Biology subjects

Rasmussen, C.

Publications and source records attributed to Rasmussen, C..

12 recordsLinked to original sources

bioRxiv2026

KATANIN is required for the formation of complete preprophase bands and subsequent division positioning of subsidiary mother cells in maize

Microtubule dynamics underpin cell division, movement, and growth in eukaryotic organisms. KATANIN p60 is a microtubule-severing protein that promotes proper cell elongation and division. In plants, division positioning is initiated in late G2 via the formation of a microtubule structure called the preprophase band (PPB). Maize p60 mutants have defects in microtubule severing and form abnormal PPBs in symmetrically dividing cells, including both incompletely assembled and misoriented PPBs. Here, we show that an asymmetric division required to generate stomatal complexes in maize p60 mutants have normally positioned but often incompletely formed PPBs. Incompletely formed PPBs lead to misoriented divisions and nuclear positioning defects in p60 mutants.

plant biology↗

bioRxiv2026

Gain and loss of gut symbionts during stingless bee diversification is linked to host group size

Microbiomes typically vary between closely related host species, but how and why they diverge during host diversification remain poorly understood. Bees provide a well-established model for the role of sociality in microbiome evolution: solitary species have generalist gut bacterial symbionts, while eusocial honey bees and bumble bees have host-specific "core" gut bacterial symbionts. Curiously however, some species of stingless bees--the most diverse clade of eusocial bees--lack the core symbionts Snodgrassella and Gilliamella. Here, we tested whether group size, a fundamental trait of social organisms, explains symbiont gain and loss in stingless bees. Using specimens from a global collection, we performed 16S rRNA gene sequencing and qPCR on 187 adult workers representing 29 species and 18 genera. Maximum reported colony sizes for these species range from [~]100 to over [~]100,000 individuals. Our phylogenetic models indicate positive feedbacks between group size and the symbionts Snodgrassella and Gilliamella. We suggest that challenges faced by large groups (e.g., disease risk) may select for symbionts that supply needed functionality (e.g., pathogen protection). Our findings highlight group size as a potentially widespread driver of microbiome evolution in social hosts.

evolutionary biology↗

bioRxiv2025

KATANIN promotes cell elongation and division to generate proper cell numbers in maize organs

Microtubule severing is essential for proper eukaryotic cell elongation and division. Here we show that the microtubule severing protein, KATANIN, is encoded by two genes in Zea mays (maize) called Discordia3a (Dcd3a) and Dcd3b. Loss of function allele combinations contribute to reduced microtubule severing and decreased cell elongation. The latter results in reduced cell number by slowing entry into mitosis. KATANIN is important for preprophase band (PPB) formation and positioning, and nuclear positioning in symmetric cell divisions. A combination of these defects contributes to generating mutant plants with small size and aberrant shape.

plant biology↗

bioRxiv2025

Prenatal Zika Virus Exposure Disrupts Social-Emotional Development and Cortical Visual Function in Infant Macaques

Prenatal exposure to Zika virus (ZIKV) results in a spectrum of outcomes, ranging from severe birth defects and early childhood developmental delays to no apparent deficits. However, the mechanisms underlying these outcomes, particularly in the context of different maternal infection conditions, remain poorly defined. In this study, we employed a translational rhesus macaque model of prenatal ZIKV infection to evaluate longitudinal visual and auditory development from 1 to 12 months of age and characterize neurodevelopmental outcomes at 12 months. Pregnant macaques, either flavivirus-naive or with prior dengue virus (DENV) exposure, were inoculated in the first trimester ([~]30 or 45 gestational days) with an Asian or African lineage of ZIKV or received a saline injection as controls. Maternal plasma viremia duration, viral RNA burden at the maternal-fetal interface, and neutralizing antibody titers did not differ between inoculation cohorts or controls. At 12 months, ZIKV-exposed infants demonstrated altered maternal attachment behaviors and reduced inhibition when approaching sensory stimuli compared to controls. Visual pathway function, assessed by electrophysiology, was significantly impaired at 3 months but normalized by 12 months. Hearing loss was more common among ZIKV-exposed infants, although not statistically significant. Developmental outcomes were associated with prenatal ZIKV exposure itself, independent of viremia duration, neutralizing antibody titer, viral lineage, or maternal DENV immunity, and were not mediated by visual impairment or hearing loss. These findings highlight that any prenatal ZIKV exposure can disrupt early neurobehavioral development and visual function, underscoring the need for prevention strategies focused on maternal infection and early intervention.

