Agrobacterium-Mediated Floral-Dip Transformation of Arabidopsis thaliana Col-0 for Stable Transgenic Line Generation

Use 4-6 independent pots, each with 4-6 Col-0 plants (n=20-30 plants total) at the optimal bolting stage (primary bolts ~5-10 cm, many unopened buds). Include one mock-dipped pot (infiltration medium + acetosyringone, no Agrobacterium) as a transformation-rate negative control and one untransformed seed batch as a selection control. Dip each plant twice, 5-7 days apart, to capture additional maturing flowers. Harvest bulked T1 seed per construct. Plate ~2,000-10,000 surface-sterilized seeds per construct on selection to recover transformants. Expected transformation rate 0.1-1% (10-100 resistant seedlings per 10,000 seeds).

BSL-1. Agrobacterium tumefaciens is a plant pathogen — handle in a designated area, autoclave all cultures and contaminated plasticware before disposal, and decontaminate surfaces with 70% ethanol. Silwet L-77 is an eye/skin irritant; wear gloves and eye protection. Glufosinate (BASTA) is a herbicide — avoid inhalation/skin contact, wear gloves, mask, and lab coat when spraying, and label treated trays. Acetosyringone is dissolved in DMSO (skin-permeant); handle with gloves. Follow institutional transgenic plant containment: prevent seed/pollen escape, bag and autoclave all transgenic plant waste. Ethanol and bleach are flammable/oxidizing — keep separate.

Mock-dip control: plants dipped in dip medium + acetosyringone + Silwet but no Agrobacterium — their progeny must be 100% sensitive on selection (confirms selection stringency and no contamination). Untransformed Col-0 seed plated on selection: negative control confirming the marker kills non-transformants (no escapes). A previously validated, known-positive transgenic line carrying the same marker as a positive selection control (confirms selection plates/spray are sub-lethal-free and scoring is correct). Empty-vector dip (vector backbone, no insert) as a control for insertion/marker-only phenotypic effects in downstream assays.

A typical successful experiment yields 0.1-1% transformation efficiency: ~10-100 BASTA- or kanamycin-resistant T1 seedlings per 10,000 plated seeds. Resistant seedlings are robustly green with expanded true leaves and healthy roots on kanamycin, while sensitive seedlings bleach and arrest at the cotyledon stage within 7-10 days. T2 progeny of single-locus insertions segregate ~3:1 resistant:sensitive (chi-square consistent with one T-DNA locus). PCR confirms the expected transgene amplicon in resistant plants and not in Col-0.

• Arabidopsis thaliana Col-0 wild-type seed
• Agrobacterium tumefaciens GV3101 (pMP90), gentamicin 25 µg/mL + rifampicin 50 µg/mL resistant, carrying the binary vector
• Binary vector (e.g., pCAMBIA, pGWB, pGreen series) with plant-selectable marker (bar or nptII) and bacterial selection (kanamycin 50 µg/mL or spectinomycin 100 µg/mL)
• LB broth and LB agar with appropriate antibiotics
• Infiltration/dip medium: 5% (w/v) sucrose, 0.02-0.05% (v/v) Silwet L-77 surfactant, 10 mM MgCl2 (optional), pH ~5.7
• Acetosyringone (3',5'-dimethoxy-4'-hydroxyacetophenone), 100-200 µM (from 100 mM DMSO stock)
• Glufosinate-ammonium (BASTA) 10-20 mg/L for soil spray, or kanamycin 50 µg/mL for plate selection
• 0.5x or 1x MS medium, 0.8% agar, 1% sucrose plates for plate selection
• 70% ethanol and 50% commercial bleach + 0.05% Tween-20 for seed surface sterilization
• Potting mix (e.g., peat:vermiculite:perlite), pots, humidity domes

To stably integrate a gene-of-interest cassette carried on a binary vector into the Arabidopsis thaliana (Col-0) genome using Agrobacterium tumefaciens strain GV3101 (pMP90) floral-dip, and to recover and validate independent T1 transformants. The method exploits transformation of the female gametophyte during the reproductive window, yielding seed-borne transgenics without tissue culture, enabling rapid generation of overexpression, reporter, or CRISPR/Cas9 lines.

