Biology subjects

Krtkova, J.

Publications and source records attributed to Krtkova, J..

6 recordsLinked to original sources

bioRxiv2026

Endogenous and environmentally modulated leaf shape plasticity in Boquila trifoliolata: how good is the evidence for mimicry?

Reports that the South American climbing vine Boquila trifoliolata modifies its leaf shape to mimic leaves of its host plant have raised considerable attention. Boquila leaf development was proposed to reflect visual inputs perceived in an unknown manner. However, the very existence of Boquila leaf shape mimicry remains inconclusive, since the reported observations are open to alternative explanations. We performed an initial quantitative characterization of leaf shape variability in glasshouse-cultured clonal Boquila plants grown without close host contact, and attempted to reproduce the leaf shape mimicry phenomenon under controlled culture conditions using live olive (Olea europaea) plants, artificial (decoy) olive or artificial ivy plants as supports. While we found leaves of variable shape (including those resembling ivy leaves) both in plants grown without host contact and in those climbing on live or decoy hosts, we did not observe any link between leaf shape and host presence or character. Instead, the leaf shape appears to be affected by environmental conditions including the season. Although our study was limited to a single Boquila genotype and an ecologically unrealistic host selection, our observations suggest that the alleged mimicry might originate from unintentional misinterpretation of intrinsic discontinuous leaf shape plasticity in field observations.

plant biology↗

bioRxiv2026

Hormone-dependent receptor docking controls calcium channel activity in plants

The phytohormone auxin is a central coordinator of plant growth and development. Besides its canonical effect on gene transcription1,2, auxin triggers an ultra-rapid calcium ion influx that initiates the root gravitropic response3. The nature of the so-called rapid auxin pathway connecting the AFB1 auxin receptor3,4 and plasma membrane calcium channels remained unknown. Here, we show that auxin induces the direct interaction of the AFB1 receptor with the CNGC14 calcium channel. As the AFB1 receptor is independent of the ubiquitin ligase complex5, the auxin-induced interaction translates into relocalization of the receptor to the plasma membrane. We identify the interaction interface and provide evidence that the docking of the receptor to the channel complex activates Ca2+ influx and triggers growth inhibition. These findings position a calcium channel as an unprecedented component of the AFB1 auxin receptor complex. The ligand-dependent localization shift of a TIR1/AFB family receptor represents a novel paradigm in signal transduction and opens the possibility of unforeseen branches of auxin signaling pathways.

plant biology↗

bioRxiv2026

In vivo imaging uncovers an abundant but rarely active pool of plant ARP2/3 complexes associated with exocyst complex subunit

The ARP2/3 complex generates branched actin networks that regulate membrane dynamics across eukaryotes. In plants, ARP2/3 is activated primarily by the WAVE/SCAR complex and is essential for cell morphogenesis, yet its spatiotemporal behavior in living cells remains poorly understood. Using high-resolution live-cell microscopy, we found that, in addition to their previously reported stable accumulation at three-way cell junctions and peroxisomes, WAVE/SCAR and ARP2/3 subunits also form abundant, highly dynamic, short-lived assemblies in the cortical cytoplasm, with lifetimes of only a few seconds. Genetic and colocalization analyses further revealed that only a minority of observed complexes are fully assembled and active, indicating that plant cells maintain a large pool of partially assembled or inactive ARP2/3 structures. Our data indicate that microtubules influence the abundance of cortical assemblies, whereas actin primarily affects their dynamics. Importantly, our analysis demonstrated a spatial and functional association between dynamic ARP2/3 foci and exocytotic events at the plasma membrane. Together, our findings suggest that the cytoplasm of plant epidermal cells contains a large reservoir of ARP2/3 complexes whose localized activation is tightly regulated and associated with membrane trafficking.

plant biology↗

bioRxiv2022

ARP2/3 complex associates with peroxisomes to participate in pexophagy in plants

ARP2/3 is a heteroheptameric protein complex evolutionary conserved in all eukaryotic organisms. Its conserved role is based on the induction of actin polymerization at the interface between membranes and the cytoplasm. Plant ARP2/3 has been reported to participate in actin reorganization at the plasma membrane during polarized growth of trichomes and at the plasma membrane-endoplasmic reticulum contact sites. We demonstrate here that individual plant subunits of ARP2/3 fused to fluorescent proteins form motile dot-like structures in the cytoplasm that are associated with plant peroxisomes. ARP2/3 dot structure is found at the peroxisome periphery and contains assembled ARP2/3 complex and WAVE/SCAR complex subunit NAP1. This dot occasionally colocalizes with the autophagosome, and under conditions that affect the autophagy, colocalization between ARP2/3 and the autophagosome increases. ARP2/3 subunits co-immunoprecipitate with ATG8f marker. Since mutants lacking functional ARP2/3 complex have more peroxisomes than WT, we link the ARP2/3 complex on peroxisomes to the process of peroxisome degradation by autophagy called pexophagy. Additionally, several other peroxisomal proteins colocalize with ARP2/3 dot on plant peroxisomes. Our results suggest a specific role of ARP2/3 and actin in the peroxisome periphery, presumably in membrane remodelling. We hypothesize that this role of ARP2/3 aids processes at the peroxisome periphery such as peroxisome degradation through autophagy or regulation of peroxisomal proteins localization or function. Significance statementARP2/3 complex-positive dots associate exclusively with peroxisomes in plant cells, where it colocalizes with autophagosome marker ATG8f and several other proteins. Our experiments link ARP2/3 to pexophagy: colocalization between ARP2/3 dots and autophagosome increases when autophagy processes are induced or inhibited; ARP2/3 and ATG8f colocalize and co-immunoprecipitate, and finally, ARP2/3 mutants cells contain more peroxisomes than WT. Our results suggest a novel role of ARP2/3 in peroxisome structure and function regulation.

