Biology subjects

Nakagami, H.

Publications and source records attributed to Nakagami, H..

At least 19 recordsLinked to original sources

bioRxiv2026

Catalase import into peroxisomes in Arabidopsis

In eukaryotes, catalases are peroxisomal antioxidant enzymes that maintain cellular reactive oxygen species (ROS) homeostasis. Plant catalases lack canonical peroxisomal targeting signals (PTS), and the mechanism underlying their PEX5-dependent peroxisomal import remains poorly understood. Here, we expressed CAT2 with N- and C-terminal GFP fusions in an Arabidopsis cat2 mutant background and found that only GFP-CAT2 completely restored wild-type function despite comparable catalase activity for both CAT2-GFP and GFP-CAT2. Only GFP-CAT2 localized to peroxisomes, indicating that altered subcellular localization prevented CAT2-GFP functional complementation. Expression of CAT2-GFP in wild-type Arabidopsis and Nicotiana benthamiana revealed in vivo interaction with endogenous catalases leading to co-import into peroxisomes. Localization of YFP fused to various CAT2 C-terminal sections identified the CAT2 C-terminal five amino acids as a functional PTS1-like sequence. These findings define a minimal C-terminal targeting motif for plant catalases that is sufficient for their peroxisomal import.

plant biology↗

bioRxiv2026

A tunable receptor separates root barrier formation from nutrient signaling through ligand-perception states

In roots, the endodermis controls nutrient entry by forming a barrier known as the Casparian strip1-3. Yet how barrier-associated processes interface with systemic signaling remains unclear. Here, we show that the receptor kinase SCHENGEN3 links local barrier surveillance to systemic nutrient signaling, with outputs that depend on the effective state of ligand perception. Unlike in Arabidopsis thaliana, SCHENGEN3 activation in Lotus japonicus requires a distinct cellular competence state and cannot be triggered by exogenous ligands alone, revealing evolutionary divergence in pathway deployment. Cross-species complementation uncouples systemic nitrogen signaling from Casparian strip formation, while transcriptomic and phosphoproteomic analyses reveal largely non-overlapping signaling- and barrier-associated programs that differ between agar and agricultural soil conditions. Mechanistically, receptor-ligand comparisons, engineered receptor variants, and co-receptor mutant analyses show that systemic nitrogen signaling is retained in receptor-perception states that are insufficient to support full Casparian strip establishment. Together, these findings reveal how a shared receptor module can separate developmental and physiological outputs by linking receptor perception state to output specificity.

plant biology↗

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↗

bioRxiv2026

A redox-regulated RCC1-like protein controls catalase activity in Arabidopsis

Reactive oxygen species (ROS) are central regulators of plant growth and stress responses. Cellular ROS levels are tightly controlled by antioxidant systems, including the evolutionarily conserved catalases that detoxify hydrogen peroxide (H2O2) predominantly within peroxisomes. Despite their importance, substantial gaps remain in our understanding of catalase biogenesis, regulation, subcellular targeting, and potential extra-peroxisomal functions. Using affinity purification of the UV-B photoreceptor UVR8 coupled with mass spectrometry, we identified a REGULATOR OF CHROMATIN CONDENSATION 1-like protein in Arabidopsis, which we named CATALASE-INTERACTING RCC1-LIKE 1 (CAIR1). CAIR1 interacts with all three catalase isoforms (CAT1-CAT3) as well as their chaperone NO CATALASE ACTIVITY 1 (NCA1). Loss-of-function cair1 mutants partially phenocopy cat2 and nca1, with reduced catalase activity, enhanced sensitivity to oxidative stress and alkaline growth conditions, and impaired primary root elongation. Mechanistically, cytosolic interaction between CAIR1 and CAT2 enhances total cellular catalase activity by facilitating peroxisomal import and proper subcellular localization of CAT2. In the absence of CAIR1, CAT2 forms aggregates, likely accounting for the observed loss of catalase activity. Notably, CAIR1 undergoes reversible, redox-dependent oligomerization that enhances its interaction with catalases. Mutation of CAIR1 at Cys-356 and Cys-545 compromises this interaction under elevated ROS conditions and fails to rescue the oxidative stress sensitivity of cair1 mutants. Moreover, UV-B exposure suppresses catalase activity by weakening the interaction between CAIR1 and catalases, thus linking environmental light signalling to cellular redox regulation. Together, our findings reveal CAIR1 as a dynamic redox-responsive regulator of catalase activity that maintains cellular redox homeostasis by coordinating catalase localization and function through reversible oligomerization.

plant biology↗

bioRxiv2026

Targeting of the barley cell-surface receptor SRF3 by the Blumeria hordei effector AVRA13 overlaps with AVRA13 recognition by MLA and the induction of NLR-mediated cell death.

