A Streamlined Protocol for Single-Molecule Localization Microscopy in Arabidopsis Nuclei

Summary

This protocol presents an efficient workflow for single-molecule localization microscopy imaging of isolated Arabidopsis nuclei, using optimized isolation, fixation, and labeling to achieve reliable nanoscale visualization of chromatin and RNA Polymerase II. This approach can be readily adapted to other chromatin-associated proteins or histone modifications for high-resolution imaging.

Abstract

While confocal fluorescence microscopy has provided valuable insights into chromatin organization in plant nuclei, its diffraction-limited resolution constrains the investigation of chromatin architecture, motivating the use of super-resolution techniques such as Single-Molecule Localization Microscopy (SMLM). Among these approaches, direct stochastic optical reconstruction microscopy (dSTORM) provides nanoscale resolution in individual cells, enabling precise visualization of chromatin domains, histone modifications, and nuclear organization. While such methods are increasingly applied in mammalian systems, their use in plant biology remains limited, largely due to technical challenges in sample preparation.

Here, we present a streamlined and reproducible workflow for SMLM imaging of nuclei isolated from Arabidopsis thaliana. This protocol starts with seedling fixation to preserve nuclear morphology, followed by gentle tissue chopping and centrifugation to enrich intact nuclei. Isolated nuclei are then fluorophore-labeled in liquid medium and immobilized on low-melting agarose pads, a strategy that enhances stability during prolonged single-molecule imaging sessions. These steps collectively minimize background fluorescence, improve labeling consistency, and increase reproducibility across biological replicates.

The resulting preparations provide enhanced clarity for visualizing chromatin modifications and nuclear architecture in plants. By lowering the technical barriers to implement SMLM imaging in Arabidopsis, this protocol provides a versatile means to investigate epigenetic regulation, chromatin organization, and nuclear topological variations at the nanoscale. This work establishes a methodological foundation for applying SMLM to plants, bridging the gap with mammalian cell biology and opening new opportunities to study how nuclear architecture contributes to genome regulation in response to developmental and environmental cues in plant systems.

Introduction

Microscopy has long been a cornerstone for studying chromatin organization and nuclear architecture, revealing how DNA and histone-associated proteins arrange within the 3D nuclear space and influence gene regulation^1,2. Conventional fluorescence microscopy has provided valuable insights into large-scale chromatin domains such as chromosome territories, chromocenters, and nuclear bodies^3,4, feasible in situ, in particular in root tissues for plants^3,5,6

Protocol

NOTE: The detailed information on the materials and instruments used in this protocol is available in the Table of Materials. Unless otherwise specified, buffers are cleared on apyrogenic 0.2 µm filters. Double-distilled ultra-pure H₂O (ddH₂O) is used throughout this protocol. Centrifugation steps are carried out in 1.5 mL microtubes using a fixed-angle rotor.

1. Seedlings’ fixation and release of nuclei

1. Place a 6-well culture plate on ice under the fume hood, then add to each well approximately 4 mL of ice-cold fixation solution prepared extemporaneously under a....

Results

The protocol described above enables the preparation of high-quality Arabidopsis thaliana nuclei suitable for SMLM. Several rounds of optimization were performed to improve nuclear integrity and reduce cytoplasmic and cellular debris that compromise image quality. After each optimization step, the quality of the nuclear preparations was evaluated by confocal imaging using an Olympus IX81 spinning-disk microscope before proceeding to super-resolution acquisition.

Confocal imagi.......

