Rhizobien in der Pflanzenmikrobiota

Rhizobia in the plant microbiota The plant microbiota is of critical importance for plant growth and survival in soil. To explore mechanisms underlying plant‐microbiota interactions, defined commensal communities can be composed from microbiota culture collections and co‐cultivated with germ‐free plants to determine their impact on plant growth and health. The order Rhizobiales belongs to the core microbiota and includes nitrogen‐fixing bacteria that are known to engage in symbiotic interactions with legumes. Compatible host‐symbiont pairs are needed for a functional symbiosis, which involves the activation of highly specialized and interdependent signaling pathways between the two partners. Comparative genome analysis of more than 1,300 legume symbionts and rhizobial root commensals from non‐leguminous plants revealed that the most recent common ancestor of rhizobia lacked the gene repertoire needed for symbiosis and was able to colonize roots of a wide variety of plants. During evolution, key symbiosis genes were acquired multiple independent times by commensals belonging to different families of the Rhizobiales order.     

The Administration of Cadmium for 2, 3 and 4 Months Causes a Loss of Recognition Memory,Promotes Neuronal Hypotrophy and Apoptosis in the Hippocampus of Rats

Cadmium (Cd) is a toxic metal and classified as a carcinogen whose exposure could affect the function of the central nervous system. There are studies that suggest that Cd promotes neurodegeneration in different regions of the brain, particularly in the hippocampus. It is proposed that its mechanism of toxicity maybe by an oxidative stress pathway, which modifies neuronal morphology and causes the death of neurons and consequently affecting cognitive tasks. However, this mechanism is not yet clear. The aim of the present work was to study the effect of Cd administration on recognition memory for 2, 3 and 4 months, neuronal morphology and immunoreactivity for caspase-3 and 9 in rat hippocampi. The results show that the administration of Cd decreased recognition memory. Likewise, it caused the dendritic morphology of the CA1, CA3 and dentate gyrus regions of the hippocampus to decrease with respect to the time of administration of this heavy metal. In addition, we observed a reduction in the density of dendritic spines as well as an increase in the immunoreactivity of caspase-3 and 9 in the same hippocampal regions of the animals treated with Cd. These results suggest that Cd affects the structure and function of the neurons of the hippocampus, which contribute to the deterioration of recognition memory. Our results suggest that the exposure to Cd represents a critical health problem, which if not addressed quickly, could cause much more serious problems in the quality of life of the human population, as well as in the environment in which they develop.

     

Gestational jet lag predisposes to later-life skeletal and cardiac disease

Circadian rhythm disturbance (CRD) increases the risk of disease, e.g. metabolic syndrome, cardiovascular disease, and cancer. In the present study, we investigated later life adverse health effects triggered by repeated jet lag during gestation. Pregnant mice were subjected to a regular light-dark cycle (CTRL) or to a repeated delay (DEL) or advance (ADV) jet lag protocol. Both DEL and ADV offspring showed reduced weight gain. ADV offspring had an increased circadian period, and an altered response to a jet lag was observed in both DEL and ADV offspring. Analysis of the bones of adult male ADV offspring revealed reduced cortical bone mass and strength. Strikingly, analysis of the heart identified structural abnormalities and impaired heart function. Finally, DNA methylation analysis revealed hypermethylation of miR17-92 cluster and differential methylation within circadian clock genes, which correlated with altered gene expression. We show that developmental CRD affects the circadian system and predisposes to non-communicable disease in adult life.     

Study on the Decomposition of Pistia stratiotes L. (Araceae) in Cisne Reservoir,Uruguay

A study on the decomposition process of Pistia stratiotes L. was carried out in Cisne Reservoir, Uruguay. For this purpose, leaves and roots were considered separately, and the process was studied in the littoral and the pelagic zone. The litter bag technique was used to estimate dry weight losses at different times. Leaves decomposed faster than roots in both zones. Pistia decomposed faster in the pelagic zone due to better oxygen conditions and a more intensive water movement that removes material from within the bags. Phosphorus, potassium, sodium and magnesium were leached rapidly during the first week. Nitrogen content in the leaves initially increased, reaching its maximum in the littoral zone that coincided with that of bacterial numbers colonizing the litter. The number of macroinvertebrates, dominated by Chironomidae, was low. A rough estimation of the phosphorus impact on the littoral zone associated to the decomposition process shows that after 24 h between 13.9 and 16.8 μg-at.1⁻¹ have been released to the water.     

Efficient and error-free fluorescent gene tagging in human organoids without double-strand DNA cleavage

CRISPR-associated nucleases are powerful tools for precise genome editing of model systems, including human organoids. Current methods describing fluorescent gene tagging in organoids rely on the generation of DNA double-strand breaks (DSBs) to stimulate homology-directed repair (HDR) or non-homologous end joining (NHEJ)-mediated integration of the desired knock-in. A major downside associated with DSB-mediated genome editing is the required clonal selection and expansion of candidate organoids to verify the genomic integrity of the targeted locus and to confirm the absence of off-target indels. By contrast, concurrent nicking of the genomic locus and targeting vector, known as in-trans paired nicking (ITPN), stimulates efficient HDR-mediated genome editing to generate large knock-ins without introducing DSBs. Here, we show that ITPN allows for fast, highly efficient, and indel-free fluorescent gene tagging in human normal and cancer organoids. Highlighting the ease and efficiency of ITPN, we generate triple fluorescent knock-in organoids where 3 genomic loci were simultaneously modified in a single round of targeting. In addition, we generated model systems with allele-specific readouts by differentially modifying maternal and paternal alleles in one step. ITPN using our palette of targeting vectors, publicly available from Addgene, is ideally suited for generating error-free heterozygous knock-ins in human organoids.

