Recombinant Arabidopsis thaliana Probable inactive receptor kinase At5g58300 (At5g58300)

What is At5g58300 and what structural features define it?

At5g58300 is classified as a probable inactive receptor kinase in Arabidopsis thaliana. The mature protein consists of 615 amino acids (positions 39-654), with several distinct domains characteristic of receptor kinases . The full sequence includes transmembrane regions and a kinase domain that contains atypical features suggesting catalytic inactivity. The protein contains key structural elements including:

• N-terminal extracellular domain with leucine-rich repeat regions

• A transmembrane domain (indicated by the hydrophobic region in the sequence: ITVIILCCCIKKKD)

• An intracellular kinase domain with altered catalytic residues

• C-terminal regulatory region

The most notable feature is the altered ATP-binding site where the catalytic lysine (position 553 in related active kinases) is substituted, likely rendering the kinase domain catalytically inactive while maintaining its structural integrity for protein-protein interactions .

Why is At5g58300 classified as "probable inactive" and what are the implications for research?

At5g58300 is classified as "probable inactive" based on sequence analysis revealing modifications in key residues essential for catalytic activity. Similar to findings with other receptor-like cytoplasmic kinases (RLCKs), these modifications include substitutions in the conserved DFG motif and alterations in the catalytic loop that typically positions substrates for phosphorylation .

For researchers, this classification has significant implications:

• Experimental design should focus on non-catalytic functions rather than direct phosphorylation assays

• The protein likely functions through protein-protein interactions or as a scaffold

• Mutations that would typically abolish kinase activity may not result in phenotypic changes, as demonstrated with MAZ, another pseudokinase that complements the corresponding mutant despite lacking catalytic activity

Multiple biochemical experiments have demonstrated that other members of this family lack catalytic protein kinase activity in vitro, suggesting a common functional mechanism involving non-catalytic roles in planta .

What expression systems are most effective for producing recombinant At5g58300 for research?

Based on available data, several expression systems have been successfully employed for producing recombinant At5g58300:

For structural studies, bacterial expression is often sufficient, while functional studies may benefit from eukaryotic expression systems that preserve post-translational modifications. The baculovirus expression system using Sf21 cells has been successfully employed for related receptor kinases and may provide properly folded At5g58300 with correct modifications .

When designing expression constructs, researchers should consider:

• Including appropriate signal sequences if studying membrane localization

• Using epitope tags that don't interfere with protein function

• Testing both N- and C-terminal tags, as placement can affect protein folding and function

• Considering codon optimization for the expression system

What approaches are recommended for studying At5g58300 localization and expression patterns?

For comprehensive localization and expression analysis of At5g58300, a multi-faceted approach is recommended:

• Transcriptional analysis:

  • RT-qPCR using verified primers (F-GGTGGGTGAAGTCTGTGGTTTCTGA, R-TCTGAAGCATCTGCACCATCTCCTC) shown to have high efficiency (1.95 ± 0.10) and appropriate melting temperature (76.29 ± 0.16°C)

  • RNA-seq analysis across different tissues and developmental stages

  • Use of promoter-reporter fusions (e.g., At5g58300pro:GUS) for tissue-specific expression patterns

• Protein localization:

  • Fluorescent protein fusions (At5g58300-GFP/RFP) for live-cell imaging

  • Immunolocalization using specific antibodies against At5g58300 or epitope tags

  • Subcellular fractionation followed by Western blot analysis

• Stimulus-dependent expression:

  • Monitor expression changes following pathogen challenge

  • Analyze responses to abiotic stresses

  • Examine expression in different genetic backgrounds (mutants in related signaling pathways)

When performing these analyses, ensure RNA quality (A260/A280 ratio between 1.9-2.1 and A260/A230 > 2.0) and verify absence of genomic DNA contamination using exon-spanning primers .

How can researchers effectively study protein-protein interactions involving At5g58300?

As a probable inactive receptor kinase, At5g58300 likely functions through protein-protein interactions. Several complementary approaches are recommended:

• In vivo approaches:

  • Bimolecular Fluorescence Complementation (BiFC) to visualize interactions in plant cells

  • Co-immunoprecipitation following transient expression with epitope tags (His or HA tags have been successfully used with related proteins)

  • Split-ubiquitin yeast two-hybrid for membrane proteins

  • Proximity labeling approaches (BioID or TurboID)

• Biochemical approaches:

  • Pull-down assays using recombinant proteins

  • Cross-linking experiments similar to those performed with SRK to examine oligomeric status

  • Size-exclusion chromatography to analyze complex formation

  • Surface plasmon resonance for binding kinetics

• High-throughput screening:

  • Yeast two-hybrid screens using the kinase domain

  • Protein arrays with recombinant At5g58300

  • Mass spectrometry after affinity purification

When designing these experiments, consider that other RLCKs in Arabidopsis have shown homo- and hetero-dimerization capability, which may be a general feature of this protein family . Similar to findings with CARK7 and MAZ, At5g58300 may form complexes with related inactive kinases or with active kinases like calcium-dependent protein kinases .