1. Sow Col-0 on moist potting mix, stratify 3 days at 4 °C, grow under long-day (16 h light/8 h dark, 120-150 µmol m⁻² s⁻¹, 22 °C, ~60% RH) until plants bolt (~4-5 weeks).
2. When primary inflorescences are 5-10 cm with many unopened buds, clip the first emerged primary bolt to stimulate secondary inflorescences and synchronize flowering (~4-7 days before dipping).
3. Streak Agrobacterium from glycerol stock onto LB agar with selection; grow 2 days at 28 °C.
4. Inoculate a 5 mL LB starter (with antibiotics), shake 28 °C, 250 rpm overnight; expand into 200-300 mL LB, grow to OD600 ~1.0-2.0.
5. Pellet cells at 4,000 × g for 15 min at room temperature; resuspend in dip medium to OD600 ~0.8-1.0. Add acetosyringone (100-200 µM) and Silwet L-77 (0.02-0.05%); mix gently.
6. Invert each plant and submerge all inflorescences/buds in the suspension for 20-30 s with gentle agitation. Avoid soaking the soil.
7. Lay dipped plants on their side in a tray, cover with a dome/plastic to maintain high humidity, and keep in low light or dark for 16-24 h.
8. Return plants upright to normal growth conditions; repeat dip after 5-7 days.
9. Stop watering when siliques yellow; harvest dry bulk T1 seed at full senescence (~3-4 weeks post-dip). Dry seed 1-2 weeks.
10. Select transformants: either surface-sterilize and plate on MS + kanamycin (50 µg/mL) and score green, true-leaf seedlings at 7-10 days; or sow densely on soil and spray BASTA (10-20 mg/L) 3× over 2 weeks, scoring survivors.
11. Transplant resistant T1 seedlings; confirm transgene by PCR with transgene-specific primers and collect T2 seed for segregation analysis.

Independent variables: Agrobacterium strain/construct, OD600 at dipping, Silwet L-77 concentration, acetosyringone presence, number of dips, plant developmental stage at dipping. Dependent variables: transformation efficiency (resistant seedlings per total seed plated, %), number of independent T1 lines recovered, T2 segregation ratio. Controlled variables: photoperiod (16/8 h), temperature (22 °C), light intensity (120-150 µmol m⁻² s⁻¹), humidity post-dip, seed batch, plating density, selection concentration, plant genotype (Col-0).

Dipping flowering Arabidopsis inflorescences into an Agrobacterium suspension carrying a T-DNA with a functional plant-selectable marker (e.g., BASTA/glufosinate resistance via bar, or kanamycin via nptII) will produce T1 seed in which 0.1-1% of progeny carry a stably integrated, heritable transgene segregating in subsequent generations, detectable by selection and PCR genotyping.

Count resistant vs. sensitive seedlings per plate/tray; compute transformation efficiency = (resistant seedlings ÷ total viable seed plated) × 100. For T2 segregation, tabulate resistant:sensitive counts per independent line and compute expected single-locus 3:1 ratios. Record number of independent T1 lines per construct. Maintain a line registry with construct ID, T1 ID, copy-number inference from segregation, and PCR/qPCR validation status. Use ImageJ cell-counting or manual counts; record germination rate to normalize efficiency to viable seed.

Low or zero transformation efficiency: plants dipped too late (few unopened buds) — dip earlier with abundant buds and clip primary bolts to synchronize; verify Silwet was added and fresh (it degrades). High seedling death of true transformants on kanamycin: selection too harsh or plates too old — recalibrate kanamycin to 50 µg/mL and use fresh plates; high seed density causes false escapes, so plate ≤2,000 seeds per 9 cm plate. Many escapes on BASTA soil selection: spray earlier (4-5 leaf stage), apply 3× over 2 weeks, ensure even coverage. Agrobacterium overgrowth/contamination on plates: add Timentin (100 µg/mL) or cefotaxime to selection plates. Poor seed set after dipping: Silwet concentration too high damaged flowers — reduce to 0.02%; ensure plants recovered upright in good light.

Test T2 segregation against the expected 3:1 single-locus Mendelian ratio with a chi-square goodness-of-fit test (df=1, α=0.05; apply Yates' continuity correction for small counts). Score at least 50-100 T2 seedlings per line for adequate power to distinguish single- from multi-locus insertions. Compare transformation efficiencies across constructs or conditions with a chi-square test of independence or Fisher's exact test on resistant/sensitive counts; apply Bonferroni or Benjamini-Hochberg correction when comparing multiple constructs.