Biology subjects

Jacobsen, S. E.

Publications and source records attributed to Jacobsen, S. E..

At least 19 recordsLinked to original sources

bioRxiv2026

Dual-Binding Scaffold RRsS1 Bridges Pol IV Transcripts and DNA Templates for Robust Reproductive siRNA Biogenesis

Cytosine DNA methylation established by RNA-directed DNA methylation (RdDM) is critical for transposon silencing and genome integrity in plants. In reproductive tissues, RNA Polymerase IV (Pol IV) is recruited to specific genomic loci by DNA motifs and the transcription factor-GDE1-CLSY3/4 complex to initiate abundant siRNA biogenesis and de novo DNA methylation, but the mechanisms that stabilize the Pol IV transcription complex at these sites remain elusive. Using immunoprecipitation-mass spectrometry of the Pol IV complex, we identify Reproductive RdDM siRNA Scaffold 1 (RRsS1) as a novel Pol IV interactor. RRsS1 colocalizes genome-wide with motif-dependent RdDM factors in floral tissues. Loss of RRsS1 significantly impairs 24-nt siRNA accumulation at a subset of CLSY3/4-dependent loci, particularly those exhibiting high Pol IV enrichment. We show that chromatin association of RRsS1 is stabilized by GDE1 and CLSY3/4. Structural modeling and biochemical assays characterize RRsS1 as a chimeric protein containing HRDC, Nudix, and DRBM modules that bind single-stranded DNA (ssDNA) and double-stranded DNA (dsRNA), respectively. Together, our findings support a model in which RRsS1 acts as a dual-binding scaffold, bridging Pol IV-RDR2 transcripts to their DNA templates within transcription bubbles to ensure robust siRNA production during plant reproduction.

plant biology↗

bioRxiv2026

Gene duplication of SNAPC1 generates transcription factors for snRNAs and sex-specific piRNAs

Piwi-interacting RNAs (piRNAs) are small non-coding RNAs essential for transposon silencing and germline integrity across metazoans. In many species, piRNA expression is sexually dimorphic, yet the molecular mechanisms underlying this sex specificity remain poorly understood. In Caenorhabditis elegans, sexually dimorphic piRNA expression is regulated at the transcriptional level. We previously identified SNPC-1.3, a paralog of the small nuclear RNA (snRNA) activating protein complex (SNAPc/SNPC) subunit SNAPC1, as a male-specific piRNA transcription factor. However, the factors governing female piRNA expression remained elusive. Here, we identify SNPC-1.2, a second SNPC-1 paralog, as a female-specific piRNA transcription factor. SNPC-1.2 interacts with the core piRNA transcriptional machinery, binds female piRNA loci, is required for female piRNA expression, and promotes hermaphrodite fertility. In contrast, a third paralog, SNPC-1.1, retains the ancestral SNAPc function in snRNA transcription and is dispensable for piRNA biogenesis. Together, these findings reveal how gene duplication and functional specialization within the snpc-1 gene family generate specificity factors that direct the core SNAP complex to distinct genomic targets, providing a molecular mechanism for sexually dimorphic piRNA expression while maintaining canonical snRNA transcription.

molecular biology↗

bioRxiv2026

Chromatin-Assisted Targeting Enables Precise DNA Methylation Editing in Plants

Precise installation of DNA methylation at selected loci offers a powerful strategy for regulating gene expression without altering DNA sequence, but existing plant epigenome editors are constrained by limited efficiency, locus dependence, and genome-wide off-target methylation. Here, we developed SunTag-MQ1v variants incorporating TRBIP1, which promotes removal of the antagonistic H3K4me3 mark, and CHLAMY, an oligomerizing alpha crystalline domain protein from Chlamydomonas reinhardtii. TRBIP1 enhanced methylation and silencing at the Arabidopsis FWA promoter but caused widespread off-target methylation and severe developmental defects. Adding CHLAMY produced SunTag-CHLAMY-TRBIP1-MQ1v (designated as SunTag-NOVA), which successfully overcame the lethality and widespread off-target effects associated with direct TRBIP1-MQ1v fusions. We demonstrate that CHLAMY drives higher-order oligomerization of the editing complex, which enhances target specificity and mitigates off-target accumulation. SunTag-NOVA robustly installed DNA methylation and repressed transcription at the endogenous FWA, FT and TMM genes with minimal genome-wide off-target consequences. These results show that combining local chromatin modification with controlled effector assembly can improve targeted DNA methylation, and establish SunTag-NOVA as a specific epigenome-editing platform for plants.

