Recombinant Morus indica NAD (P)H-quinone oxidoreductase subunit 6, chloroplastic (ndhG)

What is the NAD(P)H-quinone oxidoreductase subunit 6 (ndhG) and what is its function in Morus indica?

NAD(P)H-quinone oxidoreductase subunit 6 (ndhG) is a chloroplastic protein that forms part of the NAD(P)H dehydrogenase complex in the chloroplast thylakoid membrane of Morus indica. This complex plays a critical role in cyclic electron flow around photosystem I and chlororespiration. The ndhG subunit specifically contributes to the structural integrity of the complex and participates in electron transfer reactions. In Morus species, like other plants, this protein is encoded by the chloroplast genome and contributes to energy production, particularly under stress conditions when linear electron flow is compromised .

How can I isolate high-quality RNA from Morus indica tissues for ndhG expression studies?

For isolating high-quality RNA from Morus indica tissues:

• Select young, actively growing tissues (preferably young leaves) as they typically yield better RNA quality.

• Use a specialized RNA extraction buffer containing CTAB, PVP, and β-mercaptoethanol to counteract the high polyphenol and polysaccharide content in mulberry tissues.

• Perform RNA extraction in ice-cold conditions to minimize degradation.

• Include multiple chloroform purification steps to remove contaminants.

• Verify RNA quality using spectrophotometric analysis (A260/A280 ratio) and gel electrophoresis.

Researchers studying mulberry transcriptomes have successfully employed these techniques as evidenced by the large volume of transcriptome data that has been generated and analyzed for various Morus species .

What genomic resources are available for studying Morus indica genes including ndhG?

Several genomic resources are available for studying Morus indica genes:

• The draft genome of Morus notabilis has been sequenced, providing a reference for comparative studies with M. indica .

• Extensive transcriptome data has been generated for Morus species, including expressed sequence tags (ESTs) and suppression subtractive hybridization (SSH) data .

• Global transcriptome data is available in public repositories (https://www.ncbi.nlm.nih.gov/sra)[3].

• Degradome sequencing data provides insights into miRNA targets in mulberry, which could regulate nuclear genes encoding proteins that interact with chloroplastic components .

• The Morus genome database (MorusDB) contains valuable information for gene identification and characterization .

These resources can be utilized to identify and study the nuclear genes that may interact with chloroplast-encoded genes like ndhG or nuclear factors that regulate the expression of chloroplast genes.

What are the optimal conditions for heterologous expression of recombinant Morus indica ndhG protein?

For optimal heterologous expression of recombinant Morus indica ndhG protein:

• Expression System Selection: Use E. coli BL21(DE3) for initial expression trials due to its reducing cytoplasm which can benefit membrane protein expression. Consider Pichia pastoris for eukaryotic expression if bacterial expression is unsuccessful.

• Codon Optimization: Perform codon optimization of the ndhG sequence for the chosen expression system to enhance expression levels, as chloroplastic genes often have different codon usage than expression hosts.

• Fusion Tags: Incorporate a 6xHis tag or other affinity tags (such as MBP or GST) at the N-terminus to facilitate purification while minimizing interference with protein folding.

• Expression Conditions:

  • Induce expression at lower temperatures (16-20°C)

  • Use lower inducer concentrations (0.1-0.5 mM IPTG for E. coli)

  • Extend expression time (16-24 hours)

  • Consider specialized media formulations for membrane protein expression

• Extraction and Purification: Use mild detergents (DDM, LDAO) for solubilization of the membrane protein, followed by affinity chromatography and size exclusion methods for purification.

Similar approaches have been successfully applied to express and study plant chloroplastic proteins in diverse plant species including Morus .

How can I design primers for amplification and cloning of the ndhG gene from Morus indica chloroplast DNA?

To design effective primers for amplification and cloning of the ndhG gene from Morus indica chloroplast DNA:

• Sequence Alignment: Align available ndhG sequences from related Morus species such as M. alba and M. notabilis to identify conserved regions .

• Primer Design Criteria:

  • Target 18-25 nucleotides with 40-60% GC content

  • Ensure primer pairs have similar melting temperatures (within 2-3°C)

  • Avoid sequences that may form secondary structures or primer dimers

  • Add restriction enzyme sites at the 5' ends with additional 3-6 bases for efficient digestion

  • Consider adding sequence for affinity tags if required for downstream applications

• Verification Strategy:

  • Include primers to amplify regions flanking the ndhG gene to verify the correct insertion position

  • Design internal primers for sequencing verification

  • Consider nested PCR approaches for increased specificity

• Software Tools: Utilize specialized software like Primer3, OligoAnalyzer, or similar tools to evaluate primer properties, potential secondary structures, and specificity.

