Plasmodesmata: a signaling hub at the cellular boundary.

Effective intercellular communication is crucial for the survival of plants. Because plant cells are encased in rigid cell walls, direct cell-to-cell exchange of cytoplasmic content is only possible through plasmodesmata (PD), membrane-lined nanotubes that connect the cytoplasm of adjacent cells. PD are highly dynamic communication channels that can undergo various structural and functional modifications. Recent findings in the field suggest that defense signaling pathways are tightly linked to the regulation of PD, and the restriction of PD-mediated cell-to-cell communication is an essential innate immune response to microbial pathogens. Moreover, several plasma membrane-bound signaling components, including receptor-like kinases that are known to have non-cell autonomous function or pathogen perception at the cell periphery, are found to also partition to PD. These findings hint at the novel role of PD as a signaling hub for both symplasmic and cross-membrane pathways.