Molecular requirements for the formation of a kinetochore–microtubule interface by Dam1 and Ndc80 complexes

Kinetochores are large protein complexes that link sister chromatids to the spindle and transduce microtubule dynamics into chromosome movement. In budding yeast, the kinetochore–microtubule interface is formed by the plus end–associated Dam1 complex and the kinetochore-resident Ndc80 complex, but how they work in combination and whether a physical association between them is critical for chromosome segregation is poorly understood. Here, we define structural elements required for the Ndc80–Dam1 interaction and probe their function in vivo. A novel ndc80 allele, selectively impaired in Dam1 binding, displayed growth and chromosome segregation defects. Its combination with an N-terminal truncation resulted in lethality, demonstrating essential but partially redundant roles for the Ndc80 N-tail and Ndc80–Dam1 interface. In contrast, mutations in the calponin homology domain of Ndc80 abrogated kinetochore function and were not compensated by the presence of Dam1. Our experiments shed light on how microtubule couplers cooperate and impose important constraints on structural models for outer kinetochore assembly.     

Raptors as legitimate secondary dispersers of weed seeds

Although raptors are not usually seen as seed dispersers, we demonstrate their important ecological role as legitimate seed dispersers of weeds. On the oceanic island of Fuerteventura in the Canary Islands, up to 11 000 weed seeds from a total of 39 and 62 different plant species, respectively, were found in 300 and 319 pellets, respectively, of two native predatory birds, the Common Buzzard Buteo buteo and the Eurasian Kestrel Falco tinnunculus, which consumed European Rabbits Oryctolagus cuniculus and Barbary Ground Squirrels Atlantoxerus getulus, both invasive mammals that carried these seeds in their guts. Four and seven weed species appeared with a frequency of occurrence greater than 10% in the pellets of Kestrels and Buzzards, respectively. Despite the time interval between pellet collection and germination experiments, almost 10% of planted seeds germinated, even after passing through two digestive processes, one inside the mammal and another inside the raptor. Our study encourages a change of perspective in this regard, as raptors may be involved in complex interactive dispersal processes on a wider geographical scale.     

Assembly,molecular organization,and membrane-binding properties of development-specific septins

Septin complexes display remarkable plasticity in subunit composition, yet how a new subunit assembled into higher-order structures confers different functions is not fully understood. Here, this question is addressed in budding yeast, where during meiosis Spr3 and Spr28 replace the mitotic septin subunits Cdc12 and Cdc11 (and Shs1), respectively. In vitro, the sole stable complex that contains both meiosis-specific septins is a linear Spr28–Spr3–Cdc3–Cdc10–Cdc10–Cdc3–Spr3–Spr28 hetero-octamer. Only coexpressed Spr3 and Spr28 colocalize with Cdc3 and Cdc10 in mitotic cells, indicating that incorporation requires a Spr28-Spr3 protomer. Unlike their mitotic counterparts, Spr28-Spr3–capped rods are unable to form higher-order structures in solution but assemble to form long paired filaments on lipid monolayers containing phosphatidylinositol-4,5-bisphosphate, mimicking presence of this phosphoinositide in the prospore membrane. Spr28 and Spr3 fail to rescue the lethality of a cdc11Δ cdc12Δ mutant, and Cdc11 and Cdc12 fail to restore sporulation proficiency to spr3Δ/spr3Δ spr28Δ/spr28Δ diploids. Thus, specific meiotic and mitotic subunits endow septin complexes with functionally distinct properties.     

Crop husbandry activities and wild plant gathering,use and consumption at the EPPNB Tell Qarassa North (south Syria)

The Early Pre-Pottery Neolithic B (EPPNB) in southwest Asia is a fundamental period in research on the origins of domesticated plants. However, there are few archaeobotanical data with which to characterise the plant-based subsistence and crop husbandry activities during this time, which hinders the understanding of the factors that triggered the appearance of plant domestication. In this paper, analyses of non-woody plant macro-remains provide new insights into subsistence activities such as crop cultivation (husbandry activities and storage) and plant use (wild plant gathering and food preparation) during the EPPNB at Tell Qarassa North (south Syria). We make comparisons between Tell Qarassa North and the evidence at earlier and later periods as to how plants were used, and highlight similarities and differences in the practices attested, as well as describing some of the consequences that these plant-related activities may have had in terms of labour and social organization during EPPNB.     