This approach aligns with genomic studies conducted on Morus species, where gene-specific amplification and characterization have been successfully performed .

What bioinformatic tools and approaches are recommended for analyzing the structural features of Morus indica ndhG protein?

For comprehensive structural analysis of Morus indica ndhG protein, the following bioinformatic approaches are recommended:

• Sequence Analysis and Domain Prediction:

  • Use NCBI-CDD (https://www.ncbi.nlm.nih.gov/Structure/cdd/wrpsb.cgi) for conserved domain identification

  • Apply Pfam database (http://pfam-legacy.xfam.org/) to identify functional domains

  • Utilize HMMER (https://www.ebi.ac.uk/Tools/hmmer/) for hidden Markov model-based sequence analysis

• Physicochemical Property Analysis:

  • Calculate isoelectric point and molecular weight using ExPASy tools (http://www.expasy.org/tools/)[4]

  • Predict hydrophobicity profiles to identify membrane-spanning regions

• Subcellular Localization and Topology Prediction:

  • Verify chloroplast targeting using Plant-mPLoc (http://www.csbio.sjtu.edu.cn/bioinf/plant-multi/)[4]

  • Predict transmembrane domains using TMHMM 2.0 (https://services.healthtech.dtu.dk/services/TMHMM-2.0/)[4]

  • Analyze signal peptides with SignalP 5.0 (https://services.healthtech.dtu.dk/services/SignalP-5.0/)[4]

• Structural Modeling:

  • Generate 3D structural models using AlphaFold2 or similar protein structure prediction tools

  • Perform molecular dynamics simulations to understand flexibility and conformational changes

  • Validate models through PROCHECK, VERIFY3D, or similar validation tools

• Evolutionary Analysis:

  • Construct phylogenetic trees using MEGA11 software with bootstrap validation

  • Analyze the evolutionary relationships of ndhG with other Morus species and related plant taxa

  • Identify conserved motifs using MEME (http://meme-suite.org/tools/MEME)[4]

These approaches have been successfully applied in structural analyses of various Morus proteins, including the recent characterization of the GH9 family in Morus alba .

How does environmental stress affect the expression and function of ndhG in Morus indica?

Environmental stress significantly modulates ndhG expression and function in Morus indica:

• Drought Stress Response:

  • Under drought conditions, the NDH complex containing ndhG typically shows upregulated expression

  • This upregulation enhances cyclic electron flow around photosystem I, improving ATP production without additional water loss

  • Transcriptome and degradome sequencing studies have identified drought-responsive miRNAs in Morus that may regulate genes involved in energy metabolism pathways

• Temperature Stress Effects:

  • High temperature stress increases ndhG expression to maintain photosynthetic efficiency

  • Low temperature stress often results in differential regulation of various NDH complex subunits

  • The NDH complex functions as a protective mechanism against photooxidative damage under temperature fluctuations

• Light Intensity Response:

  • High light conditions typically induce ndhG expression to support increased cyclic electron flow

  • The protein plays a crucial role in preventing over-reduction of the electron transport chain

  • Light/dark transitions trigger regulatory changes in NDH complex activity

• Methodological Approaches for Analysis:

  • RT-qPCR for quantitative expression analysis under different stress conditions

  • Blue native PAGE for analyzing intact NDH complex assembly

  • Chlorophyll fluorescence measurements to assess functional impacts on photosynthesis

  • RNA-seq analysis for global transcriptional responses, as has been demonstrated in various mulberry stress response studies

What are the protein-protein interaction partners of ndhG in the chloroplast NDH complex of Morus indica?