A major downside of double-strand break-mediated genome editing is the need to verify the genomic integrity of the targeted locus and confirm the absence of off-target indels. This study shows that in-trans paired nicking is a mutation-free CRISPR strategy to introduce precise knock-ins into human organoids; its genomic fidelity allows all knock-in cells to be pooled, accelerating the establishment of new organoid models.     

The influence of predator community composition on photoprotective traits of copepods

Trait expression of natural populations often jointly depends on prevailing abiotic environmental conditions and predation risk. Copepods, for example, can vary their expression of compounds that confer protection against ultraviolet radiation (UVR), such as astaxanthin and mycosporine‐like amino acids (MAAs), in relation to predation risk. Despite ample evidence that copepods accumulate less astaxanthin in the presence of predators, little is known about how the community composition of planktivorous fish can affect the overall expression of photoprotective compounds. Here, we investigate how the (co‐)occurrence of Arctic charr (Salvelinus alpinus) and threespine stickleback (Gasterosteus aculeatus) affects the photoprotective phenotype of the copepod Leptodiaptomus minutus in lake ecosystems in southern Greenland. We found that average astaxanthin and MAA contents were lowest in lakes with stickleback, but we found no evidence that these photoprotective compounds were affected by the presence of charr. Furthermore, variance in astaxanthin among individual copepods was greatest in the presence of stickleback and the astaxanthin content of copepods was negatively correlated with increasing stickleback density. Overall, we show that the presence and density of stickleback jointly affect the content of photoprotective compounds by copepods, illustrating how the community composition of predators in an ecosystem can determine the expression of prey traits that are also influenced by abiotic stressors.     

Post-insemination selection dominates pre-insemination selection in driving rapid evolution of male competitive ability

Sexual reproduction is a complex process that contributes to differences between the sexes and divergence between species. From a male’s perspective, sexual selection can optimize reproductive success by acting on the variance in mating success (pre-insemination selection) as well as the variance in fertilization success (post-insemination selection). The balance between pre- and post-insemination selection has not yet been investigated using a strong hypothesis-testing framework that directly quantifies the effects of post-insemination selection on the evolution of reproductive success. Here we use experimental evolution of a uniquely engineered genetic system that allows sperm production to be turned off and on in obligate male-female populations of Caenorhabditis elegans. We show that enhanced post-insemination competition increases the efficacy of selection and surpasses pre-insemination sexual selection in driving a polygenic response in male reproductive success. We find that after 10 selective events occurring over 30 generations post-insemination selection increased male reproductive success by an average of 5- to 7-fold. Contrary to expectation, enhanced pre-insemination competition hindered selection and slowed the rate of evolution. Furthermore, we found that post-insemination selection resulted in a strong polygenic response at the whole-genome level. Our results demonstrate that post-insemination sexual selection plays a critical role in the rapid optimization of male reproductive fitness. Therefore, explicit consideration should be given to post-insemination dynamics when considering the population effects of sexual selection.     

Separate taurine and chloride efflux pathways activated during regulatory volume decrease

Organic osmolyte and halide permeability pathways activated inepithelial HeLa cells by cell swelling were studied by radiotracer efflux techniques and single-cell volume measurements. The replacement of extracellular Cl byanions that are more permeant through the volume-activated Cl channel, as indicated byelectrophysiological measurements, significantly decreasedtaurine efflux. In the presence of less-permeant anions, an increase intaurine efflux was observed. Simultaneous measurement of the¹²⁵I, used as a tracer forCl, and[³H]taurine effluxshowed that the time courses for the two effluxes differed. InCl-rich medium the increasein I efflux was transient,whereas that for taurine was sustained. OsmosensitiveCl conductance, assessed bymeasuring changes in cell volume, increased rapidly after hypotonicshock. The influx of taurine was able to counteractCl conductance-dependentcell shrinkage but only ~4 min after triggering cell swelling. Thistaurine-induced effect was blocked by DIDS. Differences in anionsensitivity, the time course of activation, and sensitivity to DIDSsuggest that the main cell swelling-activated permeability pathways fortaurine and Cl are separate.

     

Zebrafish serotonin-N-acetyltransferase-2 gene regulation: pineal-restrictive downstream module contains a functional E-box and three photoreceptor conserved elements

Pineal function is defined by a set of very narrowly expressed genes that encode proteins required for photoperiodic transduction and rhythmic melatonin secretion. One of these proteins is serotonin N-acetyltransferase (arylalkylamine N-acetyltransferase, AANAT), which controls the daily rhythm in melatonin production. Here, pineal-specific expression of the zebrafish aanat-2 (zfaanat-2) was studied using in vivo transient expression analyses of promoter-reporter constructs; this revealed that specificity is determined by two regions located 12 kb away from each other. One is the 5'-flanking region, and the other is a 257-bp sequence, located 6 kb downstream of the transcribed region. This 3'-sequence, designated pineal-restrictive downstream module (PRDM), has a dual function: enhancement of pineal expression and inhibition of extrapineal expression. The former is an autonomic property of PRDM whereas the later function requires interaction with the upstream regulatory region of zfaanat-2. Functional analyses of the PRDM sequence revealed that three photoreceptor conserved elements (TAATC) and a single perfect E-box (CACGTG) are crucial for the dual function of PRDM. These results indicate that pineal specificity of zfaanat-2 is determined by the dual functionality of the PRDM and the interaction between upstream regulatory region and downstream photoreceptor conserved elements and E-box element.