Genomes of multicellular algal sisters to land plants illuminate signaling network evolution.

Zygnematophyceae are the algal sisters of land plants. Here we sequenced four genomes of filamentous Zygnematophyceae, including chromosome-scale assemblies for three strains of Zygnema circumcarinatum. We inferred traits in the ancestor of Zygnematophyceae and land plants that might have ushered in the conquest of land by plants: expanded genes for signaling cascades, environmental response, and multicellular growth. Zygnematophyceae and land plants share all the major enzymes for cell wall synthesis and remodifications, and gene gains shaped this toolkit. Co-expression network analyses uncover gene cohorts that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution.

Identification and evolution of nsLTPs in the root nodule nitrogen fixation clade and molecular response of Frankia to AgLTP24.

Non-specific lipid transfer proteins (nsLTPs) are antimicrobial peptides, involved in several plant biological processes including root nodule nitrogen fixation (RNF). Nodulating plants belonging to the RNF clade establish symbiosis with the nitrogen-fixing bacteria rhizobia (legumes symbiosis model) and Frankia (actinorhizal symbiosis model) leading to root nodule formation. nsLTPs are involved in processes active in early step of symbiosis and functional nodule in both models. In legumes, nsLTPs have been shown to regulate symbiont entry, promote root cortex infection, membrane biosynthesis, and improve symbiosis efficiency. More recently, a nsLTP, AgLTP24 has been described in the context of actinorhizal symbiosis between Alnus glutinosa and Frankia alni ACN14a. AgLTP24 is secreted at an early step of symbiosis on the deformed root hairs and targets the symbiont in the nitrogen-fixing vesicles in functional nodules. nsLTPs are involved in RNF, but their functions and evolutionary history are still largely unknown. Numerous putative nsLTPs were found up-regulated in functional nodules compared to non-infected roots in different lineages within the RNF clade. Here, results highlight that nodulating plants that are co-evolving with their nitrogen-fixing symbionts appear to have independently specialized nsLTPs for this interaction, suggesting a possible convergence of function, which opens perspectives to investigate nsLTPs functions in RNF.

Comparative phylotranscriptomics reveals ancestral and derived root nodule symbiosis programmes.

Symbiotic interactions such as the nitrogen-fixing root nodule symbiosis (RNS) have structured ecosystems during the evolution of life. Here we aimed at reconstructing ancestral and intermediate steps that shaped RNS observed in extant flowering plants. We compared the symbiotic transcriptomic responses of nine host plants, including the mimosoid legume Mimosa pudica for which we assembled a chromosome-level genome. We reconstructed the ancestral RNS transcriptome composed of most known symbiotic genes together with hundreds of novel candidates. Cross-referencing with transcriptomic data in response to experimentally evolved bacterial strains with gradual symbiotic proficiencies, we found the response to bacterial signals, nodule infection, nodule organogenesis and nitrogen fixation to be ancestral. By contrast, the release of symbiosomes was associated with recently evolved genes encoding small proteins in each lineage. We demonstrate that the symbiotic response was mostly in place in the most recent common ancestor of the RNS-forming species more than 90 million years ago.

Number needed to vaccinate with a COVID-19 booster to prevent a COVID-19-associated hospitalization during SARS-CoV-2 Omicron BA.1 variant predominance, December 2021-February 2022, VISION Network: a retrospective cohort study.

Background: Understanding the usefulness of additional COVID-19 vaccine doses-particularly given varying disease incidence-is needed to support public health policy. We characterize the benefits of COVID-19 booster doses using number needed to vaccinate (NNV) to prevent one COVID-19-associated hospitalization or emergency department encounter. Methods: We conducted a retrospective cohort study of immunocompetent adults at five health systems in four U.S. states during SARS-CoV-2 Omicron BA.1 predominance (December 2021-February 2022). Included patients completed a primary mRNA COVID-19 vaccine series and were either eligible to or received a booster dose. NNV were estimated using hazard ratios for each outcome (hospitalization and emergency department encounters), with results stratified by three 25-day periods and site. Findings: 1,285,032 patients contributed 938 hospitalizations and 2076 emergency department encounters. 555,729 (43.2%) patients were aged 18-49 years, 363,299 (28.3%) 50-64 years, and 366,004 (28.5%) ≥65 years. Most patients were female (n = 765,728, 59.6%), White (n = 990,224, 77.1%), and non-Hispanic (n = 1,063,964, 82.8%). 37.2% of patients received a booster and 62.8% received only two doses. Median estimated NNV to prevent one hospitalization was 205 (range 44-615) and NNV was lower across study periods for adults aged ≥65 years (110, 46, and 88, respectively) and those with underlying medical conditions (163, 69, and 131, respectively). Median estimated NNV to prevent one emergency department encounter was 156 (range 75-592). Interpretation: The number of patients needed to receive a booster dose was highly dependent on local disease incidence, outcome severity, and patient risk factors for moderate-to-severe disease. Funding: Funding was provided by the Centers for Disease Control and Prevention though contract 75D30120C07986 to Westat, Inc. and contract 75D30120C07765 to Kaiser Foundation Hospitals.

