Evolution within a given virulence phenotype (pathotype) is driven by changes in aggressiveness: a case study of French wheat leaf rust populations

Plant pathogens are constantly evolving and adapting to their environment, including their host. Virulence alleles emerge, and then increase, and sometimes decrease in frequency within pathogen populations in response to the fluctuating selection pressures imposed by the deployment of resistance genes. In some cases, these strong selection pressures cannot fully explain the evolution observed in pathogen populations. A previous study on the French population of Puccinia triticina, the causal agent of wheat leaf rust, showed that two major pathotypes — groups of isolates with a particular combination of virulences — predominated but then declined over the 2005-2016 period. The relative dynamics and the domination of these two pathotypes — 166 317 0 and 106 314 0 —, relative to the other pathotypes present in the population at a low frequency although compatible, i.e. virulent on several varieties deployed, could not be explained solely by the frequency of Lr genes in the landscape. Within these two pathotypes, we identified two main genotypes that emerged in succession. We assessed three components of aggressiveness — infection efficiency, latency period and sporulation capacity — for 44 isolates representative of the four P. triticina pathotype-genotype combinations. We showed, for both pathotypes, that the more recent genotypes were more aggressive than the older ones. Our findings were highly consistent for the various components of aggressiveness for pathotype 166 317 0 grown on Michigan Amber — a ‘naive’ cultivar never grown in the landscape — or on Apache — a ‘neutral’ cultivar, which does not affect the pathotype frequency in the landscape and therefore was postulated to have no or minor selection effect on the population composition. For pathotype 106 314 0, the most recent genotype had a shorter latency period on several of the cultivars most frequently grown in the landscape, but not on ‘neutral’ and ‘naive’ cultivars. We conclude that the quantitative components of aggressiveness can be significant drivers of evolution in pathogen populations. A gain in aggressiveness stopped the decline in frequency of a pathotype, and subsequently allowed an increase in frequency of this pathotype in the pathogen population, providing evidence that adaptation to a changing varietal landscape not only affects virulence but can also lead to changes in aggressiveness

Variable Nav1.5 Protein Expression from the Wild-Type Allele Correlates with the Penetrance of Cardiac Conduction Disease in the Scn5a+/− Mouse Model

BACKGROUND: Loss-of-function mutations in SCN5A, the gene encoding Na(v)1.5 Na+ channel, are associated with inherited cardiac conduction defects and Brugada syndrome, which both exhibit variable phenotypic penetrance of conduction defects. We investigated the mechanisms of this heterogeneity in a mouse model with heterozygous targeted disruption of Scn5a (Scn5a(+/-) mice) and compared our results to those obtained in patients with loss-of-function mutations in SCN5A. METHODOLOGY/PRINCIPAL FINDINGS: Based on ECG, 10-week-old Scn5a(+/-) mice were divided into 2 subgroups, one displaying severe ventricular conduction defects (QRS interval>18 ms) and one a mild phenotype (QRS53 weeks), ajmaline effect was larger in the severely affected subgroup. These data matched the clinical observations on patients with SCN5A loss-of-function mutations with either severe or mild conduction defects. Ventricular tachycardia developed in 5/10 old severely affected Scn5a(+/-) mice but not in mildly affected ones. Correspondingly, symptomatic SCN5A-mutated Brugada patients had more severe conduction defects than asymptomatic patients. Old severely affected Scn5a(+/-) mice but not mildly affected ones showed extensive cardiac fibrosis. Mildly affected Scn5a(+/-) mice had similar Na(v)1.5 mRNA but higher Na(v)1.5 protein expression, and moderately larger I(Na) current than severely affected Scn5a(+/-) mice. As a consequence, action potential upstroke velocity was more decreased in severely affected Scn5a(+/-) mice than in mildly affected ones. CONCLUSIONS: Scn5a(+/-) mice show similar phenotypic heterogeneity as SCN5A-mutated patients. In Scn5a(+/-) mice, phenotype severity correlates with wild-type Na(v)1.5 protein expression

Aldosterone increases voltage-gated sodium current in ventricular myocytes.