What methodological approaches should be used to investigate At5g58300 in immune signaling pathways?

To investigate At5g58300's potential role in immune signaling, several methodological approaches are recommended:

• Genetic approaches:

  • Generate CRISPR/Cas9 knockout lines of At5g58300

  • Create overexpression lines using constitutive (35S) or inducible promoters

  • Develop complementation lines with site-directed mutations in key domains

  • Generate multiple mutants with related RLCKs to address functional redundancy

• Immune response assays:

  • Measure reactive oxygen species (ROS) burst following PAMP treatment

  • Quantify callose deposition after pathogen challenge

  • Analyze expression of defense marker genes via qRT-PCR

  • Perform pathogen growth assays with diverse pathogens

• Biochemical analysis:

  • Assess phosphorylation status using Phos-tag gels

  • Identify phosphorylation sites via mass spectrometry

  • Determine if At5g58300 is phosphorylated by active kinases like CPK28

  • Examine whether At5g58300 affects the phosphorylation of other proteins in immune complexes

As observed with other subgroup VIII RLCKs, At5g58300 may function redundantly with paralogs, so experimental designs should account for genetic redundancy . Additionally, since the protein is likely catalytically inactive, researchers should focus on its potential role as a scaffold or competitive inhibitor within signaling complexes.

How does At5g58300 contribute to Fusarium wilt resistance mechanisms?

At5g58300 has been identified as a candidate gene in studies of Fusarium wilt resistance in Chickpea, suggesting a potential conserved role in disease resistance mechanisms against Fusarium across plant species . To elucidate its specific contributions:

• Expression analysis during infection:

  • Monitor At5g58300 expression dynamics during Fusarium infection using the validated primers (F-GGTGGGTGAAGTCTGTGGTTTCTGA, R-TCTGAAGCATCTGCACCATCTCCTC)

  • Compare expression patterns between resistant and susceptible varieties

  • Assess whether expression changes correlate with disease progression

• Functional validation:

  • Generate transgenic lines with altered At5g58300 expression

  • Challenge these lines with Fusarium oxysporum and quantify disease symptoms

  • Measure defense-related metabolites in wild-type vs. At5g58300 mutant plants

• Signal transduction analysis:

  • Investigate if At5g58300 interacts with known components of Fusarium resistance pathways

  • Determine whether At5g58300 affects defense hormone signaling (salicylic acid, jasmonic acid, ethylene)

  • Assess if At5g58300 influences the activation of pathogenesis-related proteins

This systematic approach can help determine whether At5g58300 serves as a pattern recognition receptor for Fusarium-derived molecular patterns or functions downstream in defense signaling cascades, similar to how other subgroup VIII RLCKs function in the oxidative burst response .

What experimental designs are most effective for studying At5g58300's role in oxidative burst regulation?

Based on findings that other subgroup VIII receptor-like cytoplasmic kinases regulate immune-triggered oxidative burst in Arabidopsis , the following experimental designs are recommended for studying At5g58300's role:

• Oxidative burst measurement protocols:

  • Luminol-based chemiluminescence assays with leaf discs treated with flg22 or other PAMPs

  • In situ detection of hydrogen peroxide using DAB (3,3'-diaminobenzidine) staining

  • Fluorescent probe-based microscopy (CM-H2DCFDA) for subcellular localization of ROS

  • EPR spectroscopy for quantitative detection of specific ROS species

• Genetic analysis approach:

  • Generate single and higher-order mutants combining At5g58300 with paralogs

  • Create complementation lines with wild-type and mutated versions (e.g., phosphorylation site mutants)

  • Develop inducible expression systems to study temporal requirements

• Protein complex analysis:

  • Investigate interactions with NADPH oxidase (RBOHD)

  • Assess association with known regulators of the oxidative burst (like BIK1, CPK28)

  • Determine whether At5g58300 undergoes stimulus-dependent relocalization

When designing these experiments, consider that like MAZ and CARK7, At5g58300 may function through homo- and hetero-dimerization with other kinase family members . Additionally, since At5g58300 is likely catalytically inactive, its role may involve modulation of active kinases through competitive binding or scaffolding functions.

How can researchers determine if At5g58300's inactive kinase status confers unique regulatory functions?

Investigating the functional significance of At5g58300's probable inactive kinase status requires specialized approaches:

• Structure-function analysis:

  • Generate mutants that "restore" predicted catalytic activity through site-directed mutagenesis

  • Create chimeric proteins with catalytic domains from active kinases

  • Use phosphomimetic mutations to bypass potential phosphorylation events

• Interaction landscape analysis:

  • Compare the interactome of wild-type At5g58300 with catalytically "restored" variants

  • Identify binding partners that specifically interact with the inactive configuration

  • Determine if At5g58300 competes with active kinases for substrate binding

• Temporal dynamics studies:

  • Analyze whether At5g58300 shows stimulus-dependent changes in phosphorylation

  • Investigate if At5g58300 sequesters or delivers substrates to active kinases

  • Determine if it functions as a decoy or substrate trap

This approach has proven valuable with other pseudokinases, as demonstrated by the finding that a mutant variant of MAZ incapable of protein kinase activity successfully complements maz-1 mutants, confirming noncatalytic roles in planta . Similar methodologies may reveal whether At5g58300's inactive status is essential for its biological function.

