Functional Interactions between KCNE1 C-Terminus and the KCNQ1 Channel

The KCNE1 gene product (minK protein) associates with the cardiac KvLQT1 potassium channel (encoded by KCNQ1) to create the cardiac slowly activating delayed rectifier, IKs. Mutations throughout both genes are linked to the hereditary cardiac arrhythmias in the Long QT Syndrome (LQTS). KCNE1 exerts its specific regulation of KCNQ1 activation via interactions between membrane-spanning segments of the two proteins. Less detailed attention has been focused on the role of the KCNE1 C-terminus in regulating channel behavior. We analyzed the effects of an LQT5 point mutation (D76N) and the truncation of the entire C-terminus (Δ70) on channel regulation, assembly and interaction. Both mutations significantly shifted voltage dependence of activation in the depolarizing direction and decreased IKs current density. They also accelerated rates of channel deactivation but notably, did not affect activation kinetics. Truncation of the C-terminus reduced the apparent affinity of KCNE1 for KCNQ1, resulting in impaired channel formation and presentation of KCNQ1/KCNE1 complexes to the surface. Complete saturation of KCNQ1 channels with KCNE1-Δ70 could be achieved by relative over-expression of the KCNE subunit. Rate-dependent facilitation of K+ conductance, a key property of IKs that enables action potential shortening at higher heart rates, was defective for both KCNE1 C-terminal mutations, and may contribute to the clinical phenotype of arrhythmias triggered by heart rate elevations during exercise in LQTS mutations. These results support several roles for KCNE1 C-terminus interaction with KCNQ1: regulation of channel assembly, open-state destabilization, and kinetics of channel deactivation

Key environmental variables determining the occurrence and life span of basiphilous dune slack vegetation

Environmental processes controlling the occurrence of basiphilous pioneer vegetation were identified in seven representative dune slacks on the Dutch Wadden Sea Islands. The variation in vegetation and relations with soil and groundwater composition were established first. Cluster analysis of the vegetation in the dune slacks resulted in six subtypes of basiphilous pioneer vegetation and three types representing older succession stages. Canonical correspondence analysis suggested that moisture and pH are the main habitat factors in the dataset and that habitats of older succession stages, compared to basiphilous pioneer stages, are either acidified or eutrophicated. A principal component analysis of shallow groundwater samples from all dune slacks revealed the dominant influence of inundation with sea water in the total dataset. In the freshwater dataset Ca2+ and HCO3 concentrations predominated. Cl- and Ca2+ concentrations of shallow groundwater were, therefore, considered key variables in describing the environmental processes determining suitable habitat conditions for basiphilous pioneer vegetation. To be able to distinguish between a conditioning role of tl-le hydrological regime (c.q. exfiltration of mineral rich groundwater) and a conditioning role of (former) geomorphological processes (c.q. the presence of CaCO3 minerals), the soil CaCO3 content was added as key environmental variable. In primary dune slacks on the islands of Schiermonnikoog and Texel, having comparable initial lime contents (0.5-1%), the life span of basiphilous pioneer vegetation was estimated to be 30-50 years without a mowing regime and 100-150 years under a mowing regime. In secondary dune slacks the life span of basiphilous pioneer vegetation varies considerably with differences in local circumstances, especially in strength of prevailing pH-buffering mechanisms. These, in turn, are determined by differences in environmental conditions on a landscape scale (hydrology, geomorphological history)

Factors controlling soil development in sand dunes: evidence from a coastal dune soil cronosequence

Aerial photographs, maps and optically stimulated luminescence dates were combined with existing soil data to construct high resolution chronosequences of soil development over 140 years at a temperate Atlantic UK dune system. Since soil formation had progressed for varying duration under different climate and nitrogen deposition regimes, it was possible to infer their relative influence on soil development compared with location-specific variables such as soil pH, slope and distance to the sea. Results suggest that soil development followed a sigmoid curve. Soil development was faster in wet than in dry dune habitats. In dry dunes, rates were greater than in the literature: they increased with increasing temperature and nitrogen deposition and decreased with increasing summer gales. The combination explained 62% of the variation. Co-correlation meant that effects of nitrogen deposition could not be differentiated from temperature. In wet dune habitats rates increased with temperature and decreased with gales. The combination explained only 23% of the variation; surprisingly, rainfall was not significant. Effects of location-specific variables were not significant in either habitat type. Nitrogen accumulation was faster in wet than dry dune habitats, averaging 43 kg N ha−1 per year overall. Nitrogen accumulation greatly exceeded inputs from atmospheric deposition, suggesting rates of input for biological N fixation are 10–60 kg N ha−1 per year. Recent climate and/or nitrogen deposition regimes may have accelerated soil development compared with past rates. These data suggest the importance of changing climate on soil development rates and highlight the contribution of biological N fixation in early successional systems

Molecular markers to exploit genotype-environment interactions of relevance in organic growing systems

One of the substantial differences between conventional and organic growing systems is the degree to which the farmer can control biotic and abiotic stresses; for organic growing systems varieties are needed with a broad adaptation to annually varying factors, while at the same time a good specific adaptation is necessary with respect to more constant climate and soil conditions. This combination of requirements implies that varieties for organic farming need to be better characterised with respect to genotype x environment interactions than varieties for conventional farming. Such interactions, which often are found for quantitatively expressed traits, are in general difficult to deal with in phenotypic selection. New approaches for QTL analyses (e.g. using physiological models) facilitate estimation of effects of genes on a trait (the phenotype) as a response to environmental influences. From such analyses, markers can be identified which may help to predict the trait expression of a plant genotype in relation to defined environmental factors. The application of markers to select for loci with specific interactions with the environment could, therefore, be especially important for plant breeders targeting organic farming systems