Chromosome-level genomes of multicellular algal sisters to land plants illuminate signaling network evolution.

The filamentous and unicellular algae of the class Zygnematophyceae are the closest algal relatives of land plants. Inferring the properties of the last common ancestor shared by these algae and land plants allows us to identify decisive traits that enabled the conquest of land by plants. We sequenced four genomes of filamentous Zygnematophyceae (three strains of Zygnema circumcarinatum and one strain of Z. cylindricum) and generated chromosome-scale assemblies for all strains of the emerging model system Z. circumcarinatum. Comparative genomic analyses reveal expanded genes for signaling cascades, environmental response, and intracellular trafficking that we associate with multicellularity. Gene family analyses suggest that Zygnematophyceae share all the major enzymes with land plants for cell wall polysaccharide synthesis, degradation, and modifications; most of the enzymes for cell wall innovations, especially for polysaccharide backbone synthesis, were gained more than 700 million years ago. In Zygnematophyceae, these enzyme families expanded, forming co-expressed modules. Transcriptomic profiling of over 19 growth conditions combined with co-expression network analyses uncover cohorts of genes that unite environmental signaling with multicellular developmental programs. Our data shed light on a molecular chassis that balances environmental response and growth modulation across more than 600 million years of streptophyte evolution.

Stabilization of membrane topologies by proteinaceous remorin scaffolds.

In plants, the topological organization of membranes has mainly been attributed to the cell wall and the cytoskeleton. Additionally, few proteins, such as plant-specific remorins have been shown to function as protein and lipid organizers. Root nodule symbiosis requires continuous membrane re-arrangements, with bacteria being finally released from infection threads into membrane-confined symbiosomes. We found that mutations in the symbiosis-specific SYMREM1 gene result in highly disorganized perimicrobial membranes. AlphaFold modelling and biochemical analyses reveal that SYMREM1 oligomerizes into antiparallel dimers and may form a higher-order membrane scaffolding structure. This was experimentally confirmed when expressing this and other remorins in wall-less protoplasts is sufficient where they significantly alter and stabilize de novo membrane topologies ranging from membrane blebs to long membrane tubes with a central actin filament. Reciprocally, mechanically induced membrane indentations were equally stabilized by SYMREM1. Taken together we describe a plant-specific mechanism that allows the stabilization of large-scale membrane conformations independent of the cell wall.

Women Living with Human Immunodeficiency Virus with Intended and Unintended Pregnancy: Characteristics and Patient Outcomes.

Background: Rates of unintended pregnancy may be higher in women living with human immunodeficiency virus (WLWH) than in the general population, and it is unclear how populations of WLWH with intended and unintended pregnancy differ. We compared baseline characteristics and outcomes between WLWH with intended and unintended pregnancy. Materials and Methods: We conducted a retrospective analysis of WLWH enrolled in a human immunodeficiency virus (HIV) and Pregnancy clinic from 2003 to 2014. Data were analyzed using descriptive statistics, chi-square test, Student's t-test, one-way analysis of variance, and linear and logistic regression analysis. Two-tailed p-value <0.05 was considered significant. The study was approved by the Johns Hopkins University School of Medicine Institutional Review Board. Results: Sixty-nine (27.1%) of 255 women reported an intended pregnancy. Women with intended pregnancy (WWIP) were more likely to be older, White, married, privately insured, and college educated. WWIP were less likely to use tobacco (15.9% vs. 44.2%, p < 0.001), alcohol (2.9% vs. 11.1%, p = 0.041), opiates (0.0% vs. 19.3%, p < 0.001), or cocaine (2.9% vs. 21.0%, p < 0.001) during pregnancy, more likely to disclose their HIV status to the father of the baby by delivery (100.0% vs. 15.8%, p < 0.001), and more likely to receive less effective contraception at delivery (condoms 14.9% vs. 4.8%, p = 0.024; sterilization 11.9% vs. 22.1%, p = 0.028). In multivariate regression analysis, pregnancy intendedness was an important predictor of nondetectable viral load at pregnancy entry but not at delivery. Conclusions: WLWH vary in their baseline characteristics and pregnancy outcomes depending on pregnancy intendedness, highlighting the need to improve pregnancy timing in WLWH and intensify interventions for women with unintended pregnancy.

