In Vitro Ovule Cultivation for Live-cell Imaging of Zygote Polarization and Embryo Patterning in Arabidopsis thaliana

Summary

This manuscript describes an in vitro ovule cultivation method that enables live-cell imaging of Arabidopsis zygotes and embryos. This method is utilized to visualize the intracellular dynamics during zygote polarization and the cell fate specification in developing embryos.

Abstract

In most flowering plants, the zygote and embryo are hidden deep in the mother tissue, and thus it has long been a mystery of how they develop dynamically; for example, how the zygote polarizes to establish the body axis and how the embryo specifies various cell fates during organ formation. This manuscript describes an in vitro ovule culture method to perform live-cell imaging of developing zygotes and embryos of Arabidopsis thaliana. The optimized cultivation medium allows zygotes or early embryos to grow into fertile plants. By combining it with a poly(dimethylsiloxane) (PDMS) micropillar array device, the ovule is held in the liquid medium in the same position. This fixation is crucial to observe the same ovule under a microscope for several days from the zygotic division to the late embryo stage. The resulting live-cell imaging can be used to monitor the real-time dynamics of zygote polarization, such as nuclear migration and cytoskeleton rearrangement, and also the cell division timing and cell fate specification during embryo patterning. Furthermore, this ovule cultivation system can be combined with inhibitor treatments to analyze the effects of various factors on embryo development, and with optical manipulations such as laser disruption to examine the role of cell-cell communication.

Introduction

The basic body plan of an organism develops from a unicellular zygote. In most flowering plants, zygotic division generates an apical and a basal cell, which develop into the shoot and root, respectively¹. Therefore, it is important to understand how the plant body is formed during embryogenesis, but there has not been an effective tool to directly observe the dynamics of living zygotes and embryos because they develop deep in the flower. In several monocot species, such as maize and rice, an in vitro fertilization method has been established^2,3. In this method, isolated sperm ....

Protocol

1. Preparation of the In Vitro Ovule Culture Medium

1. Make the liquid medium forthe in vitro ovule culture ("N5T medium") containing 1x Nitsch basal salt mixture, 5% (w/v) trehalose dihydrate, 0.05% (w/v) 2-(N-morpholino)ethanesulfonic acid (MES)-KOH (pH 5.8), and 1x Gamborg's vitamin solution.
2. Adjust the pH to 5.8 with KOH.
3. Sterilize the medium by autoclaving it (121 °C, 20 min) or filtering it through a 0.22-µm filter.
   NOTE: The sterilized medium can be stored at 4 °C for 2 - 3 months.

2. Preparation of the PDMS Micropillar Array Device

1. Cut the PDMS micropillar device....

Results

By using this ovule cultivation system, this method can trace the living dynamics of zygote polarization and embryo patterning. This is an achievement because previously there was no technique to visualize the real-time behavior of the zygote and embryo, which are hidden deep in the mother tissue. Figure 3A and Supplemental Video 1 show that the microtubules (MTs) in the young zygote accumulate as a transverse ring in the subapical region

Discussion

This manuscript introduces a simple in vitro ovule cultivation protocol that is efficient for use in the live-cell imaging of developing zygotes and embryos.

The design of the PDMS device may need optimization according to the embryo stage. The first developed device was a microcage array to adjust the orientation and to fix the position of the ovules⁹, and then a micropillar device was constructed to trap ovules more efficiently⁸. Furth.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Nitsch basal salt mixture	Duchefa	N0223
trehalose dihydrate	Wako Pure Chemical	206-18455
MES	Dojindo	345-01625
Gamborg’s vitamin solution	Sigma-Aldrich	G1019
35-mm glass-bottom dish	Matsunami Glass	D111300
35 mm culture dish	Corning	430588
PDMS	Dow Corning Co.	Sylgard184
76 × 26 mm slide glass	Matsunami Glass	S1225
18 × 18 mm slide glass	Matsunami Glass	C018181
needle (gauge 0.40 mm)	Terumo	NN-2719S
Immersion medium Immersol W 2010	Zeiss	444969-0000-000
A1R MP	Nikon	A1RsiMP(1080) Ti-E-TIRF
CSU-W1	Yokogawa Electric		It is a customized equipment, and thus Catalog Number is not avairable.
CV1000	Yokogawa Electric	CV1000-SP84