Recombinant Oryza sativa subsp. japonica Formin-like protein 13 (FH13)

How is FH13 gene expression regulated across different rice tissues?

While specific rice FH13 expression data is not directly available in the search results, we can draw insights from the expression pattern of Arabidopsis FH13. In Arabidopsis, FH13 transcripts are "abundantly present in all developmental stages" including "seedlings, shoots, roots, buds and open flowers" . Semiquantitative RT-PCR shows that while FH13 is expressed in multiple tissues, it is not pollen-specific .

For studying rice FH13 expression patterns, researchers should:

• Perform tissue-specific qRT-PCR across developmental stages

• Use promoter-reporter constructs (such as pFH13:GUS) to visualize spatial expression patterns

• Analyze RNA-seq datasets from different rice tissues and conditions

• Examine expression under various stresses, as formin genes often respond to environmental changes

What are effective methods for generating and expressing recombinant rice FH13?

Based on approaches used for related proteins, recombinant production of rice FH13 can be achieved through:

• Cloning strategy:

  • Amplify the full-length FH13 CDS using gene-specific primers

  • Clone into an entry vector (e.g., pENTR™) using TOPO® Cloning as demonstrated for Arabidopsis FH13

  • Transfer to appropriate expression vectors using Gateway® LR recombination

• Expression systems:

  • Bacterial expression (E. coli) for biochemical studies

  • Plant expression using Agrobacterium-mediated transformation

  • Transient expression in rice protoplasts or BY-2 cells for localization studies

• Fusion tag selection:

  • For subcellular localization: Venus/YFP/GFP as successfully used with Arabidopsis FH13

  • For protein purification: His-tag, GST-tag, or MBP-tag

  • For functional complementation: FH13 with minimal tagging under native promoter

Researchers should validate functionality of tagged proteins as demonstrated in Arabidopsis studies where "moderate level expression of Venus-tagged FH13 is sufficient to complement the effect of the fh13-1 loss of function mutation" .

What approaches are effective for studying FH13 subcellular localization in rice cells?

For reliable subcellular localization studies of rice FH13:

• Generate fluorescent protein fusions using:

  • N- or C-terminal tagging with Venus, YFP, or GFP

  • Native promoter-driven expression (pAtFH13:AtFH13-Venus was successfully used in Arabidopsis)

  • Constitutive or inducible promoters for overexpression studies

• Imaging methodologies:

  • Spinning disc confocal microscopy (SDCM) with appropriate laser lines (488 nm for YFP/GFP)

  • Time-lapse imaging for dynamic localization studies

  • Co-localization with markers for cellular compartments

  • FRAP (Fluorescence Recovery After Photobleaching) for mobility studies

• Quantification approaches:

  • Generate intensity profiles along linear transects using tools like Fiji Plot Profile

  • Position rectangular regions of interest (ROIs) to quantify signal distribution

  • Calculate area-normalized signal intensity by dividing raw integrated density by area

This methodology successfully revealed localization patterns of Arabidopsis FH13 in pollen tubes and would be applicable to rice studies.

How can CRISPR-Cas9 or T-DNA insertional mutants be generated to study FH13 function in rice?

To generate and validate FH13 mutants in rice:

• T-DNA insertion approach:

  • Screen existing rice T-DNA libraries for insertions in FH13

  • Verify insertions by PCR using gene-specific and T-DNA border primers

  • Confirm knockout/knockdown by RT-PCR using primers targeting regions before and after the insertion site

  • Cross homozygous mutants with wild type for genetic complementation studies

• CRISPR-Cas9 strategy:

  • Design guide RNAs targeting conserved domains

  • Transform rice calli with CRISPR-Cas9 constructs

  • Screen regenerated plants for mutations by sequencing

  • Select frameshift mutations for functional studies

• Mutant validation:

  • Perform semiquantitative or quantitative RT-PCR to verify transcript disruption

  • Use primers targeting 5' and 3' portions of the transcript as demonstrated for Arabidopsis FH13

  • Run PCR reactions for an appropriate number of cycles (28 cycles was used for Arabidopsis FH13)

  • Include ubiquitin (UBQ) as a control gene (24 cycles)

How do indica and japonica rice subspecies differ in FH13 sequence and recombination patterns?

