A new study in Arabidopsis thaliana has identified the polymerase-associated factor 1 complex, or PAF1C, as a central component of the plant response to DNA replication stress. The findings reveal that PAF1C does more than support transcription: it also helps protect replication forks when DNA synthesis is disrupted. Researchers led by Li, Guo, Wang and colleagues describe a regulatory system that combines a plant-specific protein-stabilization pathway with a mechanism conserved across eukaryotes. At the center of this system is PAF1, a core component of PAF1C, whose activity is controlled by the stress-responsive kinase WEE1 and whose recruitment to damaged replication sites depends on the replication factor C complex.
DNA replication stress occurs when the machinery that copies the genome encounters obstacles or when the supply of nucleotides and other replication requirements becomes limiting. Under these conditions, replication forks can slow, pause or collapse. Unprotected stalled forks may generate abnormal DNA structures, double-strand breaks and chromosome rearrangements, threatening genome stability in dividing cells. Plants face additional challenges because environmental stresses, including drought, salinity, extreme temperatures and chemical exposure, can interfere with DNA synthesis. Although replication stress responses have been studied extensively in animals and yeast, the molecular pathways that protect plant replication forks have remained comparatively less understood.
The researchers found that plants lacking functional PAF1C were unusually sensitive to compounds that induce replication stress. This hypersensitivity indicates that PAF1C is not merely associated with the replication machinery but is required for plants to tolerate interruptions in DNA synthesis. PAF1C is best known as a transcription-associated complex that travels with RNA polymerase II and influences the production of messenger RNA. Its involvement in replication stress suggests that the complex can operate at the intersection of transcription, chromatin regulation and DNA replication. Such coordination is important because transcription and replication occur on the same DNA template and can obstruct one another, particularly in actively expressed genomic regions.
The study identifies WEE1 as a plant-specific control point in this response. WEE1 is a stress-activated kinase already recognized for its role in regulating the cell cycle. When replication is compromised, WEE1 can restrain cell-cycle progression, giving the cell additional time to repair or stabilize its DNA. In the newly described pathway, WEE1 phosphorylates PAF1. This chemical modification changes the behavior of the PAF1 protein by preventing or reducing its degradation. As a result, PAF1 remains available when replication stress requires PAF1C-dependent protection. The mechanism helps explain how a plant cell can rapidly increase the persistence of a replication-protective factor without necessarily requiring the immediate production of entirely new protein.
The WEE1–PAF1 connection also highlights an important evolutionary distinction. According to the study, WEE1-dependent stabilization of PAF1 is a plant-specific feature that is not present in yeast. This suggests that plants have incorporated their established cell-cycle stress kinase into a specialized system for maintaining PAF1C during replication problems. The finding expands the functional range of WEE1, showing that its influence may extend beyond the classic control of cell-cycle timing. It also demonstrates that conserved protein complexes can be placed under lineage-specific regulatory control as organisms adapt their genome-maintenance strategies to different biological environments.
The researchers further uncovered a second pathway involving the replication factor C complex, commonly known as RFC. RFC is a ring-shaped DNA-processing complex best known for loading proliferating cell nuclear antigen, or PCNA, onto DNA. PCNA acts as a sliding platform that helps DNA polymerases remain attached to the template during replication. When a replication fork stalls, RFC contributes to the organization of proteins at the affected site. The study shows that RFC recruits PAF1C to stalled replication forks, positioning the complex where it can directly support the stability of the paused DNA-replication structure.
Once recruited, PAF1C acts as an assembly platform for enzymes that modify chromatin. Specifically, it brings together the E2 ubiquitin-conjugating enzymes UBC1 and UBC2 and the E3 ubiquitin ligases HUB1 and HUB2. These enzymes promote monoubiquitination of histone H2B, a chemical modification in which a single ubiquitin molecule is attached to the H2B histone. Histones package DNA into chromatin, but they also provide regulatory signals that influence access to the genome. H2B monoubiquitination can alter chromatin behavior and recruit or stabilize additional DNA-repair and replication factors. In this setting, the modification appears to help maintain stalled replication forks and reduce the risk that they will deteriorate into more dangerous DNA lesions.
The RFC–PAF1–UBC1/2–HUB1/2 pathway is significant because it connects the physical detection or processing of a stalled fork with a local chromatin response. Rather than acting as a general stress signal throughout the nucleus, PAF1C is brought to the precise DNA sites where replication has become unstable. There, it helps organize the enzymatic machinery needed to modify nearby histones. This spatial coordination is a hallmark of efficient genome maintenance: replication proteins, chromatin regulators and ubiquitin enzymes must act at the same site and within a narrow time window. The findings indicate that this recruitment mechanism is conserved, even though the upstream control of PAF1 stability through WEE1 appears to be specific to plants.
Together, the two pathways create an integrated model for plant replication-stress protection. WEE1 first helps preserve the PAF1 protein by phosphorylating it and shielding it from degradation. RFC then guides the stabilized PAF1C complex to stalled replication forks. At those locations, PAF1C recruits UBC1/2 and HUB1/2, enabling H2B monoubiquitination and supporting fork stability. The model places PAF1C at the center of a molecular relay that begins with cell-cycle stress signaling and ends with a targeted chromatin modification. It also gives new meaning to the established relationship between transcriptional machinery and DNA replication, showing that a transcription-associated complex can be repurposed as a direct protector of replication intermediates.
The discovery may have implications beyond the basic biology of Arabidopsis. Plants with improved control of replication stress could potentially maintain genome stability more effectively under environmental conditions that limit growth or damage DNA. However, translating these findings into crop engineering or stress-tolerance strategies will require determining how broadly the pathway operates across plant species and how it interacts with other repair systems. The work also raises questions about whether related PAF1C functions remain undiscovered in animals and fungi, where different regulatory circuits may control the same complex. By revealing a plant-specific WEE1–PAF1 stability mechanism alongside a conserved RFC-dependent recruitment pathway, the study establishes PAF1C as a previously underappreciated component of the replication stress response and offers a new framework for understanding how plants defend their genomes when DNA copying goes off schedule.
Subject of Research: The role of the polymerase-associated factor 1 complex in plant DNA replication stress responses and replication fork stability.
Article Title: Plant-specific and conserved mechanisms of the polymerase-associated factor 1 complex in replication stress responses.
Article References: Li, C., Guo, Y., Wang, Z. et al. Plant-specific and conserved mechanisms of the polymerase-associated factor 1 complex in replication stress responses. Nat. Plants (2026). https://doi.org/10.1038/s41477-026-02387-5
Image Credits: AI Generated
DOI: https://doi.org/10.1038/s41477-026-02387-5
Keywords: Arabidopsis, DNA replication stress, PAF1C, PAF1, WEE1, replication forks, RFC complex, histone H2B monoubiquitination, ubiquitin, genome stability, plant molecular biology
Tags: conserved eukaryotic replication stress mechanismsDNA repair pathways in plantsDNA replication stress in plantsmolecular mechanisms of plant DNA replication protectionPAF1C in DNA damage responseplant genome stability under stressplant stress response to environmental challengesplant-specific PAF1 complex rolereplication fork protection in Arabidopsisrole of replication factor C complex in genome stabilitytranscription and replication coordination in plantsWEE1 kinase regulation in plants