The role of aldosterone in the pathogenesis of heart failure (HF) is still poorly understood. Recently, aldosterone has been shown to modulate the function of cardiac Ca(2+) and K(+) channels, thus playing a role in the electrical remodeling process. The goal of this work was to investigate the role of aldosterone on the cardiac Na(+) current (I(Na)). We analyzed the effects of aldosterone on I(Na) in isolated adult mouse ventricular myocytes, using the whole cell patch-clamp technique. After 24 h incubation with 1 microM aldosterone, the I(Na) density was significantly increased (+55%), without alteration of the biophysical properties and the cell membrane capacitance. Aldosterone (10 nM) increased the I(Na) by 23%. In 24-h coincubation experiments, with the use of actinomycin D, cycloheximide, or brefeldin A, the effect of aldosterone on I(Na) was abolished. Spironolactone (mineralocorticoid receptor antagonist, 10 microM) prevented the 1 microM aldosterone-dependent I(Na) increase, whereas RU-38486 (glucocorticoid receptor antagonist, 10 microM) did not. The action potential duration (APD) was longer in aldosterone-treated (APD(90): +53%) than in control myocytes. In addition, the L-type Ca(2+) current was also upregulated (+48%). We performed quantitative RT-PCR measurements and Western blots to quantify the mRNA and protein levels of Na(v)1.5 and Ca(v)1.2 (main channels mediating cardiac I(Na) and I(Ca)), but no significant difference was found. In conclusion, this study shows that aldosterone upregulates the cardiac I(Na) and suggest that this phenomenon may contribute to the HF-induced electrical remodeling process that may be reversed by spironolactone

Chronic angiotensin II stimulation in the heart produces an acquired long QT syndrome associated with IK1 potassium current downregulation.

Cardiac hypertrophy is an independent predictor of cardiovascular morbidity and mortality. It predisposes patients to heart failure, QT interval prolongation and ventricular arrhythmias. Angiotensin II (Ang II) exerts direct actions on cardiac tissue inducing cardiomyocyte hypertrophy and electro-mechanical dysfunction. However, a direct association between Ang II and cardiomyocyte electrical remodeling has yet to be demonstrated. Transgenic TG1306/1R (TG) mice with cardiac-specific Ang II overproduction demonstrate blood pressure-independent cardiac hypertrophy and exhibit significant increase in sudden death associated with mechanical dysfunction. The present study makes use of TG mice to evaluate the direct effects of high levels of intracardiac Ang II on cardiac electrophysiology. Surface-limb ECG measurements were recorded on 50- to 60-week-old TG and wild-type (WT) mice. QT interval was significantly prolonged (+20%) in TG mice relative to WT. TG mice also showed an increased incidence of ventricular arrhythmias. QT prolongation was associated with prolongation of cardiomyocyte action potential at 90% repolarization (APD90). The change in APD90 correlated with a reduction in IK1 potassium current density in TG vs. WT cardiomyocytes (at -70 mV: 0.3+/-0.1 pA/pF vs. 0.8+/-0.2 pA/pF, P<0.05). In TG mice, reduction in IK1 was associated with a significant reduction (-50%) of the mRNA encoding Kir2.1 and Kir2.2 subunits of IK1-related KCNJ2 and KCNJ12 potassium channels. These data suggest that cardiac Ang II overproduction leads to the emergence of a long QT syndrome resulting from an IK1-dependent prolongation of the action potential duration through modulation of channel subunit expression

Hole-Transfer Dyads and Triads Based on Perylene Monoimide, Quaterthiophene, and Extended Tetrathiafulvalene