plant biology↗

bioRxiv2026

J-domain proteins bridge the PKL and ATRX complex to transcription factors to fine-tune gene expression via H3.3 deposition

Epigenetic modifications, including histone modifications and DNA methylation, direct gene expression programs during the growth and development of eukaryotic organisms. In Arabidopsis thaliana, the chromatin remodeler PICKLE (PKL), a homolog of animal CHD3, plays a critical role during these processes. Previous studies of PKL have painted a complex picture of its function, including both activating and repressive roles, however, how PKL can control both transcriptional silencing and activation is unknown. We have identified a group of J-domain-containing proteins (DNAJs), usually known for their roles in protein folding, that guide PKL recruitment to various gene promoters by bridging PKL to transcription factors. Mutation of PKL's DNAJ-interacting domain disrupts PKL association with chromatin. Once recruited to transcription factor-bound sites, PKL coordinates with the histone chaperone ATRX to deposit HISTONE3.3 (H3.3) at targeted loci, which also negatively affects the accumulation of H3 lysine 27 trimethylation (H3K27me3) at promoters. We found that transcriptional outcome of PKL binding depends not only on the changes in H3.3 occupancy but also on the pre-existing chromatin context at PKL-targeted sites. Our findings outline a new mechanism for CHD3 chromatin remodeler recruitment and function.

plant biology↗

bioRxiv2026

FOXO/DAF-16 modulates the transcription factor ROR/NHR-23 and inhibits the let-7 microRNA to maintain multipotency during dauer

Animals rapidly reprogram gene expression to adapt development to environmental stress. How gene regulatory programs that drive continuous development are repressed during stress-induced developmental arrest remains poorly understood. In Caenorhabditis elegans, starvation and overcrowding trigger entry into the stress-resistant, quiescent dauer stage. Here, we identify interactions among the conserved transcription factors DAF-16/FOXO and NHR-23/ROR, and the let-7 family of microRNAs as key regulators of the switch from continuous development to dauer. We show that loss of daf-16 during dauer causes elevated let-7 family microRNAs and premature expression of the adult collagen reporter col-19p::GFP. Reducing let-7 family activity suppresses this phenotype, whereas dauer-specific let-7 expression is sufficient to induce col-19p::GFP expression. Mechanistically, DAF-16 inhibits let-7 transcription in part by repressing nhr-23, which encodes a transcriptional activator of the let-7 family and molting-cycle genes. ChIP-seq analysis reveals DAF-16 binding upstream of nhr-23, and daf-16; daf-7 mutant dauers exhibit increased nhr-23 mRNA and NHR-23 protein, supporting a model in which DAF-16 directly represses nhr-23. Integrated ChIP-seq and transcriptomic analyses identify 1,183 genes activated and 681 genes repressed by DAF-16 during dauer. Repressed targets are enriched for pro-growth genes involved in mitotic DNA replication and translational elongation. DAF-16 targets include 59 transcription factors that may mediate broader transcriptional reprogramming during dauer to maintain multipotency and establish quiescence. Together, these findings reveal that DAF-16/FOXO establishes stress-induced developmental arrest by coupling activation of protective pathways with repression of conserved developmental timing, growth, and differentiation programs. Significance statementAnimals often pause development during environmental stress and then resume normal development when conditions improve. How developmental programs are temporarily halted without disrupting later cell fates remains poorly understood. We show that, during stress-induced dauer arrest in C. elegans, the conserved FOXO transcription factor DAF-16 represses the differentiation-promoting let-7 microRNA pathway. DAF-16 inhibits the ROR homolog NHR-23, which normally activates let-7 and molting-cycle genes. Genome-wide analyses further show that DAF-16 both activates stress-response genes and represses growth and developmental genes. These findings reveal how a conserved stress-responsive factor coordinates survival, developmental arrest, and maintenance of cellular multipotency.

molecular biology↗

bioRxiv2026

Multiple approaches for CRISPR-based targeting of DNA methylation to promoters of bacterial and viral susceptibility genes in cassava

