Recent advances in understanding of meiosis initiation and the apomictic pathway in plants.

Chung-Ju R Wang,Ching-Chih Tseng

doi:10.3389/fpls.2014.00497

Abstract

Meiosis, a specialized cell division to produce haploid cells, marks the transition from a sporophytic to a gametophytic generation in the life cycle of plants. In angiosperms, meiosis takes place in sporogenous cells that develop de novo from somatic cells in anthers or ovules. A successful transition from the mitotic cycle to the meiotic program in sporogenous cells is crucial for sexual reproduction. By contrast, when meiosis is bypassed or a mitosis-like division occurs to produce unreduced cells, followed by the development of an embryo sac, clonal seeds can be produced by apomixis, an asexual reproduction pathway found in 400 species of flowering plants. An understanding of the regulation of entry into meiosis and molecular mechanisms of apomictic pathway will provide vital insight into reproduction for plant breeding. Recent findings suggest that AM1/SWI1 may be the key gene for entry into meiosis, and increasing evidence has shown that the apomictic pathway is epigenetically controlled. However, the mechanism for the initiation of meiosis during sexual reproduction or for its omission in the apomictic pathway still remains largely unknown. Here we review the current understanding of meiosis initiation and the apomictic pathway and raised several questions that are awaiting further investigation.

Highlights

Meiosis is an extremely important step in sexual reproduction
The switch of somatic fate to germinal cell fate and the mitosis–meiosis cell cycle transition occur sequentially during the development of reproductive organs. These sexual processes can be replaced by the asexual apomictic pathway in which meiosis is bypassed or a mitosis-like division occurs to produce unreduced daughter cells, followed by the development of an embryo without fertilization, apomictic plants can produce diploid seeds with identical genetic content to their maternal genome
We review the current understanding of the cell cycle transition that directs sporogenous cells to leave the mitotic cell cycle and enter the meiotic program in higher plants and discuss advances in the apomictic pathway

Summary

INTRODUCTION

Meiosis is an extremely important step in sexual reproduction. It is widely accepted that it evolved from mitosis and shares certain features with mitosis (Maynard Smith, 1978). The switch of somatic fate to germinal cell fate and the mitosis–meiosis cell cycle transition occur sequentially during the development of reproductive organs (i.e., anthers and ovules; Ma, 2005) These sexual processes can be replaced by the asexual apomictic pathway in which meiosis is bypassed or a mitosis-like division occurs to produce unreduced daughter cells, followed by the development of an embryo without fertilization, apomictic plants can produce diploid seeds with identical genetic content to their maternal genome. Different mechanisms are adopted, the final readout is likely the activation of a specific cyclin–CDK complex to initiate the meiotic S phase It was suggested from many studies that the decision to start meiosis is made before the onset of the pre-meiotic S phase (Watanabe et al, 2001). CDC28, in conjunction with the B-type S phase cyclins, Clb, and www.frontiersin.org

Initiation of meiosis and apomixis in plants

Findings

CONCLUSION