microbiology↗

bioRxiv2025

Improving allometric models to estimate the proboscis length of tropical bees

The proboscis length of bees is a key morphological trait shaping communities, pollination networks, and likely their responses to habitat loss. Despite its importance, it is rarely considered in ecological studies because of logistic limitations in obtaining accurate measurements across many different species. In two previous studies, the proboscis length of temperate bee species was estimated based on body size and bee family. However, bee taxa partially occurring in the tropics might deviate from this allometric relationship due to different functional constraints. Thus, we tested if equations developed for temperate bees can accurately predict the proboscis length in Meliponini, Euglossini (both Apidae), and Augochlorini (Halictidae), three ubiquitous and highly important tribes of tropical bees. We measured the intertegular distance (as a proxy of body size measurement) and the proboscis length of 892 specimens of 105 tropical species. We used these measurements to evaluate the previous model and found that its estimations lacked accuracy when applied to tropical bees, particularly to Meliponini and Euglossini. We developed new allometric equations estimating the proboscis length based on the intertegular distance, using (sub-) genera as an additional predictive variable to refine the estimations. We tested our approach by creating a test model for Meliponini, trained with only 80 % of the data, and evaluated this model using the remaining 20 %, resulting in a high accuracy of estimates. Our results shed additional light on the nature of the proboscis length-body size allometric relationship in tropical bees and provide a tool for future studies on the functional ecology of bees and their interactions with plants.

zoology↗

bioRxiv2025

Stratification along tropical forest succession enhances pollinator diversity via functionally unique canopies

Vertical stratification is a prominent driver of biodiversity in forests. As the proportion of successional forests increases worldwide and canopies are lost at a fast pace, it is crucial to understand the role of stratification as a driver of community recovery and ecological processes during succession, particularly for important plant mutualist groups essential for forest recovery. Within a well-resolved chronosequence in the northwestern Ecuadorian rainforest, we compiled an extensive database of over 20,000 diurnal and nocturnal pollinators and 2,000 interactions with plants and examined the interacting effects of recovery age and stratification on pollinator community and interaction network reassembly. In late successional and old-growth forests, stratification was a stronger predictor of pollinator abundance, alpha-diversity, functional richness and beta-diversity than forest legacy. While most groups were strongly associated with canopies (moths, social bees, and nocturnal bees), orchid bees exhibited an inverse pattern, also presenting the strongest functional response to stratification and recovery status. Within the entire chronosequence (0-38 years of recovery, plus old-growth forests), recovery status and stratification, alongside landscape features, acted synergistically as predictors of pollinator community parameters. Although structurally stable across the chronosequence and between strata, Interaction networks were richer and most distinct in canopies, while the highest pollinator and interaction diversity were found in old-growth canopies. In successional forests, networks were only comparable in size to active disturbances and early recovery with both strata combined, whereas complete networks in old-growth forests were more than twice as large as those in other recovery statuses. Our study underlines the importance of stratification in leveraging pollinator diversity during forest succession. By serving as havens for canopy-adapted species, tropical canopies may thus help safeguard pollination processes in disturbed landscapes.

ecology↗

bioRxiv2024

Forest edges and other semi-natural habitat edges increase wild bee species richness and habitat connectivity in intensively managed temperate landscapes.

