Biology subjects

Muller, K.

Publications and source records attributed to Muller, K..

At least 19 recordsLinked to original sources

bioRxiv2026

From Magnetosomes to Vesicles: LemA Proteins as Drivers of Bacterial Membrane Reorganization

The cellular machineries that remodel bacterial membranes during organelle and vesicle formation remain poorly defined. Herein, we report MamQ as a key determinant of the lipid invaginations that enclose the magnetosome. MamQ belongs to the broadly conserved LemA protein family, whose members localize to either the inner or outer membrane. Heterologous overproduction of 13 different LemA proteins in Escherichia coli induced extensive membrane restructuring and vesiculation, indicating a conserved membrane-remodelling activity. In Pseudomonas aeruginosa, overproduction of the inner membrane protein LemA1 (PaLemA1) promoted cytoplasmic membrane vesicle (CMV) formation, whereas the periplasmic-located outer membrane-anchored LemA2 (PaLemA2) drove the formation of bacterial outer-membrane vesicles (OMVs). Conversely, deletion of the corresponding genes reduced extracellular vesicle production. Interactome analyses identified 256 protein partners of PaLemA1 and PaLemA2, including multiple components of the cellular divisome, such as CpoB, FtsE, FtsI, FtsK, FtsN, FtsW, MinE, ParB, ZapG, ZipA. Bacterial two-hybrid assays confirmed interactions between both LemA proteins and the cell division regulator CpoB, whose perturbation markedly altered vesicle formation. Additional interaction partners included PspA, an ESCRT-III-like protein implicated in membrane remodelling. Proteins involved in cell wall metabolism, membrane turnover, lipopolysaccharide (LPS) biogenesis, protein export and maturation, energy metabolism, and stress-responsive gene regulation were also enriched, suggesting a supporting role for PaLemA proteins in coordinating membrane-associated processes. Consistent with this, LemA deletion mutants displayed altered vesicle composition and global changes in gene expression. Furthermore, PalemA2 expression was induced in stationary phase and under envelope stress via the extracytoplasmic sigma factor AlgU, itself an interaction partner of the LemA proteins. Together, our findings indicate the LemA family act as a conserved membrane-remodelling system that, in conjunction with PspA, CpoB and divisome components, organises membrane-localized protein complexes required for bacterial organelle biogenesis and vesicle formation while executing a controlled, protein-machinery-driven mechanism that operates independently of passive chemical blebbing (such as hydrophobic PQS intercalation) or lytic membrane fragmentation.

microbiology↗

bioRxiv2026

Decarboxylation of indoleacetic acid illuminates its evolution into a plant hormone

The evolution of indoleacetic acid (IAA) into the plant hormone auxin remains unclear. Here, we compared IAA response and metabolism in land plants and their closest living relatives, the streptophyte algae, using chemical treatments, phytohormone profiling, and targeted and untargeted metabolomics. Streptophyte algae showed neither plant-like auxin responses nor canonical IAA metabolism. Here, we demonstrate IAA side-chain decarboxylation as a novel pathway of cellular IAA metabolism, operating in streptophyte algae and land plants alike. Decarboxylation also underpinned IAA's innate photolability and yielded cytotoxic intermediates, which also accumulated endogenously under simulated sunlight. Together, these findings establish IAA decarboxylation as a major, conserved metabolic pathway, and suggest that the metabolic constraints arising from IAA's instability and indirect cytotoxicity contributed to its adoption as a plant hormone.

plant biology↗

bioRxiv2026

An Integrated Spatially Resolved Mechanistic Model of Hierarchical Auxin-Cytokinin-Ethylene Crosstalk Underlying Root Growth Inhibition in Arabidopsis