The protein-protein interaction network of ndhG in the chloroplast NDH complex of Morus indica includes:

• Core NDH Complex Interactions:

  • ndhG interacts directly with ndhI and ndhE to form a subcomplex within the NDH complex

  • This subcomplex serves as an assembly platform for other NDH subunits

  • Hydrophobic interactions likely stabilize these associations within the thylakoid membrane

• Regulatory Protein Interactions:

  • Associations with nuclear-encoded NDH regulatory proteins (NDH48, CRRJ, CRRL)

  • Interactions with proteins involved in complex assembly and stability (CRR6, CRR7)

  • Potential transient interactions with thioredoxins for redox regulation

• Methodological Approaches for Investigation:

  • Co-immunoprecipitation coupled with mass spectrometry

  • Yeast two-hybrid screening with appropriate modifications for membrane proteins

  • Split-GFP assays for in vivo interaction verification

  • Blue native PAGE followed by second-dimension SDS-PAGE for complex composition analysis

• Comparative Analysis Approach:

  • Leverage proteomics data available for Morus species to identify potential interaction partners

  • Use structural information from related species to predict interaction interfaces

  • Apply homology-based prediction using known NDH complex structures from model plants

Understanding these interactions provides insight into how the NDH complex is assembled and regulated in Morus indica chloroplasts, which may differ from model plant systems.

How can genome editing techniques be optimized for studying ndhG function in Morus indica?

Optimizing genome editing techniques for studying ndhG function in Morus indica requires specialized approaches for chloroplast genome modification:

• Transplastomic Approaches for ndhG Modification:

  • Design chloroplast-specific transformation vectors with homologous recombination regions flanking the ndhG gene

  • Incorporate selectable markers (typically antibiotic resistance genes under chloroplast promoters)

  • Optimize biolistic delivery parameters specifically for Morus chloroplasts

  • Establish effective selection and regeneration protocols based on successful micropropagation methods for Morus indica

• CRISPR-Cas9 Adaptations for Chloroplast Genome Editing:

  • Modify Cas9 with chloroplast transit peptides for organelle targeting

  • Design sgRNAs with high specificity for the ndhG region

  • Establish chloroplast-specific promoters for guide RNA expression

  • Develop nuclear transformation protocols for indirect chloroplast genome editing

• Regeneration and Selection Optimization:

  • Utilize the established micropropagation protocol with MS medium containing 1 mg L⁻¹ Kinetin for shoot multiplication

  • Employ MS medium with 1.5 mg L⁻¹ gibberellic acid for shoot elongation

  • Apply the two-phase rooting method using 1 mg L⁻¹ 2,4-D followed by half-strength MS medium

  • Transfer to soil with quarter-strength MS salts using humidity regulation for optimal survival rates (reported 89% success)

• Verification Methods for Editing Success:

  • PCR-based genotyping to confirm targeted modifications

  • Restriction fragment length polymorphism analysis

  • Whole chloroplast genome sequencing for comprehensive verification

  • Functional assays to assess the impact on NDH complex activity

• Alternative Approaches if Direct Editing Proves Challenging:

  • RNA interference targeting nuclear genes encoding interacting partners

  • Inducible expression of dominant negative forms of ndhG

  • Heterologous complementation studies in model plant chloroplasts

These approaches consider the unique challenges of chloroplast genome editing while leveraging the established tissue culture protocols that have proven successful for Morus indica regeneration .

How can I overcome the challenges in purifying active recombinant ndhG protein from expression systems?

Purifying active recombinant ndhG protein presents several challenges that can be addressed through the following strategies:

• Solubility Enhancement Strategies:

  • Fusion with solubility-enhancing tags like MBP, SUMO, or Trx

  • Co-expression with molecular chaperones (GroEL/GroES, DnaK/DnaJ)

  • Addition of mild detergents during cell lysis and purification

  • Incorporation of stabilizing agents such as glycerol (10-20%) and specific lipids

• Optimized Detergent Selection for Membrane Protein Extraction:

  • Test a panel of detergents (DDM, LMNG, LDAO, Fos-choline)

  • Determine the critical micelle concentration for each detergent

  • Evaluate protein stability in different detergent-lipid combinations

  • Consider amphipols or nanodiscs for final protein stabilization

• Purification Protocol Refinements:

  • Implement gradient elution during affinity chromatography

  • Include additional purification steps (ion exchange, size exclusion)

  • Maintain consistent low temperature throughout purification

  • Add specific cofactors that may stabilize the protein structure

• Activity Preservation Measures:

  • Include appropriate electron donors/acceptors in storage buffers

  • Determine optimal pH and ionic strength for activity retention

  • Add antioxidants to prevent oxidative damage

  • Consider rapid freezing techniques (flash-freezing in liquid nitrogen)

• Verification of Proper Folding and Activity:

  • Circular dichroism spectroscopy to assess secondary structure

  • Thermal shift assays to evaluate protein stability

  • Electron transfer activity assays with artificial electron acceptors

  • Limited proteolysis to verify compact folding

These approaches have been successfully applied to other challenging membrane proteins in plant research, including studies on Morus species protein complexes .

