37 research outputs found
Etn@ref: a geodetic reference frame for Mt. Etna GPS networks
In volcanology, one of the most important instruments for scientific community interested in modelling the physical processes related to magma movements in the shallow crust is geodetic data. Since the end of the 1980s, GPS surveys and Continuous GPS stations (CGPS) have greatly improved the possibility to measure such movements with high time and space resolution. However, physical modelling requires that any external influence on the data, not directly related to the investigated quantity, must be filtered. One major tricky factor in determining a deformation field using GPS displacement vectors and velocities is the correct choice of a stable reference frame. In this work, using more than a decade of GPS measurements, we defined a local reference frame in order to refer the Mt. Etna ground deformation pattern to a rigid block. In particular, we estimated the Euler pole for the rigid block by minimizing, with a weighted least squares inversion, the adjustments to two horizontal components of GPS velocity at 13 “fiducial” sites located within 350 km around Mt. Etna. The inversion inferred an Euler pole located at 38.450° N and -107.702° E and a rotation rate of 0.263 deg/Myr
Parsimonious Model of Vascular Patterning Links Transverse Hormone Fluxes to Lateral Root Initiation : Auxin Leads the Way, while Cytokinin Levels Out
An auxin maximum is positioned along the xylem axis of the Arabidopsis root tip. The pattern depends on mutual feedback between auxin and cytokinins mediated by the PIN class of auxin efflux transporters and AHP6, an inhibitor of cytokinin signalling. This interaction has been proposed to regulate the size and the position of the hormones' respective signalling domains and specify distinct boundaries between them. To understand the dynamics of this regulatory network, we implemented a parsimonious computational model of auxin transport that considers hormonal regulation of the auxin transporters within a spatial context, explicitly taking into account cell shape and polarity and the presence of cell walls. Our analysis reveals that an informative spatial pattern in cytokinin levels generated by diffusion is a theoretically unlikely scenario. Furthermore, our model shows that such a pattern is not required for correct and robust auxin patterning. Instead, auxin-dependent modifications of cytokinin response, rather than variations in cytokinin levels, allow for the necessary feedbacks, which can amplify and stabilise the auxin maximum. Our simulations demonstrate the importance of hormonal regulation of auxin efflux for pattern robustness. While involvement of the PIN proteins in vascular patterning is well established, we predict and experimentally verify a role of AUX1 and LAX1/2 auxin influx transporters in this process. Furthermore, we show that polar localisation of PIN1 generates an auxin flux circuit that not only stabilises the accumulation of auxin within the xylem axis, but also provides a mechanism for auxin to accumulate specifically in the xylem-pole pericycle cells, an important early step in lateral root initiation. The model also revealed that pericycle cells on opposite xylem poles compete for auxin accumulation, consistent with the observation that lateral roots are not initiated opposite to each other.Peer reviewe
Diffusible repression of cytokinin signalling produces endodermal symmetry and passage cells.
In vascular plants, the root endodermis surrounds the central vasculature as a protective sheath that is analogous to the polarized epithelium in animals, and contains ring-shaped Casparian strips that restrict diffusion. After an initial lag phase, individual endodermal cells suberize in an apparently random fashion to produce 'patchy' suberization that eventually generates a zone of continuous suberin deposition. Casparian strips and suberin lamellae affect paracellular and transcellular transport, respectively. Most angiosperms maintain some isolated cells in an unsuberized state as so-called 'passage cells', which have previously been suggested to enable uptake across an otherwise-impermeable endodermal barrier. Here we demonstrate that these passage cells are late emanations of a meristematic patterning process that reads out the underlying non-radial symmetry of the vasculature. This process is mediated by the non-cell-autonomous repression of cytokinin signalling in the root meristem, and leads to distinct phloem- and xylem-pole-associated endodermal cells. The latter cells can resist abscisic acid-dependent suberization to produce passage cells. Our data further demonstrate that, during meristematic patterning, xylem-pole-associated endodermal cells can dynamically alter passage-cell numbers in response to nutrient status, and that passage cells express transporters and locally affect the expression of transporters in adjacent cortical cells
Tomato fruit set driven by pollination or by the parthenocarpic fruit allele are mediated by transcriptionally regulated gibberellin biosynthesis
We investigated the role of gibberellins (GAs) in
the phenotype of parthenocarpic fruit (pat), a recessive
mutation conferring parthenocarpy in tomato (Solanum lycopersicum
L.). Novel phenotypes that parallel those reported
in plants repeatedly treated with gibberellic acid or having a
GA-constitutive response indicate that the pat mutant probably
expresses high levels of GA. The retained sensitivity to
the GA-biosynthesis inhibitor paclobutrazol reveals that this
condition is dependent on GA biosynthesis. Expression analysis
of genes encoding key enzymes involved in GA biosynthesis
shows that in normal tomato ovaries, the GA20ox1
transcript is in low copy number before anthesis and only
pollination and fertilization increase its transcription levels
and, thus, GA biosynthesis. In the unpollinated ovaries of
the pat mutant, this mechanism is de-regulated and
GA20ox1 is constitutively expressed, indicating that a high
GA concentration could play a part in the parthenocarpic
phenotype. The levels of endogenous GAs measured in the
Xoral organs of the pat mutant support such a hypothesis.
