Establishing a framework for female germline initiation in the plant ovule

Abstract

Female gametogenesis in flowering plants initiates in the ovule, where a single germline progenitor differentiates from a pool of somatic cells. Germline initiation is a fundamental prerequisite for seed development but is poorly understood at the molecular level due to the location of the cells deep within the flower. Studies in Arabidopsis have shown that regulators of germline development include transcription factors such as NOZZLE/SPOROCYTELESS and WUSCHEL, components of the RNA-dependent DNA methylation pathway such as ARGONAUTE9 and RNADEPENDENT RNA POLYMERASE 6, and phytohormones such as auxin and cytokinin. These factors accumulate in a range of cell types from where they establish an environment to support germline differentiation. Recent studies provide fresh insight into the transition from somatic to germline identity, linking chromatin regulators, cell cycle genes, and novel mobile signals, capitalizing on cell type-specific methodologies in both dicot and monocot models. These findings are providing unique molecular and compositional insight into the mechanistic basis and evolutionary conservation of female germline development in plants.

H3.1 Eviction Marks Female Germline Precursors in Arabidopsis

“…This is consistent with cellular markers like cell size, nuclear size and mitotic activity indicating that several candidate MMCs form in the ovule primordium, with a gradual canalization process that results in a single MMC [ 16 ]. The model supports the large and increasing genetic evidence demonstrating the capacity of several nucellar cells to acquire germline precursor identity [ 4 , 6 , 16 , 21 ].…”

“…Typically, a single female spore mother cell, called the Megaspore Mother Cell (MMC), adopts a reproductive fate and is committed to meiosis [ 1 , 2 ]. Compared to other cells in the organ, the MMC is distinguished by its large volume and prominent nucleus and nucleoli [ 3 , 4 ]. Although the formation of a single MMC is the general rule, multiple MMCs can occur in wild-type ovules, and MMC number varies among Arabidopsis ecotypes [ 5 ].…”

Temporal Distinction between Male and Female Floral Organ Development in Nicotiana tabacum cv. Xanthi (Solanaceae)

“…It was suggested that the position of the putative megasporocyte may be an important factor in cell specification in Arabidopsis [59]. Furthermore, the molecular factors determining the identity of megasporocyte and the molecular mechanisms controlling the selection of ovular cells as the archesporial cells have been explored in various species [60], while both auxin and cytokinin have been demonstrated to play crucial roles in the ovule primordia development [61].…”

Central Cell in Flowering Plants: Specification, Signaling, and Evolution

“…In flowering plants like Arabidopsis, a single megaspore mother cell (MMC) was initiated at the tip of each nucellus (Yadegari and Drews, 2004;Shi and Yang, 2011;Yang et al, 2010;Lora et al, 2019). Through meiosis, the MMC produces four haploid megaspores, of which only one becomes the functional megaspore, the other three are degenerated ( Figure 1A).…”