Decoding how plants integrate multiple hormone signals to coordinate growth requires tools capable of resolving pathway interactions at cellular resolution in living tissue. Here we present ACE (Auxin-Cytokinin-Ethylene) and ACE2, proof-of-concept single-locus reporters to simultaneously capture activity of multiple hormones. Deploying ACE alongside well-established reporters, exogenous hormone treatments, and reverse-genetic perturbations of hormone biosynthesis, signaling, and transport in three-day-old etiolated Arabidopsis seedlings, we dissect the spatiotemporal hierarchy governing primary root elongation and root apical meristem (RAM) size. We demonstrate that both ethylene- and cytokinin-triggered root growth inhibition involve a boost of TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS1 (TAA1)-mediated auxin biosynthesis and AUXIN RESISTANT1 (AUX1)-dependent auxin redistribution. Two spatially distinct auxin responses underlie the respective root growth effects: ethylene expands TAA1-dependent auxin biosynthesis from the root vasculature into the epidermis and promotes AUX1-mediated auxin import into the transition and elongation zones to inhibit cell elongation, while cytokinin confines ethylene-dependent TAA1-boosted activity to the vasculature and drives auxin accumulation in lateral root cap cells to reduce RAM size. Together, these data establish a reciprocal regulatory loop between these hormones, positioning ethylene as a convergence node in auxin-cytokinin crosstalk, and cytokinin as a modulator of the ethylene-auxin interaction. Critically, the changes in cross-activated reporter patterns described for different genetic backgrounds, alongside quantitative assessment of hormone-specific inhibition of the mutants growth, were consistent with the multi-hormone network established over two decades of research, and added cell-type-resolved spatial detail and a proposed hierarchy for the etiolated seedling root. Finally, a second-generation reporter, ACE2, overcomes key technical limitations of ACE, expanding the platforms capacity toward a higher-order multi-hormone monitoring system. These resources expand the Arabidopsis genetic toolkit and provide a generalizable framework instrumental for dissecting multi-hormone signaling hierarchies at the cellular level.

plant biology↗

bioRxiv2026

Deletion of Ferritin Heavy Chain Limits Tumor Growth and Promotes Iron-Dependent Stress in Medulloblastoma

Iron is essential for tumor proliferation and metabolic adaptation but becomes cytotoxic when unbuffered, creating a potential metabolic vulnerability. Ferritin, a conserved iron-storage complex, limits labile iron and establishes the upper threshold of iron tolerance in cancer cells. Here, we report the first ferritin heavy chain (FTH) knockout in a brain tumor model system. Although FTH loss was tolerated under basal conditions through adaptive remodeling of iron metabolism, it exposed profound vulnerabilities under iron stress. FTH deficiency lowered the threshold for iron toxicity, sensitizing medulloblastoma (MB) cells to both canonical ferroptosis and a mechanistically distinct iron-dependent cell death pathway. Oxidative iron stress impaired tumor growth and prolonged survival in orthotopic xenografts, whereas vitamin C-induced iron reduction triggered a selective, iron-dependent, but non-ferroptotic elimination of MB-like cells in tumor organoids. Notably, sensitivity to iron toxicity correlated strongly with cellular phenotype, with mesenchymal-like cells displaying greater susceptibility than epithelial-like counterparts. Collectively, these findings identify ferritin as a central regulator of iron tolerance in MB and establish iron toxicity, not via iron deprivation, as a therapeutically exploitable vulnerability. More broadly, this work provides a mechanistic framework for targeting iron metabolism through modulation of ferritin-dependent iron buffering and iron redox homeostasis in cancers. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=170 SRC="FIGDIR/small/739635v1_ufig1.gif" ALT="Figure 1000"> View larger version (53K): org.highwire.dtl.DTLVardef@1c499a4org.highwire.dtl.DTLVardef@431c70org.highwire.dtl.DTLVardef@2b5borg.highwire.dtl.DTLVardef@11e9ac1_HPS_FORMAT_FIGEXP M_FIG C_FIG

cancer biology↗

bioRxiv2026

Insight into GABA shunt-associated aldehyde dehydrogenases (ALDH) and stress responses of ALDH superfamily in moss and barley