Pathogens secrete effector proteins to promote virulence. Despite their recognition by barley Mla resistance genes, the structurally-related Blumeria hordei (Bh) AVRA effectors are maintained in the Bh genome, suggesting virulence functions critical for fungal pathogenicity. Using proximity-dependent protein labelling in transgenic barley, we detected distinct host protein interactomes for five AVRAs despite their structural homology and convergence on MLAs. We report the specific interaction of the highly conserved AVRA13 effector with the barley cell-surface receptor SRF3. AVRA13 disrupts HvSRF3-HvBAK1 interaction and alters HvSRF3 plasma membrane levels. AVRa13-expression desensitizes iron-induced restriction of Bh growth, suggesting that AVRA13 facilitates fungal proliferation by manipulating SRF3-mediated iron homeostasis. Our results suggest that MLAs have diversified to specifically detect the residues that underly Bh effector neo-functionalization and intrinsic AVRA virulence functions. Together, these findings identify SRF3 as molecular link between pathogen virulence, immune recognition, and iron homeostasis.

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↗

bioRxiv2025

Epigenetic gene regulation is controlled by distinct regulatory complexes utilizing specialized paralogs of TELOMERE REPEAT BINDING FACTORS

Epigenetic regulators shape chromatin landscapes, allowing cells to express distinct gene sets depending on cell-type, developmental stage or environmental cues. These regulatory complexes rely on interactions with sequence-specific DNA binding proteins, such as the small family of TELOMERE REPEAT BINDING FACTORS (TRBs). TRBs are components of chromatin regulatory complexes with opposing functions, such as the epigenetic repressors Polycomb Repressive Complex 2 (PRC2) and a JMJ14/NAC complex that respectively add and removes the repressive H3K27me3 and positive H3K4me3 modification, but also with the plant-specific PEAT complex that is linked to histone acetylation and gene activation. We dissected the partial redundancy between TRB1, TRB2 and TRB3 in target gene selection and interaction with different chromatin regulatory complexes. High redundancy of TRBs is suggested by major phenotypic changes that are only observed trb triple mutants; however, we found different target site preference between TRB1-3 and preferred partnership with chromatin complexes. Furthermore, TRB paralogs interacted with the NuA4 histone acetylation complex, both together with and in absence of PEAT. Among the three paralogs, TRB1 had more unique binding sites and correlated stronger with PEAT and NuA4 functions. In contrast, TRB2 and TRB3 were more dependent on the presence of bona fide telo-box motifs and were more likely to be found at PRC2 associated sites. Overall, we provide insight into the diverse roles of TRBs in epigenetic gene regulation and how their diversification contributes to their apparent redundancy, as well as their observed activating and repressing effects on gene expression.

plant biology↗

bioRxiv2025

Affinity-Based Interactome Mapping of Inositol Pyrophosphates Reveals 4/6-PP-InsP5-Binding Proteins in Plants

Inositol pyrophosphates (PP-InsPs) are central regulators of eukaryotic signaling events. While certain PP-InsP isomers have been conclusively linked to the regulation of phosphate homeostasis through interaction with SPX domain containing proteins in plants, the functions of the recently discovered isomer 4/6-PP-InsP5 remain largely unknown. Here, we employed two complementary affinity-based strategies - a matrix approach and a photoaffinity probe - to systematically identify 4/6-PP-InsP5-binding proteins in Arabidopsis thaliana. The two methods yielded partially overlapping protein sets, with photoaffinity enrichment likely capturing additional transient and/or weak interactions. Moreover, competition experiments with different isomers were applied to obtain information about potential isomer-specific interactions. As a proof-of-concept, one candidate interactor (FHA domain-containing protein AtFHA2) was shown to bind 4-PP-InsP5 in vitro with substantially higher affinity than InsP6. Thus, besides the SPX domain, FHA domain containing proteins, of which 18 exist in Arabidopsis, are potentially regulated by inositol pyrophosphates. More generally, our findings reveal a diverse protein network associated with 4/6-PP-InsP5 and establish a versatile platform for dissecting its biological roles in plants and other organisms.