Disparity in Built Environment and Its Impacts on Youths' Physical Activity Behaviors During COVID-19 Pandemic Restrictions.

OBJECTIVES: Guided by the social ecological model, this study aimed to examine the relations of built environments (i.e., walking/cycling infrastructure, recreation facilities, neighborhood safety/crime), youth's transition abilities, and changes of youth's physical activity (PA) and play behaviors due to COVID-19-based restrictions. Ethnic and socioeconomic status (SES) disparities were also examined on studies variables during the COVID-19 restrictions. METHOD: A cross-sectional research design was used to assess an anonymous online survey completed by US parents/guardians. The final sample had 1324 children and adolescents (Meanage = 9.75; SD = 3.95; 51.3% girls), and 35.5% the families were of upper socioeconomic class (income > $150,000). Parents reported the perceived built environment and neighborhood safety, child's PA and play behaviors during COVID-19 pandemic shelter-in-place restrictions. RESULTS: Youths who had access to safe built environment were more active and played more outdoor/indoor (p < .01). It was found playing behavior in yard and neighborhood were significantly increased, but community-based play behavior was significantly reduced during COVID-19 restrictions. The SEM analysis (χ2/df = 236.04/54; CFI = .966) supported indirect and direct effects of neighborhood safety on PA changes during COVID-19 restrictions, and the youth's ability to respond to COVID-19 restrictions served as a full mediator. Low-SES and Hispanic minority youth reported significantly less safety to walking or playing in their neighborhoods than their middle-/high-SES non-Hispanic peers (p < .001). Regardless of ethnicity, the magnitude of the reduction of MVPA was significantly higher among low-SES groups than that of the high- and middle-SES groups (p < .001). CONCLUSIONS: These findings demonstrate a need to tailor programs and policies to help high-risk groups (e.g., low SES) stay active, healthy, and resilient during and after the COVID-19 pandemic.

Relation between Demographics and Physical Activity among Preschoolers Attending Head Start.

Limited empirical evidence is available about preschoolers' sedentary behavior (SB) and physical activity (PA) patterns in Head Start programs, we explored (a) preschoolers' SB and PA patterns (ranging from SB to light-moderate-vigorous physical activity [LMVPA]) and (b) their relationships with sociodemographic factors, weight status, and motor development. Participants included 216 preschoolers (M age = 4.32 ± 0.63; girls 56.5%) from six Head Start centers in an urban area in the southwestern region of the United States, assessing Actical® activity monitor-based PA, weight status, and motor development. The findings revealed preschoolers who were female, Hispanic/Latinx, with an at risk weight level, and/or in the below average motor development group tended to engage in less MVPA/LMVPA and also had higher SB patterns while participating in the Head Start program (p < 0.05-0.001, d ranged from 0.23 to 0.62). Head Start stakeholders (e.g., policymakers, leaders, curriculum coordinators, health professionals, and teachers) need to acknowledge the PA and health disparities, and intervene in underserved preschoolers' health-promoting behaviors.

Plant phylogenetics: The never-ending cycle of evolutionary gains and losses.

The Zygnematophyceae is the sister clade to the land plants, but their biology remains mysterious. In a new study, a resolved phylogeny and a scenario for the evolution of multicellularity in that clade are proposed.

An ancestral function of strigolactones as symbiotic rhizosphere signals.

In flowering plants, strigolactones (SLs) have dual functions as hormones that regulate growth and development, and as rhizosphere signaling molecules that induce symbiosis with arbuscular mycorrhizal (AM) fungi. Here, we report the identification of bryosymbiol (BSB), an SL from the bryophyte Marchantia paleacea. BSB is also found in vascular plants, indicating its origin in the common ancestor of land plants. BSB synthesis is enhanced at AM symbiosis permissive conditions and BSB deficient mutants are impaired in AM symbiosis. In contrast, the absence of BSB synthesis has little effect on the growth and gene expression. We show that the introduction of the SL receptor of Arabidopsis renders M. paleacea cells BSB-responsive. These results suggest that BSB is not perceived by M. paleacea cells due to the lack of cognate SL receptors. We propose that SLs originated as AM symbiosis-inducing rhizosphere signaling molecules and were later recruited as plant hormone.