We explored the expression of the aldehyde dehydrogenase (ALDH) superfamily in two model plants, Physcomitrium patens (moss) and Hordeum vulgare (barley), under various stress conditions. The ALDH enzymes are crucial for oxidizing aldehydes to carboxylic acids and are involved in multiple metabolic pathways. We found significant differences in enzyme expression between moss and barley within the same ALDH families. We then focused on the ALDH5, ALDH10, and ALDH21 families, which are part of the {gamma}-aminobutyric acid (GABA) shunt, noting that the ALDH21 family is absent in barley. The kinetic properties of ALDH10 and ALDH5 enzymes were analyzed, revealing that PpALDH5F1 exhibits high specificity for succinic semialdehyde (SSAL), a product of GABA. The crystal structure of PpALDH5F1 identified key residues for SSAL binding. Knockout mutants of moss aldh5F2, aldh10A1, and aldh21A1 showed slightly smaller colonies than the wild-type. GABA and glutamate levels were elevated in aldh5F2 and aldh21A1 knockouts due to a partially blocked GABA shunt pathway, while aldh10A1 knockout showed no changes in GABA levels. Transcriptomic data revealed a link between several genes, including six upregulated glutathione-S-transferase genes in all three aldh knockouts, suggesting a direct compensatory mechanism for oxidative stress protection via conjugation of undegraded aldehydes to glutathione. HighlightMoss knockouts of GABA shunt-associated aldehyde dehydrogenases display slower growth, changes in levels of glutamate, glutamine and GABA, and result in upregulation of several unique glutathione-S-transferase genes.

plant biology↗

bioRxiv2026

Reverse molecular pharmacology identifies the non-canonical axis of IRAK as a chemoresistance factor in neuroblastoma

Owing to chemoresistance, the prognosis of relapsed neuroblastoma is dismal with less than 10% of patients surviving after 5 years. We developed a reverse molecular pharmacology approach that is based on high-throughput drug screening coupled with chemo-informatic and transcriptomic analyses. This led to the identification of IRAK1 as a key chemoresistance factor in neuroblastoma. By performing functional and pharmacological drug combination screens targeting IRAK1, we revealed a synergy between IRAK1 inhibition/silencing and BET, EGFR and mTOR inhibitors as well as microtubule-targeting agents. The synergistic combination of microtubule-targeting agent, vincristine and IRAK inhibitors was then confirmed in tumor spheroids, patient-derived tumoroids and a syngeneic orthotopic mouse model. Mechanistically, IRAK inhibition potentiated the pro-apoptotic and cell cycle arrest properties of vincristine via a pathway involving the PIDDosome complex rather than its canonical MyDDosome axis. Altogether, this study represents a proof-of-concept of our reverse molecular pharmacology approach to quickly develop biology-guided drug combinations, that could be applied to any other human diseases.

cancer biology↗

bioRxiv2025

POLYGALACTURONASES REGULATED BY AUXIN facilitate root cell elongation in Arabidopsis thaliana via pectin remodeling

Root cell elongation, the main driver of root growth, is tightly associated with cell wall remodeling, particularly through pectin modifications, which facilitate cell wall loosening and strengthening while maintaining structural integrity. Root cell elongation is precisely regulated by the phytohormone auxin, which has long been known to inhibit this process. The molecular pathways through which auxin influences cell wall modifications remain poorly understood. In this study, we explore the transcriptional regulation of cell wall-related genes by auxin in Arabidopsis thaliana roots. The nuclear auxin pathway altered the expression of numerous cell-wall related genes, suggesting dynamic modification of the cell wall during root cell elongation. We identified novel root-specific polygalacturonases (PGs), enzymes involved in pectin degradation, which we termed POLYGALACTURONASES REGULATED BY AUXIN (PGRAs). PGRAs are expressed specifically in the root epidermis, beginning at the elongation zone. Our results demonstrate that induction of PGRA1 expression initially promotes root cell elongation, while long term overexpression inhibits root growth. Auxin downregulates PGRA1 in the elongation zone, and plants lacking PGRAs fail to increase root growth rate in response to reduced auxin levels. This suggests that auxin downregulates PGRA expression to prevent PGRA-mediated pectin remodeling, thereby contributing to inhibition of root cell elongation. We established a novel link between auxin signaling and pectin modifications in the control of cell growth. These findings provide new insights into the molecular mechanisms through which auxin regulates root cell elongation, highlighting the role of pectin matrix modifications in this process.

