Abscisic acid signaling regulates primary plasmodesmata density for plant cell-to-cell communication

Cell-to-cell communication is essential for multicellular organisms. Plasmodesmata (PD) are plant-specific nanopore structures pivotal for cell-to-cell communication and plant survival. However, how PD form and their structure, regulation, and evolution remain largely unknown. Here, we demonstrate that the exogenous supply of abscisic acid (ABA), a well-conserved phytohormone in land plants, reduces primary PD density in the moss <i>Physcomitrium patens</i>. This regulation requires all core components of the ABA signaling pathway. Furthermore, we reveal that ABA-INSENSITIVE 5, a well-conserved transcription factor in the ABA signaling pathway of land plants, plays a pivotal role in PD density regulation, whereas ABA-INSENSITIVE 3 does not. Our findings show that the ABA-induced reduction in primary PD density is mediated by these ABA-responsive factors in <i>P. patens</i>. Considering previous reports on ABA-dependent PD regulation in both moss and angiosperms, we propose that the ABA-mediated control of PD biogenesis and permeability represents a conserved mechanism in land plants, with critical implications for cell-to-cell communication and stress adaptation.