Biology subjects

Ramirez, V.

Publications and source records attributed to Ramirez, V..

At least 19 recordsLinked to original sources

bioRxiv2026

Yeast surface display reveals structure-dependent β-glucan association with the plant immune receptor AtIGP1

Cell wall-derived oligosaccharides can function as immune-active signals in plants and trigger pattern-triggered immunity (PTI) through pattern recognition receptors (PRRs). In Arabidopsis thaliana, the leucine-rich repeat malectin (LRR-MAL) receptor kinase IGP1 (impaired in glycan perception 1) contributes to immune responses induced by cellulose- and mixed-linkage {beta}-1,3/1,4-glucan (MLG)-derived oligosaccharides, although whether MLG-derived oligosaccharides are directly recognized by AtIGP1 needs further clarification. We established a Saccharomyces cerevisiae surface-display system in which the AtIGP1 extracellular domain (ECD) is presented at the yeast cell surface, allowing oligosaccharide recognition to be examined separately from downstream plant signaling and without receptor purification. Previously, cellulose-derived oligosaccharides have been shown to elicit plant defense responses via AtIGP1. Here, surface-displayed AtIGP1 retained the ability to recognize fluorescently labeled cellotriose (CEL3) and cellopentaose (CEL5) ligands, supporting functional presentation of the receptor for investigating glycan recognition in a heterologous context. Using this platform, we investigated the association of AtIGP1 with fluorescently labeled MLG-derived oligosaccharides differing in degree of polymerization (DP) and glycosidic linkage arrangement. This analysis revealed a specific, competitively displaceable association with MLG DP2 (G3G; laminaribiose), whereas the DP3 (G4G3G) and DP4 (G4G4G3G) structures tested showed no detectable association. To test whether this association is relevant in planta, we treated A. thaliana seedlings with unlabeled MLG DP2, which induced a cytosolic Ca2+ response, an early readout of immune activation. This response was markedly reduced in the igp1-3 mutant. Together, these results identify laminaribiose as an additional candidate ligand of AtIGP1. The established yeast surface-display platform thus provides an approach for testing candidate oligosaccharides for association with the extracellular domains of plant PRRs.

synthetic biology↗

bioRxiv2026

Genome-wide association study in a maize diversity panel dissects the genetic basis of lignocellulosic recalcitrance

Lignocellulosic biomass is an abundant, renewable resource for the production of biorenewable products. Its efficient utilization is largely hindered by the inherent recalcitrance of lignocellulose to degradation. Natural genetic variation in biomass saccharification efficiency and lignocellulose components across diverse maize germplasm provides a powerful resource to dissect the genetic basis of lignocellulosic recalcitrance. Here, we performed high-throughput profiling of lignocellulosic components and saccharification efficiency in mature stalks across a diverse panel of 239 field grown maize inbred lines, and identified extensive natural variation in biomass properties. Saccharification efficiency was strongly positively associated with matrix glucose content, moderately positively associated with the arabinose-to-xylose (Ara:Xyl) molar ratio and crystalline cellulose content, whereas saccharification efficiency was strongly negatively associated with xylose and lignin content. Genome-wide association studies (GWAS) were conducted to identify single nucleotide polymorphisms (SNPs) associated with saccharification efficiency and lignocellulosic components. Numerous significant single nucleotide polymorphisms (SNPs) were identified, defining 79 quantitative trait loci (QTLs) across all 10 maize chromosomes. The presence of pleiotropic SNPs and the extensive co-localization of QTLs for multiple traits highlight the complex genetic architecture and shared genetic basis of maize biomass properties. Our study reveals substantial natural variation in maize biomass digestibility and identifies multiple novel genetic loci underlying variation in saccharification efficiency and lignocellulose components.

plant biology↗

bioRxiv2026

ZmPMI3 phosphomannose isomerase kinetics is associated with natural variation of watersoluble carbohydrate content in mature maize stem

