Biology subjects

Geisler, M.

Publications and source records attributed to Geisler, M..

12 recordsLinked to original sources

bioRxiv2026

Increases in therapist-patient physiological synchrony after dog-patient contact in canine-assisted psychotherapy: an exploratory pilot study

Introduction: Canine-assisted psychotherapy (CAP) introduces a therapy dog into the therapist-patient relationship and may influence interpersonal processes underlying therapeutic change. This exploratory pilot study investigated whether direct patient-dog contact is associated with changes in autonomic arousal and therapist-patient physiological synchrony. Methods: Skin conductance was recorded from 18 patients with depressive disorders and one therapist during 53 routine CAP sessions. A total of 192 episodes of direct patient-dog contact were identified from video recordings. Three-minute periods before and after each contact onsets were compared. Skin conductance level (SCL), skin conductance fluctuations (SCF), and therapist-patient physiological synchrony were assessed using zero-lag correlation and maximum cross-correlation. Sliding-window analyses examined temporal changes in synchrony, while randomly selected pseudo-events served as controls. Results: SCL increased significantly following dog contact in both patients and the therapist, whereas SCF rate over 3 min did not change significantly. Therapist-patient physiological synchrony increased significantly after dog contact, as indicated by both zero-lag correlation and maximum cross-correlation. Sliding-window analyses confirmed these increases and showed a reduction in the temporal lag between the two physiological signals. Importantly, increases in synchrony were significantly greater following genuine dog-contact events than following pseudo-events. Discussion: Direct physical contact between patients and therapy dogs is followed by increased autonomic arousal and enhanced therapist-patient physiological synchrony. These findings suggest that dog-patient contact may function as an interactional event that promotes physiological coordination and interpersonal attunement within the therapeutic dyad.

physiology↗

bioRxiv2026

The FKBP42, TWISTED DWARF1, prioritizes auxin over brassinosteroidtransport by peptidyl-prolyl cis-trans isomerization of ABCB1

The ATP-binding cassette (ABC) transporter ABCB1 transports both auxins and the brassinosteroid brassinolide (BL). ABCB1-mediated auxin (IAA) transport depends on interaction with the FKBP42 protein TWISTED DWARF1 (TWD1), yet the mechanism underlying substrate selectivity remains unclear. Here, we confirm dual IAA and BL transport by ABCB1 and show that the two substrates compete for ABCB1-mediated transport. We demonstrate that a conserved proline residue (P1008) is required for IAA, but not BL, transport. Furthermore, we identify TWD1 as a calmodulin-activated peptidyl-prolyl cis-trans isomerase (PPIase) that selectively enhances IAA, but not BL, transport through isomerization of the E1007-P1008 peptide bond. Loss of TWD1 PPIase activity abolishes ABCB1-mediated IAA export without affecting BL transport, revealing a regulatory mechanism that prioritizes auxin over brassinosteroid transport. Cryo-EM, molecular docking, and molecular dynamics simulations of wild-type ABCB1 and the ABCB1P1008G variant suggest that the P1008 loop mediates long-range communication between the nucleotide-binding domain surface and the substrate-binding pocket, thereby providing a structural mechanism by which TWD1 modulates substrate specificity. In summary, our findings establish the structural basis of ABCB1 substrate selectivity and uncover a post-translational mechanism that selectively regulates auxin transport while preserving brassinosteroid transport. One Sentence SummaryTWD1 prioritizes ABCB1-mediated auxin over brassinosteroid transport

biochemistry↗

bioRxiv2025

Context-dependent effects of microbial inoculation on sagebrush seedlings during drought stress

