Asymmetry in the bryophyte, Physcomitrium patens.

Cell polarity and asymmetric division are fundamental to plant development, governing growth, differentiation, and stress responses. The filamentous tissues of the moss Physcomitrium patens provide an excellent system to investigate these processes, as their exposed cells facilitate direct observation of cellular and intracellular dynamics. This review explores recent advances in understanding how P. patens maintains juvenile protonemal filaments and transitions to mature gametophores, highlighting the roles of Rho-related GTPases of plant (ROP signaling, auxin transport, and cytoskeletal dynamics in tip growth and division plane orientation. Key regulators, including transcriptional corepressors and peptide signaling components, orchestrate cell fate determination and gametophore formation. Additionally, the study of stem cell regeneration and stress-resistant brood cells provides insights into dedifferentiation and plasticity mechanisms, which involve the re-establishment and disruption of cell polarity, respectively. Our current knowledge suggests that these mechanisms collectively determine the identity and developmental trajectory of daughter cells, guiding them toward differentiation into a specific tissue or organ.