Recombinant Physcomitrella patens subsp. patens ATP synthase subunit a, chloroplastic (atpI)
Description
Physcomitrella patens as a Model Organism
Physcomitrella patens represents an evolutionary bridge between green algae and vascular plants, making it an invaluable model organism for studying plant evolution and adaptation. This moss species has garnered significant scientific attention due to its well-developed stress tolerance mechanisms and its position as one of the earliest land plant lineages. Researchers utilize P. patens to investigate genome-wide responses to environmental stressors through comprehensive transcriptomic analysis, which has revealed detailed profiles of gene regulation in response to various abiotic stress conditions including cold, drought, and salt treatments .
P. patens exhibits several outstanding features that make it particularly suitable for molecular and genetic studies. Its haploid dominant life cycle and high rate of homologous recombination enable precise gene targeting, offering exceptional genetic tractability compared to many other plant species . These characteristics have established P. patens as a crucial model system for understanding the evolution of genes involved in various cellular processes, including energy metabolism and stress responses .
Beyond its role as a model organism, P. patens has emerged as a promising biopharmaceutical production platform. Through genetic engineering, researchers have modified its glycosylation patterns to produce more humanized proteins suitable for therapeutic applications . This combination of research value and biotechnological potential makes P. patens and its proteins, including ATP synthase components, subjects of significant scientific interest.
ATP Synthase Architecture and Organization
ATP synthase is a remarkable molecular machine responsible for ATP production in chloroplasts, mitochondria, and bacteria. In photosynthetic organisms like P. patens, the chloroplast ATP synthase (often referred to as CF1FO ATP synthase) converts the energy of the proton gradient established during photosynthesis into chemical energy in the form of ATP.
The chloroplast ATP synthase consists of two major subcomplexes: the hydrophilic CF1 and the membrane-embedded CF0. The CF1 subcomplex comprises five different subunits with a stoichiometry of α3β3γ1δ1ε1, while the CF0 subcomplex includes four different subunits with a stoichiometry of I1II1III14IV1 . This complex molecular assembly functions through the coordinated action of a "stator" and a "rotor" component.
The stator component anchors the complex in the thylakoid membrane and includes the CF1δ subunit and CF0 subunits I (atpI), II, and IV . The α and β subunits are arranged alternately to form a spherical α3β3 hexamer containing three catalytic sites (CSs) and three non-catalytic regulatory sites (NCSs) for reversible ATP biosynthesis, located at the interfaces of the α/β subunits .
ATP Synthesis Mechanism and the Role of atpI
The mechanism of ATP synthesis represents one of nature's most elegant energy conversion processes. When the light-dependent reactions of photosynthesis establish a proton gradient across the thylakoid membrane, the resulting proton motive force drives the rotation of the c-ring (subunit III14). This rotation causes the γ-subunit to rotate within the α3β3 hexamer, inducing conformational changes that catalyze the synthesis of ATP from ADP and inorganic phosphate .
The atpI subunit (subunit a) plays a critical role in this process by forming part of the proton translocation pathway within the CF0 portion of the complex. The interface between subunit a and the rotating c-ring creates the channel through which protons flow, coupling proton translocation to the rotational motion that drives ATP synthesis .
Proton Translocation Mechanism
The atpI subunit forms a crucial part of the proton channel within the CF0 complex of ATP synthase. Its transmembrane helices span the thylakoid membrane and create a pathway that facilitates the movement of protons from the lumen to the stroma. The interface between subunit a (atpI) and the rotating c-ring (subunit III14) forms the critical pathway through which protons flow, driving the rotational motion that powers ATP synthesis .
The specific arrangement of charged and polar residues within the transmembrane domains of atpI creates an environment that guides protons through the membrane in a controlled manner. This precise molecular architecture is essential for converting the energy of the proton gradient into the mechanical energy of rotation.
Integration and Assembly within ATP Synthase
The atpI subunit is an integral component of the stator portion of the ATP synthase complex. It interacts with other CF0 subunits to form a stable anchor for the CF1 portion, maintaining the structural integrity of the complex and ensuring efficient energy conversion .
The assembly of the ATP synthase complex requires the coordinated expression and integration of both nuclear-encoded and chloroplast-encoded subunits. The atpI gene is typically found in the chloroplast genome as part of the atp operon, which includes multiple genes encoding different subunits of the ATP synthase complex . In many organisms, the gene order within this operon follows a conserved pattern: atpI(i), atpB(a), atpE(c), atpF(b), atpH(δ), atpA(α), atpG(γ), atpD(β), and atpC(ɛ) .