The leaf microbiome interacts with its plant host and can have critical positive and negative effects on plant health. However, the interactions between leaf microbiomes and host plants remain understudied, particularly in reference to context-dependency, e.g., during drought conditions. Plants naturally exist in environments with ever-changing weather and epiphytic foliar microbes are often exposed to extreme conditions. Little is known about how different environmental contexts can alter the effects of phyllosphere microbes on their plant hosts. In this study, we measured the response of seedlings to microbial inoculations and drought conditions. We used Artemisia tridentata subsp. tridentata (hereafter, sagebrush), a foundation species in the vast and critically threatened sagebrush steppe ecosystem. We grew sagebrush plants in growth chambers from sterile seed and after 6 months the seedlings were inoculated in one of four inoculation treatments: (1) no inoculant, (2) sterile water, (3) the microbes washed from the surface of the leaves (a whole natural community), and (4) the single species, Bacillus amyloliquefaciens. We then exposed the seedlings to two environmental treatments: regular watering and a tapered drought. We found context-dependent effects of inoculation on seedling health for both of our inoculation microbial treatments. For example, both inoculants had a negative effect on host plant photosynthesis, which was lessened drought conditions. Furthermore, seedlings inoculated with B. amyloliquefaciens had increased leaf nitrogen levels, and the highest survival under drought conditions. Our study shows that seedling health and survival can be influenced by leaf-associated microbes, and is dependent on environmental context.

plant biology↗

bioRxiv2024

A CELL BIOLOGY STUDY REVEALS NEW INSIGHTS INTO THE TRANSPORT MECHANISMS OF OOMYCETE EFFECTORS

Oomycete pathogens use dedicated effector proteins (also known as virulence factors) that manipulate the host during infection to the benefit of the pathogen. Despite extensive efforts, the understanding of how oomycete effector proteins are transported and delivered to the host is limited. Here, we show that Phytophthora capsici infecting Nicotiana benthamiana secretes its effectors through secretory pockets, haustoria, and from hyphae. We provide evidence that Avr3, belonging to the class of RxLR effector proteins that can be secreted and translocated to the plant cell, is found to accumulate in a distinct ring-shaped zone around the neck region of haustoria. The association with the haustorial neck is determined by an RxLR-EER motif and mutating this motif redirects Avr3 to the extrahaustorial matrix enveloping the full haustoria body. Furthermore, mass spectrometry analysis of immunoprecipitated Avr3 indicates that the RXLR motif remains intact when Avr3 is secreted from the haustorium during plant infection. We thus propose that the RXLR-EER motif determines the entry in the host cell by guiding Avr3 to the haustorial neck region, which may be a structure analogous to the Biotrophic Interfacial Complex of the fungus Magnaporthe sp.

cell biology↗

bioRxiv2024

A key residue of the extracellular gate provides quality control contributing to ABCG substrate specificity

For G-type ATP-binding cassette (ABC) transporters, a hydrophobic "di-leucine motif" as part of a hydrophobic extracellular gate has been described to separate a large substrate-binding cavity from a smaller upper cavity and proposed to act as a valve controlling drug extrusion. Here, we show that an L704F mutation in the hydrophobic extracellular gate of Arabidopsis ABCG36/PDR8/PEN3 uncouples the export of the auxin precursor indole-3-butyric acid (IBA) from that of the defense compound camalexin (CLX). Molecular dynamics simulations reveal an increase in free energy and pulling forces for CLX at both the entrance and exit sites of ABCG36L704F, respectively, providing a mechanistic rationale for the transport discrimination of CLX. Mutagenesis of L704 to tyrosine allows export of structurally related non-ABCG36 substrates, indole-3-acetic acid (IAA) and indole, suggesting an allosteric communication between the extracellular gate and the central substrate binding pocket. In summary, our work supports the conclusion that L704 is a key residue of the extracellular gate that provides a final quality control contributing to ABCG substrate specificity.

biochemistry↗

bioRxiv2024

An auxin homeostat allows plant cells to establish and control defined transmembrane auxin gradients