cell biology↗

bioRxiv2021

Stage-specific, morphological and molecular markers of encystation in Giardia lamblia

Differentiation into environmentally resistant cysts is required for transmission of the ubiquitous intestinal parasite Giardia lamblia. Encystation in Giardia requires the production, processing and transport of Cyst Wall Proteins (CWPs) in developmentally-induced, Golgi-like, Encystation Specific Vesicles (ESVs). Progress through this trafficking pathway can be followed by tracking CWP localization over time. However, there is no recognized system to distinguish the advancing stages of this process which can complete at variable rates depending how encystation is induced. Here we propose a staging system for encysting Giardia based on the morphology of CWP1-stained ESVs. We demonstrate the molecular distinctiveness of maturing ESVs at these stages by following GlRab GTPases through encystation. Previously, we established that Giardias sole Rho family GTPase, GlRac, associates with ESVs and has a role in regulating their maturation and the secretion of their cargo. As a proof of principle, we delineate the relationship between GlRac and ESV stages. Through proteomic studies, we identify putative interactors of GlRac that could be used as additional stage-specific ESV markers. This staging system provides a common descriptor of ESV maturation regardless of the source of encysting cells. Furthermore, the identified set of molecular markers for ESV stages will be a powerful tool for characterizing trafficking mutants that impair ESV maturation and morphology. ImportanceGiardiasis is a diarrheal disease that affects 280 million people worldwide. It is caused by Giardia lamblia, a protozoan parasite which rely on differentiating from host-dwelling trophozoites to environmentally-resistant cysts for transmission and survival. This encystation process requires the transport of Cyst Wall Proteins (1-3) within membrane-bound compartments called Encystation Specific Vesicles (ESV) from the endoplasmic reticulum to the surface of the cell. The whole process takes 24 hours to complete and these compartments are the only recognizable equivalent of Golgi apparatus in this minimalistic organism. Progress of this trafficking pathway can be followed by localizing Cyst Wall Protein 1 over time post induction of encystation but this can be ambiguous when specific molecular events need to be specified. Here we propose a staging system that is based on ESV morphology changes by capitalizing on the secretory/processing events we already know they represent. We validate the molecular distinctiveness of these stages by following Giardia Rabs through the pathway and characterize putative interactors of an established regulator of encystation, GlRac, to provide additional stage-specific molecular markers. This staging system will provide a definitive, yet adaptable, framework to map out functions of yet-to-be discovered players of this important pathway.

cell biology↗

bioRxiv2017

14-3-3 Negatively Regulates Actin Filament Formation In The Deep Branching Eukaryote Giardia lamblia

The phosphoserine/phosphothreonine-binding protein 14-3-3 is known to regulate actin, this function has been previously attributed to sequestration of phosphorylated cofilin. The deep branching eukaryote Giardia lamblia lacks cofilin and all other canonical actin-binding proteins (ABPs), and 14-3-3 was identified as an actin-associated protein in Giardia, yet its role in actin regulation was unknown. Gl14-3-3 depletion resulted in an overall disruption of actin organization characterized by ectopically distributed short actin filaments. Using phosphatase and kinase inhibitors, we demonstrated that actin phosphorylation correlated with destabilization of the actin network and increased complex formation with 14-3-3, while blocking actin phosphorylation stabilized actin filaments and attenuated complex formation. Giardia's sole Rho family GTPase, GlRac, modulates Gl14-3-3's association with actin, providing the first connection between GlRac and the actin cytoskeleton in Giardia. Giardia actin contains two putative 14-3-3 binding motifs, one of which (S330) is conserved in mammalian actin. Mutation of these sites reduced, but did not completely disrupt, the association with 14-3-3. Native gels and overlay assays indicate that intermediate proteins are required to support complex formation between 14-3-3 and actin. Overall, our results support a role for 14-3-3 as a negative regulator of actin filament formation.\n\nImportanceGiardia lacks canonical actin binding proteins. 14-3-3 was identified as an actin interactor but the significance of this interaction was unknown. Loss of 14-3-3 results in ectopic short actin filaments, indicating that 14-3-3 is an important regulator of the actin cytoskeleton in Giardia. Drug studies indicate that 14-3-3 complex formation is in part phospho-regulated. We demonstrate that complex formation is downstream of Giardias sole Rho family GTPase, GlRac, this result provides the first mechanistic connection between GlRac and actin in Giardia. Native gels and overlay assays indicate intermediate proteins are required to support the interaction between 14-3-3 and actin suggesting that 14-3-3 is regulating multiple actin complexes. Overall, we find that 14-3-3 is a negative regulator of actin filament formation in Giardia.

cell biology↗