Current Biology最新文献

Despite competition for both space and nutrients, bacterial species often coexist within structured, surface-attached communities termed biofilms. While these communities play important, widespread roles in ecosystems and are agents of human infection, understanding how multiple bacterial species assemble to form these communities and what physical processes underpin the composition of multispecies biofilms remains an active area of research. Using a model three-species community composed of Pseudomonas aeruginosa, Escherichia coli, and Enterococcus faecalis, we show with cellular-scale resolution that biased dispersal of the dominant community member, P. aeruginosa, prevents competitive exclusion from occurring, leading to the coexistence of the three species. A P. aeruginosa bqsS deletion mutant no longer undergoes periodic mass dispersal, leading to the local competitive exclusion of E. coli. Introducing periodic, asymmetric dispersal behavior into minimal models, parameterized by only maximal growth rate and local density, supports the intuition that biased dispersal of an otherwise dominant competitor can permit coexistence generally. Colonization experiments show that WT P. aeruginosa is superior at colonizing new areas, in comparison to ΔbqsS P. aeruginosa, but at the cost of decreased local competitive ability against E. coli and E. faecalis. Overall, our experiments document how one species' modulation of a competition-dispersal-colonization trade-off can go on to influence the stability of multispecies coexistence in spatially structured ecosystems.

Watching a speaker's face improves speech perception accuracy. This benefit is enabled, in part, by implicit lipreading abilities present in the general population. While it is established that lipreading can alter the perception of a heard word, it is unknown how these visual signals are represented in the auditory system or how they interact with auditory speech representations. One influential, but untested, hypothesis is that visual speech modulates the population-coded representations of phonetic and phonemic features in the auditory system. This model is largely supported by data showing that silent lipreading evokes activity in the auditory cortex, but these activations could alternatively reflect general effects of arousal or attention or the encoding of non-linguistic features such as visual timing information. This gap limits our understanding of how vision supports speech perception. To test the hypothesis that the auditory system encodes visual speech information, we acquired functional magnetic resonance imaging (fMRI) data from healthy adults and intracranial recordings from electrodes implanted in patients with epilepsy during auditory and visual speech perception tasks. Across both datasets, linear classifiers successfully decoded the identity of silently lipread words using the spatial pattern of auditory cortex responses. Examining the time course of classification using intracranial recordings, lipread words were classified at earlier time points relative to heard words, suggesting a predictive mechanism for facilitating speech. These results support a model in which the auditory system combines the joint neural distributions evoked by heard and lipread words to generate a more precise estimate of what was said.

Microtubules (MTs) are dynamically unstable polar biopolymers switching between periods of polymerization and depolymerization, with the switch from the polymerization to the depolymerization phase termed catastrophe and the reverse transition termed rescue.¹ In presence of MT-crosslinking proteins, MTs form parallel or anti-parallel overlaps and self-assemble reversibly into complex networks, such as the mitotic spindle. Differential regulation of MT dynamics in parallel and anti-parallel overlaps is critical for the self-assembly of these networks.^2,3 Diffusible MT crosslinkers of the Ase1/MAP65/PRC1 family associate with different affinities to parallel and antiparallel MT overlaps, providing a basis for this differential regulation.^{4,5,6,7,8,9,10,11} Ase1/MAP65/PRC1 family proteins directly affect MT dynamics¹² and recruit other proteins that locally alter MT dynamics, such as CLASP or kinesin-4.^{7,13,14,15,16} However, how Ase1 differentially regulates MT stability in parallel and antiparallel bundles is unknown. Here, we show that Ase1 selectively promotes antiparallel MT overlap longevity by slowing down the depolymerization velocity and by increasing the rescue frequency, specifically in antiparallelly crosslinked MTs. At the retracting ends of depolymerizing MTs, concomitant with slower depolymerization, we observe retention and accumulation of Ase1 between crosslinked MTs and on isolated MTs. We hypothesize that the ability of Ase1 to reduce the dissociation of tubulin subunits is sufficient to promote its enrichment at MT ends. A mathematical model built on this idea shows good agreement with the experiments. We propose that differential regulation of MT dynamics by Ase1 contributes to mitotic spindle assembly by specifically stabilizing antiparallel overlaps, compared to parallel overlaps or isolated MTs.

