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991.
Richthammer C Enseleit M Sanchez-Leon E März S Heilig Y Riquelme M Seiler S 《Molecular microbiology》2012,85(4):716-733
Rho proteins are key regulators of cellular morphogenesis, but their function in filamentous fungi is poorly understood. By generating conditional rho‐1 mutants, we dissected the function of the essential GTPase RHO1 in cell polarization and maintenance of cell wall integrity in Neurospora crassa. We identified NCU00668/RGF1 as RHO1‐specific exchange factor, which controls actin organization and the cell wall integrity MAK1 MAP kinase pathway through the direct interaction of active RHO1 with the formin BNI1 and PKC1 respectively. The activity of RGF1 is controlled by an intramolecular interaction of its DEP and GEF domains that blocks the activation of the GTPase. Moreover, the N‐terminal region including the DEP domain of RGF1 interacts with the plasma membrane sensor NCU06910/WSC1, potentially to activate the cell wall integrity pathway. RHO1 also functions as regulatory subunit of the glucan synthase. N. crassa possesses a second GTPase, RHO2, that is highly homologous to RHO1. RHO2 is of minor importance for growth and does not interact with BNI1. Conditional rho‐1;rho‐2 double mutants display strong synthetic growth and cell polarity defects. We show that RHO2 does not regulate glucan synthase activity and the actin cytoskeleton, but physically interacts with PKC1 to regulate the cell wall integrity pathway. 相似文献
992.
Alejandro Espinoza-Tenorio Matthias Wolff Marc H. Taylor Ileana Espejel 《Reviews in Fish Biology and Fisheries》2012,22(1):81-94
As tools within ecosystem-based fisheries management (EBFM), a wide range of Ecosystem Models (EMs) have been designed to
represent ecosystem complexity, but it is not always clear how the outputs of these models can be applied. We address this
debate in a literature review to illustrate how a better understanding of ecosystem modeling within the EBFM framework could
facilitate the use of EMs in the decision-making process. We classify EMs according to their complexity, and qualitatively
evaluate their level of success with regard to five general goals of EBFM. In principle, no single EM is found to successfully
accomplish all the EBFM goals. Therefore, we suggest that the way in which ecosystem modeling can effectively contribute to
EBFM is through a structured modeling process, which should be pursued according to the context of each specific area. Within
this planning strategy a range of Ems should be considered, from rather simple ones with few parameters, whose outputs are
scientifically robust but possibly of limited use within the EBFM, to those which include a large number of ecosystem elements
yet at the expense of increased uncertainty. If multiple EMs, despite their different assumptions, leads to consistent and
converging results then robust management decisions will be supported. The present paper appears particularly useful to anyone
confronted with the selection of modeling tools for the implementation of fisheries management strategies considering the
particular situation of the fishery. 相似文献
993.
Breitbach N Tillmann S Schleuning M Grünewald C Laube I Steffan-Dewenter I Böhning-Gaese K 《Oecologia》2012,168(2):425-437
Land-use intensification is a major cause for the decline in species diversity in human-modified landscapes. The loss of functionally
important species can reduce a variety of ecosystem functions, such as pollination and seed dispersal, but the intricate relationships
between land-use intensity, biodiversity and ecosystem functioning are still contentious. Along a gradient from forest to
intensively used farmland, we quantified bee species richness, visitation rates of bees and pollination success of wild cherry
trees (Prunus avium). We analysed the effects of structural habitat diversity at a local scale and of the proportion of suitable habitat around
each tree at a landscape scale. We compared these findings with those from previous studies of seed-dispersing birds and mammals
in the same model system and along the same land-use gradient. Bee species richness and visitation rates were found to be
highest in structurally simple habitats, whereas bird species richness—but not their visitation rates—were highest in structurally
complex habitats. Mammal visitation rates were only influenced at the landscape scale. These results show that different functional
groups of animals respond idiosyncratically to gradients in habitat and landscape structure. Despite strong effects on bees
and birds, pollination success and bird seed removal did not differ along the land-use gradient at both spatial scales. These
results suggest that mobile organisms, such as bees and birds, move over long distances in intensively used landscapes and
thereby buffer pollination and seed-dispersal interactions. We conclude that measures of species richness and interaction
frequencies are not sufficient on their own to understand the ultimate consequences of land-use intensification on ecosystem
functioning. 相似文献
994.