Recent research has identified specific factors involved in the assembly of chloroplast ATP synthase, such as BIOGENESIS FACTOR REQUIRED FOR ATP SYNTHASE 3 (BFA3), which interacts specifically with the CF1β subunit . The coordination between these assembly factors and the incorporation of atpI into the complex represents an active area of research.
Evolutionary Biology Studies
The study of P. patens atpI provides valuable insights into the evolution of photosynthetic energy metabolism. As P. patens occupies a key evolutionary position between green algae and vascular plants, comparative analyses of its ATP synthase components with those of other photosynthetic organisms reveal important adaptations that accompanied the transition to land plants .
Genome-wide expression analysis in P. patens has revealed significant differences compared to unicellular algae and flowering plants, indicating genomic delineation concomitant with the evolutionary movement to land . These studies highlight changes in gene family complexity and the gain or loss of genes associated with different functional groups, providing a broader context for understanding the evolution of energy metabolism in plants.
Stress Response Research
P. patens exhibits well-developed stress tolerance mechanisms, making it an excellent model for studying plant responses to various environmental stressors. ATP synthase, including the atpI subunit, plays a crucial role in energy metabolism under stress conditions. Research on P. patens has identified more than 20,000 genes expressed under various stress treatments, including those associated with abscisic acid (ABA), cold, drought, and salt stress .
Table 2: Applications of Recombinant P. patens atpI in Research and Biotechnology
| Application Area | Key Aspects | Advantages of P. patens System |
|---|---|---|
| Evolutionary Biology | Comparative analysis of ATP synthase across species | Evolutionary position between algae and vascular plants |
| Stress Response Studies | Energy metabolism under environmental stressors | Well-developed stress tolerance mechanisms |
| Protein Engineering | Structure-function studies of ATP synthase | High genetic amenability for precise modifications |
| Biopharmaceutical Production | Development of recombinant protein platforms | Humanized protein glycosylation patterns |
| Educational Research | Model system for photosynthesis studies | Well-characterized genetic and biochemical properties |
Biotechnological Applications
P. patens has emerged as a promising platform for biopharmaceutical production due to its excellent genetic amenability and ability to produce proteins with humanized glycosylation patterns . The development of P. patens for recombinant protein production has involved the characterization of various genetic elements, including promoters and terminators, to optimize expression systems .
Recent advances include the selection and characterization of novel terminators for their effects on heterologous gene expression in P. patens. Analysis of the Physcomitrella genome has identified 53,346 unique 3'UTRs (untranslated regions), providing a rich resource for optimizing expression systems . These studies have yielded a collection of endogenous terminators performing equally well as established heterologous terminators such as CaMV35S, AtHSP90, and NOS .
Furthermore, glyco-engineering approaches have successfully modified the glycosylation patterns in P. patens to produce more humanized proteins. Plant-specific β1,2-xylosylation, α1,3-fucosylation, and β1,3-galactosylation have been eliminated through targeted gene knockouts, resulting in more homogeneous N-glycan patterns suitable for biopharmaceutical applications .
Current Research Trends and Future Perspectives
Current research on P. patens ATP synthase components, including atpI, focuses on several key areas that promise to yield important insights in the coming years. These include detailed structural studies of the ATP synthase complex, investigations of its assembly and regulation, and further development of biotechnological applications.
Advances in structural biology techniques have facilitated more detailed analyses of large protein complexes like ATP synthase. Future structural studies focusing specifically on the P. patens ATP synthase complex could provide valuable insights into the adaptations of this complex in early land plants.
Research on the assembly and regulation of ATP synthase continues to uncover the complex mechanisms coordinating the expression and integration of nuclear-encoded and chloroplast-encoded subunits. Understanding these processes is crucial for comprehending how plants coordinate energy metabolism in response to changing environmental conditions.
The biotechnological potential of P. patens continues to expand with ongoing efforts to optimize expression systems and further modify its glycosylation machinery. Recent advances in introducing enzymes necessary for sialic acid synthesis and incorporation into glycoproteins represent significant steps toward developing P. patens as a versatile platform for producing complex biopharmaceuticals .
Product Specs
Note: We will prioritize shipping the format currently in stock. However, if you have specific format requirements, please indicate them in your order, and we will prepare the product accordingly.
Note: All our proteins are shipped with standard blue ice packs. If dry ice shipping is required, please inform us in advance as additional fees will apply.
