Component of the exocyst complex involved in the docking of exocytic vesicles with fusion sites on the plasma membrane during regulated or polarized secretion. Involved in polarized cell growth and organ morphogenesis. During cytokinesis, involved in cell plate initiation, cell plate maturation and formation of new primary cell wall. During cytokinesis, involved in cell plate initiation, cell plate maturation and formation of new primary cell wall. The exocyst complex is composed of SEC3, SEC5, SEC6, SEC8, SEC10, EXO70A1 and EXO84B. Interacts with EXO70A1, SEC5A and ICR1, but not with ICR2. Binds to EXO70H1 (PubMed:21199889). In interphase, SEC3A localizes to the cytoplasm and plasma membrane, where it forms immobile, punctate structures. Localizes to the early cell plate and completed division wall during cytokinesis (PubMed:23495664). Shuttles from the cytoplasm to the exocyst-positive organelle (EXPO) in the presence of EXO70E2 (PubMed:24307681). A number of isoforms are produced. According to EST sequences. Widely expressed. Preferentially expressed in tissues containing dividing and expanding cells, such as the shoot apical meristem, root tip, lateral root primordia and developing embryos. Embryonic lethality. Belongs to the SEC3 family.