Biology subjects

Harzen, A.

Publications and source records attributed to Harzen, A..

8 recordsLinked to original sources

bioRxiv2026

Homologous ABA-independent kinase tracks coalesced into osmotic stress circuits during plant terrestrialization

Land plants possess a unique system for responding to environmental stressors. How this system evolved during plant terrestrialization remains one of the major questions in plant evolutionary biology. To retrace this process, it is essential to study both land plants and their closest algal relatives, the zygnematophytes. Using the single-celled zygnematophyte Mesotaenium, we integrated physiological stress experiments with phosphoproteomics, genome-wide transcription factor binding analyses, and protein-protein interaction studies to investigate the architecture of a key stress response pathway: the signaling cascade homologous to the plant abscisic acid (ABA)-mediated pathway. Our results highlight the roles of histidine kinases (HKs) and calcium-dependent protein kinases (CDPKs) in osmotic stress signaling. Focusing on SnRK2 and ABF, key components at the downstream end of the canonical ABA signaling pathway, we provide evidence that ABF plays a central role in osmotic stress responses even in the absence of ABA. Together, our data reveal the coordinated action of parallel functional modules that were likely integrated into the ABA response cascade during plant terrestrialization.

evolutionary biology↗

bioRxiv2026

Enhanced phenylalanine biosynthesis amplifies light-stress-driven phenylpropanoid production in Arabidopsis

Phenylpropanoids are L-phenylalanine (Phe)-derived specialized metabolites with crucial roles in plant stress adaptation. Among various abiotic stresses, high-light (HL) is a major threat that leads to oxidative damage and therefore upregulates the biosynthesis of antioxidant phenylpropanoids, including anthocyanins, in plants. Phenylpropanoid production is initiated by the conversion of Phe by phenylalanine ammonia-lyase (PAL) enzyme, which acts as the key gatekeeper controlling carbon influx from the Phe pool into phenylpropanoid biosynthesis. Despite the importance of Phe as a precursor for phenylpropanoid production, we have limited knowledge of how Phe precursor availability influences downstream pathways, particularly in the context of stress adaptation. To tackle this question, Arabidopsis thaliana wild-type and production of anthocyanin pigment 1 dominant (pap1D) mutant, a line genetically enhanced for anthocyanin production, were subjected to HL treatment, followed by proteome and metabolome analyses. Our multi-omics data indicated that Phe biosynthesis was insufficiently responsive to meet the increased precursor demand from the downstream phenylpropanoid pathway, likely making Phe availability a rate-limiting factor for HL-induced phenylpropanoid production. We then generated pap1D double mutants with Phe-overaccumulating mutants. Untargeted metabolomics revealed that enhanced Phe availability had little impact on phenylpropanoid accumulation under standard growth conditions but additively promoted the accumulation of specific phenylpropanoid intermediates and anthocyanin species under HL stress. This metabolic difference between light treatment and genotypes was correlated with the activation of PAL enzymatic activity. This study demonstrates that enhanced Phe biosynthesis amplifies HL-induced phenylpropanoid biosynthesis.

plant biology↗

bioRxiv2025

Coordinated action of CRK2 and QSK1 regulate osmotic stress response in Arabidopsis

Precise control of intercellular communication is essential for normal growth and stress responses in all multicellular organisms. In Arabidopsis, two membrane-localized receptor like kinases (RLKs), the Cysteine-rich RLK CRK2 and the Leucine-rich repeat (LRR) RLK QSK1 relocalize from the general plasma membrane (PM) to plasmodesmata (PD) in response to osmotic stress. Both these RLKs regulate callose deposition thereby modulating PD permeability. However, unchecked callose deposition can block the PD and disrupt proper intercellular communication. Here, we show that under normal growth conditions, CRK2 phosphorylates and sequesters QSK1 at the general PM, preventing unnecessary callose deposition at PD. We show that osmotic stress-induced enrichment of QSK1 at PD requires functional CRK2 and establish that phosphorylation of QSK1 in its C-terminal region is inhibitory in this process. We propose that osmotic stress triggers dephosphorylation and release of QSK1 from the CRK2-QSK1 complex, enabling its relocalization from general PM to PD, where it promotes stress-induced callose deposition. Subsequently, CRK2 relocalizes to PD where it negatively influences callose deposition. Our work reveals a tightly coordinated distribution of QSK1 and CRK2 at PM, establishing a dynamic gating mechanism that balances growth and stress responsiveness.