Mature maize stems accumulate substantial amounts of water-soluble carbohydrates (WSC) providing an accessible carbon pool for industrial bioconversion. However, the genetic factors controlling WSC reserves under field conditions remain poorly resolved. In this study, we quantified total WSC including glucose, fructose, sucrose contents in the internode below the first ear of a genetically diverse maize panel at physiological maturity and associated trait variation with genome-wide SNP data. The panel displayed extensive variation in stem WSCs content, with values ranging up to 50.4 % of dry weight. Genome-wide association mapping identified 20 quantitative trait loci associated with individual sugars or total WSC content. One fructose associated region contained two adjacent gene annotations predicted to encode fragments of a phosphomannose isomerase. Sequence comparison, cDNA amplification and protein structure prediction supported a unified gene model, here designated as ZmPMI3. Biochemical characterization showed ZmPMI3 catalyzes the reversible conversion between mannose-6-phosphate and fructose-6-phosphate, a central reaction in carbohydrate metabolism. Natural protein haplotypes with distinct kinetic properties were identified correlating with significant differences in stem WSC content. Together, these findings identify ZmPMI3 as a candidate contributor to natural variation in maize stem carbohydrate reserves, potentially through altered hexose-phosphate partitioning.

plant biology↗

bioRxiv2026

Characterization of a fungal mixed-linkage glucan synthase

Mixed-linkage (1,3;1,4)-{beta}-glucan (MLG) is a cell wall polysaccharide found in fungi, bacteria, and plants, yet the enzymatic machinery and structural determinants governing fungal MLG biosynthesis remain poorly understood. In Aspergillus fumigatus, TFT1 (AfTFT1) has previously been implicated in MLG biosynthesis, but its direct biochemical activity remained unresolved. The structural characterization of A. fumigatus wall MLG revealed a distinct polymer profile. Heterologous expression of AfTFT1 in Komagataella phaffii enabled MLG production, generating an oligosaccharide profile that closely matched that of the native fungal polymer and demonstrating that AfTFT1 functions as an MLG synthase. Phylogenetic analysis placed AfTFT1 within a distinct glycosyltransferase family 2 (GT2) fungal lineage containing related candidate MLG synthases across diverse filamentous Ascomycota and separate from the major plant and bacterial synthase lineages. Structure-guided mutagenesis showed that individual substitutions within the transmembrane pore and switch motif altered the lichenase-derived oligosaccharide profile while retaining detectable MLG production, whereas replacement of the entire switch motif with the corresponding HvCSLF6 sequence resulted in no detectable MLG production. Together, these findings establish AfTFT1 as a fungal MLG synthase and identify the switch motif and adjacent transmembrane region as important determinants of MLG synthase function and product fine structure, providing insight into the structural and evolutionary diversification of MLG biosynthesis.

synthetic biology↗

bioRxiv2026

MYC2 mediated regulation of xylan substitution patterns

O-Acetylation is the most abundant xylan decoration in eudicot plants and plays a critical role in determining xylan conformation and its interactions with cellulose and lignin, thereby contributing to secondary cell wall (SCW) integrity. In Arabidopsis, loss of the xylan O-acetyltransferase TBL29/ESK1 causes collapsed xylem and growth defects that can be suppressed by mutations in strigolactone (SL) biosynthesis genes such as MAX3. However, the molecular basis of this suppression remains unknown. Hypoacetylated xylan in tbl29 has a higher frequency of methyl glucuronic acid (MeGlcA) substituents, while the ratio of GlcA/MeGlcA is recovered in tbl29 max3. Furthermore, gene expression analyses reveal that the three xylan glucuronoxylan methyltransferases (GXM1/2/3) involved in xylan MeGlcA modification are upregulated in tbl29 SCWs but downregulated in tbl29 max3. Genetic analysis shows that the transcription factor MYC2 is required for max3-mediated suppression: the loss of MYC2 in tbl29 max3 prevents growth recovery and reverts GXM genes expression and xylan MeGlcA substitution levels. We propose a model where SL deficiency enhances MYC2 transcription, which in turn represses GXMs, thereby fine-tuning xylan methylation and re-establishing the MeGlcA/GlcA substitution balance under conditions of reduced O-acetylation. Our findings identify a MYC2-dependent regulatory module linking SL signalling to xylan methylation and reveal a genetically encoded compensatory mechanism that mitigates the consequences of defective xylan O-acetylation. More broadly, this work demonstrates that plants can preserve SCW function through adaptive remodelling of polysaccharide substitution patterns, highlighting an unexpected plasticity in SCW biosynthesis. Significance StatementSecondary cell wall integrity depends on the coordinated modification of xylan. We show that defects caused by reduced xylan O-acetylation can be alleviated through a strigolactone- and MYC2-dependent pathway that alters xylan methylglucuronidation. Rather than restoring the original wall composition, this mechanism appears to compensate for the loss of O-acetyl groups by remodelling polysaccharide substitution patterns to maintain cell wall function, revealing a new layer of plasticity in secondary wall biosynthesis.

