Recombinant Oryza sativa subsp. japonica Bidirectional sugar transporter SWEET11 (SWEET11)
Description
Introduction to SWEET11
SWEET11 belongs to the Sugar Will Eventually be Exported Transporters (SWEET) family, which represents a unique class of sugar transporters found across biological kingdoms. In rice (Oryza sativa subsp. japonica), SWEET11 (also known as Os8N3 or XA13) functions as a bidirectional sugar transporter that facilitates the movement of sucrose and other sugars across plasma membranes . The gene is located on chromosome 8 (LOC_Os08g42350) and encodes a 307-amino acid protein that is critical for various physiological processes in rice plants .
The SWEET transporters are classified into four phylogenetic clades (I-IV), with SWEET11 belonging to clade III. This classification is significant as clade III SWEETs are primarily involved in sucrose transport and have been implicated in both plant development and pathogen susceptibility . Recent genomic analyses have revealed that rice possesses six clade III SWEET genes, including the newly identified OsSWEET11b, which shares functional similarities with SWEET11 (now sometimes referred to as OsSWEET11a for clarity) .
Discovery and Characterization
SWEET11 was initially identified through studies investigating sugar transport mechanisms in plants. Its significance became more pronounced when researchers discovered its role in bacterial blight susceptibility, as it is targeted by the bacterial pathogen Xanthomonas oryzae pv. oryzae (Xoo) . Subsequent research has established SWEET11 as a multifunctional protein with roles extending beyond pathogen interactions to include essential developmental processes, particularly in reproductive tissues.
Sugar Transport and Phloem Loading
SWEET11 plays a critical role in plant carbon partitioning by facilitating the efflux of sucrose from parenchyma cells to the apoplasm in rice . This function is essential for phloem loading, the process by which sugars produced in photosynthetic source tissues (primarily leaves) are transported to the phloem for long-distance transport to sink tissues such as roots, developing organs, and seeds .
As a low-affinity sugar transporter, SWEET11 moves sucrose down concentration gradients across the plasma membrane. This is a crucial step in the apoplasmic phloem loading pathway, where sucrose must first exit the photosynthetic cells before being actively taken up into the phloem by other transporters, particularly SUT (Sucrose Transporter) proteins .
Coordination with Other Transporters
SWEET11 does not function in isolation but works in coordination with other transporters, particularly OsSUT1 and OsSWEET14, to efficiently transport sucrose from source to sink tissues . Research has shown that the transcription factor OsDOF11 regulates the expression of these three transporters by directly binding to their promoters, suggesting a coordinated regulatory mechanism controlling sucrose translocation in rice .
The coordinated action of these transporters is illustrated by studies showing that overexpression of OsSUT1, OsSWEET11, and OsSWEET14 together can modulate long-distance sugar transport more effectively than manipulating individual transporters . This synergistic activity is critical for efficient carbon allocation throughout the plant.
Role in Plant Development and Reproduction
Recent research has uncovered the essential role of SWEET11 in rice reproductive development, particularly in male fertility. While single mutants of either SWEET11a (the original SWEET11) or the newly identified SWEET11b maintain fertility, double mutants of both genes are sterile . This functional redundancy suggests that these two transporters share overlapping roles in providing sugars to developing reproductive tissues.
The sterility phenotype observed in double mutants underscores the critical importance of SWEET-mediated sucrose transport for reproductive success. Although some SWEET transporters in the same clade can transport gibberellic acid (GA), a hormone important for spikelet fertility, experiments have shown that OsSWEET11b does not mediate detectable GA transport . This indicates that the fertility defects in sweet11 mutants are likely due specifically to impaired sucrose transport rather than hormone transport deficiencies.
Interaction with Bacterial Pathogens
One of the most significant aspects of SWEET11 biology is its involvement in disease susceptibility, particularly to bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo). This bacterial pathogen employs transcription activator-like effectors (TALes) that bind to specific promoter sequences and induce the expression of host susceptibility genes, including SWEET11 .
The induction of SWEET11 by bacterial TALes leads to increased sugar efflux into the apoplasm, providing nutrients that support bacterial proliferation. This mechanism represents a sophisticated strategy by which pathogens manipulate host physiology to create a favorable environment for their growth and reproduction .
SWEET11 as a Susceptibility Target
SWEET11 is one of three SWEET genes (along with SWEET13 and SWEET14) whose expression is required for susceptibility to certain strains of Xoo . Different Xoo strains from Asia and Africa may target different combinations of these SWEET genes through distinct TALe effectors, highlighting the evolutionary arms race between the pathogen and its host.
The recent discovery of SWEET11b has added another dimension to this interaction, as it has been identified as a sixth bacterial blight susceptibility gene in rice . Experiments have shown that ectopic induction of SWEET11b by designer TALes enables otherwise TALe-free Xoo strains to cause disease, confirming its role as a susceptibility factor .