Mycorrhizal responsiveness trends in annual crop plants and their wild relatives—a meta-analysis on studies from 1981 to 2010 总被引:1,自引:0,他引:1
Anika Lehmann E. Kathryn Barto Jeff R. Powell Matthias C. Rillig 《Plant and Soil》2012,355(1-2):231-250
Background and aims
Year of release of a cultivar reflects the agricultural and breeding practices of its time; we hypothesize that there are differences in mycorrhizal responsiveness of new high yielding and old crop plants and landraces. We evaluated the importance of the year of release on mycorrhizal responsiveness, arbuscular mycorrhizal (AM) fungal root colonization and P efficiency. We also analyzed the effect of experimental treatments, P efficiency (P acquisition and P utilization efficiency) and AM fungal root colonization on a potential mycorrhizal responsiveness trend for year of release.Methods
We conducted a meta-analysis on 39 publications working on 320 different crop plant genotypes.Results
New cultivars were less intensely colonized but were more mycorrhiza-responsive (and possibly dependent) compared to ancestral genotypes. This trend was potentially influenced by the moderator variables density, pre-germination, plant, plant type and AMF species. AM root colonization was also important for the mycorrhizal responsiveness trend for year of release, but P efficiency was not.Conclusions
With the data available we could find no evidence that new crop plant genotypes lost their ability to respond to mycorrhiza due to agricultural and breeding practices. 相似文献995.
Biological soil crusts, formed by an association of soil particles with cyanobacteria, lichens, mosses, fungi and bacteria in varying proportions, live in or directly on top of the uppermost soil layer. To evaluate their role in the global carbon cycle, gas exchange measurements were conducted under controlled conditions. Moss-dominated soil crusts were first analyzed as moss tufts on soil, then the mosses were removed and the soil was analyzed separately to obtain the physiological response of both soil and individual moss stems. Net photosynthetic response of moss stems and complete crusts was decreased by insufficient and excess amounts of water, resulting in optimum curves with similar ranges of optimum water content. Light saturation of both sample types occurred at high irradiance, but moss stems reached light compensation and saturation points at lower values. Optimum temperatures of moss stems ranged between 22 and 27°C, whereas complete crusts reached similar net photosynthesis between 7 and 27°C. Under optimum conditions, moss stems reached higher net photosynthesis (4.0 vs. 2.8 μmol m?2 s?1) and lower dark respiration rates (?0.9 vs. ?2.4 μmol m?2 s?1). Respiration rates of soil without moss stems were high (up to ?2.0 μmol m?2 s?1) causing by far lower absolute values of NP/DR ratios of soil crusts as compared to moss stems. In carbon balances, it therefore has to be clearly distinguished between measurements of soil crust components versus complete crusts. High rates of soil respiration may be caused by leaching of mosses, creating high-nutrient microsites that favor microorganism growth. 相似文献
996.
997.
Beyer T Danilchik M Thumberger T Vick P Tisler M Schneider I Bogusch S Andre P Ulmer B Walentek P Niesler B Blum M Schweickert A 《Current biology : CB》2012,22(1):33-39
In vertebrates, most inner organs are asymmetrically arranged with respect to the main body axis [1]. Symmetry breakage in fish, amphibian, and mammalian embryos depends on cilia-driven leftward flow of extracellular fluid during neurulation [2-5]. Flow induces the asymmetric nodal cascade that governs asymmetric organ morphogenesis and placement [1, 6, 7]. In the frog Xenopus, an alternative laterality-generating mechanism involving asymmetric localization of serotonin at the 32-cell stage has been proposed [8]. However, no functional linkage between this early localization and flow at neurula stage has emerged. Here, we report that serotonin signaling is required for specification of the superficial mesoderm (SM), which gives rise to the ciliated gastrocoel roof plate (GRP) where flow occurs [5, 9]. Flow and asymmetry were lost in embryos in which serotonin signaling was downregulated. Serotonin, which we found uniformly distributed along the main body axes in the early embryo, was required for Wnt signaling, which provides the instructive signal to specify the GRP. Importantly, serotonin was required for Wnt-induced double-axis formation as well. Our data confirm flow as primary mechanism of symmetry breakage and suggest a general role of serotonin as competence factor for Wnt signaling during axis formation in Xenopus. 相似文献
998.