developmental biology↗

bioRxiv2026

A chromosome-scale super-pangenome of the lichen genus Peltigera reveals genome architecture and expanded interaction repertoires shared across pathogenic and mutualistic fungi

Fungi engage in associations with other organisms across a continuum from pathogenic to mutualistic lifestyles. Hence, they require a compendium of molecular capacities, including partner recognition, extracellular signaling, nutrient exchange, immune modulation, and control of microbial competitors. In filamentous pathogens such traits are frequently associated with compartmentalized genomes, including rapidly evolving secreted proteins known as effectors and expanded receptor families, but it remains unclear whether similar genomic principles shape mutualistic fungal symbioses. Here, we generated a chromosome-scale super-pangenome for the lichen-forming genus Peltigera, comprising 41 mycobiont assemblies representing eleven species, together with genomes of associated Nostoc and, in tripartite species, Coccomyxa photobionts. The mycobiont genomes revealed extensive variation in genome size, transposable element content, biosynthetic gene clusters, and lineage-specific gene content, with pronounced expansions in tripartite species. Across Peltigera, secreted protein encoding genes were preferentially located in TE-rich regions. We further identified Starship-like transposon elements, expanded antimicrobial protein repertoires, and a large, previously underestimated repertoire of fungal GPCRs dominated by Pth11-like receptors. Layer-specific transcriptomics of a P. rufescens thallus showed differential expression of several interaction-associated gene families, e.g. lectins, antimicrobial proteins and Pth11-like GPCRs. These data indicate that pathogenic and mutualistic fungi might exhibit shared genomic principles, including genome compartmentalization, mobile-element-associated diversification, and the expansion of molecular repertoires involved in recognition, extracellular control and signaling.

genomics↗

bioRxiv2026

Plasma proteomics reveals divergent sex-specific senescence and bone biology signatures across neurodegenerative diseases

Neurodegenerative diseases are often accompanied by systemic comorbidities, including changes in bone health, but the molecular relationship between neurodegeneration, skeletal decline, and cellular senescence remains poorly understood. In this study, we investigated sex-specific changes in circulating bone- and senescence-related proteins across the spectrum of Alzheimers disease(AD), Lewbody dementia(LB) and Parkinsons disease(PD). Plasma proteomic profiling was performed on samples from 408 participants deeply phenotyped for neurodegenerative diseases, followed by differential protein and pathway analyses. This study reveals sex-dependent alterations in bone and senescence-related circulating proteins in AD-related, PD and LB-related neurodegenerative diseases, providing insights into the complex relationship between neurodegeneration and bone health. Several candidate proteins were also associated with established plasma neurodegeneration biomarkers, particularly pTau181. Pathway analyses revealed shared mitochondrial and metabolic dysfunction across neurodegenerative diseases, with disease-specific features including vesicle trafficking disruption in AD and inflammatory-senescence pathways in LB, plus sex-divergent patterns in inflammatory signaling and bone-related pathways.

neuroscience↗

bioRxiv2026

Somatic DNA methylation heterogeneity predicts extreme transgenerational epimutation hotspots in Arabidopsis

Spontaneous epimutations are stochastic and heritable changes in cytosine methylation that arise independently of DNA sequence alterations. In plants, they occur predominantly at CG sites, accumulate across generations at high and clock-like rates, and contribute substantially to constitutive epigenetic diversity. Although these features are well established, the developmental origin of spontaneous epimutations remains poorly understood. One model proposes that they arise during somatic growth in different cell layers of the shoot apical meristem, where lineage bottlenecks enable nascent epimutations to clonally propagate into developing organs. Such layer-specific dynamics are expected to generate spatial mosaics of methylation states within tissues that manifest as heterogeneity in bulk bisulfite sequencing data. Here, we quantified genome-wide CG methylation heterogeneity in single Arabidopsis leaves using read-level methylation discordance metrics adopted from cancer epigenomics. We identified thousands of highly heterogeneous loci and show that they overlap extreme transgenerational epimutation hotspots. Analysis of multiple leaves from the same individuals further revealed that methylation divergence at these loci scales with developmental distance and recapitulates the branching architecture of the shoot. Together, these results support a meristematic origin of spontaneous epimutations and highlight a shared susceptibility to methylation-maintenance errors in both developmental and transgenerational contexts.