Two families of dyad and triad systems based on perylene monoimide (PMI), quaterthiophene (QT), and 9,10-bis(1,3-dithiol-2-ylidene)-9,10- dihydroanthracene (extended tetrathiafulvalene, exTTF) molecular components have been designed and synthesized. The dyads (D1 and D2) are of the PMI–QT type and the triads (T1 and T2) of the PMI–QT–exTTF type. The two families differ in the saturated or unsaturated nature of the linker groups (ethynylene in D1 and T1, ethylene in D2 and T2) that bridge the molecular components. The dyads and triads have been characterized by electrochemical, photophysical, and computational methods. Both the experimental and the computational (DFT) results indicate that in the unsaturated systems strong intercomponent interactions lead to substantial perturbation of the properties of the subunits. In particular, in T1, delocalization is particularly effective between the QT and exTTF units, which would be better viewed combined as a single electronic subsystem. For the dyad systems, the photophysics observed following excitation of the PMI unit is solvent-dependent. In moderately polar solvents (dichloromethane, diethyl ether) fast charge separation is followed by recombination to the ground state. In toluene, slow conversion to the chargeseparated state is followed by intersystem crossing and recombination to yield the triplet state of the PMI unit. The behavior of the triads, on the other hand, is remarkably similar to that of the corresponding dyads, which indicates that, after primary charge separation, hole shift from the oxidized QT component to exTTF is quite inefficient. This unexpected result has been rationalized on the basis of the anomalous (simultaneous two-electron oxidation) electrochemistry of exTTF and with the help of DFT calculations. In fact, although exTTF is electrochemically easier to oxidize than QT by around 0.6 V, the one-electron redox orbitals (HOMOs) of the two units in triad T2 are almost degenerate

Design of cyclometallated 5-π-delocalized donor-1,3-di(2-pyridyl)benzene platinum(II) complexes with second-order nonlinear optical properties

International audienceThe effect on the second-order nonlinear optical properties of the nature of the π-delocalized moiety in the position 5 of a 1,3-di(2-pyridyl)benzene cyclometallated to a platinum(II) center was investigated. The influence of the substitution of a double bond with a triple bond as bridge between a triphenylamino group and the cyclometallated phenyl ring was studied and turned out to be negligible. Remarkably, the novel easily-prepared platinum(II) complex with a cyclometallated 5-styryl-1,3-di(2-pyridyl)benzene is characterized by a good second-order NLO response, as determined in solution by the EFISH technique; it is a good candidate for application in photonics

Cardiac sodium channel Nav1.5 is regulated by a multiprotein complex composed of syntrophins and dystrophin.

The cardiac sodium channel Na(v)1.5 plays a key role in cardiac excitability and conduction. The purpose of this study was to elucidate the role of the PDZ domain-binding motif formed by the last three residues (Ser-Ile-Val) of the Na(v)1.5 C-terminus. Pull-down experiments were performed using Na(v)1.5 C-terminus fusion proteins and human or mouse heart protein extracts, combined with mass spectrometry analysis. These experiments revealed that the C-terminus associates with dystrophin, and that this interaction was mediated by alpha- and beta-syntrophin proteins. Truncation of the PDZ domain-binding motif abolished the interaction. We used dystrophin-deficient mdx(5cv) mice to study the role of this protein complex in Na(v)1.5 function. Western blot experiments revealed a 50% decrease in the Na(v)1.5 protein levels in mdx(5cv) hearts, whereas Na(v)1.5 mRNA levels were unchanged. Patch-clamp experiments showed a 29% decrease of sodium current in isolated mdx(5cv) cardiomyocytes. Finally, ECG measurements of the mdx(5cv) mice exhibited a 19% reduction in the P wave amplitude, and an 18% increase of the QRS complex duration, compared with controls. These results indicate that the dystrophin protein complex is required for the proper expression and function of Na(v)1.5. In the absence of dystrophin, decreased sodium current may explain the alterations in cardiac conduction observed in patients with dystrophinopathies