biochemistry↗

bioRxiv2025

Conservation and divergence of UVR8-COP1/SPA-HY5 signaling in UV-B responses of Marchantia polymorpha

Ultraviolet-B radiation (UV-B) poses a major challenge to all forms of plant life. The liverwort Marchantia polymorpha (Marchantia) serves as a key model organism to study signaling pathways and to infer their evolution throughout the green lineage. Marchantia expresses key components of UV-B signaling, including the photoreceptor UV RESISTANCE LOCUS 8 (MpUVR8), the WD40-repeat protein REPRESSOR OF UV-B PHOTOMORPHOGENESIS (MpRUP), the E3 ubiquitin ligase complex CONSTITUTIVELY PHOTOMORPHOGENIC 1 / SUPPRESSOR OF phyA-105 (MpCOP1/MpSPA), and the transcriptional regulator ELONGATED HYPOCOTYL 5 (MpHY5). Here, we show that MpUVR8 exists as a homodimer in its ground-state in vivo, then monomerizes and accumulates in the nucleus upon UV-B activation. Activated MpUVR8 interacts with MpCOP1, triggering growth inhibition, genome-wide gene expression changes, biosynthesis of UV-absorbing metabolites, and photoprotection, which overall contributes to UV-B stress tolerance. MpRUP facilitates redimerization of MpUVR8 and Mprup null mutants show enhanced UV-B photomorphogenesis, demonstrating that MpRUP efficiently represses MpUVR8 signaling. Unlike the case in Arabidopsis and in contrast to the strong Mpcop1 mutant phenotype, Mpspa mutants develop only a very weak constitutive photomorphogenesis phenotype, indicating that COP1 function is much more independent of SPA in Marchantia than in Arabidopsis. Moreover, in contrast to Arabidopsis SPAs, Mpspa is linked with a hyper-responsive UV-B phenotype, suggesting that MpSPA is a negative regulator of MpUVR8 signaling. Similar to Arabidopsis HY5/HYH, MpHY5 functions antagonistically to MpCOP1, but its role in UV-B-mediated gene expression changes is more limited. Our findings demonstrate that although core components of UV-B signaling existed in the last common ancestor of extant land plants, regulatory interactions have diversified in different lineages since their divergence more than 400 million years ago.

plant biology↗

bioRxiv2025

Emergence of isochorismate-based salicylic acid biosynthesis within Brassicales

Salicylic acid (SA) is a major defense phytohormone. In Arabidopsis thaliana, the isochorismate (IC) pathway is the primary route for pathogen-induced SA biosynthesis. First, the IC synthase (ICS) catalyzes the isomerization of chorismate to IC in chloroplasts. Second, the chloroplast-localized MATE transporter EDS5 appears to transport IC from chloroplasts to the cytosol. Cytosolic IC is then further converted to SA via the GH3 amino acid-conjugating enzyme PBS3. While this pathway is genetically well-characterized in A. thaliana, its evolutionary origin and conservation remain controversial. In this study, through comprehensive phylogenetic, structural, and functional analyses, we demonstrate that the IC pathway emerged within the Brassicales order in a time span between the divergence of Carica papaya and Capparis spinosa. The evolution of the IC pathway was driven by three key adaptations during the time span: (1) enhancement of ICS activity, (2) neofunctionalization of EDS5 after duplication of its ancestral gene, and (3) evolution of a PBS3, whose activity is specialized for glutamate-conjugation to IC. Structural modeling and functional assays reveal that an enhanced salt bridge network in ICS enhanced its activity. One of the duplicated genes, EDS5, acquired key amino acid substitutions in the C-lobe, which likely contributed to the EDS5 neofunctionalization. In addition, the functional PBS3 clade, including A. thaliana PBS3, is restricted to a Brassicales clade. Taken together, this study addresses the evolutionary trajectory of IC-based SA biosynthesis.