Pollinator conservation schemes are typically focused on conserving existing-, restoring degraded- or establishing new wild bee habitats. The effectiveness of such conservation schemes depends on the presence of dispersal corridors that allow habitat colonization by bees. Nonetheless, we lack an understanding of the role of semi-natural habitats edges on the connectivity of pollinator communities across intensively managed landscapes. Here, we use data from wild bee communities comprising 953 occurrences from 79 species of non-parasitic bees, sampled at 68 locations distributed across a Norwegian and a Danish landscape to show that the proportion of semi-natural habitat edges is positively correlated to bee species richness and habitat connectivity. Specifically, we found that wild bee species richness sampled along roadsides increased with the proportion of semi-natural habitat edges within1.5 km of the study sites and with local plant species richness. We combined maps showing the proportion of seminatural habitat edges with least cost path analysis to find the most likely dispersal route between our bee communities. We find that these least cost path lengths provide better models of bee species compositional similarity than geographic distance (|{Delta}AICc| > 2), suggesting that seminatural habitat edges act as dispersal corridors in intensively managed landscapes. However, we also find that compositional similarity between communities depend on site-specific plant species richness stressing the importance of improving the habitat quality of edge habitats if they are to function as dispersal corridors. We discuss potential management options for improving wild bee habitat conditions along seminatural habitat edges and illustrate how maps of least cost paths can be used to identify dispersal corridors between pollinator habitats of conservation priority. Maps of dispersal corridors can be used to direct wild bee habitat management actions along seminatural habitat edges to facilitate the dispersal of bees between larger grassland habitats.

ecology↗

bioRxiv2024

PIN2-mediated self-organizing transient auxin flow contributes to auxin maxima at the tip of Arabidopsis cotyledons

Directional auxin transport and formation of auxin maxima are critical for embryogenesis, organogenesis, pattern formation, and growth coordination in plants, but the mechanisms underpinning the initiation and establishment of these auxin dynamics are not fully understood. Here we show that a self-initiating and - terminating transient auxin flow along the marginal cells (MCs) contributes to the formation of an auxin maximum at the tip of Arabidopsis cotyledon that globally coordinates the interdigitation of puzzle-shaped pavement cells in the cotyledon epidermis. Prior to the interdigitation, indole butyric acid (IBA) is converted to indole acetic acid (IAA) to induce PIN2 accumulation and polarization in the marginal cells, leading to auxin flow toward and accumulation at the cotyledon tip. When IAA levels at the cotyledon tip reaches a maximum, it activates pavement cell interdigitation as well as the accumulation of the IBA transporter TOB1 in MCs, which sequesters IBA to the vacuole and reduces IBA availability and IAA levels. The reduction of IAA levels results in PIN2 down-regulation and cessation of the auxin flow. Hence, our results elucidate a self-activating and self-terminating transient polar auxin transport system in cotyledons, contributing to the formation of localized auxin maxima that spatiotemporally coordinate pavement cell interdigitation.

plant biology↗

bioRxiv2024

De Novo TANGLED1 Recruitment to Aberrant Cell Plate Fusion Sites in Maize

Division plane positioning is critical for proper growth and development in many organisms. In plants, the division plane is established before mitosis, by accumulation of a cytoskeletal structure called the preprophase band (PPB). The PPB is thought to be essential for recruitment of division site localized proteins, which remain at the division site after the PPB disassembles. Here, we show that a division site localized protein, TANGLED1 (TAN1), is recruited independently of the PPB to the cell cortex at sites, by the plant cytokinetic machinery, the phragmoplast. TAN1 recruitment to de novo sites on the cortex is partially dependent on intact actin filaments and the myosin XI motor protein OPAQUE1 (O1). These data imply a yet unknown role for TAN1 and possibly other division site localized proteins during the last stages of cell division when the phragmoplast touches the cell cortex to complete cytokinesis. Summary StatementThe plant division site protein TANGLED1 is recruited to de novo cell plate insertion sites independently of the preprophase band.

plant biology↗

bioRxiv2022

The localization of PHRAGMOPLAST ORIENTING KINESIN1 at the division site depends on two microtubule binding proteins TANGLED1 and AUXIN-INDUCED-IN-ROOT-CULTURES9 in Arabidopsis.