plant biology↗

bioRxiv2025

SnRK1.1 Coordinates Organ-Specific Growth-Defense Programs via Transcriptomic Rewiring in Arabidopsis thaliana

SnRK1 (Sucrose non-fermenting-1-Related Kinase 1) is a master regulator of cellular energy homeostasis in plants, coordinating developmental and metabolic responses under environmental and internal stress conditions. Here, we demonstrate that its catalytic subunit, KIN10, orchestrates organ-specific growth-defense programs in Arabidopsis thaliana through transcriptomic rewiring. Using RNA-seq profiling, we reveal that kin10 knockout mutants exhibit extensive transcriptional reprogramming in roots, particularly in pathways linked to signal perception, cell wall remodeling, and intracellular trafficking, which correlates with impaired root growth and reduced root hair elongation upon Pseudomonas syringae infection. In contrast, KIN10 overexpression (KIN10-OE) lines display constitutive defense activation in shoots, including elevated expression of genes associated with reactive oxygen species (ROS) production and salicylic acid (SA) signaling, leading to enhanced ROS accumulation and growth trade-offs. kin10 roots show muted responses to biotic stimuli, while KIN10-OE shoots prioritize defense over growth. These findings position KIN10 as a critical integrator of energy status and immune signaling, enabling fine-tuned, tissue-specific responses essential for optimizing plant adaptation to dynamic environmental challenges.

plant biology↗

bioRxiv2025

Analysing the Role of KIN10 in Directional Root Growth Regulation in Arabidopsis thaliana

Root growth directionality is critical for plant survival, optimizing anchorage and resource acquisition. While the role of hormonal signaling in root gravitropism is well established, the contribution of metabolic status remains less understood. Here, we investigate the function of the catalytic SnRK1 subunit KIN10 in integrating carbon availability with root growth regulation in Arabidopsis thaliana. A combination of growth phenotyping, transcriptomics, and hormonomic profiling suggest that KIN10 loss disrupts energy-linked developmental processes. Compared to wild-type Col-0, kin10 displayed reduced sensitivity to glucose-induced root growth inhibition. Transcriptomic analysis of kin10 roots revealed widespread reprogramming of metabolic and hormonal pathways, with significant changes in secondary metabolism, cell wall remodeling, and hormone-related gene expression. Hormone profiling further indicated that KIN10 modulates auxin and jasmonate pathways in a carbon source- and organ-dependent manner, especially under sucrose supplementation. Our results demonstrate that KIN10 plays a central role in integrating energy status with developmental and environmental signaling.

plant biology↗

bioRxiv2025

Approximating Signal Sources in Stereo-EEG Single Pulse Electrical Stimulation using Re-referencing and Spectral Analysis

Stereoelectroencephalography (sEEG) is a method of epilepsy monitoring that uses stereotactically placed depth electrodes. Connectivity between brain regions may be assessed by delivering a current pulse from sEEG electrode(s) and monitoring all other electrodes for Brain Stimulation-Evoked Potentials (BSEPs). However, the shape, magnitude, and spectral content of BSEPs are sensitive to the analysis approaches used to study them. In order to understand the nuance between analysis and interpretation of BSEP data, we carefully apply and contrast modified common average & bipolar re-referencing techniques, combined with wavelet-based spectral analysis on measured data from 4 human subjects. Comparison between analysis approaches allows us to identify recording sites within, near, or far from the tissue source of the BSEPs they record. We further explore the interaction between re-referencing techniques and dipole source orientation, providing methods to estimate source location and upper bound of far field recordings. This systematic application and comparison of different analysis tools can enable those who study BSEPs to localize potential sources within, near, or far from measurement sites, and more accurately constrain how brain connectivity is understood from stimulation experiments.