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

Ustilago maydis disrupts carbohydrate signaling networks to induce hypertrophy in host cells

Ustilago maydis is a biotrophic fungus infecting maize, secreting effector proteins to manipulate host cellular processes and create nutrient-rich environments for its growth. Three effectors, Hap1-3 (hypertrophy-associated proteins), were identified as virulence factors promoting hypertrophic mesophyll tumor cells (HTT). Immunoprecipitation and mass spectrometry revealed interactions among Hap effectors, suggesting potential effector complex formation. CRISPR-Cas9 triple knockout of hap1-3 demonstrated Hap1s role in HTT formation. Infection assays identified Hap1 as a key virulence factor interacting with maize Snf1-related kinase 1 (SnRK1), a central energy regulator. RNA-seq analysis showed that Hap1 promotes cell cycle and starch biosynthesis genes, while CR-hap1 induced defense-related WRKY transcription factors. Phosphoproteomics revealed increased phosphorylation of SnRK1 and metabolic enzymes during SG200 infection. Our findings support a model where U. maydis induces hypertrophy through Hap1, targeting the SnRK1 subunit to prevent SnRK1 inhibition by high trehalose-6-phosphate (T6P), disrupting the antagonistic relationship between T6P and SnRK1. This reprograms host transcription to enhance starch metabolism and induce endoreduplication, leading to hypertrophy induction, while suppressing sugar-induced immune signaling.

plant biology↗

bioRxiv2024

NUDIX Hydrolases Target Specific Inositol Pyrophosphates and Regulate Phosphate and Iron Homeostasis, and the Expression of Defense Genes in Arabidopsis

Inositol pyrophosphates (PP-InsPs) are important signaling molecules that regulate diverse cellular processes in eukaryotes, including energy homeostasis, phosphate (Pi) signaling, and phytohormone perception. Yet, in plants, the enzymes responsible for their turnover remain largely unknown. Using a non-hydrolysable PP-InsP analog in a pull-down approach, we identified a family of Arabidopsis NUDIX hydrolases (NUDTs) that group into two closely related subclades. Through in vitro assays, heterologous expression systems, and higher-order gene-edited mutants, we explored the substrate specificities and physiological roles of these hydrolases. Using a combination of strong anion exchange (SAX)-HPLC, PAGE, and capillary electrophoresis electrospray ionization mass spectrometry (CE-ESI-MS), we found that their PP-InsP pyrophosphatase activity is enantiomer-selective and Mg2+-dependent. Specifically, subclade I NUDTs preferentially hydrolyze 4-InsP7, while subclade II NUDTs target 3-InsP7, with minor activity against other PP-InsPs, including 5-InsP7. In higher-order mutants of subclade II NUDTs, we observed defects in both Pi and iron homeostasis, accompanied by increased levels of 1/3-InsP7 and 5-InsP7, with a markedly larger increase in 1/3-InsP7. Ectopic expression of NUDTs from both subclades induced local Pi starvation responses (PSRs), while RNA-seq analysis comparing wildtype (WT) and subclade II nudt12/13/16 loss-of-function plants indicates additional PSR-independent roles, potentially involving 1/3-InsP7 in the regulation of plant defense. Consistently, nudt12/13/16 mutants displayed enhanced resistance to Pseudomonas syringae infection, indicating a role in bacterial pathogen susceptibility. Expanding beyond subclade II NUDTs, we demonstrated susceptibility of the 3PP-position of PP-InsPs to enzymatic activities unrelated to NUDTs, and found that such activities are conserved across plants and humans. Additionally, we found that NUDT effectors from pathogenic ascomycete fungi exhibit a substrate specificity similar to subclade I NUDTs. Collectively, our findings reveal new roles for NUDTs in PP-InsP signaling, plant nutrient and immune responses, and highlight a cross-kingdom conservation of PP-InsP-metabolizing enzymes.