Proper plant growth and development requires spatial coordination of cell divisions. Two unrelated microtubule-binding proteins, TANGLED1 (TAN1) and AUXIN-INDUCED-IN-ROOT-CULTURES9 (AIR9), are together required for normal growth and division-plane orientation in Arabidopsis. tan1 air9 double mutants have synthetic growth and division-plane orientation defects while single mutants lack obvious defects. Here we show that the division-site localized protein, PHRAGMOPLAST-ORIENTING-KINESIN1 (POK1), was aberrantly lost from the division site during metaphase and telophase in tan1 air9 mutants. Since TAN1 and POK1 interact via the first 132 amino acids of TAN1 (TAN11-132), we assessed its localization and function in the tan1 air9 double mutant. TAN11-132 rescued tan1 air9 mutant phenotypes and localized to the division site in telophase. However, replacing six amino-acid residues within TAN11-132 that disrupts POK1-TAN1 interaction in the yeast-two-hybrid system caused loss of both rescue and division-site localization of TAN11-132 in tan1 air9 mutants. Full-length TAN1 with the same alanine substitutions had defects in phragmoplast guidance and reduced TAN1 and POK1 localization at the division site but rescued most tan1 air9 mutant phenotypes. Together, these data suggest that TAN1 and AIR9 are required for POK1 localization, and yet unknown proteins may stabilize TAN1-POK1 interactions. One sentence summarySpecific amino acids within TAN1 are required for its correct localization and function partially through interaction with POK1; both TAN1 and AIR9 mediate POK1 division site localization.

plant biology↗

bioRxiv2021

The OPAQUE1/DISCORIDA2 myosin XI is required for phragmoplast guidance during asymmetric cell division in maize

Formative asymmetric divisions produce cells with different fates and are critical for development. We show the myosin XI protein, OPAQUE1 (O1), is necessary for asymmetric divisions during maize stomatal development. We analyzed stomatal precursor cells prior to and during asymmetric division to determine why o1 mutants have abnormal division planes. Cell polarization and nuclear positioning occur normally in the o1 mutant, and the future site of division is correctly specified. The defect in o1 occurs during late cytokinesis, when the phragmoplast forms the nascent cell plate. Initial phragmoplast guidance in o1 is correct; however, as phragmoplast expansion continues o1 phragmoplasts become misguided. To understand how O1 contributes to phragmoplast guidance, we identified O1-interacting proteins. Maize kinesins related to the Arabidopsis thaliana division site markers PHRAGMOPLAST ORIENTING KINESINs (POKs), which are also required for correct phragmoplast guidance, physically interact with O1. We propose that different myosins are important at multiple steps of phragmoplast expansion, and the O1 actin motor and POK-like microtubule motors work together to ensure correct late-stage phragmoplast guidance.

plant biology↗

bioRxiv2021

Functional characterization of TANGLED1 interaction with PHRAGMOPLAST ORIENTING KINESIN1 during mitosis in Arabidopsis

Cell division plane orientation is critical for plant and animal development and growth. TANGLED1 (TAN1) and AUXIN-INDUCED-IN-ROOT-CULTURES9 (AIR9) are division-site localized microtubule-binding proteins required for division plane positioning. tan1 and air9 Arabidopsis thaliana single mutants have minor or no noticeable phenotypes but the tan1 air9 double mutant has synthetic phenotypes including stunted growth, misoriented divisions, and aberrant cell-file rotation in the root differentiation zone. These data suggest that TAN1 plays a role in nondividing cells. To determine whether TAN1 is required in elongating and differentiating cells in the tan1 air9 double mutant, we limited its expression to actively dividing cells using the G2/M-specific promoter of the syntaxin KNOLLE (pKN:TAN1-YFP). Unexpectedly, in addition to rescuing division plane defects, pKN:TAN1-YFP rescued root growth and the root differentiation zone cell file rotation defects in the tan1 air9 double mutant. This suggests that defects that occur in the meristematic zone later affect the organization of elongating and differentiating cells. Summary StatementExpression of TAN1 in the root meristematic zone rescues cell file rotation defects in tan1 air9 mutants, suggesting defects that occur in mitosis may influence organization of nondividing cells.

plant biology↗