plant biology↗

bioRxiv2024

An Omics approach on Marchantia polymorpha single FERONIA and MARIS homologs confirms links between cell wall integrity and abscisic acid

Plant cells are surrounded by an extracellular cell wall that shields them from their abiotic and biotic environment. To coordinate their growth with their cell wall status, plant cells have developed cell wall integrity (CWI) mechanisms, at the center of which lies the transmembrane Malectin-like receptor kinase FERONIA (FER). FER controls a myriad of plant developmental processes including sexual reproduction, cell growth and morphogenesis, often intersecting with phytohormones-dependent pathways such as abscisic acid (ABA) signaling or plant immunity. Interestingly, FER together with its downstream receptor-like cytoplasmic kinase MARIS (MRI) was shown to similarly control root hair and rhizoid integrity in the vascular angiosperm Arabidopsis and the early diverging bryophyte Marchantia polymorpha, respectively. Here, we performed comparative transcriptomics and proteomics on the M. polymorpha mutant plants, Mpfer-1 and Mpmri-1, and their corresponding wild-type accessions Tak-1 and Tak-2. Large and significant overlaps were observed between differentially expressed genes and differentially abundant proteins in both mutants. Our multi-omics approach revealed that MpFER and MpMRI largely cooperate to negatively regulate transcriptional and translational networks, particularly those related to plant defense and ABA responses. Moreover, our phenotypic analyses showed that Mpfer-1 plants are hypersensitive to ABA-dependent growth inhibition, indicating that FERs function of negatively regulating ABA-related growth responses is conserved between bryophytes and vascular plants.

plant biology↗

bioRxiv2024

Conserved role of the SERK-BIR module in development and immunity across land plants

SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASES (SERKs), which are subfamily II of leucine-rich repeat receptor-like kinases (LRR-RLKs), play diverse roles in development and immunity in the angiosperm Arabidopsis thaliana. AtSERKs act as co-receptors for many LRR-RLKs, including BRASSINOSTEROID INSENSITIVE 1 (BRI1) and FLAGELLIN SENSITIVE 2 (FLS2).1-4 The conserved tyrosine (Y) residue in AtSERK3 is crucial for signaling specificity in differentiating BRI1- and FLS2-mediated pathways.5 BRI1-ASSOCIATED RECEPTOR KINASE 1 (BAK1)-INTERACTING RECEPTOR-LIKE KINASES (BIRs) interact with SERKs under resting conditions, negatively regulating SERK-mediated pathways.6,7 SERK and BIR are highly conserved in land plants, whereas BRI1 and FLS2 homologs are absent or poorly conserved in bryophyte lineages.8,9 The biological functions of SERK homologs in non-flowering plants are largely unknown. The genome of the liverwort Marchantia polymorpha encodes single homologs for SERK and BIR, namely MpSERK and MpBIR.9 We here show that Mpserk disruptants display growth and developmental defects with no observable sexual or vegetative reproduction. Complementation analysis revealed a contribution of the conserved Y residue of MpSERK to growth. Proximity labelling-based interactomics identified MpBIR as a MpSERK interactor. Mpbir disruptants displayed defects in reproductive organ development. Patterns of development- and immunity-related gene expression in Mpserk and Mpbir were antagonistic, suggesting that MpBIR functions as a MpSERK repressor. The pathogenic bacterium Pseudomonas syringae pv. tomato DC3000 grew poorly on Mpbir, indicating a significant role of the MpSERK1MpBIR module in immunity. Taken together, we propose that the SERK-BIR functional module was already regulating both development and immunity in the last common ancestor of land plants.