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↗

bioRxiv2023

The leucine-rich repeat receptor kinase QSK1 is a novel regulator of PRR-RBOHD complex and is employed by the bacterial effector HopF2Pto to modulate plant immunity

Plants detect pathogens using cell-surface pattern recognition receptors (PRRs) like EFR and FLS2, which recognize bacterial EF-Tu and flagellin, respectively. These PRRs, belonging to the leucine-rich repeat receptor kinase (LRR-RK) family, activate the production of reactive oxygen species via the NADPH oxidase RBOHD. The PRR-RBOHD complex is tightly regulated to prevent unwarranted or exaggerated immune responses. However, certain pathogenic effectors can subvert these regulatory mechanisms, thereby suppressing plant immunity. To elucidate the intricate dynamics of the PRR-RBOHD complex, we conducted a comparative co-immunoprecipitation analysis using EFR, FLS2, and RBOHD. We identified QSK1, an LRR-RK, as a novel component of the PRR-RBOHD complex. QSK1 functions as a negative regulator of PRR-triggered immunity (PTI) by downregulating the abundance of FLS2 and EFR. QSK1 is targeted by the bacterial effector HopF2Pto, a mono-ADP ribosyltransferase, resulting in the reduction of FLS2 and EFR levels through both transcriptional and transcription-independent pathways, thereby inhibiting PTI. Furthermore, HopF2Pto reduces transcript levels of PROSCOOP genes encoding important stress-regulated phytocytokines and their receptor MIK2. Importantly, HopF2Pto requires QSK1 for its accumulation and virulence functions within plants. In summary, our results provide novel insights into the mechanism by which HopF2Pto employs QSK1 to desensitize plants to pathogen attack. One Sentence SummaryQSK1, a novel component in the plant immune receptor complex, downregulates these receptors and phytocytokines, and is exploited by bacterial effector HopF2Pto to desensitize plants to pathogen attack.

plant biology↗

bioRxiv2023

The cell cycle controls spindle architecture in Arabidopsis by modulating the augmin pathway

To ensure an even segregation of chromosomes during somatic cell division, eukaryotes rely on specific microtubule structures called mitotic spindles. There are, however, striking differences in overall spindle organization among eukaryotic super groups, and in particular little is known about how spindle architecture is determined in plants. As a foundation for our work, we have measured prime characteristics of Arabidopsis mitotic spindles and built a three-dimensional dynamic model of the Arabidopsis mitotic spindle using Cytosim. Next, we identified the cell-cycle regulator CYCLIN-DEPENDENT KINASE B1 (CDKB1) together with its cyclin partner CYCB3;1 as key regulators of spindle shape and organization in Arabidopsis. Loss of CDKB1 function resulted in a high number of astral microtubules that are normally absent from plant spindles, as opposed to animal ones. We identified an augmin complex member, ENDOSPERM DEFECTIVE1 (EDE1), as a substrate of the CDKB1;1-CYCB3;1 complex. A non-phosphorylatable mutant of EDE1 displayed spindles with extended pole-to-pole distance, resembling the phenotypes of cycb3;1 and cdkb1 mutants. Moreover, we found that the mutated EDE1 version associated less efficiently with spindle microtubules. Consistently, reducing the level of augmin in Cytosim simulations largely recapitulated the spindle phenotypes observed in cycb3;1 and cdkb1 mutants. Our results emphasize the importance of cell cycle-dependent phospho-control of the mitotic spindle in plant cells. They also support the validity of our computational model as a framework for the exploration of mechanisms controlling the organization of the spindle in plants and in other species.

developmental biology↗

bioRxiv2023

The fungal pathogen Ustilago maydis targets the maize corepressor TPL2 to modulate host transcription for tumorigenesis

Ustilago maydis is a biotrophic fungus that causes tumor formation on all aerial parts of maize. U. maydis secretes effector proteins during penetration and colonization to successfully overcome the plant immune response and reprogram host physiology to promote infection. In this study, we functionally characterized the U. maydis effector protein Topless (TPL) interacting protein 6 (Tip6). We found that Tip6 interacts with the N-terminus of ZmTPL2 through its two EAR (Ethylene-responsive element binding factor-associated amphiphilic repression) motifs. We show that the EAR motifs are essential for the virulence function of Tip6 and critical for altering the nuclear distribution pattern of ZmTPL2. We propose that Tip6 mimics the recruitment of ZmTPL2 by plant repressor proteins, thus disrupting host transcriptional regulation. We show that a large group of AP2/ERF B1 subfamily transcription factors are misregulated in the presence of Tip6. Our study suggests a regulatory mechanism where the U. maydis effector Tip6 utilizes repressive domains to recruit the corepressor ZmTPL2 to disrupt the transcriptional networks of the host plant.

plant biology↗