neuroscience↗

bioRxiv2025

Gibberellin-deactivating GA2OX enzymes act as a hub for auxin-gibberellin crosstalk in Arabidopsis thaliana root growth regulation

Plant bodies are built from immobile cells, making the regulation of cell expansion essential for growth, development, and adaptation. In roots, cell elongation executes the movement of the root tips through soil. This process is tightly controlled by numerous signaling pathways. Among these, gibberellin and auxin signaling stand out for their contrasting effects on root growth, interacting through complex crosstalk at multiple regulatory levels. Here we reveal the molecular basis of the auxin-gibberellin crosstalk in the model plant Arabidopsis thaliana. We show that auxin signaling pathway steers the expression of GIBBERELLIN 2-OXIDASES (GA2OX), key gibberellin-deactivating enzymes in the root elongation zone. GA2OX are negative regulators of root cell elongation; GA2OX8 overexpression decreases gibberellin levels and inhibits root cell elongation, in contrast, the ga2ox heptuple mutant roots show elevated gibberellin levels in the elongation zone and grow longer roots. Shoot derived auxin can regulate GA2OX8 expression in roots, linking systemic auxin signaling to local gibberellin modulation. In addition, GA2OX8 is active in vascular tissues and the stem cell niche, tissues with high auxin levels. Loss of GA2OX genes results in altered stem cell niche, including increased quiescent center size and expanded root cell layers, highlighting the role of these enzymes in maintaining tissue organization. Together, our findings identify GA2OX6 and GA2OX8 enzymes as key mediators of auxin-gibberellin crosstalk, providing insights into their roles in root elongation, vascular development, and stem cell niche maintenance. These results expand our understanding of how auxin integrates with gibberellin signaling to coordinate root development and growth dynamics.

plant biology↗

bioRxiv2025

Nanodomain distribution and function of PIN-FORMED auxin efflux carriers in the plasma membrane of tobacco cells are defined by their interactions with the cell wall

Plant development is under the morphogenic control of auxin. In addition to biosynthesis and metabolism, auxin concentration gradients are maintained by directional intercellular transport via PIN-FORMED (PIN) auxin efflux carriers. Although the structure-function properties of PINs have been described, it is still unclear whether individual members of PIN family could localize differently within the plasma membrane (PM) and whether their nanodomain distribution defines their function. To address this, we used cultured tobacco cells (Nicotiana tabacum L., cv. BY-2) and revealed by RNA-seq and RT-qPCR the cell stage-specific presence of transcripts of tobacco PIN homologs. We used high-resolution light microscopy and two independent immunoelectron microscopy techniques in cell lines expressing functional GFP-tagged inducible versions of NtPIN11T, NtPIN2T and NtPIN3bT. We show that NtPINs are distributed within specific PM nanodomains and that removal of the cell wall alters their appearance. By a series of in vivo microscopic observations, we provide evidence that NtPIN11T is the most homogenously distributed and the least mobile NtPIN. Pharmacological treatments suggested that the immobilization of NtPIN11T depends on the actin and microtubular cytoskeleton and the cell wall composition. Using comparative co-immunoprecipitation (co-IP) analysis of isolated membrane fractions for all three NtPINs we finally identified several novel interaction partners indicating a preferential association of NtPIN11T with cell wall GPI-anchored arabinogalactan proteins. In conclusion, our results suggest a model in which specific immobilization of PINs through interactions with the cell wall affects their function.

plant biology↗

bioRxiv2024

Comprehensive Model of Cell-to-Cell Cytokinin Transport Reveals A Specific Mode of Cytokinin Riboside Influx