plant biology↗

bioRxiv2022

miniTurbo-based interactomics of two plasma membrane-localized SNARE proteins in Marchantia polymorpha

O_LIMarchantia polymorpha is a model liverwort and its overall low genetic redundancy is advantageous for dissecting complex pathways. Proximity-dependent in vivo biotin-labelling methods have emerged as powerful interactomics tools in recent years. However, interactomics studies applying proximity labelling are currently limited to angiosperm species in plants. C_LIO_LIHere, we established and evaluated a miniTurbo-based interactomics method in M. polymorpha using MpSYP12A and MpSYP13B, two plasma membrane- localized SNARE proteins, as baits. C_LIO_LIWe show that our method yields a manifold of potential interactors of MpSYP12A and MpSYP13B compared to a co-immunoprecipitation approach. Our method could capture specific candidates for each SNARE. C_LIO_LIWe conclude that a miniTurbo-based method is a feasible tool for interactomics in M. polymorpha and potentially applicable to other model bryophytes. Our interactome dataset on MpSYP12A and MpSYP13B will be a useful resource to elucidate the evolution of SNARE functions. C_LI

plant biology↗

bioRxiv2020

Pathogen effector recognition-dependent association of NRG1 with EDS1 and SAG101 in TNL receptor immunity

Plants utilise intracellular nucleotide-binding, leucine-rich repeat (NLR) immune receptors to detect pathogen effectors and activate local and systemic defence. NRG1 and ADR1 "helper" NLRs (RNLs), cooperate with enhanced disease susceptibility 1 (EDS1), senescence-associated gene 101 (SAG101) and phytoalexin-deficient 4 (PAD4) lipase-like proteins to mediate signalling from TIR domain NLR receptors (TNLs). However, the mechanism of RNL/EDS1-family protein cooperation is poorly understood. Here, we provide genetic and molecular evidence for exclusive EDS1/SAG101/NRG1 and EDS1/PAD4/ADR1 co-functions in TNL immunity. Using immunoprecipitation and mass spectrometry, we show effector recognition-dependent association of NRG1 with EDS1 and SAG101, but not PAD4. An EDS1-SAG101 complex associates with NRG1, and EDS1-PAD4 associates with ADR1, only in an immune-activated state. NRG1 requires an intact nucleotide-binding P-loop motif, and EDS1 a functional EP domain and its partner SAG101, for induced association and immunity. Thus, two distinct modules (NRG1/EDS1/SAG101 and ADR1/EDS1/PAD4) are required to execute TNL receptor defence signalling.

plant biology↗

bioRxiv2019

CRK2-mediated control of ROS production by phosphorylation of the RBOHD C-terminus in Arabidopsis

Reactive oxygen species (ROS) are important messengers in eukaryotic organisms and their production is tightly controlled. Active extracellular ROS production by NADPH oxidases in plants is triggered by receptor-like protein kinase (RLK)-dependent signaling networks. Here we show that the cysteine-rich RLK CRK2 kinase activity is required for plant growth and CRK2 exists in a preformed complex with the NADPH oxidase RBOHD in Arabidopsis. Functional CRK2 is required for the full elicitor-induced ROS burst and consequently the crk2 mutant is impaired in defense against the bacterial pathogen Pseudomonas syringae pv. tomato DC3000. Our work demonstrates that CRK2 regulates plant innate immunity. We identified in vitro CRK2-dependent phosphorylation sites in the C-terminal region of RBOHD. Phosphorylation of S703 RBOHD is enhanced upon flg22 treatment and substitution of S703 with alanine reduced ROS production in Arabidopsis. Phylogenetic analysis suggests that phospho-sites in C-terminal region of RBOHD are conserved throughout the plant lineage and between animals and plants. We propose that regulation of NADPH oxidase activity by phosphorylation of the C-terminal region might be an ancient mechanism and that CRK2 is an important element in regulating MAMP-triggered ROS production. One-sentence summaryCRK2 associates with and activates RBOHD to trigger MAMP-induced ROS production and reveals a novel regulatory mechanism for plant NADPH oxidases through phosphorylation of the C-terminus.

plant biology↗