Plant-microbe interactions that have impacted plant terrestrializations.

Plants display a tremendous diversity of developmental and physiological features, resulting from gains and losses of functional innovations across the plant phylogeny. Among those, the most impactful have been undoubtedly the ones that allowed plant terrestrializations, the transitions from an aquatic to a terrestrial environment. Although the embryophyte terrestrialization has been particularly scrutinized, others occurred across the plant phylogeny with the involvement of mutualistic symbioses as a common theme. Here, we review the current pieces of evidence supporting that the repeated colonization of land by plants has been facilitated by interactions with mutualistic symbionts. In that context, we detail two of these mutualistic symbioses: the arbuscular mycorrhizal symbiosis in embryophytes and the lichen symbiosis in chlorophyte algae. We suggest that associations with bacteria should be revisited in that context, and we propose that overlooked symbioses might have facilitated the emergence of other land plant clades.

An integrated approach reveals how lipo-chitooligosaccharides interact with the lysin motif receptor-like kinase MtLYR3.

N-acetylglucosamine containing compounds acting as pathogenic or symbiotic signals are perceived by plant-specific Lysin Motif Receptor-Like Kinases (LysM-RLKs). The molecular mechanisms of this perception are not fully understood, notably those of lipo-chitooligosaccharides (LCOs) produced during root endosymbioses with nitrogen-fixing bacteria or arbuscular mycorrhizal fungi. In Medicago truncatula, we previously identified the LysM-RLK LYR3 (MtLYR3) as a specific LCO-binding protein. We also showed that the absence of LCO binding to LYR3 of the non-mycorrhizal Lupinus angustifolius, (LanLYR3), was related to LysM3, which differs from that of MtLYR3 by several amino acids and, particularly, by a critical tyrosine residue absent in LanLYR3. Here, we aimed to define the LCO binding site of MtLYR3 by using molecular modelling and simulation approaches, combined with site-directed mutagenesis and LCO binding experiments. 3D models of MtLYR3 and LanLYR3 ectodomains were built, and homology modelling and molecular dynamics (MD) simulations were performed. Molecular docking and MD simulation on the LysM3 identified potential key residues for LCO binding. We highlighted by steered MD simulations that in addition to the critical tyrosine, two other residues were important for LCO binding in MtLYR3. Substitution of these residues in LanLYR3-LysM3 by those of MtLYR3-LysM3 allowed the recovery of high-affinity LCO binding in experimental radioligand-binding assays. An analysis of selective constraints revealed that the critical tyrosine has experienced positive selection pressure and is absent in some LYR3 proteins. These findings now pave the way to uncover the functional significance of this specific evolutionary pattern.

PERKing up our understanding of the proline-rich extensin-like receptor kinases, a forgotten plant receptor kinase family.

Proline-rich extensin-like receptor kinases (PERKs) are an important class of receptor-like kinases (RLKs) containing an extracellular proline-rich domain. While they are thought to be putative sensors of the cell wall integrity, there are very few reports on their biological functions in the plant, as compared with other RLKs. Several studies support a role for PERKs in plant growth and development, but their effect on the cell wall composition to regulate cell expansion is still lacking. Gene expression data suggest that they may intervene in response to environmental changes, in agreement with their subcellular localization. And there is growing evidence for PERKs as novel sensors of environmental stresses such as insects and viruses. However, little is known about their precise role in plant immunity and in the extracellular network of RLKs, as no PERK-interacting RLK or any coreceptor has been identified as yet. Similarly, their signaling activities and downstream signaling components are just beginning to be deciphered, including Ca2+ fluxes, reactive oxygen species accumulation and phosphorylation events. Here we outline emerging roles for PERKs as novel sensors of environmental stresses, and we discuss how to better understand this overlooked class of receptor kinases via several avenues of research.

The mediating roles of sleep quality and sedentary behavior between physical fitness and depression among female college freshmen.