Collectively, the data indicate that transcriptional regulation
of GA20ox1 mediates pollination-induced fruit set in tomato
and that parthenocarpy in pat results from the mis-regulation
of this mechanism. As genes involved in the control of GA
synthesis (LeT6, LeT12 and LeCUC2) and response (SPY)
are also altered in the pat ovary, it is suggested that the pat
mutation aVects a regulatory gene located upstream of the
control of fruit set exerted by GAs
Genetic diversity, structure and marker-trait associations in a collection of tomato (Solanum Lycopersicon L.) landraces from central Italy
Genetic diversity, structure and marker-trait associations in a collection of Italian tomato (Solanum lycopersicum L.) landraces
The study of phenotypic and genetic diversity in
landrace collections is important for germplasm conservation.
In addition, the characterisation of very diversified
materials with molecular markers offers a unique opportunity
to define significant marker-trait associations of biological
and agronomic interest. Here, 50 tomato landraces
(mainly collected in central Italy), nine vintage and modern
cultivars, and two wild outgroups were grown at two locations
in central Italy and characterised for 15 morpho-physiological
traits and 29 simple sequence repeat (SSR) loci.
The markers were selected to include a group of loci in
regions harbouring reported quantitative trait loci (QTLs)
that affect fruit size and/or shape (Q-SSRs) and a group of
markers that have not been mapped or shown to have
a priori known linkage (NQ-SSRs). As revealed by univariate
and multivariate analyses of morphological data, the
landraces grouped according to vegetative and reproductive
traits, with emphasis on fruit size, shape and final destination
of the product. Compared to the low molecular polymorphism
reported in tomato modern cultivars, our data reveal a
high level of molecular diversity in landraces. Such diversity
has allowed the inference of the existence of a genetic structure
that was factored into the association analysis. As the
proportion of significant associations is higher between the
Q-SSR subset of markers and the subset of traits related to
fruit size and shape than for all of the other combinations,
we conclude that this approach is valid for establishing true positive marker-trait relationships in tomato
MARKER-TRAIT ASSOCIATIONS IN A COLLECTION OF DIVERSIFIEDTOMATO (SOLANUM LYCOPERSICUM L.) LANDRACES ANDCULTIVARS
Report on the methodology applied by EFSA to provide a quantitative assessment of pest-related criteria required to rank candidate priority pests as defined by Regulation (EU) 2016/2031
In agreement with Article 6(2) of the Regulation (EU) 2016/2031 on protective measures against pestsof plants, the European Commission has been tasked by the Council and European Parliament toestablish a list of Union quarantine pests which qualify as priority pests. The prioritisation is based onthe severity of the economic, social and environmental impact that these pests can cause in the Unionterritory. The Commission’s Joint Research Centre (JRC) is in charge of developing a methodologybased on a multi-criteria decision analysis and composite indicators. In this context, EFSA has providedtechnical and scientific data related to these pests, in particular: (i) the potential host range anddistribution of each of these pests in the Union territory at the level of NUTS2 regions; (ii) parametersquantifying the potential consequences of these pests, e.g. crop losses in terms of yield and quality,rate of spread and time to detection. Expert knowledge elicitation methodology has been applied byEFSA in order to provide those parameters in a consistent and transparent manner