What are the best approaches to analyze differential expression of ndhG under various experimental conditions?

For comprehensive analysis of ndhG differential expression under various experimental conditions, researchers should consider the following approaches:

• RNA-Based Expression Analysis:

  • RT-qPCR with carefully validated reference genes specific to Morus tissues and conditions

  • RNA-seq analysis with appropriate depth for chloroplast transcriptome coverage

  • Northern blotting for direct visualization of transcript abundance

  • Circular RNA enrichment techniques to capture chloroplast transcripts

• Protein-Based Expression Analysis:

  • Western blotting with specific antibodies against ndhG or epitope tags

  • Multiple reaction monitoring (MRM) mass spectrometry for quantitative proteomics

  • Blue native PAGE to assess intact NDH complex assembly levels

  • Immunolocalization to determine subcellular distribution changes

• Experimental Design Considerations:

  • Include appropriate time course sampling to capture dynamic responses

  • Maintain biological replicates (minimum n=3) for statistical validity

  • Include additional NDH complex subunits as comparators

  • Analyze nuclear-encoded regulators of chloroplast gene expression

• Data Analysis and Normalization Strategies:

  • Normalize chloroplast gene expression to chloroplast rRNA or other stable chloroplast transcripts

  • Apply appropriate statistical tests for differential expression (DESeq2, edgeR)

  • Use clustering analysis to identify co-regulated genes

  • Integrate transcriptomic and proteomic data for comprehensive understanding

• Validation Techniques:

  • Transgenic reporter systems (if transformation protocols are available)

  • In vitro transcription/translation assays

  • Chlorophyll fluorescence measurements to correlate expression with functional changes

These methodologies align with approaches used in mulberry transcriptome studies, where complex responses to environmental conditions have been successfully characterized .

How can I determine if alternative splicing or RNA editing affects ndhG transcripts in Morus indica chloroplasts?

To investigate alternative splicing and RNA editing in ndhG transcripts from Morus indica chloroplasts:

• RNA Extraction and Transcript Isolation:

  • Use chloroplast isolation procedures prior to RNA extraction for enrichment

  • Apply DNase treatment to eliminate chloroplast DNA contamination

  • Consider circular RNA enrichment techniques to capture chloroplast transcripts

  • Implement strand-specific library preparation for directional sequencing

• Detection of RNA Editing Sites:

  • Compare genomic DNA and cDNA sequences to identify C-to-U or U-to-C editing events

  • Use high-throughput sequencing with adequate depth (>100x coverage)

  • Apply specialized RNA editing site prediction tools (PREP-Cp, PREPACT)

  • Confirm editing sites using Sanger sequencing of specific RT-PCR products

• Alternative Splicing Investigation:

  • Design primers spanning potential intron regions for RT-PCR analysis

  • Use long-read sequencing technologies (PacBio, Nanopore) for full-length transcript analysis

  • Apply specific computational pipelines for identifying splice variants

  • Quantify the abundance of different transcript isoforms

• Comparative Analysis:

  • Compare editing patterns across different tissues, developmental stages, and stress conditions

  • Analyze conservation of editing sites across different Morus species

  • Correlate editing events with protein structural features and functional domains

  • Examine co-regulation of editing with nuclear-encoded factors

• Functional Characterization:

  • Express edited and unedited versions of the protein to assess functional differences

  • Perform structural modeling to predict the impact of edited amino acids on protein structure

  • Analyze the correlation between editing efficiency and environmental conditions

  • Investigate interactions between editing sites and protein binding partners

This comprehensive approach builds upon the genomic and transcriptomic resources available for Morus species while addressing the specific challenges of chloroplast gene expression analysis.

Optimal Tissue Culture Conditions for Regeneration of Transformed Morus indica

The following table summarizes optimal conditions for tissue culture and regeneration of Morus indica, which would be essential for functional studies of ndhG through genetic transformation:

This two-phase rooting method has proven significantly more effective than conventional approaches, producing thicker lateral roots with root hairs and shorter maturation periods (28 days vs 45 days) .

Predicted Structural Features of Morus indica ndhG Protein Based on Bioinformatic Analysis

This structural prediction employs similar bioinformatic approaches to those used in recent genomic analyses of Morus proteins , adapted specifically for the chloroplastic ndhG protein.