Stem cells often rely on signals from a niche, which in many tissues adopts a precise morphology. What remains elusive is how niches are formed and how morphology impacts function. To address this, we leverage the Drosophila gonadal niche, which affords genetic tractability and live-imaging. We have previously shown mechanisms dictating niche cell migration to their appropriate position within the gonad and the resultant consequences on niche function. Here, we show that once positioned, niche cells robustly polarize filamentous actin (F-actin) and non-muscle myosin II (MyoII) toward neighboring germ cells. Actomyosin tension along the niche periphery generates a highly reproducible smoothened contour. Without contractility, niches are misshapen and exhibit defects in their ability to regulate germline stem cell behavior. We additionally show that germ cells aid in polarizing MyoII within niche cells and that extrinsic input is required for niche morphogenesis and function. Our work reveals a feedback mechanism where stem cells shape the niche that guides their behavior.

Pollinator behavior is vital to plant-pollinator interactions, affecting the acquisition of floral rewards, patterns of pollen transfer, and plant reproductive success. During buzz pollination, bees produce vibrations with their indirect flight muscles to extract pollen from tube-like flowers. Vibrations can be transmitted to the flower via the mandibles, abdomen, legs, or thorax directly. Vibration amplitude at the flower determines the rate of pollen release and should vary with the coupling of bee and flower. This coupling often occurs through anther biting, but no studies have quantified how biting affects flower vibration. Here, we used high-speed filmography to investigate how flower vibration amplitude changes during biting in Bombus terrestris visiting two species of buzz-pollinated flowering plants: Solanum dulcamara and Solanum rostratum (Solanaceae). We found that floral buzzing drives head vibrations up to 3 times greater than those of the thorax, which doubles the vibration amplitude of the anther during biting compared with indirect vibration transmission when not biting. However, the efficiency of this vibration transmission depends on the angle at which the bee bites the anther. Variation in transmission mechanisms, combined with the diversity of vibrations across bee species, yields a rich assortment of potential strategies that bees could employ to access rewards from buzz-pollinated flowers.

Epithelial homeostasis can be critically influenced by how cells respond to mechanical forces, both local changes in force balance between cells and altered tissue-level forces.¹ Coupling of specialized cell-cell adhesions to their cytoskeletons provides epithelia with diverse strategies to respond to mechanical stresses.^2,3,4 Desmosomes confer tissue resilience when their associated intermediate filaments (IFs)^2,3 stiffen in response to strain,^{5,6,7,8,9,10,11} while mechanotransduction associated with the E-cadherin apparatus^12,13 at adherens junctions (AJs) actively modulates actomyosin by RhoA signaling. Although desmosomes and AJs make complementary contributions to mechanical homeostasis in epithelia,^6,8 there is increasing evidence to suggest that these cytoskeletal-adhesion systems can interact functionally and biochemically.^{8,14,15,16,17,18,19,20} We now report that the desmosome-IF system integrated by desmoplakin (DP) facilitates active tension sensing at AJs for epithelial homeostasis. DP function is necessary for mechanosensitive RhoA signaling at AJs to be activated when tension was applied to epithelial monolayers. This effect required DP to anchor IFs to desmosomes and recruit the dystonin (DST) cytolinker to apical junctions. DP RNAi reduced the mechanical load that was applied to the cadherin complex by increased monolayer tension. Consistent with reduced mechanical signal strength, DP RNAi compromised assembly of the Myosin VI-E-cadherin mechanosensor that activates RhoA. The integrated DP-IF system therefore supports AJ mechanotransduction by enhancing the mechanical load of tissue tension that is transmitted to E-cadherin. This crosstalk was necessary for efficient elimination of apoptotic epithelial cells by apical extrusion, demonstrating its contribution to epithelial homeostasis.

