A Tradeoff Drives the Evolution of Reduced Metal Resistance in Natural Populations of Yeast

Various types of genetic modification and selective forces have been implicated in the process of adaptation to novel or adverse environments. However, the underlying molecular mechanisms are not well understood in most natural populations. Here we report that a set of yeast strains collected from Evolution Canyon (EC), Israel, exhibit an extremely high tolerance to the heavy metal cadmium. We found that cadmium resistance is primarily caused by an enhanced function of a metal efflux pump, PCA1. Molecular analyses demonstrate that this enhancement can be largely attributed to mutations in the promoter sequence, while mutations in the coding region have a minor effect. Reconstruction experiments show that three single nucleotide substitutions in the PCA1 promoter quantitatively increase its activity and thus enhance the cells' cadmium resistance. Comparison among different yeast species shows that the critical nucleotides found in EC strains are conserved and functionally important for cadmium resistance in other species, suggesting that they represent an ancestral type. However, these nucleotides had diverged in most Saccharomyces cerevisiae populations, which gave cells growth advantages under conditions where cadmium is low or absent. Our results provide a rare example of a selective sweep in yeast populations driven by a tradeoff in metal resistance

Joining S100 proteins and migration:for better or for worse, in sickness and in health

The vast diversity of S100 proteins has demonstrated a multitude of biological correlations with cell growth, cell differentiation and cell survival in numerous physiological and pathological conditions in all cells of the body. This review summarises some of the reported regulatory functions of S100 proteins (namely S100A1, S100A2, S100A4, S100A6, S100A7, S100A8/S100A9, S100A10, S100A11, S100A12, S100B and S100P) on cellular migration and invasion, established in both culture and animal model systems and the possible mechanisms that have been proposed to be responsible. These mechanisms involve intracellular events and components of the cytoskeletal organisation (actin/myosin filaments, intermediate filaments and microtubules) as well as extracellular signalling at different cell surface receptors (RAGE and integrins). Finally, we shall attempt to demonstrate how aberrant expression of the S100 proteins may lead to pathological events and human disorders and furthermore provide a rationale to possibly explain why the expression of some of the S100 proteins (mainly S100A4 and S100P) has led to conflicting results on motility, depending on the cells used. © 2013 Springer Basel

Quantification and Prediction of Nighttime Evapotranspiration for Two Distinct Grassland Ecosystems

©2019. American Geophysical Union. All Rights Reserved. Evapotranspiration (ET) is, after precipitation, the second largest flux at the land surface in the water cycle and occurs mainly during daytime. Less attention has been given to water fluxes from the land surface into the atmosphere during nighttime (i.e., between sunset and sunrise). The nighttime ET (ETN) may be estimated based on models that use meteorological data; however, due to missing experimental long-term data, the verification of ETN estimates is limited. In this paper, the amount of ETN for two grassland ecosystems was determined from highly temporally resolved and precise weighing lysimeter data. We found that annual ETN ranged between 3.5% and 9.5% of daytime annual ET (ETD) and occurred mainly during wet soil and canopy surface conditions, which suggests that ETN is largely related to evaporation. ETN was positively correlated with wind speed. Dew formation, ranging from 4.8% to 6.4% of annual precipitation, was in absolute terms larger than ETN. The prediction of ETN with the Penman-Monteith model improved if the aerodynamic and surface resistance parameters were based on vegetation height observations and the nighttime stomatal resistance parameter was assumed to be zero. The occurrence of hot days during the observation period showed to increase average ETN rates. Our results suggest that ETN can be observed with precision weighing lysimeters, was a not negligible component in the water balance of the grassland ecosystems, and thus needs more attention when simulating land surface hydrological processes.status: publishe

Soil hydraulic conductivity in the state of nonequilibrium

Hydraulic nonequilibrium in soil during water infiltration and drainage is a well-known phenomenon. During infiltration, water initially invades easily accessible pores before it slowly redistributes towards some state of energetic minimum. In analogy, during drainage, easily drainable pores are emptied more rapidly than those blocked by bottlenecks. The consequence is that the water content is lagging behind the water potential and both state variables do not follow a unique water retention curve as typically assumed when applying Richards equation. Current models that account for nonequilibrium allow for the required decoupling of water content and water potential; however, they do not consider the consequences for the hydraulic conductivity. In this contribution, we present a physically based approach to estimate hydraulic conductivity during nonequilibrium, which depends on both water content and water potential during nonequilibrium conditions. This approach of a dynamic hydraulic conductivity function is demonstrated for an infiltration process into relatively dry soil and for a stepwise drainage and rewetting with decreasing and increasing water fluxes (i.e., multistep flux experiment). The new approach reproduces well-known phenomena such as pressure overshoot and preferential flow across infiltration fronts using a unified concept for hydraulic conductivity. This was not possible with existing models assuming some fixed unsaturated conductivity function depending on either water content or water potential