Targeted epigenetic modifications of specific gene regulatory regions have the potential to confer beneficial traits for crop improvement. Two recently developed CRISPR/Cas9-based epigenome editing tools were tested in transgenic cassava to target cytosine methylation to the promoter region of MeSWEET10a, a necessary gene for infection by the Cassava bacterial blight pathogen, Xanthomonas phaseoli pv. manihotis. The two systems leverage unique methyltransferases, and each induced distinct DNA methylation profiles at the targeted site, decreased effector-triggered MeSWEET10a expression, and attenuated water-soaking symptoms in inoculated leaves. Further, DNA methylation was simultaneously targeted, in addition to MeSWEET10a, to two susceptibility genes for Cassava brown streak virus. Relative levels of de novo DNA methylation at the three loci were inversely correlated with DNA methylation-antagonizing H3K4me3 marks. Finally, an initial assessment of DNA methylation after one generation indicated specific inheritance of CpG methylation that was unstable in the absence of the methyltransferase systems.

plant biology↗

bioRxiv2026

A Fungal Natural Product that Targets Cellulose Synthase Complex and Inhibits Plant Cellulose Biosynthesis

Cellulose, a primary component of plant cell walls, is synthesized by cellulose synthase complexes (CSCs) at the plasma membrane. Targeting this process with cellulose biosynthesis inhibitors (CBIs) has significantly advanced our understanding of plant cell wall formation and provided valuable compounds for herbicide development. Here, we identified a fungal natural product, 8-methyldichlorodiaporthin (MDD), as a broad-spectrum plant CBI. Structure-activity relationship analyses demonstrate that methylation modifications on the isocoumarin ring and chlorination of side chain are crucial for MDD-induced growth inhibition. A chemical forward genetic screen in Arabidopsis thaliana revealed two semi-dominant CESA1 mutations, causing A903T and H1024Y substitutions, that confer insensitivity to MDD. Both mutations locate to transmembrane domains of CESA1, and we show that MDD depletes CSCs from the plasma membrane and reduces cellulose content. Further genetic analyses indicate that the cesa1mddi1-1 A903T mutant also confers resistance to CBIs quinoxyphen and C17, but not to CBIs isoxaben, indaziflam, or ES20. Stacking additional point mutations conferring resistance to other CBIs, cesa3ixr1-1 G998D, and cesa6es20-r3 G935E into the cesa1mddi1-1 A903T background yields multiple-drugs resistant lines that maintain normal growth. These findings establish MDD, as a novel, natural CBI that likely targets CESA1, thereby extending our understanding of CSC regulation and abilities to develop multi-drugs resistant crop varieties. These findings offer new perspectives for weed management and plant biotechnology. Significance StatementCellulose, a fundamental structural component of plant cell walls, is synthesized by cellulose synthase complexes (CSCs) and represents a critical herbicide target. While synthetic cellulose biosynthesis inhibitors (CBIs) like isoxaben and quinoxyphen have helped in the elucidation of CSC function and aided in weed control, natural CBIs remain largely undiscovered. Here, we identify 8-methyldichlorodiaporthin (MDD), a fungal-derived isocoumarin natural product, as a CBI that inhibits plant growth by depleting CSCs from the plasma membrane. Genetic screens reveal MDD-resistant cesa1 mutations, and combining these with other CBI-resistant alleles yields multi-herbicide resistant plants that can grow normally. This research enhances our understanding of cellulose biosynthesis and paves the way for multi-herbicide resistant crops with agricultural benefits.

plant biology↗

bioRxiv2026

Multiple redundant mechanisms account for the majority of gene silencing downstream of DNA methylation

DNA methylation is a conserved epigenetic modification crucial for silencing genes and transposable elements (TEs). However, the mechanisms that cause silencing remain unclear, partly because methyl reader protein mutants in both plants and animals show minimal transcriptional changes. To explore the possibility of redundancy among these silencing mechanisms, we generated combinatorial mutants of H1.1, H1.2, ADCP1, MOM1, MBD2, MBD5, and MBD6 lacking key methyl readers and related silencing pathways. We observed massive derepression of genes and TEs at DNA-methylated loci, showing that these pathways account for 73% of silencing compared to DNA methylation-free mutants. We also observed that immune response genes were upregulated, causing an imbalance between growth and defense. Loss of downstream silencing pathways further disrupted 3D genome organization, leading to increased euchromatin-heterochromatin interactions. These findings highlight the cooperative action of multiple downstream mechanisms in DNA methylation-mediated silencing and genome organization.

molecular biology↗

bioRxiv2026

Efficient transgene-free multiplexed genome editing via viral delivery of an engineered TnpB.

