Biology subjects

Maika, J. E.

Publications and source records attributed to Maika, J. E..

6 recordsLinked to original sources

bioRxiv2026

Structural and functional insights into the role of Cysteine-Rich Receptor-Like Kinase 18 (CRK18) in Arabidopsis

Plants perceive and integrate diverse environmental signals through receptor kinase (RK) networks at the plasma membrane. Within this, Cysteine-Rich Receptor-Like Kinases (CRKs) constitute a large but not well-understood subfamily characterised by extracellular domains (ECDs) enriched in cysteine residues. CRKs have been implicated in plant responses to biotic and abiotic stress, as well as in developmental processes. Additionally, several CRKs have been proposed to act as redox sensors. Here, we investigate the homodimerization mechanism of Arabidopsis CRK18 and its regulation by redox conditions. By modulating pH and redox state, we assessed the stability and binding dynamics of the CRK18 ECD and its cysteine mutants. We also tested the plasma membrane localisation of all the cysteine mutants involved in the predicted disulfide bonds, and only CRK18C227A, C228A-ECD resembled the plasma membrane localization of wild-type CRK18. We combine co-immunoprecipitation, Forster resonance energy transfer-fluorescence lifetime imaging microscopy and microscale thermophoresis to quantify CRK18 self-association in planta and in vitro. Furthermore, we place CRK18 dimerization in a broader signalling context by identifying CRK18 interaction partners and CRK18-dependent signalling outputs. Using Arabidopsis CRK18 overexpression lines, we perform (phospho)proteomic and immunoprecipitation-mass spectrometry (IP-MS) analyses to map CRK18-centred signalling networks associated with stress-related responses. The constitutive activation of the CRK18 kinase domain and its interaction with many putative (cell wall) glycan-sensing RKs, including PERK15, suggest a regulatory role for CRK18. The absence of significant changes in the proteome and phosphoproteome of CRK18 overexpression lines in the absence of any trigger, and its restricted mobility after elicitation, suggest that CRK18 requires a stimulus for activation and possibly induces membrane microdomain reorganisation. This is in line with the infection assay with the nematode Heterodera schachtii, which causes modification and targeted damage to plant cell walls during infection, revealing that CRK18 acts as negative regulator of this process.

biochemistry↗

bioRxiv2026

Structural Mapping of the EIN2-EIN3 Interaction Core and Its Integration with ENAP1 in Ethylene Signaling

Ethylene regulates diverse developmental processes, yet the molecular function of its central regulator, ETHYLENE INSENSITIVE 2 (EIN2), has remained unclear. Although EIN2 nuclear import is mediated by the Importin-/{beta} pathway, the molecular events initiated by EIN2 after nuclear entry were unknown. Here we show that EIN2 directly engages the transcription factor EIN3, establishing a mechanistic link between EIN2 nuclear accumulation and transcriptional activity. Microscale thermophoresis, yeast two-hybrid analysis and in planta FLIM-FRET consistently support this interaction. Domain mapping identifies EIN3 residues 86-173 as the core EIN2-binding region, and structural modeling refines the interface to a conserved segment within residues 86-120 that contacts a conserved region near the N-terminus of the EIN2-CEND fragment. In planta, EIN2 residues 1042-1214 are sufficient for EIN3 binding, revealing multiple interaction-competent surfaces with distinct affinities. The chromatin-associated protein ENAP1 also binds EIN2 and competes with EIN3, indicating a dynamic, concentration-dependent regulatory mechanism rather than a stable ternary complex. These findings define the molecular basis of the EIN2-EIN3 interaction and provide a mechanistic framework for EIN2-dependent transcriptional control in ethylene signaling.

plant biology↗

bioRxiv2025

The developing leaf of the wild grass Brachypodium distachyon at single-cell resolution

Leaves are the plants main photosynthetic organs and drive Earths primary production. Grasses form longitudinal leaves with parallel venation and graminoid stomata. Yet, how distinct leaf tissues coordinatively develop to build functional grass leaf anatomy is not well understood. Here, we decoded the developing grass leaf from vegetative meristems to mature tissues using single-cell RNA-sequencing in the wild grass Brachypodium distachyon. In-depth analysis of epidermal clusters and multiplexed whole-mount RNA-fluorescence in situ hybridization resolved most epidermal lineages and confirmed them in planta. Gene regulatory network analysis distinguished the targetome of the two co-expressed, yet functionally divergent stomatal transcription factors BdMUTE and BdFAMA. Finally, we used our dataset to identify and functionally describe BdGRAS32s role in cell division inhibition and a stomata-specific function for a cell wall modifying enzyme. Together, our single-cell grass leaf atlas enables the dissection of developmental processes that shape the leaf sustaining global food production.

