Plasmodesmata: Gatekeepers for cell-to-cell transport of developmental signals in plants

Cell walls separate individual plant cells. To enable essential intercellul ar communication, plants have evolved membrane-lined channels, termed plasm odesmata, that interconnect the cytoplasm between neighboring cells. Histor ically, plasmodesmata were viewed as facilitating traffic of low-molecular weight growth regulators and nutrients critical to growth. Evidence for mac romolecular transport via plasmodesmata was solely based on the exploitatio n of plasmodesmata by plant viruses during infectious spread. Now plasmodes mata are revealed to transport endogenous proteins, including transcription factors important for development. Two general types of proteins, non-targ eted and plasmodesmata-targeted, traffic plasmodesmata channels. Size and s ubcellular location influence non-targeted protein transportability. Superi mposed on cargo-specific parameters, plasmodesmata themselves fluctuate in aperture between closed, open, and dilated. Furthermore, plasmodesmata alte r their transport capacity temporally during development and spatially in d ifferent regions of the plant. Plasmodesmata are exposed as major gatekeepe rs of signaling molecules that facilitate or regulate developmental program s, maintain physiological status, and respond to pathogens.