Objective: This study aimed to investigate interactions among physical fitness, sleep quality, sedentary behavior, and depression among female college freshmen. Participants: A cohort of 1,514 Chinese female college freshmen (Mage = 18.8 ± .63) were recruited from four universities. Methods: Participants completed a survey assessing depression, sleep quality (sleep duration and sleep onset latency), and sedentary behavior, and performed physical fitness measurements. Results: Physical fitness indexes were associated with sleep quality and sedentary behavior (ps < .05) but not with depression. Depression was positively associated with sedentary behavior and sleep onset latency, but negatively associated with sleep duration (ps < .01). The model tests revealed that sleep quality (ß = -.57, p < .01) and sedentary behavior (ß = .14, p < .01) served as mediators between physical fitness and depression, respectively. Conclusions: Increasing sleep quality and minimizing sedentary behavior may build resilience to depression among Chinese female college freshmen.

Healthy eating patterns and epigenetic measures of biological age.

BACKGROUND: Healthy eating is associated with lower risks of disease and mortality, but the mechanisms underlying these associations are unclear. Age is strongly related to health outcomes, and biological age can be estimated using the blood methylome. OBJECTIVES: To determine whether healthy eating patterns are associated with methylation-based measures of biological age. METHODS: Among women in the Sister Study, we calculated scores on 4 recommendation-based healthy eating indexes [Dietary Approaches to Stop Hypertension diet, Healthy Eating Index-2015, Alternative Healthy Eating Index (aHEI-2010), and the Alternative Mediterranean diet] using a validated 110-item Block FFQ completed at enrollment. Genome-wide DNA methylation data were generated using the HumanMethylation450 BeadChip on whole blood samples collected at enrollment from a case-cohort sample of 2694 women and were used to calculate 4 measures of epigenetic age acceleration (Hannum AgeAccel, Horvath AgeAccel, PhenoAgeAccel, and GrimAgeAccel). Linear regression models, adjusted for covariates and cohort sampling weights, were used to examine cross-sectional associations between eating patterns and measures of biological age. RESULTS: All 4 healthy eating indexes had inverse associations with epigenetic age acceleration, most notably with PhenoAgeAccel and GrimAgeAccel. Of these, the strongest associations were for aHEI-2010 [per 1-SD increase in diet quality, PhenoAgeAccel ß = -0.5 y (95% CI: -0.8 to -0.2 y) and GrimAgeAccel ß = -0.4 y (95% CI: -0.6 to -0.3 y)]. Although effect modification was not observed for most lifestyle factors, in analyses stratified by physical activity, the benefits of a healthy diet on epigenetic age acceleration were more pronounced among women who did not meet physical activity guidelines (reporting <2.5 h/wk of exercise). CONCLUSIONS: Higher diet quality is inversely associated with methylation-based measures of biological age. Improving diet could have the most benefits in lowering biological age among women with lower levels of physical activity. This trial was registered at clinicaltrials.gov as NCT00047970.

NIN-Like Proteins: Interesting Players in Rhizobia-Induced Nitrate Signaling Response During Interaction with Non-Legume Host Arabidopsis thaliana.

Nitrogen is an essential macronutrient and a key cellular messenger. Plants have evolved refined molecular systems to sense the cellular nitrogen status. This is exemplified by the root nodule symbiosis between legumes and symbiotic rhizobia, where nitrate availability inhibits this mutualistic interaction. Additionally, nitrate also functions as a metabolic messenger, resulting in nitrate signaling cascades which intensively crosstalk with other physiological pathways. Nodule inception-like proteins (NLPs) are key players in nitrate signaling and regulate nitrate-dependent transcription during legume-rhizobia interactions. Nevertheless, the coordinated interplay between nitrate signaling pathways and rhizobacteria-induced responses remains to be elucidated. In our study, we investigated rhizobia-induced changes in the root system architecture of the non-legume host arabidopsis under different nitrate conditions. We demonstrate that rhizobium-induced lateral root growth and increased root hair length and density are regulated by a nitrate-related signaling pathway. Key players in this process are AtNLP4 and AtNLP5, because the corresponding mutants failed to respond to rhizobia. At the cellular level, AtNLP4 and AtNLP5 control a rhizobia-induced decrease in cell elongation rates, while additional cell divisions occurred independently of AtNLP4. In summary, our data suggest that root morphological responses to rhizobia are coordinated by a newly considered nitrate-related NLP pathway that is evolutionarily linked to regulatory circuits described in legumes.[Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY 4.0 International license.

Multilaboratory Collaborative Study of a Nontarget Data Acquisition for Target Analysis (nDATA) Workflow Using Liquid Chromatography-High-Resolution Accurate Mass Spectrometry for Pesticide Screening in Fruits and Vegetables.