genetics↗

bioRxiv2026

The transcription factor SiROCX controls a monocot-specific CAZyme program for host cell wall remodeling during symbiotic root colonization

Intracellular accommodation of beneficial fungi requires controlled remodeling of host cell walls while avoiding activation of plant immune responses. During colonization of monocot roots, the endophytic fungus Serendipita indica induces a suite of carbohydrate-active enzymes (CAZymes) targeting xylan and cellulose. Weighted gene co-expression network analysis identified the basidiomycete-specific transcription factor SiROCX as a key regulator of this monocot-adapted program. DNA affinity purification sequencing (DAP-seq) defined the SiROCX binding motif and revealed a CAZyme-enriched target regulon. Inducible SiROCX overexpression selectively activated motif-containing CAZyme genes and markedly enhanced xylanase and cellulase activities on xylan and native barley root cell walls. Premature activation of this program triggered expression of a plant immune marker despite comparable fungal biomass, indicating that precise temporal control of CAZyme deployment is required to maintain symbiotic compatibility. Together, these findings identify SiROCX as a central regulator of a monocot-adapted cell wall-degrading secretome and reveal a basidiomycete-specific regulatory module that coordinates host cell wall remodeling with immune-compatible symbiotic colonization. SignificanceBeneficial fungi colonize living plant cells, requiring host cell wall remodeling while avoiding immune activation. However, the key transcriptional regulators coordinating this process in basidiomycetes during symbiotic root colonization remain unknown. We identify SiROCX, a conserved basidiomycete-specific transcription factor, as a master activator of a monocot-adapted xylan/cellulose degradation program in the root endophyte Serendipita indica. By integrating in planta co-expression networks, DAP-seq, secretome proteomics, and enzymatic assays, we show that SiROCX overexpression markedly enhances secretion and activity of xylan- and cellulose-degrading enzymes, boosting sugar release from monocot cell walls. These findings reveal a basidiomycete-specific regulatory module for immune-compatible host cell wall remodeling, providing a framework to engineer fungal CAZyme programs for crop symbiosis and biomass conversion.

microbiology↗

bioRxiv2026

Effect of endogenous and exogenous ketosis in acute spinal cord injury in Wistar rats.

Acute spinal cord injury is a condition with a poor prognosis, leading to reduced quality of life and high economic costs for both patients and health systems, and only a minority of patients with this injury can achieve a meaningful recovery. Given the high frequency of traumatic events such as vehicle collisions and falls, research aimed at limiting injury extension, promoting neuronal recovery, and improving prognosis is essential. It has been shown that ketone bodies have anti-inflammatory properties and also mediate the Nrf2 pathway, exerting antioxidant effects. The aim was to identify any alternative to mitigate the extension and progression of secondary injury by using 1,3 butanediol as a {beta}-hydroxybutyrate source. An experimental model (n= 60) of clinically healthy male Wistar rats were used, divided into five groups (n=12) as a control group, while the remaining rats were subjected to extradural spinal cord clipping according to the following groups (n=12): Spinal Cord Injury (SCI); endogenous ketosis + methylprednisolone (Endo-K+MP); exogenous ketosis + methylprednisolone (Exo-K+MP), and methylprednisolone (MP). After 8 hours of spinal cord injury, tissue was collected, immunohistochemistry and PCR analyses were carried out. Nrf2 and 3NT for the antioxidant pathway, and HIF-1, NFkB, NLRP3, TNF-[a] and IL-1{beta} for inflammation were analyzed. Results demonstrated that the groups thrown into a ketosis state had better outcomes, and, according to the Exo-k+MP and Endo-k+MP groups, increased Nrf2 and decreased 3NT (p < 0.05), which resulted in an upregulation of antioxidant pathways. According to HIF-1 and NF{kappa}B, Endo-K+MP showed better outcomes p<0.05 and proinflammatory cytokines showed the same pattern as the standard treatment (MP) p<0.05). Overall, our results also demonstrated a downregulation of inflammatory pathways. Author SummarySpinal cord injury is a devastating condition that frequently results in permanent neurological damage, reduced quality of life, and high social and healthcare costs. Current treatments are limited and mainly focus on reducing inflammation after injury, with methylprednisolone being one of the most commonly used therapies despite its associated adverse effects. Previous studies have shown that ketosis, a metabolic state characterized by increased ketone bodies, has anti-inflammatory and antioxidant properties in several neurological conditions. In this study, we investigated whether inducing ketosis could improve early outcomes after acute spinal cord injury. Using a rat model, we compared the effects of endogenous ketosis (induced by fasting) and exogenous ketosis (induced by ketone precursors), alone or in combination with methylprednisolone. We analyzed inflammatory and oxidative stress pathways using immunohistochemistry and molecular techniques. Our findings show that ketosis enhances the anti-inflammatory and antioxidant effects of methylprednisolone, leading to reduced activation of inflammatory pathways and increased antioxidant responses during the first hours after injury. These results suggest that metabolic interventions such as ketosis may represent a promising complementary strategy to improve early management of spinal cord injury.