1Ribosylated forms of plant hormones cytokinins (CKs) are the dominant CK species translocated at long distances. Their particular roles in plant physiology imply the existence of a yet uncharacterized CK riboside-specific membrane transport system. In this work, we report significant differences in the kinetics of the membrane transport of CK nucleobases and ribosides and the overall affinity of membrane-bound carriers towards the two CK forms. We show that CK ribosides can inhibit the uptake of CK nucleobases in tobacco Bright Yellow 2 cell suspensions but not vice versa, confirming the existence of a membrane transport system that strictly recognizes CK ribosides. We further characterize the membrane transport of CK nucleobases and ribosides mediated by AtENT3 (EQULIBRATIVE NUCLEOSIDE TRANSPORTER 3), showing its preference towards trans-zeatin riboside (tZR) over isopentenyl adenosine (iPR). With the molecular docking and molecular dynamics, we assess the interactions among the side chain of tZR and AtENT3 residues Tyr61 and Asp129, which are conserved in all AtENTs but not in the ENTs from non-plant species. Lastly, we show that atent3 mutation affects shoot phenotype, demonstrating the impact of CK riboside membrane transport on shoot development.

plant biology↗

bioRxiv2024

ER-located PIN5 transporter generates potent auxin sinks driven by the IAA decarboxylation pathway

Auxin is an essential and well-investigated regulator of plant development. Still, many aspects determining its (sub-)cellular distribution, as well as its metabolic turnover, are obscure. PIN5 is a transporter that resides on the endoplasmic reticulum and is presumed to influence internal auxin homeostasis by direct sequestration and subsequent degradation. Due to its distinct expression pattern and incomplete metabolomics analyses, the exact role of PIN5 protein and the identity of downstream auxin degradation products show significant gaps. To this end, we utilized morphologically homogeneous tobacco BY-2 cell cultures. We show that the expression of Arabidopsis thaliana AtPIN5 in the BY-2 system phenocopies so-called auxin starvation defects. Moreover, we reveal that the activity of AtPIN5 leads, in extreme cases, to the broad range of processes accompanying programmed cell death (PCD). Notably, based on the recently updated knowledge on auxin metabolism, we also show that a significant part of auxin metabolites downstream of the AtPIN5 activity are part of the re-emerged auxin decarboxylation pathway. Taking together, we report the direct induction of PCD by auxin stimulus and propose the physiological framework of the auxin decarboxylation route.

plant biology↗

bioRxiv2023

Diversity and connectivity of principal neurons in the lateral and basal nuclei of the mouse amygdala

The basolateral amygdala is a non-layered cortical structure playing a role in various cognitive processes. Despite many studies focusing on local information processing within the circuits of the basolateral amygdala, the characteristics of excitatory principal neurons (PNs) are still not fully revealed. Here, we combined neuroanatomical, electrophysiological, and tracing techniques to determine the single-cell features, dendritic and axonal projections of PNs within the lateral (LA) and basal amygdala (BA). Using a mouse reporter line, we found that cholecystokinin (CCK) expression defines two spatially and functionally segregated groups of PNs both in the LA and BA. PNs in CCK-positive (CCK+) areas of the LA (LAa) had small somata and short dendrites which matched their single-cell electrophysiological properties. PNs in CCK-negative (CCK-) areas of the LA (LAp) and all BA had similarly ramified dendrites and single-cell features with some differences. Importantly, the dendritic arbors of PNs were restricted to the subnuclei defined by CCK expression, which corresponded to various extra-amygdalar afferents indicating specific inputs on distinct PN groups. Axonal arborization patterns of PNs within the basolateral amygdala and surrounding areas showed consistency to their soma location. For instance, BA PNs that projected to the medial prefrontal cortex but not to the lateral nucleus of the central amygdala were present in CCK+ areas. In contrast, those BA PNs that projected to the lateral part of the central nucleus were found in the subnucleus lacking CCK. Our study revealed that the basolateral amygdala is composed of functionally different subnuclei with specific inputs and outputs. This structural arrangement may empower the LA and BA to flexibly channel processed information toward their downstream regions, which can be a key requirement for diverse amygdala functions in cognitive operation.

