Establishment of Positional Signals in Megaspore Mother Cell Specification: An Updated Review

The megaspore mother cell (MMC), the initial cell of the female germline in flowering plants, differentiates from a distal subepidermal somatic cell in the ovule. Positional signals guide this process, yet the mechanisms by which multiple signals integrate to specify a single MMC remain poorly understood. Here, we summarize recent advances in MMC specification, focusing on the interplay between positional signals and positional competence. Positional signals include phytohormone gradients, mobile cues, cell wall-derived physical boundaries, and mechanical signals. Positional competence is the ability of a cell to interpret these signals. We propose an integrated model in which chemical gradients define the potential reproductive region, mobile signals establish inhibitory fields, the cell wall gates signal movement, and the cytoskeleton coordinates signal delivery, division-plane patterning, and mechanical transduction. This review provides a conceptual basis for understanding how a single somatic cell is selected to acquire MMC identity and highlights potential targets for further research and crop improvement.