The timely deposition of callose is essential for cytokinesis in Arabidopsis

The primary plant cell wall is laid down over a brief period of time during cytokinesis. Initially, a membrane network forms at the equator of a dividing cell. The cross-wall is then assembled and remodeled within this membrane compartment. Callose is the predominant luminal component of the nascent cross-wall or cell plate, but is not a component of intact mature cell walls, which are composed primarily of cellulose, pectins and xyloglucans. Widely accepted models postulate that callose comprises a transient, rapid spreading force for the expansion of membrane networks during cytokinesis. In this study, we clone and characterize an Arabidopsis gene, MASSUE / AtGSL8 , which encodes a putative callose synthase. massue mutants are seedling-lethal and have a striking cytokinesis-defective phenotype. Callose deposition was delayed in the cell plates of massue mutants. Mutant cells were occasionally bi- or multi-nucleate, with cell-wall stubs, and we frequently observed gaps at the junction between cross-walls and parental cell walls. The results suggest that the timely deposition of callose is essential for the completion of plant cytokinesis. Surprisingly, confocal analysis revealed that the cell-plate membrane compartment forms and expands, seemingly as far as the parental wall, prior to the appearance of callose. We discuss the possibility that callose may be required to establish a lasting connection between the nascent cross-wall and the parental cell wall.     

Eurosiberian meadows at their southern edge: patterns and phytogeography in the NW Tien Shan

Question: What are the community types, underlying gradients and phytogeographical affinities of montane meadows in the western Tien Shan? Location: Aksu‐Jabagly Nature Reserve, South Kazakhstan, Middle Asia. Methods: Species composition, structural and environmental variables were studied in 98 plots. Species composition was classified by cluster analysis and gradients explored using NMDS. Relationships between species richness, environmental and structural variables were investigated with regression analysis. Phytogeographic patterns were assessed by examining species distribution types. Results: Seven community types were distinguished by cluster analysis. Three axes of the NMDS explained 77% of the variation, showing different overlap of communities with environmental and structural properties. Species richness showed linear relationships with pH, altitude, heat load, soil skeletal content and structural variables. Middle Asian and Eurosiberian species constituted the majority of the species pool and cover. Conclusion: The studied communities represent a unique mixture of Middle Asian and Eurosiberian species that exhibit structural and environmental similarities to Eurosiberian meadows. The Tien Shan mountain meadows can thus be considered an endemic‐rich southern outlier of the broader Eurosiberian meadow formation. Shifts in land‐use patterns pose a potential threat that deserves more attention from conservationists.     

Sequence–structure relationships in RNA loops: establishing the basis for loop homology modeling

The specific function of RNA molecules frequently resides in their seemingly unstructured loop regions. We performed a systematic analysis of RNA loops extracted from experimentally determined three-dimensional structures of RNA molecules. A comprehensive loop-structure data set was created and organized into distinct clusters based on structural and sequence similarity. We detected clear evidence of the hallmark of homology present in the sequence–structure relationships in loops. Loops differing by <25% in sequence identity fold into very similar structures. Thus, our results support the application of homology modeling for RNA loop model building. We established a threshold that may guide the sequence divergence-based selection of template structures for RNA loop homology modeling. Of all possible sequences that are, under the assumption of isosteric relationships, theoretically compatible with actual sequences observed in RNA structures, only a small fraction is contained in the Rfam database of RNA sequences and classes implying that the actual RNA loop space may consist of a limited number of unique loop structures and conserved sequences. The loop-structure data sets are made available via an online database, RLooM. RLooM also offers functionalities for the modeling of RNA loop structures in support of RNA engineering and design efforts.     

Prevention of bacterial adhesion

Management of bacterial infections is becoming increasingly difficult due to the emergence and increasing prevalence of bacterial pathogens that are resistant to available antibiotics. Conventional antibiotics generally kill bacteria by interfering with vital cellular functions, an approach that imposes selection pressure for resistant bacteria. New approaches are urgently needed. Targeting bacterial virulence functions directly is an attractive alternative. An obvious target is bacterial adhesion. Bacterial adhesion to surfaces is the first step in colonization, invasion, and biofilm formation. As such, adhesion represents the Achilles heel of crucial pathogenic functions. It follows that interference with adhesion can reduce bacterial virulence. Here, we illustrate this important topic with examples of techniques being developed that can inhibit bacterial adhesion. Some of these will become valuable weapons for preventing pathogen contamination and fighting infectious diseases in the future.     

KCNE beta subunits determine pH sensitivity of KCNQ1 potassium channels.

BACKGROUND/AIMS: Heteromeric KCNEx/KCNQ1 (=KvLQT1, Kv7.1) K(+) channels are important for repolarization of cardiac myocytes, endolymph secretion in the inner ear, gastric acid secretion, and transport across epithelia. They are modulated by pH in a complex way: homomeric KCNQ1 is inhibited by external acidification (low pH(e)); KCNE2/KCNQ1 is activated; and for KCNE1/KCNQ1, variable effects have been reported. Methods: The role of KCNE subunits for the effect of pH(e) on KCNQ1 was analyzed in transfected COS cells and cardiac myocytes by the patch-clamp technique. RESULTS: In outside-out patches of transfected cells, hKCNE2/hKCNQ1 current was increased by acidification down to pH 4.5. Chimeras with the acid-insensitive hKCNE3 revealed that the extracellular N-terminus and at least part of the transmembrane domain of hKCNE2 are needed for activation by low pH(e). hKCNE1/hKCNQ1 heteromeric channels exhibited marked changes of biophysical properties at low pH(e): The slowly activating hKCNE1/hKCNQ1 channels were converted into constitutively open, non-deactivating channels. Experiments on guinea pig and mouse cardiac myocytes pointed to an important role of KCNQ1 during acidosis implicating a significant contribution to cardiac repolarization under acidic conditions. CONCLUSION: External pH can modify current amplitude and biophysical properties of KCNQ1. KCNE subunits work as molecular switches by modulating the pH sensitivity of human KCNQ1.     

Peripherally administered growth hormone increases brain dopaminergic activity and swimming in rainbow trout

There is increasing evidence that growth hormone (GH) has important behavioral effects in fish, but the underlying mechanisms are not well understood. To investigate if peripherally administered GH influences the monoaminergic activity of the brain, and how this is correlated to behavior, juvenile rainbow trout were implanted intraperitoneally with ovine GH. Fish were either kept isolated or in groups of five. The physical activity and food intake of the isolated fish were observed after 1 and 7 days, when brains were also sampled. The content of serotonin, dopamine, and noradrenaline and their metabolites in hypothalamus, telencephalon, optic tectum, and brain stem was then analyzed. For fish kept isolated for 7 days following implant, GH increased swimming activity and the levels of the dopamine metabolite 3, 4-hydroxy-phenylacetic acid (DOPAC) were higher in all brain parts examined. In the optic tectum, the levels of the dopamine metabolite homovanillic acid (HVA) were lowered by the GH treatment. One-day GH implant did not affect behavior or monoamine levels of isolated fish. In the fish kept in groups, a 7-day GH implant increased the hypothalamic levels of DOPAC, but not in the other brain parts examined, which may indicate an effect on the brain dopaminergic system from social interactions. It can be concluded that peripherally administered GH may function as a neuromodulator, affecting the dopaminergic activity of the rainbow trout brain, and this is associated with increased swimming activity.