carrier-mediated transport alone cannot explain the experimentally determined auxin distribution in the root tip. In contrast, a composite model that incorporates both carrier-mediated and plasmodesmatal auxin fluxes re-capitulates the root-tip auxin distribution. We found that auxin fluxes through plasmodesmata enable auxin reflux and increase total root-tip auxin. We conclude that auxin fluxes through plasmodesmata modify the auxin distribution created by efflux and influx carriers

Genomic evidence of pre-invasive clonal expansion, dispersal and progression in bronchial dysplasia

The term ‘field cancerization’ is used to describe an epithelial surface that has a propensity to develop cancerous lesions, and in the case of the aerodigestive tract this is often as a result of chronic exposure to carcinogens in cigarette smoke 1, 2. The clinical endpoint is the development of multiple tumours, either simultaneously or sequentially in the same epithelial surface. The mechanisms underlying this process remain unclear; one possible explanation is that the epithelium is colonized by a clonal population of cells that are at increased risk of progression to cancer. We now address this possibility in a short case series, using individual genomic events as molecular biomarkers of clonality. In squamous lung cancer the most common genomic aberration is 3q amplification. We use a digital PCR technique to assess the clonal relationships between multiple biopsies in a longitudinal bronchoscopic study, using amplicon boundaries as markers of clonality. We demonstrate that clonality can readily be defined by these analyses and confirm that field cancerization occurs at a pre-invasive stage and that pre-invasive lesions and subsequent cancers are clonally related. We show that while the amplicon boundaries can be shared between different biopsies, the degree of 3q amplification and the internal structure of the 3q amplicon varies from lesion to lesion. Finally, in this small cohort, the degree of 3q amplification corresponds to clinical progression. Copyright © 2011 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd

Fluctuations in auxin levels depend upon synchronicity of cell divisions in a one-dimensional model of auxin transport

Auxin is a well-studied plant hormone, the spatial distribution of which remains incompletely understood. Here, we investigate the effects of cell growth and divisions on the dynamics of auxin patterning, using a combination of mathematical modelling and experimental observations. In contrast to most prior work, models are not designed or tuned with the aim to produce a specific auxin pattern. Instead, we use well-established techniques from dynamical systems theory to uncover and classify ranges of auxin patterns as exhaustively as possible as parameters are varied. Previous work using these techniques has shown how a multitude of stable auxin patterns may coexist, each attainable from a specific ensemble of initial conditions. When a key parameter spans a range of values, these steady patterns form a geometric curve with successive folds, often nicknamed a snaking diagram. As we introduce growth and cell division into a one-dimensional model of auxin distribution, we observe new behaviour which can be explained in terms of this diagram. Cell growth changes the shape of the snaking diagram, and this corresponds in turn to deformations in the patterns of auxin distribution. As divisions occur this can lead to abrupt creation or annihilation of auxin peaks. We term this phenomenon ‘snake-jumping’. Under rhythmic cell divisions, we show how this can lead to stable oscillations of auxin. We also show that this requires a high level of synchronisation between cell divisions. Using 18 hour time-lapse imaging of the auxin reporter DII:Venus in roots of Arabidopsis thaliana, we show auxin fluctuates greatly, both in terms of amplitude and periodicity, consistent with the snake-jumping events observed with non-synchronised cell divisions. Periodic signals downstream of the auxin signalling pathway have previously been recorded in plant roots. The present work shows that auxin alone is unlikely to play the role of a pacemaker in this context

Chemical Composition of Faint (I~21 mag) Microlensed Bulge Dwarf OGLE-2007-BLG-514S

We present a high-resolution spectrum of a microlensed G dwarf in the Galactic bulge with spectroscopic temperature T_eff = 5600 +/- 180 K. This I~21 mag star was magnified by a factor ranging from 1160 to 1300 at the time of observation. Its high metallicity ([Fe/H] = 0.33 +/- 0.15) places this star at the upper end of the bulge giant metallicity distribution. Using a K-S test, we find a 1.6% probability that the published microlensed bulge dwarfs share an underlying distribution with bulge giants, properly accounting for a radial bulge metallicity gradient. We obtain abundance measurements for 15 elements and perform a rigorous error analysis that includes covariances between parameters. This star, like bulge giants with the same metallicity, shows no alpha enhancement. It confirms the chemical abundance trends observed in previously analyzed bulge dwarfs. At supersolar metallicities, we observe a discrepancy between bulge giant and bulge dwarf Na abundances.Comment: 13 pages, 8 figures, 5 tables, submitted to Ap

Cell migration leads to spatially distinct but clonally related airway cancer precursors

Background Squamous cell carcinoma of the lung is a common cancer with 95% mortality at 5 years. These cancers arise from preinvasive lesions, which have a natural history of development progressing through increasing severity of dysplasia to carcinoma in situ (CIS), and in some cases, ending in transformation to invasive carcinoma. Synchronous preinvasive lesions identified at autopsy have been previously shown to be clonally related. Methods Using autofluorescence bronchoscopy that allows visual observation of preinvasive lesions within the upper airways, together with molecular profiling of biopsies using gene sequencing and loss-of-heterozygosity analysis from both preinvasive lesions and from intervening normal tissue, we have monitored individual lesions longitudinally and documented their visual, histological and molecular relationship. Results We demonstrate that rather than forming a contiguous field of abnormal tissue, clonal CIS lesions can develop at multiple anatomically discrete sites over time. Further, we demonstrate that patients with CIS in the trachea have invariably had previous lesions that have migrated proximally, and in one case, into the other lung over a period of 12 years. Conclusions Molecular information from these unique biopsies provides for the first time evidence that field cancerisation of the upper airways can occur through cell migration rather than via local contiguous cellular expansion as previously thought. Our findings urge a clinical strategy of ablating high-grade premalignant airway lesions with subsequent attentive surveillance for recurrence in the bronchial tree