neuroscience↗

bioRxiv2023

Chitosan stimulates root hair callose deposition and inhibits root hair growth

Although angiosperm plants have a general capacity to react after the immunity elicitor chitin or chitosan treatment by the cell wall callose deposition, this response in particular cell types and its evolutionary conservation is not understood. Here we show that also the growing root hairs (RHs) of Arabidopsis can respond to a mild (0.001%) chitosan treatment by the callose deposition and by a deceleration of the RH growth. We demonstrate that the glucan synthase-like 5 (GSL5)/PMR4 is vital for chitosan-induced callose deposition but not for RH growth inhibition. Upon the higher chitosan concentration (0.01%) treatment, RHs do not deposit callose, while growth inhibition is prominent. To understand the specificities of the low and high concentration chitosan treatments, we analysed the corresponding PTI signalling components, gene expression, and RH cellular endomembrane and cytoskeleton modifications. Importantly, chitosan-induced callose deposition is also present in the functionally analogous and evolutionarily only distantly related RH-like structures rhizophores (lycophytes) and rhizoids (bryophytes). Our results point to the RH callose deposition as a conserved strategy of soil-anchoring plant cells (rhizoids/rhizophores/RHs) to deal with mild biotic stress. At the same time, high chitosan concentration prominently disturbs intracellular dynamics, tip-localised endomembrane compartments and RH growth, precluding callose deposition.

plant biology↗

bioRxiv2023

Study of auxin metabolism using stable isotope labeling and LCMS; evidence for in planta auxin decarboxylation pathway.

The natural plant hormone auxin indole-3-acetic acid (IAA) influences many physiological processes in plants. Here, the metabolism of IAA was studied in detail using tobacco BY-2 cells as a model and compared with the in planta metabolism in several plant species. A combination of labeled/unlabeled substrate feeding, global untargeted mass spectrometric (MS) scanning, and selective MS filtering allowed the detection of 17 auxin metabolites, 15 of which were identified. Subsequent study of intermediate metabolism and dynamics revealed eight major pathways: three amino acid conjugation pathways with aspartate, glutamate, and glutamine, followed by their 2-oxidation with the help of the DAO enzyme; side-chain glucosyl ester formation; direct 2-oxidation; two decarboxylation pathways; and a pathway producing an unidentified metabolite. Interestingly, the first intermediates of the two decarboxylation pathways, indole-3-carbinol and oxoindole-3-carbinol, were formed outside the cells. We found that the majority of the detected auxin metabolites occur naturally in several plant species and that IAA is their precursor, indicating that the auxin metabolic pathways observed in BY-2 cells also occur in planta. Our finding that the IAA decarboxylation pathway occurs in planta, and the previous reports of auxin activity of some metabolites of this pathway, suggest that at least some of the biological effects of IAA may be explained by its conversion to decarboxylative metabolites.

plant biology↗

bioRxiv2023

Auxin coreceptor IAA17/AXR3 controls cell elongation in Arabidopsis thaliana root by modulation of auxin and gibberellin perception

The nuclear TIR1/AFB - Aux/IAA auxin pathway plays a crucial role in regulating plant growth and development. Specifically, the IAA17/AXR3 protein participates in root development, and the accumulation of its mutant variant, AXR3-1, which cannot bind auxin, leads to severe root growth phenotype and agravitropism. However, the mechanism by which AXR3 regulates cell elongation is not fully understood. Here we show that the inducible expression of AXR3-1 in the Arabidopsis thaliana root triggers excessive cell elongation that is followed by growth arrest of the root. We exploited this effect to reveal the underlying molecular mechanism of AXR3 action. We show that AXR3-1 acts exclusively in the nucleus where it interferes with the nuclear auxin transcriptional pathway, while the rapid cytoplasmic auxin root growth response is not affected. The analysis of the transcriptome of the induced AXR3-1 roots revealed changes in phytohormone perception and homeostasis. We show that the accumulation of AXR3-1 disturbs auxin homeostasis which leads to excessive auxin accumulation. At the same time, the reaction of the AXR3-1 roots to gibberellin is altered. These results show that the IAA17/AXR3 maintains an optimal cell elongation rate by controlling the auxin response, auxin homeostasis and the interplay with gibberellin signaling.

plant biology↗