Engineering Disease Resistance
Understanding the role of SWEET11 in disease susceptibility has led to innovative approaches for engineering resistance to bacterial blight. Researchers have used CRISPR-Cas9 genome editing to introduce mutations in the promoters of SWEET genes, including SWEET11, to prevent their induction by bacterial TALes while maintaining their native functions in plant development .
This strategy has proven successful in creating broad-spectrum resistance to bacterial blight in rice, highlighting the practical applications of basic research on SWEET11 function . The ability to engineer resistance by modifying SWEET gene promoters rather than eliminating the genes themselves is particularly valuable, as it preserves the essential developmental functions of these transporters.
Table 2: SWEET11's Role in Disease Susceptibility and Resistance Strategies
| Aspect | Details |
|---|---|
| Pathogen | Xanthomonas oryzae pv. oryzae (Xoo) |
| Bacterial Effectors | Transcription activator-like effectors (TALes) |
| Mechanism | TALes bind SWEET11 promoter and induce expression |
| Consequence | Increased sugar efflux supporting bacterial growth |
| Related SWEET Genes | SWEET11, SWEET13, SWEET14, and SWEET11b |
| Resistance Strategy | CRISPR-Cas9 editing of promoter TALe binding sites |
| Resistance Outcome | Broad-spectrum resistance to bacterial blight |
Recombinant Expression Systems
For research and biotechnological applications, recombinant SWEET11 protein is typically produced in E. coli expression systems. The full-length protein (1-307 amino acids) is expressed with an N-terminal His-tag to facilitate purification and subsequent analyses .
The recombinant protein is generally supplied as a lyophilized powder that can be reconstituted in appropriate buffers for various applications. Storage recommendations typically include keeping the protein at -20°C/-80°C, with aliquoting to avoid repeated freeze-thaw cycles .
Applications in Research
Recombinant SWEET11 has numerous applications in plant biology research:
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Structural studies: The purified protein can be used for crystallography and other structural analyses to better understand the sugar transport mechanism.
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Functional assays: Reconstituted SWEET11 in artificial membrane systems allows for detailed kinetic studies of sugar transport.
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Antibody production: The recombinant protein serves as an antigen for generating specific antibodies used in immunolocalization and Western blot analyses.
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Protein-protein interaction studies: Purified SWEET11 can be used to identify interacting partners that may regulate its function or localization.
Biotechnological Applications
Beyond basic research, understanding SWEET11 function has important biotechnological applications:
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Crop improvement: Manipulating SWEET11 expression or activity could potentially enhance sugar translocation to developing seeds, increasing yield in rice and other cereals.
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Disease resistance: As described earlier, editing SWEET11 promoters can confer resistance to bacterial blight, an important rice disease .
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Carbon partitioning optimization: Coordinated expression of SWEET11 with other sugar transporters could potentially redirect carbon resources to desired plant organs, enhancing specific traits of agricultural interest .
Product Specs
Note: While we prioritize shipping the format currently in stock, we will accommodate any specific format requirements. Please indicate your preference in the order notes, and we will prepare the product accordingly.
Note: All proteins are shipped with standard blue ice packs. If dry ice shipping is required, please notify us in advance, as additional charges will apply.
Generally, liquid forms have a shelf life of 6 months at -20°C/-80°C. Lyophilized forms typically have a shelf life of 12 months at -20°C/-80°C.
Target Background
Q&A
What is the molecular structure and function of OsSWEET11?
OsSWEET11 is a transmembrane protein consisting of 307 amino acids with the sequence beginning with MAGGFLSMANPAVTLSGVAGNIISFLVFLAPVATFLQVYKK and continuing through multiple transmembrane domains . It functions as a bidirectional sugar transporter primarily involved in phloem loading and long-distance sucrose transport in rice plants . The protein is localized to plasma membranes of phloem parenchyma and mesophyll cells .
Functionally, OsSWEET11 works in coordination with OsSUT1 (Sucrose Transporter 1) to facilitate the export of photosynthetically-derived sucrose from source tissues to sink tissues through the phloem . The transporter allows sucrose to move across membranes, which is essential for proper carbon partitioning and energy distribution throughout the plant.
How does OsSWEET11 differ from other SWEET transporters in rice?
OsSWEET11 belongs to the SWEET family of transporters but has specific expression patterns and functional roles that distinguish it from other family members:
While both OsSWEET11 and OsSWEET14 are involved in phloem loading and targeted by bacterial pathogens, they likely have some non-redundant functions in different tissues or developmental stages .
What methods are recommended for studying OsSWEET11 expression patterns?
To study OsSWEET11 expression patterns, researchers should consider these methodological approaches:
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RT-qPCR analysis: Use gene-specific primers to quantify OsSWEET11 transcript levels in different tissues and under various conditions. This approach was successfully used to measure expression in transgenic rice lines with modified SWEET11 expression .