O_LIExtracellular auxin maxima and minima are important to control plant developmental programs. Auxin gradients are provided by the concerted action of proteins from the three major plasma membrane auxin transporter classes AUX1/LAX, PIN and ABCB transporters. But neither genetic nor biochemical nor modelling approaches have been able to reliably assign the individual roles and interplay of these transporter types. C_LIO_LIBased on the thermodynamic properties of the transporters, we show here by mathematical modeling and computational simulations that the concerted action of different auxin transporter types allow the adjustment of specific transmembrane auxin gradients. The dynamic flexibility of the "auxin homeostats" comes at the cost of an energy-consuming "auxin cycling" across the membrane. C_LIO_LIAn unexpected finding was that functional ABCB-PIN coupling appears to allow an optimization of the trade-off between the speed of auxin gradient adjustment on the one hand and ATP consumption and disturbance of general anion homeostasis on the other. C_LIO_LIIn conclusion, our analyses provide fundamental insights into the thermodynamic constraints and flexibility of transmembrane auxin transport in plants. C_LI Plain language summaryThe phytohormone auxin controls essentially plant development. Plant cells produce auxin and export it to establish patterns by local auxin minima and maxima. Although several transporter proteins are known to contribute to this process, the mechanism by which a defined auxin gradient can be produced is not clear. This study now uses mathematical modeling based on the thermodynamic features of the auxin transporters to illustrate in computational simulations the fundamental characteristics of an "auxin homeostat". The concerted interplay of different auxin transporters allows plant cells to establish defined transmembrane auxin gradients that are the indispensable basis for polarized auxin maxima and minima and auxin fluxes within tissues.

plant biology↗

bioRxiv2022

Cytokinin synthesis and export from symbiotic root nodules coordinates shoot growth with nitrogen fixation

O_LIDevelopment of symbiotic root nodules is a cytokinin-dependent process that is critical to nitrogen acquisition in legumes. The extent and manner in which root nodules contribute to whole-plant cytokinin and nitrogen supply signalling is unknown. C_LIO_LIUsing a combination of genetic, biochemical and physiological approaches, we characterised the role of cytokinin synthesis, export and perception in coordination of symbiotic nodule development and shoot growth in the legume Lotus japonicus. C_LIO_LILjPup1 encodes a plasma membrane localised cytokinin exporter with isopentenyladenine (iP) and trans-Zeatin (tZ) export capacity. LjPup1 shows a distinct nodule-specific expression pattern with greatest transcript levels detected in mature nodules. Mutants accumulate more isopentenyladenine riboside (iPR) in nodule tissues and demonstrate hallmarks of reduced cytokinin signalling. Despite normal nodule numbers and function, shoot growth is markedly reduced in Ljpup1 mutants, as well as in mutants impaired in tZ biosynthesis. C_LIO_LIWe found symbiotic root nodules contribute to shoot growth via export of active cytokinins. A cytokinin exporter in the purine permease family thus contributes to long-distance cytokinin homeostasis regulating plant development. C_LI

plant biology↗

bioRxiv2022

A key residue of plant ABC transporter modulates access path geometry and phenylpropanoid substrate selectivity

ABCG46 of the legume Medicago truncatula is an ABC-type transporter responsible for highly selective translocation of the phenylpropanoids, 4-coumarate and liquiritigenin, over the plasma membrane. To investigate molecular determinants of the observed substrate selectivity, we applied a combination of phylogenetic and biochemical analyses, AlphaFold2 structure prediction, molecular dynamics simulations, and mutagenesis. We discovered an unusually narrow transient access path to the central cavity of MtABCG46 that constitutes an initial filter responsible for the selective translocation of these phenylpropanoids through a lipid bilayer. Furthermore, we identified remote residue F562 as pivotal for maintaining the stability of this filter. The determination of individual amino acids that impact the selective transport of specialized metabolites may provide new opportunities associated with ABCGs being of interest, as a clinically relevant group of proteins.

biochemistry↗

bioRxiv2021

AlphaFold2 transmembrane protein structure prediction shines

Transmembrane (TM) proteins are major drug targets, indicated by the high percentage of prescription drugs acting on them. For a rational drug design and an understanding of mutational effects on protein function, structural data at atomic resolution are required. However, hydrophobic TM proteins often resist experimental structure determination and in spite of the increasing number of cryo-EM structures, the available TM folds are still limited in the Protein Data Bank. Recently, the DeepMinds AlphaFold2 machine learning method greatly expanded the structural coverage of sequences, with high accuracy. Since the employed algorithm did not take specific properties of TM proteins into account, the validity of the generated TM structures should be assessed. Therefore, we investigated the quality of structures at genome scales, at the level of ABC protein superfamily folds, and also in specific individual cases. We tested template-free structure prediction also with a new TM fold, dimer modeling, and stability in molecular dynamics simulations. Our results strongly suggest that AlphaFold2 performs astoundingly well in the case of TM proteins and that its neural network is not overfitted. We conclude that a careful application of its structural models will advance TM protein associated studies at an unexpected level.