The idea that copulation might increase predation risk is a classic suggestion [1-3], but empirical evidence to support it is surprisingly scarce. While some early work found decreased vulnerability to predation during mating [2], two lab and one very recent field study documented increased predation during mating in freshwater amphipods [4], water striders [5] and locusts [6]. Decreased vigilance, less efficient escape responses, and increased conspicuousness of mating pairs have been suggested as mechanisms that might underpin elevated predation risk during copulation [2]. However, these putative mechanisms have never been investigated empirically. Here we describe a bat-insect system within which copulation greatly increases predation risk. We experimentally demonstrate that wild Natterer's bats (Myotis nattereri) 'eavesdrop' on acoustic cues emanating from copulating flies (Musca domestica) in a cowshed (Figure 1). With this evidence, we pinpoint increased conspicuousness as a relevant mechanism for elevated predation risk during mating. 相似文献
999.
Sagner A Merkel M Aigouy B Gaebel J Brankatschk M Jülicher F Eaton S 《Current biology : CB》2012,22(14):1296-1301
Epithelial tissues develop planar polarity that is reflected in the global alignment of hairs and cilia with respect to the tissue axes. The planar cell polarity (PCP) proteins form asymmetric and polarized domains across epithelial junctions that are aligned locally between cells and orient these external structures. Although feedback mechanisms can polarize PCP proteins intracellularly and locally align polarity between cells, how global PCP patterns are specified is not understood. It has been proposed that the graded distribution of a biasing factor could guide long-range PCP. However, we recently identified epithelial morphogenesis as a mechanism that can reorganize global PCP patterns; in the Drosophila pupal wing, oriented cell divisions and rearrangements reorient PCP from a margin-oriented pattern to one that points distally. Here, we use quantitative image analysis to study how PCP patterns first emerge in the wing. PCP appears during larval growth and is spatially oriented through the activities of three organizer regions that control disc growth and patterning. Flattening morphogen gradients emanating from these regions does not reduce intracellular polarity but distorts growth and alters specific features of the PCP pattern. Thus, PCP may be guided by morphogenesis rather than morphogen gradients. 相似文献
1000.
Fürst MA Durey M Nash DR 《Proceedings. Biological sciences / The Royal Society》2012,279(1728):516-522
Social insect colonies are like fortresses, well protected and rich in shared stored resources. This makes them ideal targets for exploitation by predators, parasites and competitors. Colonies of Myrmica rubra ants are sometimes exploited by the parasitic butterfly Maculinea alcon. Maculinea alcon gains access to the ants' nests by mimicking their cuticular hydrocarbon recognition cues, which allows the parasites to blend in with their host ants. Myrmica rubra may be particularly susceptible to exploitation in this fashion as it has large, polydomous colonies with many queens and a very viscous population structure. We studied the mutual aggressive behaviour of My. rubra colonies based on predictions for recognition effectiveness. Three hypotheses were tested: first, that aggression increases with distance (geographical, genetic and chemical); second, that the more queens present in a colony and therefore the less-related workers within a colony, the less aggressively they will behave; and that colonies facing parasitism will be more aggressive than colonies experiencing less parasite pressure. Our results confirm all these predictions, supporting flexible aggression behaviour in Myrmica ants depending on context. 相似文献