Biology subjects

Mikulkova, P.

Publications and source records attributed to Mikulkova, P..

9 recordsLinked to original sources

bioRxiv2026

A Cajal body assembly factor regulates cell fate transitions in Arabidopsis

Ribonucleoprotein (RNP) condensates are emerging as key regulators of cell fate transitions, yet their functions have been largely linked to mRNA storage and translational control. Here, we uncover a role for Cajal body (CB)-mediated pre-mRNA splicing in coordinating the transition from stem cell divisions to differentiation in plants. We identify THREE-DIVISION MUTANT 3 (TDM3) as a cell cycle-regulated factor required for post-mitotic CB assembly. Loss of TDM3 or the CB scaffold protein COILIN delays differentiation and prolongs formative cell divisions. Transcriptome analysis revealed that TDM3 and COILIN jointly regulate pre-mRNA splicing, including transcripts controlling cell cycle and fate transitions. These findings establish CB-mediated splicing as a mechanism linking cell cycle progression to cellular differentiation.

cell biology↗

bioRxiv2026

MO25 binds CBL-interacting protein kinases associated with ribonucleoprotein condensates and regulates meiotic exit

Meiotic (M)-bodies are multiphasic ribonucleoprotein (RNP) condensates composed of a P-body core surrounded by a stress granule-like shell that promote meiotic exit through transient translational repression. This process depends on the phosphoserine-binding protein SMG7, which recruits the meiotic regulator TDM1 to M-bodies during meiosis II. Here, we identify the evolutionarily conserved scaffold protein MO25 as a regulator of SMG7 and TDM1 partitioning into M-bodies in Arabidopsis thaliana. Disruption of MO25A1 enhances the accumulation of SMG7 and TDM1 in M-bodies and increases the reduced fertility in the hypomorphic smg7-6 mutant, which exhibits impaired M-body association. In fungi and animals, MO25 proteins act as allosteric activators of STE20-family kinases. Interaction screening revealed that, whereas Arabidopsis MO25B proteins interact with STE20-family MAP4K kinases, MO25A paralogues have evolved specificity toward a subset of CBL-interacting protein kinases (CIPKs). Notably, the MO25A-interacting CIPKs localize to diverse nuclear and cytoplasmic RNP condensates. Among them, CIPK6 is required for fertility and pollen development, and disruption of its MO25-binding domain enhances SMG7 condensation. Together, our findings identify a previously unrecognized MO25A-CIPK interaction module that regulates M-body organization and may more broadly contribute to the regulation of RNP condensates.

plant biology↗

bioRxiv2025

Post-transcriptional regulation of meiotic transcripts by the RNA binding protein CDM1 is associated with cytoplasmic condensate assemblies

The transition from diploid to haploid life phases requires extensive reprogramming of gene expression that drive meiotic cell division and the differentiation of haploid forms. A hallmark of meiosis is widespread post-transcriptional regulation, including delayed translation that ensures timely protein production at specific stages. Here, we identify a mechanism controlling the translation of meiotic transcripts in Arabidopsis pollen mother cells, mediated by CALLOSE DEFECTIVE MICROSPORES1 (CDM1). We show that CDM1 affects several meiotic processes, including chromosome pairing, condensation, and cytokinesis. CDM1 forms dynamic, meiosis specific cytoplasmic foci that associate with components of processing bodies and stress granules, giving rise to three-phase condensate assemblies. Biochemical and cellular analyses reveal that CDM1 is an RNA-binding protein with an intrinsic ability to form ribonucleoprotein condensates. Furthermore, we demonstrate that CDM1 binds mRNAs expressed in prophase I and represses their translation until later meiotic stages, coinciding with the disassembly of CDM1 condensates. These findings establish CDM1 as a key post-transcriptional regulator that fine-tunes the expression of meiotic genes to ensure proper progression of microsporogenesis.

plant biology↗

bioRxiv2025

SMG7 and eIF4A constitute a homeostatic module controlling P-body condensation and function of Meiotic bodies

Processing bodies (P-bodies) are ribonucleoprotein condensates that regulate RNA processing and storage. Although present constitutively in most cells, their size and composition dynamically change in response to developmental and environmental cues. However, mechanisms governing P-body assembly and remodelling remain poorly understood. Here we show that in Arabidopsis, SMG7 interacts with the eIF4A helicases and recruits them to P-bodies. eIF4As limit P-bodies condensation and also restrict stress granule (SG) formation under heat stress. We further identify meiotic (M-)bodies as composite RNP granules with a P-body core surrounded by a SG-like shell. The SMG7-eIF4A module regulates the recruitment of the meiosis-specific protein TDM1 into M-bodies, influencing meiotic exit and plant reproduction. Our findings suggest that SMG7 functions as an adaptor protein that recruits client proteins into P-bodies and, together with eIF4A, forms a regulatory module that regulates P-body composition and maintains their size homeostasis.

cell biology↗

bioRxiv2024

Cytokinin acts as a systemic signal coordinating reproductive effort in Arabidopsis

The duration of the flowering phase is a key adaptive trait related to reproductive effort and plant longevity. In plants with indeterminate inflorescences, the number of flowers produced is determined by the activity of the inflorescence meristem. However, the integration of inflorescence meristem activity with the physiological and developmental status of a plant is not well understood. We combined quantitative imaging of the inflorescence meristem with the manipulation of cytokinin levels and distribution to investigate how meristem activity is regulated. Our data support the hypothesis that emerging fruits drain the acropetal flow of cytokinin away from the meristem inducing its proliferative arrest. We further show that the duration of flowering and cytokinin signaling in the inflorescence meristem is influenced by nitrate availability. Taken together, these data suggest that cytokinin functions as a systemic signal that integrates information about ongoing reproductive effort and plant nutrient status to control flower production.