Generally, the shelf life for the liquid form is 6 months at -20°C/-80°C. The shelf life for the lyophilized form is 12 months at -20°C/-80°C.
Target Background
KEGG: ppp:PhpapaCp056
Q&A
What is the functional role of ATP synthase subunit a (atpI) in Physcomitrella patens chloroplasts?
ATP synthase subunit a (atpI) is an essential component of the chloroplast ATP synthase complex in Physcomitrella patens. It forms part of the membrane-embedded F₀ sector of the ATP synthase and plays a critical role in proton translocation across the thylakoid membrane. The proton gradient generated during photosynthesis drives ATP synthesis through this complex. In Physcomitrella, as in other photosynthetic organisms, atpI contributes to the rotary mechanism that couples proton movement to ATP production, making it fundamental for energy conversion during photosynthesis .
What vectors and promoters are most effective for expressing recombinant atpI in Physcomitrella patens?
For recombinant expression of atpI in Physcomitrella patens, researchers should consider the following approach:
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Vector selection: Vectors containing homologous flanking sequences (500-1000 bp) for targeted integration are most effective, as Physcomitrella patens has exceptional homologous recombination efficiency .
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Promoter options:
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For constitutive expression: The rice actin promoter or the maize ubiquitin promoter
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For inducible expression: Heat-shock or glucocorticoid-inducible systems
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For native-like expression: The endogenous atpI promoter
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Selection markers: nptII (G418 resistance) or hpt (hygromycin resistance) are commonly used .
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Terminator selection: Recent studies have shown that terminator choice significantly impacts recombinant protein expression levels in Physcomitrella. Testing multiple terminators is advisable as their performance can vary depending on the gene of interest .
How can I optimize homologous recombination efficiency for atpI manipulation in Physcomitrella patens?
Optimizing homologous recombination for atpI targeting requires:
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Homology arm length: Use 500-1000 bp homology arms flanking your construct. Longer homology regions generally increase targeting efficiency .
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DNA quality and quantity: Use high-quality DNA (OD260/280 ≈ 1.8) at a concentration of 15-20 μg per transformation.
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Protoplast preparation: Use 7-day-old protonema cultured in liquid medium under continuous light for protoplast isolation.
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Cell cycle synchronization: Culture tissue under standardized conditions prior to protoplast isolation to enrich for cells in S/G2 phases when homologous recombination is most active .
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DNA-DSB response elements: Consider co-expressing factors like PpCtIP, which mediates homology-dependent DSB resection and significantly enhances gene targeting efficiency .
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Post-transformation selection: Apply selection pressure gradually to allow recovery of transformants.
| Factor | Recommended Condition | Impact on Recombination Efficiency |
|---|---|---|
| DNA concentration | 15-20 μg | +++ |
| Homology arm length | 500-1000 bp | +++ |
| Protoplast density | 1.5 × 10⁶ cells/ml | ++ |
| PEG concentration | 30% | ++ |
| Recovery period | 5-7 days | ++ |
| DSB repair factors | PpCtIP co-expression | +++ |
How does atpI interact with other ATP synthase subunits during complex assembly?
The assembly of the chloroplast ATP synthase complex in Physcomitrella patens involves coordinated interactions between multiple subunits. The atpI subunit plays a crucial role in this process:
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Initial assembly: AtpI integrates into the thylakoid membrane early in the assembly process, providing a foundation for subsequent subunit incorporation.
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Interactions with peripheral stalk: Research indicates that atpI interacts closely with the peripheral stalk subunits AtpF and ATPG, which are essential for proper ATP synthase biogenesis .
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Coordination with CF₁ sector: The assembly of the membrane-embedded F₀ sector (including atpI) must be synchronized with the assembly of the catalytic CF₁ sector to form a functional complex.
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Dependence relationships: Studies in Chlamydomonas (a related photosynthetic organism) show that impairment of peripheral stalk subunits significantly reduces the abundance of other ATP synthase components, suggesting interdependent assembly mechanisms likely applicable to Physcomitrella .
What methods are most effective for analyzing atpI mutants in Physcomitrella patens?
Analyzing atpI mutants requires a multi-faceted approach:
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Phenotypic characterization:
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Biochemical analysis:
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Functional measurements:
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Electrochromic shift (ECS) measurements to assess proton motive force
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Oxygen evolution and consumption rates
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ATP/ADP ratio determination in chloroplasts
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Genetic complementation:
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Wild-type atpI reintroduction
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Mutated versions of atpI for structure-function analysis
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Heterologous expression of atpI from other species
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How can I investigate the regulation of atpI mRNA stability in Physcomitrella patens?
