In biology, organismal complexity evolved in parallel with the development of specialized communication and nutrient delivery systems.Early events gave rise to the development and refinement of cell-autonomous regulatory networks involving intracellular and trans-membrane signaling cascades.One of the most significant advancements, at the single cell level, involved the formation of the nucleus in which the nuclear pore complex acquired the pivotal function of mediating RNA and protein trafficking between the nucleoplasm and the cytoplasm.By exerting control over such trafficking, eukaryotic organisms were afforded an enhanced capacity for regulation of complex patterns of gene expression.In this genetic background, multicellular organisms emerged and evolved the capacity for non-cell-autonomous signaling by a combination of receptors and mobile ligands, plus cell-to-cell communication via gap junctions in animals and plasmodesmata (PD) in plants.In the advanced forms of the algae and lower non-vascular forms of land plants, PD serve an important role in establishing cytoplasmic continuity between neighboring cells within tissues and organs.