Virus-induced genome editing (VIGE) using compact RNA-guided endonucleases is a transformational new approach in plant biotechnology, enabling tissue-culture-independent and transgene-free genome editing (Hu et al. 2025; Liu et al. 2025; Weiss et al. 2025). We recently established a VIGE approach for heritable editing at single loci in Arabidopsis by delivering the compact genome editor ISYmu1 TnpB (Ymu1) and its guide RNA (gRNA) via Tobacco Rattle Virus (TRV) (Weiss et al. 2025). Here, we greatly improved this approach by devising a multiple gRNA expression system and by utilizing an engineered high-activity Ymu1 variant (Ymu1-WFR) (Zhou et al. 2026) to develop an efficient multiplexed genome editing platform.

plant biology↗

bioRxiv2026

Stepwise DNA unwinding gates TnpB genome-editing activity

TnpB is a compact RNA-guided endonuclease and evolutionary ancestor of CRISPR-Cas12 that offers a promising platform for genome engineering. However, the genome-editing activity of TnpBs remains limited and its underlying determinants are poorly understood. Here, we used biochemical and single-molecule assays to examine the DNA-unwinding mechanism of Youngiibacter multivorans TnpB (Ymu1 TnpB). DNA unwinding proceeds through a discrete, long-lived partially unwound intermediate state before reaching a fully unwound open state. The open state forms inefficiently and collapses readily in the absence of negative supercoiling. An optimized variant, Ymu1-WFR, stabilizes formation of both the intermediate and open states, resulting in enhanced DNA cleavage in vitro and increased genome editing in plants. These findings identify the physical basis for the observed minimal activities of natural TnpBs, revealing how stabilizing specific unwinding states enables efficient DNA targeting.

biochemistry↗

bioRxiv2025

Structure and evolution-guided design of minimal RNA-guided nucleases

The design of RNA-guided nucleases with properties not limited by evolution can expand programmable genome editing capabilities. However, generating diverse multi-domain proteins with robust enzymatic properties remains challenging. Here we use an artificial intelligence-driven strategy that couples structure-guided inverse protein folding with evolution-informed residue constraints to generate active, divergent variants of TnpB, a minimal CRISPR-Cas12-like nuclease. High-throughput functional screening of AI-generated variants yielded editors that retained or exceeded wild-type activity in bacterial, plant and human cells. Cryo-EM-based structure determination of the most divergent active variant revealed new stabilizing contacts in the RNA/DNA interfaces across conformational states, demonstrating the design potential of this approach. Together these results establish a strategy for creating non-natural RNA-guided nucleases and conformationally active nucleic acid binders, enlarging the designable protein space. One-sentence abstractAn evolution- and structure-conditioned model enables design of active RNA-guided nucleases with new nucleic acid contacts resolved by cryo-EM.

synthetic biology↗

bioRxiv2025

Virus induced transgene- and tissue-culture free heritable genome editing in tomato

Genome editing has emerged as a powerful tool for genome manipulation and trait improvement in crops. However, most commonly used approaches rely on tissue culture and transgenic materials, which are time-consuming, labor-intensive, and often strongly genotype-dependent. Here, we developed a tobacco rattle virus (TRV)-based system to deliver the compact ISYmu1 TnpB endonuclease, coupled with in planta shoot regeneration, to achieve somatic and heritable genome editing across different tomato cultivars without tissue culture. By targeting SlPDS, we successfully generated virus-free homozygous mutant progeny in a single generation. Furthermore, we extended this system to the functional analysis of the previously uncharacterized SlDA1 locus, revealing its involvement in organ size regulation, and recovered transgene-free SlDA1 mutants displaying enlarged fruits. Given the wide host range of TRV, our system should be broadly applicable for rapid, non-transgenic and less genotype-dependent heritable genome editing, thereby advancing both functional genomics and crop improvement. SignificanceEfficient genome editing without the need for transgenesis or tissue culture remains a major challenge in crop breeding. Here, we establish a simple single-step system for transgene- and tissue culture-free genome editing in tomato based on Tobacco Rattle Virus-mediated delivery of the compact RNA-guided TnpB enzyme ISYmuI and its guide RNA. This strategy enabled somatic editing of de novo shoots and heritable transmission of targeted mutations to the next generation. Notably, editing an agronomically relevant gene produced tomato plants with larger fruits, highlighting the potential of this system for crop improvement.