Investigating atpI mRNA stability requires specialized approaches:
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RNA half-life determination:
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Transcription inhibition assays using actinomycin D or cordycepin
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Quantitative RT-PCR or northern blotting to track mRNA levels over time
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Analysis of regulatory elements:
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5′ and 3′ UTR deletion/mutation analysis
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RNA electrophoretic mobility shift assays (REMSA) to identify RNA-binding proteins
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Identification of RNA-binding proteins:
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Genetic approaches:
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CRISPR-Cas9 knockout of candidate RNA-binding proteins
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Analysis of atpI transcript levels in RNA metabolism mutants
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What approaches can be used to study the impact of environmental stressors on atpI expression and ATP synthase function?
Environmental stress response studies should include:
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Stress treatments:
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High light stress (100-500 μmol photons m⁻² s⁻¹)
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Temperature stress (cold: 4°C, heat: 32-37°C)
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Oxidative stress (H₂O₂, methyl viologen)
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Nutrient limitation (nitrogen, phosphorus)
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Expression analysis:
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RT-qPCR for transcript levels
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Western blotting for protein abundance
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Polysome profiling for translation efficiency
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Functional assessment:
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Ultrastructural analysis:
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Electron microscopy to examine thylakoid organization
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Immunogold labeling to track atpI localization during stress
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Why might I observe low expression levels of recombinant atpI in Physcomitrella patens?
Low expression of recombinant atpI could result from several factors:
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Transcriptional issues:
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Post-transcriptional factors:
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Protein-level concerns:
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Technical considerations:
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Integration site effects if random integration occurred
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Incomplete selection leading to chimeric plants
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Incomplete import into chloroplasts
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Troubleshooting approaches:
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Test multiple promoter-terminator combinations
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Use a chloroplast transit peptide fusion if expressing from the nuclear genome
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Consider co-expression with chaperones or protease inhibitors
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Examine transcript levels to distinguish between transcription, translation, or protein stability issues
How can I verify successful chloroplast localization of recombinant atpI in Physcomitrella patens?
Verifying chloroplast localization requires multiple complementary approaches:
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Fluorescent protein fusions:
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C-terminal GFP fusion (if function is not disrupted)
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Confocal microscopy co-localization with chlorophyll autofluorescence
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Cellular fractionation:
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Isolation of intact chloroplasts
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Further fractionation into thylakoid membrane, stroma, and envelope fractions
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Western blotting with compartment-specific markers
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Protease protection assays:
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Treatment of intact chloroplasts with thermolysin (cannot penetrate membranes)
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Treatment of disrupted chloroplasts as control
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Western blotting to detect protected fragments
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Immunogold electron microscopy:
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Ultra-thin sectioning of fixed tissue
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Immunolabeling with atpI-specific antibodies
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Quantification of gold particle distribution across cellular compartments
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How can CRISPR-Cas9 technology be optimized for editing the chloroplast genome to modify atpI in Physcomitrella patens?
Chloroplast genome editing with CRISPR-Cas9 in Physcomitrella requires specialized approaches:
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Delivery methods:
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Transfection of purified Cas9-gRNA ribonucleoproteins
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Biolistic delivery of expression constructs
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Plastid-targeted expression of Cas9 from the nuclear genome
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Guide RNA design considerations:
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Selection of targets unique to the chloroplast genome
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Evaluation of potential off-targets in both nuclear and chloroplast genomes
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Testing multiple gRNAs targeting different regions of atpI
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Selection strategies:
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Use of spectinomycin resistance as a co-editing marker
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PCR-based screening for edits
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Enrichment of edited plastids through repeated rounds of selection
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Homoplasmy achievement:
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Extended cultivation under selective pressure
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Single-cell isolation and regeneration
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Molecular verification of homoplasmic state through quantitative PCR
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What is the relationship between atpI function and photosynthate transport in Physcomitrella patens?
The relationship between ATP synthase function and photosynthate transport involves complex physiological connections:
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Energetic requirements:
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Feedback mechanisms:
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ATP/ADP ratios influence photosynthetic electron transport
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Changes in ATP synthase activity affect carbon fixation rates and subsequent carbohydrate availability
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Research approaches:
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Developmental considerations:
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Examination of sporophyte development in atpI mutants
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Analysis of transfer cell formation and function when ATP synthase activity is compromised
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