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Promoter-reporter fusions: Create transgenic plants expressing reporter genes (GFP, YFP, GUS) under the control of the native OsSWEET11 promoter to visualize expression patterns in different tissues and cell types.
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In situ hybridization: For precise tissue and cell-specific localization of OsSWEET11 transcripts without genetic modification.
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Immunolocalization: Using antibodies against OsSWEET11 to detect protein localization, as demonstrated in studies with fluorescent protein fusions like AtSWEET11-YFP .
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RNA-seq analysis: For genome-wide expression profiling that can reveal co-expression patterns with other sugar transporters and related genes.
How does the interaction between OsSWEET11 and bacterial pathogens function at the molecular level?
The molecular mechanism of OsSWEET11 exploitation by bacterial pathogens, particularly Xanthomonas oryzae pv. oryzae (Xoo), involves a sophisticated hijacking of host sugar transport machinery:
Xoo employs Transcription Activator-Like (TAL) effectors that are injected into plant cells through the type III secretion system. These TAL effectors bind to specific promoter elements in the OsSWEET11 gene, inducing its expression . At least four different bacterial TAL effectors are known to induce either OsSWEET11 or OsSWEET14 in rice .
The induced expression of OsSWEET11 increases sucrose export from plant cells, likely providing nutrients to the extracellular bacteria residing in the apoplast . This nutrient acquisition strategy is crucial for bacterial proliferation and pathogenicity.
Disease-resistant rice varieties often contain mutations in the TAL effector binding sites in the OsSWEET11 promoter, preventing pathogen-induced expression while maintaining normal developmental expression . This explains why OsSWEET11 is also known as "Disease resistant allele Xa13" .
What are the metabolic consequences of altered OsSWEET11 expression in rice?
In transgenic rice plants overexpressing OsSWEET11 (along with OsSUT1 and OsSWEET14), several metabolic changes were observed:
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Reduced photosynthetic carbon assimilation: Transgenic lines showed up to 40% reduction in photosynthetic rates .
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Altered diurnal starch patterns: While starch content was lower at the end of the day, it was significantly higher (~200%) at the end of the night in transgenic lines compared to wild type .
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Impaired sucrose transport: Despite overexpression of transporters, plants showed reduced movement of radiolabeled [14C] sucrose through leaves .
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Reduced soluble sugar content: Sucrose, glucose, and fructose levels were significantly decreased (by 18-40%) in transgenic leaves .
These metabolic changes result in several phenotypic consequences, including:
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Reduced plant height
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Decreased tiller numbers
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Smaller panicle size
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Lower grain weight
The severity of these phenotypic alterations correlated with the expression levels of OsSWEET11 and OsSWEET14 .
What is the relationship between OsSWEET11 function and plant immunity?
OsSWEET11 function is intricately linked to plant immunity through several mechanisms:
What are the best approaches for generating and validating OsSWEET11 mutants in rice?
When designing experiments to study OsSWEET11 function through mutagenesis, researchers should consider these methodological approaches:
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CRISPR/Cas9 genome editing:
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Design guide RNAs targeting exonic regions of OsSWEET11
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Screen for mutations using PCR amplification and sequencing
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Confirm protein loss using immunoblotting or functional assays
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Consider creating promoter mutations specifically in TAL effector binding sites to generate disease-resistant varieties
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RNAi-mediated knockdown:
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Design hairpin constructs specific to OsSWEET11 to avoid off-target effects on other SWEET family members
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Use native or tissue-specific promoters to restrict knockdown to specific tissues
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Validate knockdown efficiency by RT-qPCR and protein analysis
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T-DNA or transposon insertional mutants:
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Screen existing mutant collections for insertions in OsSWEET11
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Confirm homozygosity and transcriptional disruption
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Complementation studies to confirm phenotypes are due to OsSWEET11 disruption
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Functional validation:
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Consider genetic redundancy:
How should researchers design experiments to study OsSWEET11 involvement in plant-pathogen interactions?
To effectively study OsSWEET11's role in plant-pathogen interactions, researchers should implement these experimental approaches:
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Pathogen inoculation studies:
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Compare wild-type and OsSWEET11 mutant plants using standardized inoculation methods
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Measure disease progression through lesion length quantification
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Assess bacterial growth kinetics in planta
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Consider different pathogen strains, including those with mutations in specific TAL effectors
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Promoter analysis:
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Identify TAL effector binding elements (EBEs) in the OsSWEET11 promoter
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Create synthetic promoters with modified EBEs to test specificity of interactions
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Use reporter gene assays to quantify promoter activation by specific TAL effectors
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Gene expression dynamics:
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Monitor OsSWEET11 expression at various time points after pathogen infection
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Compare with expression patterns of defense-related genes
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Analyze global transcriptome changes in OsSWEET11 mutants versus wild type
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Sugar transport measurements during infection:
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Quantify apoplastic sugar levels in infected versus uninfected tissues
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Track movement of radiolabeled sugars in infected plants
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Measure carbon partitioning between host and pathogen using isotope labeling
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Hormone signaling analysis:
How can contradictory phenotypes in OsSWEET11 studies be reconciled?