Nontarget data acquisition for target analysis (nDATA) workflows using liquid chromatography-high-resolution accurate mass (LC-HRAM) spectrometry, spectral screening software, and a compound database have generated interest because of their potential for screening of pesticides in foods. However, these procedures and particularly the instrument processing software need to be thoroughly evaluated before implementation in routine analysis. In this work, 25 laboratories participated in a collaborative study to evaluate an nDATA workflow on high moisture produce (apple, banana, broccoli, carrot, grape, lettuce, orange, potato, strawberry, and tomato). Samples were extracted in each laboratory by quick, easy, cheap, effective, rugged, and safe (QuEChERS), and data were acquired by ultrahigh-performance liquid chromatography (UHPLC) coupled to a high-resolution quadrupole Orbitrap (QOrbitrap) or quadrupole time-of-flight (QTOF) mass spectrometer operating in full-scan mass spectrometry (MS) data-independent tandem mass spectrometry (LC-FS MS/DIA MS/MS) acquisition mode. The nDATA workflow was evaluated using a restricted compound database with 51 pesticides and vendor processing software. Pesticide identifications were determined by retention time (tR, ±0.5 min relative to the reference retention times used in the compound database) and mass errors (δM) of the precursor (RTP, δM ≤ ±5 ppm) and product ions (RTPI, δM ≤ ±10 ppm). The elution profiles of all 51 pesticides were within ±0.5 min among 24 of the participating laboratories. Successful screening was determined by false positive and false negative rates of <5% in unfortified (pesticide-free) and fortified (10 and 100 µg/kg) produce matrices. Pesticide responses were dependent on the pesticide, matrix, and instrument. The false negative rates were 0.7 and 0.1% at 10 and 100 µg/kg, respectively, and the false positive rate was 1.1% from results of the participating LC-HRAM platforms. Further evaluation was achieved by providing produce samples spiked with pesticides at concentrations blinded to the laboratories. Twenty-two of the 25 laboratories were successful in identifying all fortified pesticides (0-7 pesticides ranging from 5 to 50 µg/kg) for each produce sample (99.7% detection rate). These studies provide convincing evidence that the nDATA comprehensive approach broadens the screening capabilities of pesticide analyses and provide a platform with the potential to be easily extended to a larger number of other chemical residues and contaminants in foods.

Lipid exchanges drove the evolution of mutualism during plant terrestrialization.

Symbiosis with arbuscular mycorrhizal fungi (AMF) improves plant nutrition in most land plants, and its contribution to the colonization of land by plants has been hypothesized. Here, we identify a conserved transcriptomic response to AMF among land plants, including the activation of lipid metabolism. Using gain of function, we show the transfer of lipids from the liverwort Marchantia paleacea to AMF and its direct regulation by the transcription factor WRINKLED (WRI). Arbuscules, the nutrient-exchange structures, were not formed in loss-of-function wri mutants in M. paleacea, leading to aborted mutualism. Our results show the orthology of the symbiotic transfer of lipids across land plants and demonstrate that mutualism with arbuscular mycorrhizal fungi was present in the most recent ancestor of land plants 450 million years ago.

Formin-mediated bridging of cell wall, plasma membrane, and cytoskeleton in symbiotic infections of Medicago truncatula.

Legumes have maintained the ability to associate with rhizobia to sustain the nitrogen-fixing root nodule symbiosis (RNS). In Medicago truncatula, the Nod factor (NF)-dependent intracellular root colonization by Sinorhizobium meliloti initiates from young, growing root hairs. They form rhizobial traps by physically curling around the symbiont.1,2 Although alterations in root hair morphology like branching and swelling have been observed in other plants in response to drug treatments3 or genetic perturbations,4-6 full root hair curling represents a rather specific invention in legumes. The entrapment of the symbiont completes with its full enclosure in a structure called the "infection chamber" (IC),1,2,7,8 from which a tube-like membrane channel, the "infection thread" (IT), initiates.1,2,9 All steps of rhizobium-induced root hair alterations are aided by a tip-localized cytosolic calcium gradient,10,11 global actin re-arrangements, and dense subapical fine actin bundles that are required for the delivery of Golgi-derived vesicles to the root hair tip.7,12-14 Altered actin dynamics during early responses to NFs or rhizobia have mostly been shown in mutants that are affected in the actin-related SCAR/WAVE complex.15-18 Here, we identified a polarly localized SYMBIOTIC FORMIN 1 (SYFO1) to be required for NF-dependent alterations in membrane organization and symbiotic root hair responses. We demonstrate that SYFO1 mediates a continuum between the plasma membrane and the cell wall that is required for the onset of rhizobial infections.