Strong negative feedback from Erk to Raf confers robustness to MAPK signalling

This study shows that MAPK signalling is robust against protein level changes due to a strong negative feedback from Erk to Raf. Surprisingly, robustness is provided through a fast post-translational mechanism although variation of Erk levels occurs on a timescale of days

Verticillium suppression is associated with the glucosinolate composition of Arabidopsis thaliana leaves.

The soil-borne fungal pathogen Verticillium longisporum is able to penetrate the root of a number of plant species and spread systemically via the xylem. Fumigation of Verticillium contaminated soil with Brassica green manure is used as an environmentally friendly method for crop protection. Here we present a study focused on the potential role of glucosinolates and their breakdown products of the model plant Arabidopsis thaliana in suppressing growth of V. longisporum. For this purpose we analysed the glucosinolate composition of the leaves and roots of a set of 19 key accessions of A. thaliana. The effect of volatile glucosinolate hydrolysis products on the in vitro growth of the pathogen was tested by exposing the fungus to hydrated lyophilized plant tissue. Volatiles released from leaf tissue were more effective than from root tissue in suppressing mycelial growth of V. longisporum. The accessions varied in their efficacy, with the most effective suppressing mycelial growth by 90%. An analysis of glucosinolate profiles and their enzymatic degradation products revealed a correlation between fungal growth inhibition and the concentration of alkenyl glucosinolates, particularly 2-propenyl (2Prop) glucosinolate, respectively its hydrolysis products. Exposure of the fungus to purified 2Prop glucosinolate revealed that its suppressive activity was correlated with its concentration. Spiking of 2Prop glucosinolate to leaf material of one of the least effective A. thaliana accessions led to fungal growth suppression. It is suggested that much of the inhibitory effect observed for the tested accessions can be explained by the accumulation of 2Prop glucosinolate

Genotypic Variation of Glucosinolates and Their Breakdown Products in Leaves of <i>Brassica rapa</i>

An in-depth glucosinolate (GLS) profiling was performed on a core collection of 91 <i>Brassica rapa</i> accessions, representing diverse morphotypes of heterogeneous geographical origin, to better understand the natural variation in GLS accumulation and GLS breakdown product formation. Leaves of the 91 <i>B. rapa</i> accessions were analyzed for their GLS composition by UHPLC-DAD and the corresponding breakdown products by GC–MS. Fifteen different GLSs were identified, and aliphatic GLSs prevailed regarding diversity and concentration. Twenty-three GLS breakdown products were identified, among them nine isothiocyanates, ten nitriles, and four epithionitriles. Epithionitriles were the prevailing breakdown products due to the high abundance of alkenyl GLSs. The large scale data set allowed the identification of correlations in abundance of specific GLSs or of GLS breakdown products. Discriminant function analysis identified subspecies with high levels of similarity in the acquired metabolite profiles. In general, the five main subspecies grouped significantly in terms of their GLS profiles

Cobalt Cross-Linked Redox-Responsive PEG Hydrogels: From Viscoelastic Liquids to Elastic Solids

We describe cobalt cross-linked redox-responsive 4-arm histidine-modified PEG (4A-PEG-His) hydrogels, which can be switched from self-healing viscoelastic liquids to form stable elastic solids through a simple oxidation step from Co²⁺ to Co³⁺. The dramatic change in gel properties is quantified in rheological measurements and is associated with the altered ligand exchange rate of the cross-linking cobalt ions. While Co²⁺ forms kinetically labile coordination bonds with low thermodynamic stability, Co³⁺ forms kinetically inert and highly stable coordination bonds. Unlike the Co²⁺ cross-linked hydrogels, the Co³⁺ cross-linked hydrogels do not dissolve in buffer and swell overtime, where they remain intact longer with increasing gel connectivity, increasing polymer concentration and decreasing temperature. Remarkably, these gels can even resist the strong chelator EDTA and withstand both low and high pH due to the low ligand exchange rates in the primary coordination sphere. Overall, the Co^2+/3+ redox pair provides an attractive platform to produce redox-responsive materials with big deviations in mechanical and chemical properties

Systemic spread of <i>Verticillium longisporum</i> 43-3, VD-1 and <i>V. dahliae</i> GU060637 within the leaf and root of <i>Arabidopsis thaliana</i> accessions Ler-0 and Bur-0, as measured by qRT-PCR, five weeks after inoculation.

<p>Data represent the mean of three batches consisting of five plants each, measured in technical triplicates via qRT-PCR. Bars denote standard deviations. Significant differences between Ler-0 and Bur-0 are indicated by asterisks (*: <i>p</i><0.001).</p

Fungitoxicity of 2Prop-ITC on growth of <i>Verticillium longisporum</i> 43-3.

<p>Effect of hydrolysed 2Prop glucosinolate on the <i>in vitro</i> growth of <i>V. longisporum</i> 43-3 was demonstrated using the biofumigation assay (A). Data represent the mean of five technical replicates per biological sample and error bars represent the standard error. Significant differences between the control mycelia and those exposed to 2Prop-ITC are indicated by asterisks (*: <i>p</i><0.001). The formation of 2Prop-ITC through myrosinase-driven glucosinolate breakdown was verified by GC-MS analysis (B). GC-MS chromatograms display the product of hydrolysed 2Prop glucosinolate (black) in comparison to the hydrolysed fraction accession Wu-0 (green line).</p

Hierarchical clustering of the glucosinolate composition of the leaf tissue of a range of <i>Arabidopsis thaliana</i> accessions.

<p>Each column represents one accession and each row the concentration of glucosinolates (µmol g⁻¹ DW) using colour coding.</p

Relative growth of <i>Verticillium longisporum</i> 43-3 on PDA at 25°C for four days when exposed to volatiles emitted from 19 <i>Arabidopsis thaliana</i> accessions.

<p>Red bars represent mycelial growth in the absence of plant tissue and black bars represent (A) leaf and (B) root tissue. Data represent the mean of five replicates, and the error bar represents the standard error. Significant differences between the control mycelia and those exposed to plant material are indicated by asterisks (*: <i>p</i><0.05, **: <i>p</i><0.01, ***: <i>p</i><0.001). (C) The effect on the <i>in vitro</i> growth of <i>V. longisporum</i> 43-3 of leaf volatiles emitted from the three most suppressive accessions after four days of exposure. The red circle indicates a diameter of 1.6 cm.</p