While the search results don't directly address FH13 sequence differences between indica and japonica, they provide important context about recombination patterns between these subspecies:

• Recombination suppression:

  • Crosses between indica and japonica rice show significant recombination suppression near centromeres

  • Large linkage blocks (4.1-10 megabases) form in indica-japonica crosses

  • In contrast, indica-indica crosses show much smaller linkage blocks (800kb to 2.1 megabases)

• Implications for FH13 research:

  • If FH13 is located near a centromere or in a region of low recombination, breeding efforts involving this gene between subspecies may be challenging

  • Sequence comparison of FH13 between subspecies should be accompanied by analysis of surrounding genomic regions

  • Researchers should consider subspecies-specific effects when interpreting phenotypes

• Experimental approach for subspecies comparison:

  • Sequence FH13 from multiple indica and japonica varieties

  • Perform allele-specific expression studies in F1 hybrids

  • Use chromosome substitution lines to study subspecies-specific effects

What is the role of FH13 in rice pollen development and how does it compare to Arabidopsis FH13?

Based on studies of Arabidopsis FH13 and other plant formins:

• Arabidopsis FH13 function in pollen:

  • Loss of function mutations in Arabidopsis FH13 affect pollen tube growth rate

  • Moderate expression of Venus-tagged FH13 complements the fh13-1 mutation

  • High-level expression of YFP-tagged FH13 produces an opposite phenotype to loss-of-function mutations

• Expected role in rice pollen:

  • Like Arabidopsis FH13, rice FH13 likely regulates actin organization in pollen tubes

  • Rice Class II formin FH5/RMD acts as a positive regulator of pollen tube growth , suggesting functional conservation

  • Dose-dependent effects may be common across species, warranting careful expression level control in studies

• Experimental approaches:

  • Compare pollen grain size, germination rate, and tube growth between wild-type and FH13 mutant rice

  • Visualize actin organization using LifeAct-GFP in wild-type and mutant backgrounds

  • Analyze in vitro and in vivo pollination efficiency and seed set

How does FH13 interact with stress response pathways in rice?

While direct information on FH13's role in stress responses is not provided, we can draw insights from studies of other rice genes involved in stress response:

• Potential involvement in stress responses:

  • Cytoskeletal reorganization is a common response to both biotic and abiotic stresses

  • Rice WRKY13 regulates cross-talk between drought and disease resistance pathways

  • WRKY13 expression is significantly suppressed during drought and salt stress

• Research approach for stress-related studies:

  • Analyze FH13 expression under various stresses (drought, salt, pathogens)

  • Compare stress responses between wild-type and FH13 mutant rice

  • Investigate potential interactions with known stress regulators like WRKY13

• Molecular interaction studies:

  • Perform yeast two-hybrid or co-immunoprecipitation to identify FH13 interaction partners

  • Use ChIP-seq to identify transcription factors regulating FH13 expression

  • Conduct RNAseq on FH13 mutants under various stress conditions to identify downstream pathways

How is FH13 function conserved across different grass species?

Understanding FH13 conservation requires:

• Sequence analysis:

  • Identify FH13 orthologs across grass species through reciprocal BLAST

  • Perform phylogenetic analysis of the formin gene family

  • Compare protein domain structure and conservation

• Expression pattern comparison:

  • Analyze expression data from public databases for FH13 orthologs

  • Compare tissue specificity and developmental regulation

  • Identify conserved cis-regulatory elements in promoter regions

• Experimental validation:

  • Test functional complementation across species (e.g., can rice FH13 complement Arabidopsis fh13 mutations?)

  • Compare subcellular localization patterns in heterologous systems

  • Study effects on actin organization across species

What structural features distinguish rice FH13 from other formin family members?

While specific structural information about rice FH13 isn't provided in the search results, we can suggest approaches to characterize its structural features:

• Domain organization analysis:

  • Class II formins typically contain a PTEN-like domain and FH1-FH2 domains

  • Compare domain conservation between rice FH13 and other formin family members

  • Identify unique structural features through protein modeling

• Functional domain mapping:

  • Generate truncated versions of FH13 to determine essential regions for function

  • Create chimeric proteins with domains from other formins to test domain specificity

  • Use site-directed mutagenesis to identify critical residues

• Research methodology:

  • Protein structure prediction using tools like AlphaFold

  • Circular dichroism spectroscopy for secondary structure analysis

  • Limited proteolysis to identify stable domains

  • X-ray crystallography or cryo-EM for high-resolution structure determination