Epigenetic Regulation of Megaspore Mother Cell Formation.

Ting Jiang,Binglian Zheng

doi:10.3389/fpls.2021.826871

Abstract

In flowering plants, the female gametophyte (FG) initiates from the formation of the megaspore mother cell (MMC). Among a pool of the somatic cells in the ovule primordium, only one hypodermal cell undergoes a transition of cell fate to become the MMC. Subsequently, the MMC undergoes a series of meiosis and mitosis to form the mature FG harboring seven cells with eight nuclei. Although SPL/NZZ, the core transcription factor for MMC formation, was identified several decades ago, which and why only one somatic cell is chosen as the MMC have long remained mysterious. A growing body of evidence reveal that MMC formation is associated with epigenetic regulation at multiple layers, including dynamic distribution of histone variants and histone modifications, small RNAs, and DNA methylation. In this review, we summarize the progress of epigenetic regulation in the MMC formation, emphasizing the roles of chromosome condensation, histone variants, histone methylation, small RNAs, and DNA methylation.

Highlights

Different from that in animals, the germline cells are not specialized during embryo development in plants
Besides small interfering RNA (siRNA) biogenesis machinery (Pol IV, RDR2, and DCL3) and siRNA effectors AGO4, AGO6, and AGO9 have been involved in megaspore mother cell (MMC) formation, a recent finding show that the de novo DNA methyltransferases DRM1 and DRM2 are required for the restriction of additional MMC formation (Mendes et al, 2020), further indicating that the RdDM pathway is necessary for MMC specification and differentiation
Classical genetic strategies have identified that several key developmental factors promote MMC specification and differentiation, such as SPL/NZZ, KIPRELATED PROTEIN (KRP), RETINOBLASTOMA-RELATED 1 (RBR1), and WUS

Summary

Introduction

Different from that in animals, the germline cells are not specialized during embryo development in plants. HTR13, a H3.1 variant that is usually related inactive transcription activity (Jacob et al, 2014), can be gradually evicted in multiple L2 cells of the nucellus during early ovule development, but this eviction was only limited to the MMC once the identity of the MMC is designated (Hernandez-Lagana and Autran, 2020; Figure 2).

Results

Conclusion