plant biology↗

bioRxiv2023

Heat stress impairs centromere structure and segregation of meiotic chromosomes in Arabidopsis

Heat stress is a major threat to global crop production, and understanding its impact on plant fertility is crucial for developing climate-resilient crops. Despite the known negative effects of heat stress on plant reproduction, the underlying molecular mechanisms remain poorly understood. Here, we investigated the impact of elevated temperature on centromere structure and chromosome segregation during meiosis in Arabidopsis thaliana. Consistent with previous studies, heat stress leads to a decline in fertility and micronuclei formation in pollen mother cells. Our results reveal that elevated temperature causes a decrease in the amount of centromeric histone and the kinetochore protein BMF1 at meiotic centromeres with increasing temperature. Furthermore, we show that heat stress increases the duration of meiotic divisions and prolongs the activity of the spindle assembly checkpoint during meiosis I, indicating an impaired efficiency of the kinetochore attachments to spindle microtubules. Our analysis of mutants with reduced levels of centromeric histone suggests that weakened centromeres sensitize plants to elevated temperature, resulting in meiotic defects and reduced fertility even at moderate temperatures. These results indicate that the structure and functionality of meiotic centromeres in Arabidopsis are highly sensitive to heat stress, and suggest that centromeres and kinetochores may represent a critical bottleneck in plant adaptation to increasing temperatures.

plant biology↗

bioRxiv2022

A complex role of Arabidopsis CDKD;3 in meiotic progression and cytokinesis

Meiosis is a specialized cell division that halves the number of chromosomes in two consecutive rounds of chromosome segregation. In angiosperm plants is meiosis followed by mitotic divisions to form rudimentary haploid gametophytes. In Arabidopsis, termination of meiosis and transition to gametophytic development is governed by TDM1 and SMG7 that mediate inhibition of translation. Mutants deficient in this mechanism do not form tetrads, but instead undergo multiple cycles of aberrant nuclear divisions, that are likely caused by the failure to downregulate cyclin dependent kinases during meiotic exit. A suppressor screen to identify genes that contribute to meiotic exit uncovered a mutation in CDKD;3 that alleviates meiotic defects in smg7 deficient plants. The CDKD;3 deficiency prevents aberrant meiotic divisions observed in smg7 mutants, or delays their onset after initiation of cytokinesis, which permits formation of functional microspores. Although CDKD;3 acts as an activator of CDKA;1, the main cyclin dependent kinase that regulates meiosis, cdkd;3 mutation appears to promote meiotic exit independently of CDKA;1. Furthermore, analysis of CDKD;3 interactome revealed enrichment for proteins implicated in cytokinesis suggesting a more complex function of CDKD;3 in cell cycle regulation.

plant biology↗

bioRxiv2021

A CENH3 mutation promotes meiotic exit and restores fertility in SMG7-deficient Arabidopsis

Meiosis in angiosperm plants is followed by mitotic divisions to form multicellular haploid gametophytes. Termination of meiosis and transition to gametophytic development is, in Arabidopsis, governed by a dedicated mechanism that involves SMG7 and TDM1 proteins. Mutants carrying the smg7-6 allele are semi-fertile due to reduced pollen production. We found that instead of forming tetrads, smg7-6 pollen mother cells undergo multiple rounds of chromosome condensation and spindle assembly at the end of meiosis, resembling aberrant attempts to undergo additional meiotic divisions. A suppressor screen uncovered a mutation in centromeric histone H3 (CENH3) that increased fertility and promoted meiotic exit in smg7-6 plants. The mutation led to inefficient splicing of the CENH3 mRNA and a substantial decrease of CENH3, resulting in smaller centromeres. The reduced level of CENH3 delayed formation of the mitotic spindle but did not have an apparent effect on plant growth and development. We suggest that impaired spindle re-assembly at the end of meiosis limits aberrant divisions in smg7-6 plants and promotes formation of tetrads and viable pollen. Furthermore, the reduced level of CENH3 did not induce haploid plants in crosses with wild plants, indicating that differences in centromere size is not the key determinant of centromere-mediate genome elimination.

genetics↗

bioRxiv2019

Imaging plant germline differentiation within Arabidopsis flower by light sheet microscopy

In higher plants, germline differentiation occurs during a relatively short period within developing flowers. Understanding of the mechanisms that govern germline differentiation lags behind other plant developmental processes. This is largely because the germline is restricted to relatively few cells buried deep within floral tissues, which makes them difficult to study. To overcome this limitation, we have developed a methodology for live imaging of the germ cell lineage within floral organs of Arabidopsis using light sheet fluorescence microscopy. We have established reporter lines, cultivation conditions, and imaging protocols for high-resolution microscopy of developing flowers continuously for up to several days. We used multiview imagining to reconstruct a three-dimensional model of a flower at subcellular resolution. We demonstrate the power of this approach by capturing male and female meiosis, asymmetric pollen division, movement of meiotic chromosomes, and unusual restitution mitosis in tapetum cells. This method will enable new avenues of research into plant sexual reproduction.

plant biology↗