What comparative genomic approaches reveal evolutionary insights about At5g58300 function?

Comparative genomic approaches can provide valuable evolutionary context for understanding At5g58300 function:

• Phylogenetic analysis protocol:

  • Collect homologous sequences across diverse plant species

  • Generate multiple sequence alignments focusing on key functional domains

  • Construct maximum likelihood phylogenetic trees

  • Map known functional mutations onto the phylogeny

• Selection pressure analysis:

  • Calculate dN/dS ratios across different regions of At5g58300

  • Identify sites under positive or purifying selection

  • Compare selection patterns between catalytic and non-catalytic regions

• Synteny analysis:

  • Examine conservation of genomic context around At5g58300

  • Identify co-evolved gene clusters that may function together

  • Trace duplication events that generated paralogs with potentially redundant functions

When conducting these analyses, researchers should pay particular attention to conservation patterns in the altered catalytic site, as maintained inactivity across evolutionary time would strongly support functional importance of the pseudokinase state. Such patterns have been observed in other subgroup VIII RLCKs that regulate immune responses in Arabidopsis .

What quality control measures are critical when working with recombinant At5g58300 protein?

Ensuring high-quality recombinant At5g58300 preparation is essential for reliable research outcomes. Implement these key quality control measures:

• Protein expression verification:

  • SDS-PAGE analysis with Coomassie staining to assess purity

  • Western blot using antibodies against At5g58300 or epitope tags

  • Mass spectrometry to confirm protein identity and integrity

  • Size-exclusion chromatography to evaluate oligomeric state

• Functional assessment:

  • Circular dichroism to verify proper folding

  • Thermal shift assays to assess stability

  • ATP binding assays (even if catalytically inactive, binding may still occur)

  • Interaction assays with known binding partners as positive controls

• Storage and handling protocols:

  • Store in Tris-based buffer with 50% glycerol at -20°C for short-term or -80°C for long-term storage

  • Avoid repeated freeze-thaw cycles

  • Prepare working aliquots for storage at 4°C for up to one week

  • Monitor protein stability over time

For expression systems, both E. coli and insect cell (Sf21) systems have been successfully used for related proteins, with the latter potentially providing better folding and post-translational modifications .

What RNA and DNA quality control measures are essential for gene expression studies of At5g58300?

For reliable gene expression studies of At5g58300, implement these critical quality control measures:

• RNA quality assessment:

  • Ensure RNA has A260/A280 ratio between 1.9-2.1 and A260/A230 greater than 2.0

  • Treat RNA samples with DNase I to eliminate genomic DNA contamination

  • Verify RNA integrity using bioanalyzer or gel electrophoresis

  • Test for gDNA contamination in cDNA samples using primers spanning intron-exon junctions

• Primer validation protocol:

  • Use validated primers: F-GGTGGGTGAAGTCTGTGGTTTCTGA, R-TCTGAAGCATCTGCACCATCTCCTC

  • Verify primer efficiency (1.95 ± 0.10) and melting temperature (76.29 ± 0.16°C)

  • Check for amplicon secondary structure using MFOLD software

  • Confirm single product amplification via melt curve analysis

• Experimental controls:

  • Include no-template and no-RT controls in qPCR reactions

  • Use multiple reference genes for normalization

  • Include biological replicates (minimum n=3) and technical replicates

  • Create standard curves for absolute quantification when needed

When designing experiments targeting At5g58300, consider the genomic context (Ca2: 24365119-24365227) and ensure primers are specific to avoid amplification of paralogous sequences .

What emerging technologies will advance our understanding of At5g58300 function?

Several cutting-edge technologies show promise for revealing deeper insights into At5g58300 function:

• Structural biology approaches:

  • Cryo-electron microscopy to determine At5g58300 structure alone and in complexes

  • AlphaFold or RoseTTAFold prediction for structure-based functional analysis

  • Hydrogen-deuterium exchange mass spectrometry to study conformational dynamics

• Single-cell and spatial technologies:

  • Single-cell RNA-seq to capture cell-specific expression patterns

  • Spatial transcriptomics to map At5g58300 expression in tissue contexts

  • Super-resolution microscopy for subcellular localization studies

• Systems biology approaches:

  • Multi-omics integration (transcriptomics, proteomics, metabolomics)

  • Network analysis to position At5g58300 in signaling cascades

  • Mathematical modeling of At5g58300's impact on immune signaling dynamics