neuroscience↗

bioRxiv2025

LsrL modulates Lsr2-induced chromatin structure to tune biosynthetic gene cluster regulation in Streptomyces venezuelae

Specialized biosynthetic gene clusters in Streptomyces are subject to complex regulation involving both transcriptional control and chromosome organization. The nucleoid-associated protein Lsr2 silences many of these clusters, yet how it shapes the global chromatin structure and how its conserved paralog LsrL contributes to this process remain poorly understood. In this study, we applied a multi-omics approach, combining transcriptional activity, genome-wide protein-DNA binding profiles, and three-dimensional chromosome conformation to characterize the coordination of Lsr2 and LsrL in exerting transcriptional control and genome architecture in Streptomyces venezuelae. In line with established Lsr2 functions, we find that Lsr2 sets broad transcriptional boundaries, while LsrL acts in a more context-specific manner that depends on the presence of Lsr2 and may function to reinforce or modulate Lsr2-mediated silencing. Loss of Lsr2 reshaped the chromatin landscape genome-wide, relieving its restriction on short-range contacts, triggering strong transcriptional changes and new domain boundaries near de-repressed biosynthetic gene clusters. These findings establish Lsr2 as a dominant but contextually modulated regulator whose interplay with LsrL coordinates specialized metabolism with higher-order chromosome organization.

microbiology↗

bioRxiv2025

Host-adapted enzymatic deconstruction of acetylated xylan enables mutualistic colonization of monocot roots

Intracellular accommodation of mutualistic fungi in plant roots depends on selective remodeling of host cell walls while minimizing activation of plant immune responses. In this study, we identify a host-adapted enzymatic module in the root endophyte Serendipita indica that targets acetylated xylan, a major structural component of monocot cell walls. The glycoside hydrolase SiGH11 cleaves the xylan backbone and releases O-acetylated oligosaccharides, which are subsequently deacetylated by the XynE-like esterase SiAXE. These enzymes are co-expressed within a monocot-specific transcriptional program that is enriched in carbohydrate-active enzymes and sugar transporters. Their combined activity enhances enzymatic degradation and facilitates downstream hydrolysis by exo-xylanases, which reduces the production of apoplastic reactive oxygen species triggered by damage-associated molecular patterns. Functional analysis shows that overexpression of SiAXE promotes early root colonization, while deletion of the gene compromises fungal proliferation during later stages. These findings define a coordinated and immune-compatible strategy for host cell wall deconstruction that enables fungal adaptation and endophytic colonization of monocot roots. In BriefSerendipita indica utilizes a transcriptionally coordinated xylanase and esterase module to degrade acetylated xylan in monocot roots. This enzyme cooperation enhances substrate breakdown, suppresses immune responses, and enables endophytic colonization, illustrating how mutualistic fungi adapt saprotrophic enzymes for host-specific intracellular accommodation. HighlightsO_LIMutualistic fungal endophyte repurposes saprotrophic enzymes to enable monocot-specific intracellular root colonization C_LIO_LICoordinated xylanase and esterase activity remodels host cell walls and dampens immune responses C_LIO_LIExpression of cell wall degrading enzymes is regulated by host species and colonization stage C_LIO_LIResults reveal fungal adaptation to monocot roots along the saprotrophy to symbiosis transition C_LI

plant biology↗

bioRxiv2024

Mitochondrial fission controls astrocyte morphogenesis and organization in the cortex