Discussion

The preparation of Arabidopsis thaliana nuclei for single-molecule localization microscopy (SMLM) requires several critical steps that strongly influence the final sample quality. As described previously^19,35, thorough and consistent tissue chopping is essential to maximize the recovery of intact nuclei. Using microtome blades instead of standard razor blades produces cleaner and more uniform tissue fragmentation, thereby improving nuclei release. Subseq.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Anti-RNA polymerase II CTD repeat YSPTSPS (phospho S2) antibody	Abcam	ab5095	Primary antibody used at 1/200 dilution in immunostaining buffer to visualize the active form of the polymerase (Polyclonal antibody raised in rabbit )
Acquisition software	Abbelight	NEO LiveImaging v2.18
Bovine Serum Albumin	Sigma-Aldrich	A7906
Catalase	Sigma-Aldrich	C40
Certified Low Melting Agarose	Bio-Rad	1613111
Coverslips thickness 1.5H round	Marienfeld	117640	Ø: 24 mm
D-(+)-Glucose, anhydrous, 99%	Thermo Scientific	A16828-36
Dichroic mirror	Semrock	Di03-R405/488/561/635-t1	Dichroic mirror for excitation/emission separation
Dulbecco’s Phosphate Buffered Saline 10´	biowest	X0515 - 500	Work in sterile conditions
Epredia Ultra Disposable Microtome Blades	FisherScientific	12191830	Low profile, single use
Falcon 6-well Clear Flat Bottom TC-treated Multiwell Cell Culture Plate, with Lid	Falcon	353046
Formaldehyde solution 37%	Carl Roth	7398	Work under the fume hood
Glucose oxidase	Sigma-Aldrich	G2133
Glycerol	VWR	24388.295
Goat anti-Rabbit IgG (H+L) Highly Cross-Adsorbed Secondary Antibody, Alexa Fluor Plus 647	Thermo Scientific	A32733TR	Used at 1/200 as secondary antibody coupled to AF647
Hoechst 33258 solution	Sigma-Aldrich	94403	Used at 1/500 to counterstain the DNA, added to the agarose pad
Hydrochloric Acid Solution	Chem-Lab	CL05.0311.1000
JF549-Hoechst	Lavis lab and Open Chemistry team (Janelia)	JF549-Hoechst	Used to counterstain DNA, added to the agarose pad at 1.5 nM final concentration
KIMBLE Dounce tissue grinder set	Sigma-Aldrich	D8938	2 mL tube with both large (0.0030-0.0050 inch) and small (0.0005-0.0025 inch) clearance pestles
Lasers unit	Oxxius	L6Cc	Equipped with six lasers: 405 nm - 100 mW, 488 nm - 200 mW, 532 nm - 500 mW, 561 nm - 300 mW, 640 nm - 500 mW and 730 nm - 30 mW
Magnesium chloride hexahydrate	Carl Roth	HN03
Mercaptoethylamine (MEA)	Sigma-Aldrich	30070
MOPS sodium salt 98%	Fisher Scientific SAS	352590010
Multiband emission filter	Semrock	FF01-446/523/600/677	Multiband emission filtration to block laser scatter light
Nanodiamonds	Adamas Nanotechnologies	NDNV100nmHiWGA2ml	Stock 1 mg/mL
ORCA-Fusion Digital CMOS camera	Hamamatsu	C14440-20UP
Petri dish, 100/20 mm, PS, clear, with vents, sterile	Greiner Bio-One	664161	Used to grow plants on 1/2 MS medium
Petri dish, square, PS, clear, 120/120/17 mm, sterile	Greiner Bio-One	688161	Used when chopping the plant seedlings
pluriStrainer Mini cell strainer	pluriSelect	43-10030-50	Mesh size 30 µm, suitable for 1.5 mL Eppendorf tube
Potassium Chloride	Sigma-Aldrich	P9333
Single band emission filter	Semrock	FF01-698/70	Specific emission filter for AF647 channel
Single band emission filter	Chroma	ET600/50m	Specific emission filter for JF549 channel
Sodium chloride (99,5%)	Euromedex	1112-A
Star-Frost slides 76 x 26 mm	Knittel	VS112711FKB.01
Sterile syringe filterø 33 mm porosity 0.2 µm Luer Lock cone	ClearLine	146560
Super-resolution system	Abbelight	SAFe360	Olympus IX83 equipped with 100x NA1.5 oil-immersion objective
Tri-Sodium Citrate 2H2O Gen-Apex Biomole	Prolabo	PRO-33615.268
Tris Base Molecular Biology Grade	Promega	H5135
Tris(2-carboxyethyl)phosphine hydrochloride (TCEP)	Thermo Scientific	20491
Triton X-100	Euromedex	2000-B
Tween 20	Euromedex	2001-B
Twinsil Speed	Picodent	13001002	Silicone sealant
Ultraviolet Ozone cleaning system UVOCS oven	UVOCS Inc.	T10X10	20 min exposure for coverslip cleaning
Vacuum pump	Vacuubrand	VP 100C
Heraeus Megafuge 16R Centrifuge	Thermo Scientific		Rotor TX-400 75003629. Centrifugation performed with Eppendorf tubes.