plant biology↗

bioRxiv2025

Imputation integrates single-cell and spatial gene expression data to resolve transcriptional networks in barley shoot meristem development

Grass inflorescences are composite structures, featuring complex sets of meristems as stem cell niches that are initiated in a repetitive manner. Meristems differ in identity and longevity, generate branches or split to form flower meristems that finally produce seeds. Within meristems, distinct cell types are determined by positional information and the regional activity of gene regulatory networks. Understanding these local microenvironments requires precise spatio-temporal information on gene expression profiles, which current technology cannot achieve. Here we investigate transcriptional changes during barley development, from the specification of meristem and organ founder cells to the initiation of distinct floral organs, based on an imputation approach integrating deep single-cell RNA sequencing with spatial gene expression data. The expression profiles of more than 40.000 genes can be analysed at cellular resolution in multiple barley tissues using the web-based graphical interface BARVISTA, which enables precise virtual microdissection to analyse any sub-ensemble of cells. Our study pinpoints previously inaccessible key transcriptional events in founder cells during primordia initiation and specification, characterises complex branching mutant phenotypes by barcoding gene expression profiles, and defines spatio-temporal trajectories during flower development. We thus uncover the genetic basis of complex developmental processes, providing novel opportunities for precisely targeted manipulation of barley traits.

plant biology↗

bioRxiv2024

CLAVATA signalling shapes barley inflorescence architecture by controlling activity and determinacy of shoot apical and rachilla meristems

Grasses exhibit a large variety of diverse inflorescence architectures, from complex branched inflorescences in Oryzeae (rice) to simple spike-type inflorescences in Triticeae (e.g. barley, wheat). Inflorescence architecture depends on shape, longevity and determinacy of meristems that direct growth of the main rachis and lateral branches, but how individual meristem activities are determined and integrated within complex inflorescences is not yet understood. We found that activity of distinct meristems in the barley inflorescence is coordinated by a signalling pathway comprising the receptor like kinase Hordeum vulgare CLAVATA1 (HvCLV1) and the secreted CLAVATA3/ENDOSPERM SURROUNDING REGION (CLE)-family peptide FON2- LIKE CLE PROTEIN1 (HvFCP1). HvFCP1 interacts with HvCLV1 to promote spikelet formation but restricts inflorescence meristem and rachilla meristem proliferation. Hvfcp1 or Hvclv1 mutants generate branched inflorescences with additional rows of spikelets and supernumerary florets. Transcriptome analysis reveals that HvFCP1/HvCLV1 signalling controls inflorescence branching through the regulation of trehalose-6-phosphate synthesis and sugar transport. Our discoveries reveal the potential to engineer barley inflorescence architecture by manipulating regulation of distinct meristem activities.

plant biology↗

bioRxiv2024

Catalytically inactive subgroup VIII receptor-like cytoplasmic kinases regulate the immune-triggered oxidative burst in Arabidopsis thaliana

Protein kinases are key components of multiple cell signaling pathways. Several protein kinases of the receptor-like cytoplasmic kinase (RLCK) family have demonstrated roles in immune and developmental signaling across various plant species, making them a family of interest in the study of phosphorylation-based signal relay. Here, we present our investigation of a subfamily of RLCKs in Arabidopsis thaliana. Specifically, we focus on subgroup VIII RLCKs: MAZ and its paralog CARK6, as well as CARK7 and its paralog CARK9. We found that both MAZ and CARK7 associate with the calcium-dependent protein kinase CPK28 in planta, and furthermore that CPK28 phosphorylates both MAZ and CARK7 on multiple residues in areas that are known to be critical for protein kinase activation. Genetic analysis suggests redundant roles for MAZ and CARK6 as negative regulators of the immune-triggered oxidative burst. We find evidence that supports homo- and hetero-dimerization between CARK7 and MAZ, which may be a general feature of this protein family. Multiple biochemical experiments suggest that neither MAZ nor CARK7 demonstrate catalytic protein kinase activity in vitro. Interestingly, we find that a mutant variant of MAZ incapable of protein kinase activity is able to complement maz-1 mutants, suggesting noncatalytic roles of MAZ in planta. Overall, our study identifies subgroup VIII RLCKs as new players in Arabidopsis immune signaling and highlights the importance of noncatalytic functions of protein kinases.

plant biology↗