Dysfunctional mitochondrial dynamics are a hallmark of devastating neurodevelopmental disorders such as childhood refractory epilepsy. However, the role of glial mitochondria in proper brain development is not well understood. We show that astrocyte mitochondria undergo extensive fission while populating astrocyte distal branches during postnatal cortical development. Loss of mitochondrial fission regulator, Dynamin-related protein 1 (Drp1), decreases mitochondrial localization to distal astrocyte processes, and this mitochondrial mislocalization reduces astrocyte morphological complexity. Functionally, astrocyte-specific conditional deletion of Drp1 induces astrocyte reactivity and disrupts astrocyte organization in the cortex. These morphological and organizational deficits are accompanied by loss of perisynaptic astrocyte process (PAP) proteins such as gap junction protein Connexin 43. These findings uncover a crucial role for mitochondrial fission in coordinating astrocytic morphogenesis and organization, revealing the regulation of astrocytic mitochondria dynamics as a critical step in neurodevelopment. SummaryDuring cortical astrocyte morphogenesis, mitochondria fragment and decrease in size to populate distal astrocyte processes. Drp1-mediated mitochondrial fission is necessary for peripheral astrocyte process formation. Astrocyte-specific Drp1 loss induces astrocyte reactivity, disrupts cortical astrocyte organization, and dysregulates PAP proteins including gap-junction protein Connexin 43 abundance.

cell biology↗

bioRxiv2024

Worldwide study of the taste of bitter medicines and their modifiers

The bitter taste of medicines hinders patient compliance, but not everyone experiences these difficulties because people worldwide differ in their bitterness perception. To better understand how people from diverse ancestries perceive medicines and taste modifiers, 338 adults, European and recent US and Canada immigrants from Asia, South Asia, and Africa, rated the bitterness intensity of taste solutions on a 100-point generalized visual analog scale and provided a saliva sample for genotyping. The taste solutions were five medicines, tenofovir alafenamide (TAF), moxifloxacin, praziquantel, amodiaquine, and propylthiouracil (PROP), and four other solutions, TAF mixed with sucralose (sweet, reduces bitterness) or 6-methylflavone (tasteless, reduces bitterness), sucralose alone, and sodium chloride alone. Bitterness ratings differed by ancestry for two of the five drugs (amodiaquine and PROP) and for TAF mixed with sucralose. Genetic analysis showed that people with variants in one bitter receptor variant gene (TAS2R38) reported PROP was more bitter than did those with a different variant (p= 7.6e-19) and that people with either an RIMS2 or a THSD4 genotype found sucralose more bitter than did others (p=2.6e-8, p=7.9e-11, resp.). Our findings may help guide the formulation of bad- tasting medicines to meet the needs of those most sensitive to them.

physiology↗

bioRxiv2021

Household transmission of SARS-CoV-2 from humans to dogs in Washington and Idaho: burden and risk factors

SARS-CoV-2 is believed to have emerged from an animal reservoir; however, the frequency of and risk factors for inter-species transmission remain unclear. We carried out a community-based study of pets in households with one or more confirmed SARS-CoV-2 infection in humans. Among 119 dogs and 57 cats with completed surveys, clinical signs consistent with SARS-CoV-2 were reported in 20 dogs (21%) and 19 cats (39%). Out of 81 dogs and 32 cats sampled for testing, 40% of dogs and 43% of cats were seropositive, and 5% of dogs and 8% of cats were PCR positive; this discordance may be due to delays in sampling. Respondents commonly reported close human-animal contact and willingness to take measures to prevent transmission to their pets. Reported preventative measures showed a slightly protective trend for both illness and seropositivity in pets, while sharing of beds and bowls had slight harmful effects.

microbiology↗

bioRxiv2020

Degradation of mixed-linkage (1,3;1,4)-β-D-glucan in maize is mediated by the CAL1 licheninase

