The B regulatory subunit may modulate substrate selectivity and catalytic activity, and also may direct the localization of the catalytic enzyme to a particular subcellular compartment (By similarity). The holoenzyme composed of PP2AA1, PP2A4 and B'ZETA acts as negative regulator of plant innate immunity by controlling BAK1 phosphorylation state and activation in surface-localized immune receptor complexes (PubMed:25085430). Required for the formation of the PP2A holoenzyme that negatively regulates brassinosteroid signaling by dephosphorylating and inactivating BRI1 in the cytoplasm (PubMed:26517938). Involved in growth regulation and stress signaling. Involved in the regulation of reactive oxygen species (ROS) signaling (PubMed:26012558). PP2A consists of a common heteromeric enzyme, composed of a catalytic subunit (subunits C), a constant regulatory subunit (subunit A), and a variety of regulatory subunits such as subunits B (the R2/B/PR55/B55, R3/B''/PR72/PR130/PR59 and R5/B'/B56 families). Expressed in roots, emerging lateral roots, cotyledons, leaves, floral stalks and flowers. No visible phenotype under normal growth conditions. Belongs to the phosphatase 2A regulatory subunit B56 family.