In both mammals and flies, circadian brain neurons orchestrate physiological oscillations and behaviors like wake and sleep-these neurons can be subdivided by morphology and by gene expression patterns. Recent single-cell sequencing studies identified 17 Drosophila circadian neuron groups. One of these includes only two lateral neurons (LNs), which are marked by the expression of the neuropeptide ion transport peptide (ITP). Although these two ITP⁺ LNs have long been grouped with five other circadian evening activity cells, inhibiting the two neurons alone strongly reduces morning activity, indicating that they also have a prominent morning function. As dopamine signaling promotes activity in Drosophila, like in mammals, we considered that dopamine might influence this morning activity function. Moreover, the ITP⁺ LNs express higher mRNA levels than other LNs of the type 1-like dopamine receptor Dop1R1. Consistent with the importance of Dop1R1, cell-specific CRISPR-Cas9 mutagenesis of this receptor in the two ITP⁺ LNs renders flies significantly less active in the morning, and ex vivo live imaging shows Dop1R1-dependent cyclic AMP (cAMP) responses to dopamine in these two neurons. Notably, the response is more robust in the morning, reflecting higher morning Dop1R1 mRNA levels in the two neurons. As mRNA levels are not elevated in constant darkness, this suggests light-dependent upregulation of morning Dop1R1 transcript levels. Taken together with the enhanced morning cAMP response to dopamine, the data indicate how light and dopamine promote morning wakefulness in flies, mimicking the important effect of light on morning wakefulness in humans.

Plants have powerful defense mechanisms and extensive immune receptor repertoires, yet crop monocultures are prone to epidemic diseases. Rice (Oryza sativa) is susceptible to many diseases, such as rice blast caused by Magnaporthe oryzae. Varietal resistance of rice to blast relies on intracellular nucleotide binding, leucine-rich repeat (NLR) receptors that recognize specific pathogen molecules and trigger immune responses. In the Yuanyang terraces in southwest China, rice landraces rarely show severe losses to disease whereas commercial inbred lines show pronounced field susceptibility. Here, we investigate within-landrace NLR sequence diversity of nine rice landraces and eleven modern varieties using complexity reduction techniques. We find that NLRs display high sequence diversity in landraces, consistent with balancing selection, and that balancing selection at NLRs is more pervasive in landraces than modern varieties. Notably, modern varieties lack many ancient NLR haplotypes that are retained in some landraces. Our study emphasizes the value of standing genetic variation that is maintained in farmer landraces as a resource to make modern crops and agroecosystems less prone to disease. The conservation of landraces is, therefore, crucial for ensuring food security in the face of dynamic biotic and abiotic threats.

Chlorosis dormancy resulting from nitrogen starvation and its resuscitation upon available nitrogen contributes greatly to the fitness of cyanobacterial population under nitrogen-fluctuating environments. The reinstallation of the photosynthetic machinery is a key process for resuscitation from a chlorotic dormant state; however, the underlying regulatory mechanism is still elusive. Here, we reported that red light is essential for re-greening chlorotic Synechocystis sp. PCC 6803 (a non-diazotrophic cyanobacterium) after nitrogen supplement under weak light conditions. The expression of dark-operative protochlorophyllide reductase (DPOR) governed by the transcriptional factor RpaB was strikingly induced by red light in chlorotic cells, and its deficient mutant lost the capability of resuscitation from a dormant state, indicating DPOR catalyzing chlorophyll synthesis is a key step in the photosynthetic recovery of dormant cyanobacteria. Although light-dependent protochlorophyllide reductase is widely considered as a master switch in photomorphogenesis, this study unravels the primitive DPOR as a spark to activate the photosynthetic recovery of chlorotic dormant cyanobacteria. These findings provide new insight into the biological significance of DPOR in cyanobacteria and even some plants thriving in extreme environments.

Eukaryotic chromosome segregation requires kinetochores, multi-megadalton protein machines that assemble on the centromeres of chromosomes and mediate attachments to dynamic spindle microtubules. Kinetochores are built from numerous complexes, and there has been progress in structural studies on recombinant subassemblies. However, there is limited structural information on native kinetochore architecture. To address this, we purified functional, native kinetochores from the thermophilic yeast Kluyveromyces marxianus and examined them by electron microscopy (EM), cryoelectron tomography (cryo-ET), and atomic force microscopy (AFM). The kinetochores are extremely large, flexible assemblies that exhibit features consistent with prior models. We assigned kinetochore polarity by visualizing their interactions with microtubules and locating the microtubule binder, Ndc80c. This work shows that isolated kinetochores are more dynamic and complex than what might be anticipated based on the known structures of recombinant subassemblies and provides the foundation to study the global architecture and functions of kinetochores at a structural level.