The WASP-Arp2/3 complex signal cascade is involved in actin-dependent sperm nuclei migration during double fertilization in tobacco and maize

Xiongbo Peng,Tingting Yan,Mengxiang Sun

doi:10.1038/srep43161

Abstract

Sperm nuclear migration during fertilization in Arabidopsis and rice has recently been found to be actin-dependent, but the driving force behind this actin cytoskeleton-dependent motion is unclear. Here, we confirmed that the actin-dependent sperm nuclei migration during fertilization is a conserved mechanism in plants. Using in vitro fertilization systems, we showed that a functional actin is also essential in maize and tobacco for sperm nuclei migration after gamete membrane fusion. Cytoskeleton depolymerization inhibitor treatments supported the view that sperm nuclei migration is actin-dependent but microtubule-independent in both egg cell and central cell during double fertilization. We further revealed that the actin-based motor myosin is not the driving force for sperm nuclear migration in maize and tobacco. The WASP-Arp2/3 complex signal cascade is shown here to be involved in the regulation of sperm nuclear migration in maize and tobacco. It is interesting that sperm nuclei migration within somatic cell also need WASP-Arp2/3 complex signal cascade and actin, suggesting that the mechanism of sperm nuclear migration is not gamete specific.

Highlights

Sperm nuclear migration during fertilization in Arabidopsis and rice has recently been found to be actin-dependent, but the driving force behind this actin cytoskeleton-dependent motion is unclear
Sperm nucleus remained at the entry point after fusion and was unable to move toward polar nuclei (Fig. 6C and Ci). These results suggested the N-Wiskott–Aldrich Syndrome protein (WASP) activated Arp2/3 complex mediated actin assembly is involved in sperm nuclear migration in tobacco and maize
Studies on male pronuclear migration in animal cells have demonstrated that microtubules are the preferred tracks for male pronuclear movement[60], while it was recently reported that microtubules are dispensable for migration of male and female gamete nuclei of Arabidopsis and rice, where the presence of intact F-actin cables is necessary[9,27,28]

Summary

Introduction

Sperm nuclear migration during fertilization in Arabidopsis and rice has recently been found to be actin-dependent, but the driving force behind this actin cytoskeleton-dependent motion is unclear. Observations on artificial zygotes or primary endosperm cells in maize and tobacco demonstrated that sperm nuclear migration clearly depend on the actin cytoskeleton. The fusion products of sperm cell and central cell were treated by 5 μM wiskostatin 10 min after fusion, when sperm nucleus had already travelled along the cytoplasmic strand to polar nuclei (Fig. 6A and Ai).

Results

Conclusion