Researchers studying OsSWEET11 often encounter seemingly contradictory results that require careful interpretation:
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Overexpression versus knockout phenotypes:
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While OsSWEET11 is exploited by bacterial pathogens, overexpression lines showed enhanced resistance rather than increased susceptibility
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This apparent contradiction may be explained by considering whole-plant physiology—overexpression disrupted normal sucrose distribution, potentially creating a less favorable environment for pathogen growth despite increased transporter activity
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Single versus multiple gene manipulations:
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Tissue-specific versus constitutive expression effects:
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Integration of metabolic and defense phenotypes:
When analyzing seemingly contradictory data, researchers should:
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Consider spatial and temporal dynamics of gene expression
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Examine broader metabolic contexts rather than isolated pathways
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Account for compensatory mechanisms that may mask expected phenotypes
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Design experiments with appropriate controls for each specific hypothesis being tested
What analytical approaches best capture the dynamic nature of sugar transport during pathogen infection?
To effectively analyze the dynamic changes in sugar transport during pathogen infection, researchers should consider these methodological approaches:
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Time-resolved measurements:
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Sample at multiple time points during infection progression
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Correlate sugar transport changes with pathogen population dynamics and defense activation
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Use time-series analysis methods to identify critical transition points
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Spatial resolution techniques:
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Employ cell-type specific transcriptomics and metabolomics
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Use micro-dissection approaches to separate infected from adjacent tissues
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Apply imaging techniques to visualize sugar movement with fluorescent analogs
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Multi-omics integration:
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Combine transcriptomics, proteomics, and metabolomics data
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Use network analysis to identify relationships between sugar transport and defense pathways
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Apply machine learning approaches to identify patterns in complex datasets
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Mathematical modeling:
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Develop models of source-sink relationships during infection
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Simulate changes in sugar partitioning based on transporter activity
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Predict outcomes of different intervention strategies
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Comparative analyses:
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Study multiple pathosystems that target SWEET transporters
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Compare compatible and incompatible interactions
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Analyze responses across different genetic backgrounds and environmental conditions
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What are promising strategies for engineering disease resistance through OsSWEET11 modification?
Based on current understanding of OsSWEET11 function, several promising approaches for engineering enhanced disease resistance include:
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Promoter engineering:
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Modify TAL effector binding elements in the OsSWEET11 promoter using genome editing
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Create synthetic promoters that maintain developmental expression but are immune to bacterial TAL effector activation
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This approach mimics naturally occurring resistant alleles where mutations in promoter regions prevent pathogen-induced expression
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Tissue-specific expression manipulation:
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Develop constructs that allow normal expression in tissues needed for growth while restricting expression in pathogen-accessible tissues
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Use inducible promoters to dynamically control OsSWEET11 expression during infection
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Protein engineering:
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Modify the OsSWEET11 protein structure to maintain sugar transport function while preventing interactions with pathogen effectors
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Create chimeric transporters that combine functional domains from different SWEET family members
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Pathway integration:
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Multi-gene strategies:
How might advanced techniques in protein structure and dynamics enhance our understanding of OsSWEET11 function?
Advanced structural biology and protein dynamics approaches offer new opportunities to understand OsSWEET11 at the molecular level:
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Cryo-electron microscopy:
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Determine the 3D structure of OsSWEET11 in different conformational states
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Analyze the transport mechanism by capturing intermediate states during sugar binding and release
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Visualize interactions with regulatory proteins or pathogen effectors
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Molecular dynamics simulations:
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Model sugar binding and transport through the membrane channel
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Simulate effects of mutations on transporter function
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Predict interactions with other proteins in the sugar transport pathway
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In situ structural biology:
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Examine OsSWEET11 structure in native membrane environments
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Analyze oligomerization and complex formation in vivo
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Identify structural changes during pathogen infection
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Single-molecule biophysics:
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Measure transport kinetics at the single-molecule level
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Analyze conformational changes during transport cycles
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Determine how pathogen effectors modify transporter function
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Proteomic interactome analysis:
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Identify proteins that interact with OsSWEET11 under different conditions
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Analyze post-translational modifications that regulate transporter activity
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Map the dynamic changes in protein interactions during development and stress responses
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These advanced approaches can provide mechanistic insights that connect molecular function to whole-plant phenotypes, potentially revealing new targets for precise genetic engineering of sugar transport and disease resistance.