plant biology↗

bioRxiv2025

An antagonistic epigenetic mechanism regulating gene expression in pollen revealed through single-nucleus multiomics

Arabidopsis MBD5, MBD6, and MBD7 are CG-specific methyl-readers with opposite functions: MBD5 and MBD6 (MBD5/6) repress methylated loci in pollen vegetative nuclei (VN), while MBD7 prevents transgene silencing, possibly by promoting DNA demethylation. Here we show that loss of MBD7 rescues transcriptional defects at a large subset of MBD5/6-bound loci. Using simultaneous profiling of DNA methylation and transcription in single pollen nuclei, we found that MBD5/6-bound loci that are actively demethylated in immature VN lose additional methylation in mbd5/6, prior to transcriptional derepression. A subset of these loci is also bound by MBD7, correlating with demethylation and transcriptional derepression in mbd5/6 that are both reversed by loss of MBD7. Conversely, ectopically recruiting the MBD7 complex to MBD5/6 targets causes partial demethylation and upregulation. We propose that MBD5/6 maintain silencing in VN in part by preventing the MBD7 complex from enhancing the active demethylation that occurs during VN maturation.

molecular biology↗

bioRxiv2025

CDCA7 facilitates MET1-mediated CG DNA methylation maintenance in centromeric heterochromatin via histone H1

DNA methylation is a conserved epigenetic modification essential for maintaining genome stability. However, how methyltransferases maintain CG methylation within compact chromatin, including centromeres, remains unclear. In humans, CDCA7 is necessary for the inheritance of DNA methylation at juxta-centromeres. Mutations that impair its ability to bind chromatin result in Immunodeficiency, Centromeric Instability, and Facial Anomalies (ICF) syndrome, characterized by centromeric instability. To investigate whether CDCA7 function is conserved, we identified two Arabidopsis thaliana orthologs, CDCA7A and CDCA7B. The loss of both copies results in CG hypomethylation at pericentromeric regions and centromeric satellite repeat arrays. Machine learning analysis suggested that heterochromatic nucleosomes, with enrichment of H1, H2A.W, and H3K9me2 levels, depend heavily on CDCA7 proteins for CG methylation maintenance of the associated DNA. Loss of H1 restores heterochromatic DNA methylation in cdca7a cdca7b mutants, indicating that CDCA7A and CDCA7B mainly remodel H1-containing nucleosomes for methyltransferases to access DNA. Notably, in h1.1 h1.2 mutants, CG methylation shows a significant increase in centromeres, which reveals a new inhibitory role of H1 in DNA methylation maintenance within satellite repeat arrays. Centromeric DNA hypermethylation is lost in h1.1 h1.2 cdca7a cdca7b quadruple mutants, demonstrating that CDCA7A and CDCA7B can act independently of H1 to enhance MET1 activity. Overall, these findings establish CDCA7A and CDCA7B as conserved regulators of DNA methylation within heterochromatin and centromeric satellite repeat arrays.

molecular biology↗

bioRxiv2025

Targeting dCas9-SunTag to a susceptibility gene promoter is sufficient for CRISPR interference