bioinformatics↗

bioRxiv2021

ABA homeostasis and long-distance translocation is redundantly regulated by ABCG ABA importers

The effects of abscisic acid (ABA) on plant growth, development and response to the environment depend on local ABA concentrations. Here, we exploited a genome-scale amiRNA screen, targeting the Arabidopsis transportome, to show that ABA homeostasis is regulated by two previously unknown ABA transporters. ABCG17 and ABCG18 are localized to the plasma membranes of leaf mesophyll and stem cortex cells to redundantly promote ABA import, leading to conjugated inactive ABA sinks, thus restricting stomatal closure. ABCG17 and ABCG18 double knockdown revealed that the transporters encoded by these genes not only limit stomatal aperture size, conductance and transpiration while increasing water-use efficiency but also control ABA translocation from the shoot to the root to regulate lateral root emergence. The proposed ABCG17- and ABCG18-dependent ABA glucosyl ester shoot sink mechanism is restrained under abiotic stress conditions to further activate the ABA responses.

plant biology↗

bioRxiv2020

ABCB-mediated auxin transport in outer root tissues regulates lateral root spacing in Arabidopsis

Root branching is an important strategy to explore efficiently large volumes of soil. To economize this process, lateral roots (LR) are formed along the growing root at discrete positions that are instructed by oscillating auxin signals derived from the lateral root cap (LRC). This assumes that auxin moves from the LRC across multiple layers to accumulate in the pericycle. Here, we identified, using gene silencing and CRISPR based approaches, a group of five genetically linked, closely related ABCBs that control LR spacing by modulating the amplitude of the auxin oscillation. The transporters localize to the plasma membrane and reveal significant auxin export activity. These ABCBs are mainly expressed in the LRC and epidermis where they contribute to auxin transport towards the root oscillation zone. Our findings highlight the importance of auxin transport in the outer tissues of the root meristem to regulate LR spacing.

plant biology↗

bioRxiv2020

A conserved D/E-P motif in the nucleotide binding domain of plant ABCB/PGP-type ABC transporters defines their auxin transport capacity

Auxin transport activity of ABCB1 was suggested to be regulated by physical interaction with the FKBP42/Twisted Dwarf1 (TWD1), a bona fide peptidylprolyl cis-trans isomerase (PPIase), but all attempts to demonstrate such a PPIase activity on TWD1 have failed so far. By using a structure-based approach we have identified a series of surface-exposed proline residues in the C-terminal nucleotide binding fold and linker of Arabidopsis ABCB1 that do not alter ABCB1 protein stability or location but its catalytic transport activity. P1.008 was uncovered as part of a conserved signature D/E-P motif that seems to be specific for Auxin-Transporting ABCBs, we now refer to as ATAs. Beside the proline, also mutation of the acidic moiety prior to the proline abolishes auxin transport activity by ABCB1. So far, all higher plant ABCBs for that auxin transport was safely proven carry this conserved motif underlining its diagnostic potential. Introduction of this D/E-P motif into malate importer, ABCB14, increases both its malate and its background auxin transport activity, suggesting that this motif has an impact on transport capacity. The D/E-P1.008 motif is also important for ABCB1-TWD1 interaction and activation of ABCB1-mediated auxin transport by TWD1, supporting a scenario in that TWD1 acts as an activator of ABCB1 transport activity by means of its PPIase. In summary, our data imply a dual function for TWD1 acting as an ABCB co-chaperone required for ABCB biogenesis and as a putative activator of ABCB-mediated auxin transport by cis-trans isomerization of peptidyl-prolyl bonds.

biochemistry↗