Phylogenetic analysis of the composition of bacterial communities in human-exploited coastal environments from Mallorca Island (Spain)

The phylogenetic analysis of bacterial communities in environments receiving anthropogenic impact could help us to understand its effects and might be useful in the development of monitoring or management strategies. A study of the composition of 16S rDNA clone libraries prepared from bacterial communities in water samples from a marina and a beach on the coast of Mallorca (W. Mediterranean) was undertaken at two time points, corresponding to periods of maximum and minimum anthropogenic use of this area for nautical and recreational activities. Libraries generated from the marina were significantly different from those from the beach and a non-impacted, bay sample. In the marina, a predominance of sequence types was observed related to bacterioplankton from nutrient-enriched environments or typically associated with phytoplankton, such as certain phylotypes of the Roseobacter clade, OM60 clade and Bacteroidetes. Similar results were found in the summer beach library but not in the winter one, in which there was an increase in the number of clones from oligotrophic groups, in agreement with lower chlorophyll content and bacterial counts. Therefore, nutrient enrichment seemed to be an important driver of the composition of bacterial communities in sites receiving direct human impact. Interesting sequence types from the Cryomorphaceae and group agg58 (Bacteroidetes) were exclusively found in beach libraries, and the reasons for this distribution deserve further study. Clones related to putative hydrocarbon-degrading bacteria of the genus Acinetobacter were observed in the marina, in agreement with a certain degree of pollution at this site. Non-marine sequences belonging to the Actinobacteria predominated over marine groups in the summer library from the marina and, therefore, unusual communities might be transiently present in this enclosed environment. Overall, the composition of the bacterial communities in these environments agreed well with the defining characteristics of the environments sampled.     

Response of mycorrhizal grapevine to Armillaria mellea inoculation: disease development and polyamines

A study was conducted with the vine rootstock Richter 110 (Vitis berlandieri Planch. x Vitis rupestris L.) in order to assess whether the colonisation by the arbuscular mycorrhizal fungus (AMF) Glomus intraradices (BEG 72) can delay the disease development in plants inoculated with the root-rot fungus Armillaria mellea (Vahl:Fr) Kummer, and to elucidate if the levels of polyamines (PAs) are modified in response to G. intraradices, A. mellea or by the dual infection. Four treatments were considered: control and G. intraradices-inoculated plants infected or not with A. mellea. Plant growth, mycorrhizal colonisation and disease development were monitored throughout the experiment. High performance liquid chromatography (HPLC) in combination with fluorescence spectrophotometry was used to separate and quantify free root and leaf polyamines. The slower development of pathogenic symptoms and the higher plant biomass of mycorrhizal plants inoculated with A. mellea indicate an increase of tolerance due to the AMF inoculation. The variations in free PA levels detected at the beginning of the pathogenic infection suggest that PAs may have a potential role in the signalling mechanisms of the tolerance of mycorrhizal plants against A. mellea.     

The impact of salt stress on the water status of barley plants is partially mitigated by elevated CO2

With the changing climate, plants will be facing increasingly harsh environmental conditions marked by elevated salinity in the soils and elevated concentrations of CO₂ in the atmosphere. These two factors have opposite effects on water status in plants. Therefore, our objective was to determine the interaction between these two factors and to determine whether elevated [CO₂] might alleviate the adverse effects of salt stress on water status in two barley cultivars, Alpha and Iranis, by studying their relative water content and their water potential and its components, transpiration rate, hydraulic conductance, and water use efficiency. Both cultivars maintained their water status under salt stress, increasing water use efficiency and conserving a high relative water content by (1) reducing water potential via passive dehydration and active osmotic adjustment and (2) decreasing transpiration through stomatal closure and reducing hydraulic conductance. Iranis showed a greater capacity to achieve osmotic adjustment than Alpha. Under the combined conditions of salt-stress and elevated [CO₂], both cultivars (1) achieved osmotic adjustment to a greater extent than at ambient [CO₂], likely due to elevated rates of photosynthesis, and (2) decreased passive dehydration by stomatal closure, thereby maintaining a greater turgor potential, relative water content, and water use efficiency. Therefore, we found an interaction between salt stress and elevated [CO₂] with regard to water status in plants and found that elevated [CO₂] is associated with improved water status of salt-stressed barley plants.