Cassava production in sub-Saharan Africa is severely impacted by diseases. Most pathogens require interaction with host susceptibility factors to complete their life cycles and cause disease. Targeted DNA methylation is an epigenetic strategy to alter gene expression in plants and we previously reported that a zinc-finger fused to DMS3 could establish methylation at the promoter of MeSWEET10a, a bacterial susceptibility gene, and this resulted in decreased disease. Here, we attempt a similar strategy for cassava brown streak disease. This disease is caused by the ipomoviruses CBSV and UCBSV. These viruses belong to the family Potyviridae, which has been shown extensively to require host eIF4E-family proteins to infect plants and cause disease. We previously found that cassava plants with simultaneous knockout mutations in two eIF4E genes, nCBP-1 and nCBP-2, resulted in decreased susceptibility to CBSD. Here, we report successful simultaneous targeting of both promoters with methylation using a dCas9-DMRcd-SunTag system. However, in contrast to our previous work with MeSWEET10a, controls indicate that CRISPR interference is occurring in these lines and is sufficient for reduction of gene expression. Future research will use genetic crosses to segregate away the DNA methylation reagents and, if DNA methylation proves heritable, assess whether methylation alone is sufficient increase resistance to CBSD.

plant biology↗

bioRxiv2025

The epigenetic reader MORC3 is required for T cell development in the thymus

Cell fate decisions are orchestrated by an interplay of epigenetic factors in collaboration with transcriptional activators and repressors. The epigenetic reader MORC3 is known as a silencer of endogenous retroviruses in mouse embryonic stem cells. Here, we show that mouse MORC3 is expressed in the thymus and reveal that MORC3 loss of function leads to a severe arrest in T cell development at the DN1 stage, accompanied by an expansion of natural killer and myeloid cells. MORC3 function in thymus depends on its ATPase and its ability to bind H3K4me via the CW-type zinc finger domain. We find altered chromatin accessibility at regulatory elements of key T cell transcription factors in DN1 cells and show that re-expressing TCF1 in MORC3-deficient progenitor cells, rescues T cell development. Our work indicates a novel function for MORC3 in modulating regulatory sites essential for T cell lineage commitment at the level of chromatin.

genetics↗

bioRxiv2025

Arabidopsis REM transcription factors and GDE1 shape the DNA methylation landscape through the recruitment of RNA Polymerase IV transcription complexes.

DNA methylation plays crucial roles in gene regulation and transposon silencing. In plants, the maintenance of DNA methylation is controlled by several self-reinforcing loops involving histone methylation and non-coding RNAs. However, how methylation is initially patterned at specific loci is unknown. Here, we describe four Arabidopsis REM transcription factors, VDD, VAL, REM12 and REM13, that recognize specific sequence regions, and together with the protein GENETICS DETERMINES EPIGENETICS1 (GDE1), recruit RNA polymerase IV transcription complexes to generate 24-nucleotide small interfering RNAs (24nt-siRNAs) that guide DNA methylation to specific loci. In the absence of GDE1, Pol IV transcription complexes redistribute to sites bound by a different factor called REM8. These results suggest that REM proteins act as sequence specific DNA binding proteins that pattern siRNAs and methylation at specific sites in the genome, highlighting the role of genetic information in determining epigenetic patterns.

plant biology↗

bioRxiv2025

CRISPR targeting of H3K4me3 activates gene expression and unlocks centromeric crossover recombination in Arabidopsis

H3K4me3 is a fundamental and highly conserved chromatin mark across eukaryotes, playing a central role in many genome-related processes, including transcription, maintenance of cell identity, DNA damage repair, and meiotic recombination. However, identifying the causal function of H3K4me3 in these diverse pathways remains a challenge, and we lack the tools to manipulate it for agricultural benefit. Here we use the CRISPR-based SunTag system to direct H3K4me3 methyltransferases in the model plant, Arabidopsis thaliana. Targeting of SunTag-SDG2 activates the expression of the endogenous reporter gene, FWA. We show that SunTag-SDG2 can be employed to increase pathogen resistance by targeting the H3K4me3-dependent disease resistance gene, SNC1. Meiotic crossover recombination rates impose a limit on the speed with which new traits can be transferred to elite crop varieties. We demonstrate that targeting of SunTag-SDG2 to low recombining centromeric regions can significantly stimulate proximal crossover formation. Finally, we reveal that the effect is not specific to SDG2 and is likely dependent on the H3K4me3 mark itself, as the orthogonal mammalian-derived H3K4me3 methyltransferase, PRDM9, produces a similar effect on gene expression with reduced off-target potential. Overall, our study supports an instructive role for H3K4me3 in transcription and meiotic recombination and opens the door to precise modulation of important agricultural traits.

plant biology↗