The presence of mixed-linkage (1,3;1,4)-{beta}-D-glucan (MLG) in plant cell walls is a key feature of grass species such as cereals - the main source of calorie intake for humans and cattle. Accumulation of this polysaccharide involves the coordinated regulation of biosynthetic and metabolic machineries. While several components of the MLG biosynthesis machinery have been identified in diverse plant species, degradation of MLG is poorly understood. A large-scale forward genetic maize screen for mutants with altered cell wall polysaccharide structural properties resulted in the identification of candy-leaf1 (cal1). Cell walls of CAL1-deficient plants contain higher amounts of MLG in several tissues, including adult leaves and senesced organs, where only trace amounts of MLG are usually detected. In addition, cal1 plants exhibit increased saccharification yields upon enzymatic digestion. Stacking cal1 with lignin-deficient mutations results in synergistic saccharification increases. Identification of the causative mutation revealed that CAL1 encodes a GH17 licheninase. Maize plants overexpressing CAL1 exhibit a 90% reduction in MLG content, indicating that CAL1 is not only required, but its expression sufficient to degrade MLG. CAL1 specifically hydrolyzes (1,3;1,4)-{beta}-D-Glucans in vitro, and the single CAL1E262K amino acid substitution is able to block all detectable activity. Time profiling experiments indicate that wall MLG content is modulated during day/night cycles inversely correlating with CAL1 transcript accumulation. This cycling is absent in the cal1 mutant, suggesting that the mechanism involved requires MLG degradation that may in turn regulate CAL1 gene expression. One sentence summary Mixed-linkage glucan is degraded by the CAL1 licheninase in maize

plant biology↗

bioRxiv2019

Genetic dissection of cell wall defects and the strigolactone pathway in Arabidopsis.

Defects in the biosynthesis and/or deposition of secondary plant cell wall polymers result in the collapse of xylem vessels causing a dwarfed plant stature and an altered plant architecture termed irregular xylem (irx) syndrome. For example, reduced xylan O-acetylation causes strong developmental defects and increased freezing tolerance. Recently, we demonstrated that the irx syndrome in the trichome birefringence-like 29/eskimo1 (tbl29/esk1) mutant is dependent on the biosynthesis of the phytohormone strigolactone (SL). In this report, we show that other xylan- and cellulose-deficient secondary wall mutants exhibit increased freezing tolerance correlated with the irx syndrome. In addition, blocking SL synthesis has also a suppressor effect on these phenotypes, suggesting a more general interaction between secondary wall defects and SL biosynthesis. In contrast, SLs do not play a role in developmental defects triggered by primary wall deficiencies, suggesting that the interaction is restricted to vascular tissue.\n\nThrough a reverse genetics approach the requirement of different components of the SL pathway impacting the irx syndrome in tbl29 was evaluated. Our results are consistent with a specific role for carlactone in this process, and suggest that a MORE AXILLARY GROWTH 2 (MAX2)-independent SL perception mechanism might be involved.

plant biology↗

bioRxiv2019

Fecal microbiota dysbiosis in macaques and humans within a shared environment

Traditional zoonotic disease research focuses on detection of recognized pathogens and may miss opportunities to understand broader microbial transmission dynamics between humans, animals, and the environment. We studied human-macaque microbiome overlap in Kosum Phisai District, Maha Sarakham Province, Thailand, where a growing population of long-tailed macaques (Macaca fascicularis) in Kosumpee Forest Park interact with humans from an adjacent village. We surveyed workers in or near the park with elevated exposure to macaques to characterize tasks resulting in exposure to macaque feces in addition to dietary and lifestyle factors that influence gut microbiome composition. Fecal samples were collected from 12 exposed workers and 6 controls without macaque exposure, as well as 8 macaques from Kosumpee Forest Park and 4 from an isolated forest patch with minimal human contact. The V4 region of the 16S rRNA gene from fecal sample extracted DNA was amplified and sequenced using Illumina HiSeq to characterize the microbial community. A permuted betadisper test on the weighted UniFrac distances revealed significant differences in the dispersion patterns of gut microbiota from exposed and control macaques (p=0.03). The high variance in gut microbiota composition of macaques in contact with humans has potential implications for gut microbiome stability and susceptibility to disease, described by the Anna Karenina principle (AKP). Human samples had homogenous variance in beta diversity but different spatial medians between groups (p=0.02), indicating a shift in microbial composition that may be explained by fundamental lifestyle differences between the groups unrelated to exposure status. SourceTracker was used to estimate the percent of gut taxa in exposed humans that was contributed by macaques. While one worker showed evidence of elevated contribution, the overall trend was not significant. Task observations among workers revealed opportunities to employ protective measures or training to reduce exposure to occupational hazards. These results suggest the potential for hygiene measures to mitigate negative aspects of contact between humans and macaques in order to optimize the health of both populations.

microbiology↗